The monitoring of photosensitizers (PSs) and tissue oxygen are both important in photodynamic therapy. PSs can be monitored by the magnetic resonance imaging of Gd-porphyrins. Dissolved oxygen measurements based on hematoporphyrin monomethyl ether coordinated to trivalent gadolinium ion (Gd-HMME) and free base HMME were studied for determining the PSs and tissue oxygen concentrations simultaneously. Fluorescence of HMME is independent of oxygen, while phosphorescence of Gd-HMME is observed to be sensitive to oxygen. Ratiometric oxygen sensing based on Gd-HMME phosphorescence and HMME fluorescence was proposed, and the relationship between the ratio of phosphorescence to fluorescence and oxygen concentration was found to be linear. The relative uncertainty of the measured values for oxygen concentration reaches its minimum when the fluorescence intensity equals the phosphorescence intensity because of the obtainment of high signal-to-noise ratio for them. The uncertainty of the measured values for 62.5 μM oxygen was 1.2 μM, which indicates that the measurement range and precision of the oxygen measurement system we proposed can reach 0–300 μM and 1.9%, respectively. For detection of oxygen at different concentrations, the measurement uncertainty can be decreased by using HMME and Gd-HMME with suitable concentration ratio to equalize the fluorescence and phosphorescence intensities. Our results indicate that the ratiometric oxygen detection method can fulfill the requirement for tissue oxygen evaluation.

Er3+ doped ferroelectric Pb(Mg1/3Nb2/3)O3–0.25PbTiO3 (PMN–PT) ceramic was grown by using a two-stage sintering method. The sample shows relatively strong upconversion (UC) visible fluorescence under a 980 nm diode laser excitation and the fluorescence spectra were recorded in the temperature (T) range of 300–600 K. The fluorescence intensity ratios (FIR) of different energy levels, like 2H11/2, 4S3/2, 4F9/2, and its stark sublevels, were studied as functions of temperature. The responses of FIR adopted here have a linear response to temperature in certain temperature range, and the resolutions achieved for temperature sensing using this material can be 0.5 K with the sensitivity as high as 2.9% K−1.

To eliminate the “decoupling” effect, which causes the fluorescence intensity ratios (FIR) to deviate from the pure Boltzmann distribution law, a correcting method for an upvonversion pumped system was theoretical derived and experimentally verified. Theoretical results indicated that the double exponential decay of the lower level was entirely involved in the decay of the upper level, which could be used to determine the thermal population degree (η). Taking Tm3+ ions as examples, by analyzing the temperature dependence of the fluorescent dynamic curves originating from the thermally coupled pair, the η values at different temperatures were obtained and the corresponding correcting curve is given. The corrected FIR abides by the Boltzmann law, even in the lower temperature range.

•Water-soluble gadolinium porphyrin was developed as a multifunctional agent.•The developed probe is a viable photosensitizer and MRI contrast agent.•Phosphorescence-based oxygen sensing and photosensitivity were examined.•Overall, the probe may have numerous useful and interesting biomedical applications.Photodynamic therapy (PDT) is the most advanced treatment method for cancer. Challenges including quantification of the photosensitizer (PS) and oxygen necessitate the development of multifunctional PS that can function as oxygen indicators and magnetic resonance imaging (MRI) contrast agents (CA). A water-soluble gadolinium-containing porphyrin, gadolinium-containing sinoporphyrin sodium (Gd-DVDMS), was developed as a multifunctional theranostic agent: a PS for PDT, an MRI CA, and a phosphorescence-based oxygen indicator. The MRI enhancing effect of the PS can be used to measure its concentration. The luminescence and photosensitivity of Gd-DVDMS were studied and compared to those of Gd-hematoporphyrin monomethyl ether (Gd-HMME). The molar absorption coefficient of Gd-DVDMS was greater than that of Gd-HMME because it has two porphyrin rings. The emission of Gd-DVDMS at 712 nm was confirmed to be phosphorescence with a lifetime of 49 μs and quantum yield of 0.015. The phosphorescence was effectively quenched by oxygen: the phosphorescence intensity in air-saturated methanol was 33% of that in deoxygenated methanol. The phosphorescence quenching highlights the potential utility of Gd-DVDMS in the quantification of oxygen in PDT. The singlet oxygen quantum yield of Gd-DVDMS was 0.46, which was slightly higher than that of Gd-HMME. Overall, Gd-DVDMS is a promising multifunctional PS with many advantages over existing PS. In particular, DVDMS with double porphyrin rings can coordinate to two different metal ions in order to design agents with more functions.

Photodynamic therapy (PDT) is a non-invasive therapy with many advantages over other therapeutic methods, but it is restricted to treat superficial cancers due to the shallow tissue penetration of visible light. The biological window in the near infrared region (NIR) offers hope to extend the penetration depth, but there is no natural NIR excited photosensitizer. Here, we report a novel photosensitizer: NaYbF4 nanoparticles (NPs). By using a 1,3-diphenylisobenzofuran (DPBF) sensor, we show that the Yb3+ ions can absorb the NIR light and transfer energy directly to oxygen to generate reactive oxygen species (ROS). The efficiency of transferring energy to oxygen by NaYbF4 NPs is comparable to that of traditional photosensitizers. We have carried out PDT both in vitro and in vivo based on NaYbF4 NPs; the results demonstrate that NaYbF4 NPs are indeed an effective NIR photosensitizer, which can help extend the application of PDT to solid tumors owing to the much deeper penetration depth of NIR light.

•3D Ti3C2 aerogel is first synthesized by a simple EDA-assisted self-assembly process.•The aerogel structure exhibit a large specific surface area of 176.3 m2 g−1.•The binder-free Ti3C2 aerogel electrode exhibit a high areal capacitance of 1012.5 mF cm−2.Novel 3D Ti3C2 aerogel has been first synthesized by a simple EDA-assisted self-assembly process. Its inside are channels and pores structure. The interconnected aerogel structure could efficiently restrain restacking of Ti3C2 flakes. Thus, it exhibits a large specific surface area as high as 176.3 m2 g−1. The electrochemical performances have been measured. The Ti3C2 aerogel achieves a quite high areal capacitance of 1012.5 mF cm−2 for the mass loading of 15 mg at a scan rate of 2 mV s−1 in 1 M KOH electrolyte. An asymmetric supercapacitor (ASC) has been assembled by using the Ti3C2 aerogel electrode as the negative electrode and electrospinning carbon nanofiber film as the positive electrode. The device can deliver a high energy density of 120.0 μWh cm−2 and a maximum power density of 26123 μW cm−2. A lamp panel with nineteen red light-emitting diodes has been powered by two ASCs in series.Download high-res image (232KB)Download full-size image

•Sensitive sulfur dioxide sensing system based on the broadband absorption spectroscopy in wavelength range of 198–222 nm was developed.•Sulfur dioxide concentration detection limit of 17 ppb per meter was achieved.•Sensitive and uncertainty improvements of more than 10 times were achieved comparing to that based on absorption band in 300 nm.•Home-made LabVIEW-based software was developed.A highly sensitive sulfur dioxide detection system based on broadband absorption spectroscopy was developed using the 198–222 nm wavelength range. The compact and simple measurement system was constructed utilizing fiber optoelectronic sensing device. A modified approach based on differential optical absorption spectroscopy was used for the computation of sulfur dioxide concentrations. The results of sulfur dioxide concentration were calibrated and displayed using a LabVIEW-based software. A system detection limit of 17 ppb per meter has been reached, and a ten-fold improvement in sensitive and uncertainty has been achieved for measuring sulfur dioxide concentrations. The system is suitable for monitoring sulfur dioxide concentration in air as well as for the fault diagnosis of gas insulated switchgears.

Conventional photodynamic therapy (PDT) uses red light for deeper penetration. A natural compound, aloe emodin (AE) with anticancer and photosensitising capabilities, excited by blue light, is proposed to treat superficial diseases. The photophysical properties and singlet oxygen quantum yield (ΦΔ) of AE, as well as the cytotoxic effects of AE on human cells, were investigated. The absorption and emission spectra of AE were analyzed. The ΦΔ of AE was measured by a relative method. In order to study the relationship between ΦΔ and the oxygen concentration, the dependence of ΦΔ on the oxygen concentration was investigated. The cytotoxic effects of AE alone and AE-mediated PDT were compared. The relationship between cells’ survival rate and PDT conditions was studied. According to spectral analysis, the energy levels of AE were identified. The maximum absorption peak of AE is in the blue region, which makes AE-mediated PDT suitable for superficial diseases. The ΦΔ of AE was determined to be 0.57(2), which was found to be dependent on the oxygen concentration. The studies under low oxygen concentration proved that there is no type I reaction between AE and the probe for singlet oxygen detection. The effect of AE-mediated PDT was significantly higher than that of AE alone and increased with the concentration of AE or fluence. AE-mediated PDT can provide a new strategy to treat superficial diseases using blue light, thus protecting deeper normal tissues.

•Homogeneous core-shell nanocrystals (NCs) were synthesized by a one-step process.•The quantity of ligand oleic acid (OA) directly affects the uniformity of shell.•The optimum quantity of ligand OA was experimentally determined.•Core-shell NCs were synthesized under the optimum quantity of ligand OA.•The upconversion emission intensity is enhanced exponentially with shell thickness.Homogeneous core-shell nanocrystals (NCs) with highly tunable and uniform thickness shells were synthesized with a one-step, seed-mediated process. It was determined that the quantity of ligand oleic acid (OA) directly affects the uniformity of shell precursor epitaxial growth on core NCs. The optimum quantity of ligand OA was experimentally determined. Based on this finding, NaYF4:Yb, Tm/NaYF4 core-shell NCs with shell thicknesses tuned to 1 nm, 3 nm, 5 nm, 10 nm, and 15 nm were synthesized. TEM and EDS analysis confirmed the successful synthesis of core-shell NCs with the aforementioned specifications. Under 980 nm excitation, the upconversion (UC) fluorescence intensity of the core-shell NCs is enhanced exponentially with shell thickness (d) in the form of (1−0.9exp (−d/d0)). For the 800 nm emission intensity of our core-shell NCs, the d0 was determined as about 5.8 nm, corresponding to an enhancement of about 13 times. When the shell thickness is beyond d0, the UC fluorescence intensity increase becomes quite slow.

•Ratiometric oxygen sensing using metalloporphyrins as single indicator was realized.•Balanced phosphorescence and fluorescence emissions were obtained from Lu-HMME.•A ratiometric oxygen sensing system was established based on Lu-HMME.•Measurement uncertainty of 0.06 μM for oxygen concentration in air-saturated solution was achieved.In order to improve the signal to noise ratio in ratiometric oxygen sensing, comparable phosphorescence and fluorescence intensities are required. To balance the room temperature phosphorescence (RTP) and fluorescence intensities, lutetium labeled hematoporphyrin monomethyl ether (Lu-HMME) was used and its luminescence and oxygen quenching properties were studied. Luminescence spectrum indicates that RTP and fluorescence intensities of Lu-HMME are in the same order of magnitude in air-saturated solution. As expected, the fluorescence emission of Lu-HMME was independent of dissolved oxygen while RTP emission was strongly dependent on oxygen. A compact and simple ratiometric oxygen measurement system based on Lu-HMME was constructed utilizing fiber optoelectronic sensing device. The intensity response (Initrogen/Ioxygen) of Lu-HMME RTP to dissolved oxygen is higher than 4.6. The measurement uncertainty of 0.06 μM in air-saturated methanol solution was achieved using Lu-HMME. Our results suggest a high accuracy method for ratiometric dissolved oxygen measurement based on balanced phosphorescence and fluorescence emissions.

•We grow Eu3+ doped LiNbO3 single crystal and develop FIR thermometer.•Influence of scattering light on FIR temperature measurement is effectively reduced.•5D0-7F2 and 5D1-7F1 transitions can be used for FIR temperature measurement.•Sensitivity is better using 5D0-7F2 and 5D1-7F1 than 5D0-7F1 and 5D1-7F1.An optical temperature sensor (OTS) based on the fluorescence intensity ratio (FIR) method of Eu3+ in LiNbO3 (LN) single crystal has been developed, and this OTS can effectively avoid the fluorescence measurement disturbance due to the low scattering factor of the host LN single crystal. The sensitivity achieved here is as high as 3916/T2 (4% K−1 at 303 K) in the temperature range of 303–723 K by using FIRs between 5D0-7F2 (625 nm) and 5D1-7F1 (541 nm), and it is significantly superior compared with using the FIRs between 5D1-7F1 and 5D0-7F1 of traditional thermally coupled levels (TCLs). Because of the high fluorescence efficiency of this sample, strong fluorescence intensity with high signal to noise ratio (SNR) is achieved under a low excitation power density of only 0.2 W/cm2. In our OTS system the average acquisition time of temperature is less than 2 s and the resolution is as high as 0.3 K at 573 K.

•Intensity SV plot of Gd-HMME was linear for 10–100% oxygen but downward for 0–10%.•The lifetime SV plot has the similar nonlinear trend.•The intensity and lifetime plots perfectly satisfy the nonlinear solubility model.•Intensity plot is higher than lifetime plot reflecting static quenching.•Static quenching rate constant is unchanged and the percentage is about 35%.Nonlinear phosphorescence quenching mechanism of gadolinium labeled hematoporphyrin monomethyl ether (Gd-HMME) by oxygen on the filter paper was studied. The intensity Stern–Volmer plot was found to be approximately linear for oxygen concentration from 10% to 100%, but showing a negative curvature from 0% to 10%. The lifetime plot has similar changing trend. The intensity plot is slightly higher than the lifetime plot reflecting the existence of static quenching. The nonlinear responses were related to the nonlinear solubility of oxygen, which perfectly satisfy the nonlinear solubility model. Data analysis indicates that the static quenching rate constant is unchanged and the percentage of static quenching is about 35% ± 3% in the whole range of oxygen concentration.The intensity Stern–Volmer plot of Gd-HMME on filter paper was found to be approximately linear for oxygen concentration from 10% to 100%, but showing negative curvature from 0% to 10%. The lifetime plot has similar changing trend. The intensity plot is slightly higher than the lifetime plot reflecting the existence of static quenching. The nonlinear intensity and lifetime plots perfectly satisfy the nonlinear solubility model. The static quenching rate constant is unchanged and the percentage of static quenching is about 35% ± 3%.

The spin–orbit coupling mechanism was generally used to explain heavy atom effect induced room-temperature phosphorescence (RTP). Here, we demonstrate that the mechanism of RTP induced by Gd3+ from hematoporphyrin monomethyl ether (HMME) is due to the mixing of singlet (S) and triplet (T) states. The spin-forbidden transition between S and T states was partly allowed due to the states mixing, as indicated by the direct absorption corresponding to transition from S0 to T1, which was observed for the first time from RTP. The quantum yield of T1 was determined to be 0.80, and the percent of each energy transfer process was determined. Meanwhile there is no nonradiative relaxation from HMME to Gd3+ because of the large energy gap between the excited and ground states of Gd3+. The special energy level of Gd3+ as well as the states mixing between S and T states produced the strong phosphorescence emission. The population and deactivation of triplet states in heavy atom induced RTP can be used to analyze the mechanism of phosphorescent emission.

The influence of free gadolinium ion (Gd3+) on room-temperature phosphorescence (RTP) of gadolinium labeled hematoporphyrin monomethyl ether (Gd-HMME) was studied. Twenty-fold enhancement of Gd-HMME RTP by the titration of free Gd3+ was achieved. We found that the absorption from the ground (S0) to singlet excited states of Gd-HMME did not change with the addition of Gd3+, which means that the phosphorescence quantum yield has been tuned from 1.4% to 28%. According to the excitation spectra, the transition possibility from S0 to the lowest triplet excited state (T1) is increased by 1.2-fold because of the heavy atom effect of free Gd3+. The phosphorescence lifetime of Gd-HMME with free Gd3+ is 7.0-fold greater than that of Gd-HMME itself, which demonstrates that the nonradiative processes of Gd-HMME is decreased by Gd3+ with the rate constant of nonradiative processes decreasing from 2.2(2) × 105 to 2.8(2) × 104 s–1. This sharp decrease is mainly responsible for the huge enhancement of Gd-HMME RTP. The reason for the decrease of nonradiative processes is due to the formation of a rigid microenvironment, which protects Gd-HMME from being quenched.

A special core/shell/shell structured NaYF4/NaYF4:Yb3+,Er3+/NaYF4 (CSS) nanocrystal was designed to ensure each luminescence center in the emitting shell had the same surroundings. The nanocrystal includes a support core NaYF4 nanoparticle in the center coated by a thin emitting shell NaYF4:Yb3+,Er3+ and another NaYF4 shell with adjustable thickness as the outer shielding shell. The green upconversion fluorescence intensity Ig(d) of the CSS nanoparticles shows an exponential relationship with the thickness d of the shielding shell. When d decreased to 0, Ig(0) was ~356 times smaller than Ig(∞) due to the drastic fluorescence quenching of the rare earth luminescence centers by the surroundings. Our experimental results indicate that ~90% of the severe effect of the surroundings can be eliminated by coating with a ~4 nm-thick NaYF4 shielding shell.

To develop a fluorescent bioprobe for high-contrast deep tissue fluorescence imaging, monochromatic 800 nm upconversion emissions based on NaYF4: Yb3+, Tm3+ upconversion nanoparticles are investigated. The ratio of I800 to I470, which is used to describe the monochromaticity, showing exponential growth with the increase of Tm3+ doping concentration in NaYF4: Yb3+, Tm3+ nanoparticles, can reach as high as 757 at 4% Tm3+. At such a doping level, the absolute quantum efficiency can reach 3.9 × 10–3 as measured by a calibrated integrating sphere, which is sufficient for fluorescence imaging. High-contrast fluorescence phantom imaging was obtained by adjusting monochromaticity of 800 nm upconversion emission under the excitation of a 980 nm diode laser.

•Low cost methane on-line monitoring system was present by using tunable multi-mode diode laser absorption spectroscopy.•The single absorption signal superposed of several absorption signals increase the detection sensitivity.•High linearity between the peak value of WMS-2f signals and concentrations was obtained.•The sensitivity and accuracy of this system were evaluated.Tunable multi-mode diode laser absorption spectroscopy for methane detection was demonstrated. The exclusive dependence of the 1318 nm laser modes distribution on the input current and temperature was justified. Stable absorption signals related to the methane concentrations were obtained based on second-harmonic detection technique. A real-time data recording and analyzing software program was developed to realize the on-line gas concentration monitoring. A measurement sensitivity of 25 ppm m and an accuracy of 0.27% of this system were achieved.

By increasing the content of Yb3+ ions from 20% to 98% in NaTm0.02YbxY0.98−xF4 (x=0.2−0.98) nanocrystals with size about 10 nm, the intensities of near infrared (800 nm) and blue (470 nm) upconversion (UC) luminescence can be enhanced by orders of 45 and 49 times, respectively, under 970 nm diode laser excitation. Pump power dependence illustrated that the 800 and 470 nm radiations are still two- and three-photon processes, respectively. TEM imaging showed that the enhancement is not from the change of the crystal size. Steady-state equation and the measured lifetimes indicated that the enhanced 800 nm radiations can induce the enhancement of the 470 nm emissions, which is in good agreement with the experimental data.Highlights► UC emissions of Tm3+ in NaYF4 can be enhanced by increasing Yb3+ ions. ► Blue emissions have higher enhancement than NIR. ► Analysis of steady-state equations is in good agreement with the experimental results.

Ultraviolet (UV) upconversion (UC) emissions of Gd3+ ion were investigated in Y1.838−xGdxYb0.16Ho0.002O3 (x=0, 0.16, 0.4, 1, 1.4) bulk ceramics under 976 nm laser diode (LD) excitation. The UC emissions centered at 309 and 315 nm are assigned to the transition of 6P5/2→8S7/2 (Gd) and 6P7/2→8S7/2 (Gd). The 6PJ levels of Gd3+ ions are populated by an energy transfer (ET) process from 8S7/2 (Gd)+(3P1, 3L8, 3M10) (Ho)→6PJ (Gd)+5I8 (Ho). A four-photon ET UC process was confirmed by the dependence of the 6P7/2 level emission intensity on the pumping power. We found that the intensity of the UC emissions increased with Gd3+ ion concentration and peaked at 8 mol%, then starts to decrease until the Gd3+ ion concentration reached 70 mol%. The variation in the UV emission intensity is the result of the competition between the ET process and concentration quenching effect. Theoretical calculations based on steady-state equations validated the proposed UC mechanisms.

Upconversion (UC) spectra of Ho3+/Yb3+ codoped Y2O3, Gd2O3 bulk ceramics were obtained under the excitation of a 976 nm diode laser. Systematic experimental studies, including power dependence, luminescence lifetime, and the intensity ratio σ for the green to NIR emissions, were carried out in order to confirm the UC mechanism of Ho3+ ions. Our results demonstrated that the NIR emission was associated with the 5F4/5S2→5I7 transition of Ho3+ ions without the contribution of the 5I4→5I8 transition for Ho3+/Yb3+ codoped Y2O3 and Gd2O3 bulk ceramics. Additionally, population saturation in the 5I7 energy level had been observed in Ho3+/Yb3+ codoped Y2O3, Gd2O3 bulk ceramics. All experimental observations can be well explained by the steady-state rate equations.Research Highlights► We demonstrate that the NIR emission (754 nm) is associated with the 5F4/5S2→5I7 transition of Ho3+ ions without the contribution of the 5I4→5I8 transition for Ho3+/Yb3+ codoped Y2O3 and Gd2O3 bulk ceramics. ► Population saturation in the 5I7 energy level has been observed in Ho3+/Yb3+ codoped Y2O3, Gd2O3 bulk ceramics. ► We demonstrate the result, the NIR emission (754 nm) is associated with the 5F4/5S2→5I7 transition of Ho3+ ions, by the steady-state rate equations.

The upconversion (UC) luminescence in sol–gel synthesized Li+, Zn2+, or Li+–Zn2+ codoped Y2O3:Er3+ nanocrystals were investigated under the excitation of a 970 nm diode laser. Compared to undoped Y2O3:Er3+ samples, proper doping of Li+–Zn2+ leads to an drastic increase of the UC luminescence centered at 560 nm by a factor of 28. The UC luminescence enhancement is a result of the increased lifetime of the intermediate state 4I11/2 (Er). The intensity ratio of the green over red emissions (green/red) is also affected by the codoping of Zn2+, Li+ and Li+–Zn2+ ions. Our results demonstrated that the Li+–Zn2+ codoping in Y2O3:Er3+ phosphors produced remarkable enhancement of the UC luminescence and green/red ratio, making this nanocrystal a promising candidate for photonic and biological applications.Graphical abstract.Research highlights▶ Li+–Zn2+ ions codoping in Y2O3:Er3+ phosphors produced remarkable enhancement of the UC luminescence and green/red ratio. ▶ Codoping Li+–Zn2+ ions can decrease the OH groups in the nanocrystals and increase the lifetime of the intermediate state I11/24 (Er).

Ultraviolet and violet upconversion luminescence spectra of holmium-doped Y2O3 were produced under the excitation of a compact continues-wave 532 nm solid-state laser. Emissions around 306, 362, 412, 390 and 428 nm can be assigned to the transitions of 3D3 → 5IJ (J = 8, 7, 6), 5G4 → 5I8 and 5G5 → 5I8, respectively. Power dependence and upconversion dynamics analysis demonstrated that both the energy transfer upconversion (ETU) and the excited state absorption (ESA) processes were involved in the population of 3D3 state via the coupled intermediate states 5S2/5F4. Fluorescence spectra in the visible and infrared ranges showed that 5G4 and 5G5 states were populated by the ESA process from 5I6 and 5I7 states, respectively, while the 5I6 and 5I7 states were radiatively populated from the excited 5S2/5F4 states. Upconversion mechanisms have been evaluated based on a rate equation model.Research highlights▶ Using a continuous wave solid state green laser to induce ultraviolet upconversion emissions in Ho3+-doped Y2O3 ceramic. ▶ With the help of an electro-optic modulator which is modulated by square wave signals, the time-resolved fluorescence spectra were measured under the CW laser excitation. The measured decay curve contains information about the level population evolution process which is origin from the steady state, i.e., the energy transfer process was involved in the result. Thus, such measurement is different from traditional method of employing pulse laser as pumping source. ▶ A rate equation model was employed and well explained the experimental results.

Upconversion (UC) emissions at 360 ((5F, 3F, 5G)2 → 5I8), 392 (3K7/5G4 → 5I8), 428 (5G5 → 5I8), 554 (5S2/5F4 → 5I8), 667 (5F5 → 5I8) and 754 (5S2/5F4 → 5I7) nm were obtained in 0.1 mol% Ho3+/x mol% Yb3+:Y2O3 (x = 2, 5, 8, 11, 15) bulk ceramics under infrared (IR) excitation at 976 nm. The intensity of the UC luminescence centered at 554 and 754 nm increased with Yb3+ concentration from 2 to 5 mol% and decreased from 5 to 15 mol%, while the UC luminescence centered at 392, 428 and 667 nm increased with Yb3+ concentration from 2 to 11 mol%, then started to reduce with Yb3+ concentration until 15 mol%. This comes from the competition between the energy back transfer (EBT) process [5S2/5F4(Ho) + 2F7/2(Yb) → 5I6(Ho) + 2F5/2(Yb) as well as 5F5(Ho) + 2F7/2(Yb) → 5I7(Ho) + 2F5/2(Yb)] and spontaneous radiation process. The intensity of the UC luminescence centered at 360 nm always increases with Yb3+ concentration from 2 to 15 mol%. We believe that it may come from the cooperation of energy transfer process from Yb3+ ions in the 2F5/2 state and the cross energy transfer process 5S2/5F4 + 5I6 → (5F, 3F, 5G)2 + 5I8.Research Highlights►We observed that the intensity of the UC luminescence centered at 360 nm increased with Yb3+ concentration from 2 to 15 mol%. ►We also observed that the intensity of UC emissions centered at (554, 754) and (392, 428, 667) nm decreased when the Yb3+ ion concentrations are 5 and 11 mol%, respectively. ►Further increase the Yb3+ ion concentration can increase the intensity of the UV UC emission at 360 nm, and at the same time, decrease the intensity of other UC emissions.

Ultraviolet upconversion emissions around 314 nm from 6PJ states of Gd3+ ions have been observed in Y1.98 − xGdxHo0.02O3 (x = 0.02, 0.10, 0.20, and 0.30) oxide ceramics under the excitation of a continuous-wave 532-nm laser. We found that the energy transfer process from Ho3+ to Gd3+ plays an important role in populating the 6PJ states of Gd3+. The doping of Gd3+ ions does not affect 5G4 and 5G5 states but only the 3D3 state of Ho3+. The emissions from 3D3 state decrease with the increase of Gd3+ concentration. Power dependence curves and time-resolved spectra have been measured to identify the proposed upconversion mechanism.Research highlights► Ultraviolet upconversion emission of Gd3+ in oxide host was never being observed before. ► It is the first time that Gd3+ ion was successfully sensitized by the excited Ho3+ ions. ► In order to measure the time-resolved fluorescence, the CW laser was modulated by an electro-optic modulator with square wave modulations.

Photodynamic therapy (PDT) has been applied in the treatment of artery restenosis following balloon injury. This study aimed to detect the accumulation of 5-aminolevulinic acid (ALA)-derived protoporphyrin IX (PpIX) in inflamed atherosclerotic plaque in rabbit model and evaluate the efficacy of PDT. The inflamed atherosclerotic plaque in the common carotid artery was produced by combination of balloon denudation injury and high cholesterol diet. After intravenous administration of ALA, the fluorescence of PpIX in plaque was detected. At the peak time, the correlation between the fluorescence intensity of PpIX and the macrophage infiltration extent in plaque was analyzed. Subsequently, PDT (635 nm at 50 J/cm2) on the atherosclerotic plaques (n = 48) was performed and its effect was evaluated by histopathology and immunohistochemistry. The fluorescence intensity of PpIX in the plaque reached the peak 2 h after injection and was 12 times stronger than that of adjacent normal vessel segment, and has a positive correlation with the macrophage content (r = 0.794, P < 0.001). Compared with the control group, the plaque area was reduced by 59% (P < 0.001) at 4 week after PDT, the plaque macrophage content decreased by 56% at 1 week and 64% at 4 week respectively, the smooth muscle cells (SMCs) was depleted by 24% at 1 week (P < 0.05) and collagen content increased by 44% at 4 week (P < 0.05). It should be pointed out that the SMC content increased by 18% after PDT at 4 week compared with that at 1 week (P < 0.05). Our study demonstrated that the ALA-derived PpIX can be detected to reflect the macrophage content in the plaque. ALA mediated PDT could reduce macrophage content and inhibit plaque progression, indicating a promising approach to treat inflamed atherosclerotic plaques.

Upconversion (UC) luminescence of Y2O3:Ho3+, Yb3+ nanocrystals codoped with different concentrations of Eu3+ ions were investigated to improve the monochromaticity of the UC emission. The results show that the monochromaticity, quantified by a parameter SR, increases as the concentration of Eu3+ ions becomes higher, which is due to the energy transfer between 5I7 (Ho3+) and 7F6 (Eu3+). The energy transfer accelerates the relaxation of Ho3+ ions from the 5I7 to 5I8 state and then quenches the red emission. The influence of the Eu3+ concentration on the pump power dependence of the red UC fluorescence in Y2O3:Ho3+, Yb3+, Eu3+ nanocrystals is verified using the steady-state rate equation theory.

The influence of Eu3+ on the upconversion (UC) fluorescence of Er3+ in Y 2O3:Er3+, Y b3+ nanocrystals was investigated. Room-temperature UC spectra show that the intensity ratio of red to green lights was increased from 8.6 to 19.3 with 1.0 mol% Eu3+ doping. Additionally, with the increase of Eu3+ ion concentration, the nn values for both green and red UC emissions in Y 2O3:Er3+, Y b3+ nanocrystals become larger. Our analysis shows that the energy transfer between Eu3+ and Er3+ ions is the main cause for the enhancement of 2H11/2, 4S3/2→4F9/2 and 4I11/2→4I13/2 transitions of Er3+ ions.

Photodynamic therapy (PDT) has been shown to attenuate atherosclerotic plaque progression and decrease macrophage-infiltration. The effectiveness of PDT depends strongly on the type of photosensitizers. Hematoporphyrin monomethyl ether (HMME) is a promising second-generation porphyrin-related photosensitizer for PDT. This study is designed to characterize effects of HMME-based PDT on THP-1 cell-derived macrophages and define the cell-death pathway. HMME was identified to accumulate in the macrophages by fluorescence microscopy and confocal scanning laser microscope. Our data demonstrated that the intensity of laser-induced HMME fluorescence in macrophages steadily increased with the increasing incubation concentration of HMME. The survival rate of macrophages determined by MTT assay decreased with the increasing HMME concentration and irradiation time. HMME-based PDT induced macrophage apoptosis via caspase-9 and caspase-3 activation pathway detected by caspase fluorescent assay kit and flow cytometer. The PDT increased the number of apoptotic macrophages by 14-fold at 12 h post irradiation by 9 J/cm2 635 nm diode laser. These results imply that photodynamic therapy with HMME may therefore be a useful clinical treatment for unstable atherosclerotic plaques.

Non-invasive fluorescence imaging is an important technique in biology. However, detection of traditional biomarker emissions is accompanied by a high background signal. In this study we examined whether upconversion sodium yttrium fluoride (NaYF4) nanocrystals were suitable for autofluorescence-free multicolor fluorescence imaging in a living animal. Tissue autofluorescence was induced with a 405 nm light source, then rats were subjected to injection of fluorescein isothiocyanate (FITC), cadmium selenide/zinc sulfide (CdSe/ZnS) quantum dots (QDs), or NaYF4:ytterbium/thulium (Yb3+/Tm3+), NaYF4:Yb3+/holmium (Ho3+), and NaYF4:Yb3+/Ho3+/cerium (Ce3+) nanocrystals. Imaging with NaYF4 nanocrystals (974 nm laser) completely removed the high tissue autofluorescence, in marked contrast to imaging with FITC and QDs (405 nm light). Optical imaging experiments demonstrated that multiple biological targets and organs could be imaged at the same time using multicolor NaYF4 upconversion nanocrystals under a single excitation wavelength (974 nm). These data demonstrated the proof-of-principle that autofluorescence-free multicolor imaging using near-infrared to visible upconversion of NaYF4 nanocrystals excited by laser can be performed in a living animal.

Ultraviolet upconversion emissions at 262, 276, 308 and 320 nm were observed from Er3+-doped Y2O3 with a 532 nm continuous wave compact solid-state laser excitation. Power-dependence analysis demonstrates that two-photon upconversion process populates the 4D5/2, 2H9/2 and 2P3/2 states. The energy transfer upconversion (ETU) plays an important role in populating 4D5/2 and 2P3/2 states. It appears that 2P3/2 state population originates from ETU 2H11/2+2H11/2→4I13/2+2P3/2, moreover, a subsequent excited state absorption (ESA) from the 4I9/2 level.

Ultraviolet (UV) upconversion (UC) luminescence in Yb3+/Er3+-codoped yttrium oxide (Y2O3) nanocrystals can be enhanced by orders of magnitude via tridoping further with Li+ ions under diode laser excitation of 970 nm. Sensitized three-photon UC radiations at 390 and 409 nm, corresponding to the 4G11/2→4I15/2 and 4H9/2→4I15/2 of Er3+ ions, respectively, present an enhancement time of about 33 times, which is larger than the 24 times enhancement for the UC green radiation. The UV UC radiation at 320 nm that corresponds to the 2P3/2→4I15/2 of Er3+ ions has also been greatly enhanced. Theoretical calculations interpret that all the observed enhancement times of UV UC radiations arise from the prolonged lifetimes of their intermediate states.

Upconversion (UC) luminescence in monodisperse NaYF4:Yb3+/Tb3+ nanocrystals was observed under diode laser excitation of 970 nm, which were synthesized by a hydrothermal method. UC emissions at 380, 413, 436 nm and at 488, 542, 584, 620 nm arise from transitions 5D3(5G6) → 7FJ(J = 6, 5, 4) and 5D4 → 7FJ(J = 6, 5, 4, 3) of Tb3+ ions, respectively. UC mechanisms are proposed based on spectral, kinetic, decay time measurements, and pump power dependence analyses. Blue, green and red emissions originate from the same long-lived (milliseconds) upper 5D4 state, which promises the potential applications of these monodisperse Yb3+/Tb3+-codoped NaYF4 nanocrystals in the field of photonics, lasers and biomedicine.

ZnO nanowires with nanoislands attached are synthesized by thermal evaporation process using Sb as dopant. The electron microscopy and energy-dispersive X-ray spectroscopy show that the nanowires grow along [0 1¯ 1 1] with ±(1 0 1¯ 1) as side surfaces. The nanoislands are composed of SiOx shelled ZnO clusters and attached to polar surface (1 0 1¯ 1). We believe that the Sb dopant induces the growth along the distinct direction and leads the formation of additional structures on ZnO nanowires’ polar surface. The temperature-dependent photoluminescence confirms the existence of acceptor level related to Sb.

Ultraviolet (UV) and blue upconversion (UC) radiations with large and anomalous enhancement were observed in Y 2O3:Er3+ nanocrystals under laser excitation of 970 nm. Three-photon UV and blue UC radiations were enhanced by about 60 times via codoping with Li+ ions, in remarked contrast to the 45 times enhancement for two-photon green UC radiation. The integrated intensity of enhanced UV and blue UC radiations in Y 2O3:Er3+, Li+ nanocrystals can reach about half that in Y 2O3:Er3+ ceramic bulk. Such anomalous enhancement behavior for UV and blue UC radiations originates from the fact that the tailored lifetime of the S3/24 state was further involved for their generation, contrasted to the green UC emission involving only the tailored lifetime of the I11/24 state. Theoretical calculations based on steady state equations evidenced these conclusions.

This study aimed to assess the effect of toluidine blue (TB)-mediated photodynamic inactivation of periodontal pathogens (PP) from periodontopathic patients. Photodynamic therapy (PDT) was carried out using TB and 635 nm laser light irradiation. The bactericidal effect was evaluated, and important PDT parameters including light intensity, energy dose, and TB concentration were determined. Our findings suggest that TB-mediated lethal photosensitization of PP in vivo is possible. However, to obtain ideal bactericidal effect, higher doses of light and photosensitizer should be required in treatment in vivo than their planktonic counterparts. The best therapeutic effect was observed in treatment by 1 mg/ml TB combined with 12 J/cm2 at 159 mW/cm2 light irradiation. Moreover, because of the considerable interindividual differences of bacterial populations, TB-mediated PDT might not be equally effective among periodontopathic patients, and further studies on improvement of this therapeutic modality is needed.

We demonstrate that tridoping with Li+ ions enhances the visible green and red upconversion (UC) emissions in Er3+/Yb3+-codoped Y2O3 nanocrystals by up to half of the bulk counterpart, i.e., about 2 orders of magnitude higher than previous results. X-ray diffraction and decay time investigations give evidence that tridoping with Li+ ions can tailor the local crystal field of the Y2O3 host lattice. Theoretical calculations illustrate well that a significant UC intensity enhancement arises from the synthesized tailoring effect induced by the Li+ ions, which increase lifetimes in the intermediate 4I11/2 (Er) and 2F5/2 (Yb) states, increase optically active sites in the Y2O3 host lattice, and dissociate the Yb3+ and Er3+ ion clusters in the nanocrytals. The general theoretical description of the visible UC radiations shows that the Yb3+ ion sensitization and the tailoring effect induced by the Li+ ions are two independent enhancement mechanisms, which is expected to lead to an increasing number of photonic and biomedical applications in the future.

Room-temperature blue and violet upconversion (UC) emissions of Er3+ at 409 nm (2H9/2 → 4I15/2) and 390 nm (4G11/2 → 4I15/2) were observed in Y2O3:Yb3+–Er3+ nanocrystals by diode laser excitation of 980 nm. At low Yb3+ concentration both wavelengths result from three-photon UC processes. Unexpectedly, a four-photon and a decreased three-photon UC processes were observed at high Yb3+ concentration for the violet and the blue emissions, respectively. The four-photon process supposably results from the cross relaxation 4D7/2 + 4I15/2 → 4G11/2 + 4I13/2 of Er3+ ions with the 4D7/2 state populated by the 22F5/2(Yb) + 4F9/2(Er) → 22F7/2(Yb) + 4D7/2(Er) process, whereas the decreased photon process arises from the larger UC rate at high Yb3+ concentration.Four-photon and decreased three-photon UC processes were observed at high Yb3+ concentration for the violet and the blue emissions, respectively.

Polycrystalline Sm1.4Sr1.2Ca0.4Mn2O7 has been successfully synthesized and investigated with respect to its magnetic and electrical properties. It is found that the sample shows a metal insulator (M–I) transition at 88 K. The maxima of the magnetoresistance (MR) ratio are 95.38% and 98.55% under applied fields of 2 T and 5 T, respectively. At 10 K, the MR attains ∼75% at 5 T. The large MR at low temperature can be attributed to the effects of nearly fully spin-polarized carriers tunneling through the insulating (Sm, Sr, Ca)2O2 layers between the adjacent MnO2 bi-layers. The magnetization data indicates the existence of ferromagnetic clusters.

Successful periodontal therapy requires sensitive techniques to discriminate dental calculus from healthy teeth. The aim of the present study was to develop a fluorescence-based procedure to enable real-time detection and quantification of dental calculus. Thirty human teeth – 15 teeth with sub- and supragingival calculus and 15 healthy teeth – covered with a layer of physiological saline solution or blood were illuminated by a focused blue LED light source of 405 nm. Autofluorescence spectra recorded along a randomly selected line stretching over the crown-neck-root area of each tooth were utilized to evaluate a so called calculus parameter R, which was selected to define a relationship between the integrated intensities specific for healthy teeth and for calculus in the 477–497 nm (SA) and 628–685 nm (SB) wavelength regions, respectively. Statistical analysis was performed and a cut-off threshold of R = 0.2 was found to distinguish dental calculus from healthy teeth with 100% sensitivity and specificity under various experimental conditions. The results of the spectral evaluation were confirmed by clinical and histological findings. Automated real-time detection and diagnostics for clinical use were implemented by a corresponding software program written in Visual Basic language. The method enables cost-effective and reliable calculus detection, and can be further developed for imaging applications.

Ultraviolet (UV) and blue upconversion (UC) radiations with large and anomalous enhancement were observed in Y 2O3:Er3+ nanocrystals under laser excitation of 970 nm. Three-photon UV and blue UC radiations were enhanced by about 60 times via codoping with Li+ ions, in remarked contrast to the 45 times enhancement for two-photon green UC radiation. The integrated intensity of enhanced UV and blue UC radiations in Y 2O3:Er3+, Li+ nanocrystals can reach about half that in Y 2O3:Er3+ ceramic bulk. Such anomalous enhancement behavior for UV and blue UC radiations originates from the fact that the tailored lifetime of the S3/24 state was further involved for their generation, contrasted to the green UC emission involving only the tailored lifetime of the I11/24 state. Theoretical calculations based on steady state equations evidenced these conclusions.

•This work is an interdisciplinary research which combines the photoluminescence (PL) spectrum of rare earth ions and phase structure of ferroelectrics.•The Curie point determination by PL method has been proposed for the first time in this article.•It's non-contact, non-destructive, accurate, and cheap compared with the existing methods such as dielectric temperature spectrum, XRD analysis, or Raman spectrum analysis.•Furthermore, the found critical behavior of both PL intensity and peak position will make a difference for future application of “fluorescence ferroelectric/piezoelectric”.We developed a non-contact and non-destructive method to detect Curie point (TC) in Er3+ doped Ba0.77Ca0.23TiO3 (BCT) ferroelectric ceramic. Through investigating the photoluminescence (PL) spectra of Er3+ doped BCT ceramic we found that PL characteristics in ferroelectrics demonstrates critical behavior around TC. Both intensity and peak positions of the Stark sub-peaks originating from 4S3/2 to 4I15/2 transition change dramatically, and can be fitted with two different lines below and above TC. The inflection points of the PL characteristics are at the same temperature of 381(1) K, and coincident with the TC (381 K) determined by the dielectric temperature spectrum.

The luminescence and oxygen sensing properties of a series of palladium(II)- and gadolinium(III)-porphyrins were evaluated and compared. Spectral analysis indicates that absorption and luminescence of Gd-porphyrins are red-shifted compared to those of Pd-porphyrins. This demonstrates that the energy levels of excited states in Gd-porphyrins are lower than those in the corresponding Pd-porphyrins. Phosphorescence quantum yield of Pd-hematoporphyrin monomethyl ether (HMME) was about 3-fold higher than that of Gd-HMME due to the decreased non-radiative decay rate of triplet states in Pd-HMME, which was confirmed by the longer phosphorescence lifetime of Pd-HMME. This is attributed to the higher first excited triplet state (T1) in Pd-HMME as compared to that of Gd-HMME. However, the phosphorescence intensity and lifetime responses of Gd-HMME to oxygen were larger than those of Pd-HMME. To understand this difference, oxygen quenching constants (kq) of Gd- and Pd-HMME were evaluated and were found to be 4972.9 and 26.4 s−1, respectively. The huge difference in kq between the two species is responsible for their disparate oxygen responses. We suggest that the greater kq of Gd-HMME results from the better energy matching between its T1 (12658–14006 cm−1) and the second excited state (13123 cm−1) of oxygen, which was demonstrated by the higher singlet oxygen quantum yield of Gd-HMME. The same phenomena (spectral red-shifts, lower phosphorescence quantum yields, shorter lifetimes, and larger oxygen responses) were also observed upon substituting Pd(II) by Gd(III) in other porphyrins studied in this work.

A mechanism for the enhanced room-temperature phosphorescence (RTP) of gadolinium-coordinated hematoporphyrin monomethyl ether (Gd-HMME) in the presence of imidazole and free gadolinium ions (Gd3+) is revealed. Imidazole, the molten solvent used in the synthesis of Gd-HMME, was effective in enhancing the Gd-HMME RTP. In the presence of imidazole, further enhancement of the Gd-HMME RTP was observed upon adding Gd3+. Overall, a 40-fold enhancement of Gd-HMME RTP intensity was achieved by adding both imidazole and Gd3+. In addition, there was an increase in the RTP lifetime. Through spectroscopic analysis, we deduced that a protective medium is formed by the imidazole and the degree of this protection is further increased by Gd3+. The protective medium enhances the Gd-HMME RTP by partially inhibiting energy transfer from the lowest triplet state of Gd-HMME to oxygen. This was demonstrated by the presence of lower levels of singlet oxygen in the Gd-HMME solution after the addition of imidazole. These results indicate that imidazole could have potential application as an RTP enhancer or triplet state protector.