A series of novel blue long-lasting phosphorescence phosphors Sr6Al18Si2O37:Eu2+,RE3+ (RE3+=Ho3+, Gd3+, Dy3+ and Pr3+) were prepared by the conventional high-temperature solid-state reaction in a reductive atmosphere. Their properties were systematically investigated utilizing X-ray diffraction (XRD), photoluminescence, phosphorescence and thermoluminescence (TL) spectra. The phosphors emitted blue light that was related to the emission of Eu2+ due to 5d-4f transition. Bright blue long-lasting phosphorescence (LLP) could be observed after the excitation source was switched off. For the optimized sample, the blue long-lasting phosphorescence could last for nearly 4 h in the light perception of the dark-adapted human eye (0.32 mcd/m2). The effects of RE3+ ions on phosphorescence properties of the phosphors were studied, and the results showed that the co-doping of RE3+ ions greatly enhanced the intensity of the peak around 315 K which was related to the long lasting phosphorescence of the phosphors at room temperature and consequently improved the performance of the blue phosphorescence such as intensity and persistent time.LLP spectra of SASO:Eu2+,RE3+ (RE=Ho, Gd, Dy and Pr) measured 3 min after the excitation source was switched off (Inset: CIE1931 Chromaticity Diagram)

A new aluminosilicate long-lasting phosphor with composition of NaAlSiO4:Eu2+,Ho3+ was synthesized and investigated. Under UV light excitation, the phosphor emitted yellow light corresponding to the characteristic emission of Eu2+ due to 5d-4f transition. Bright yellow phosphorescence sustaining for more than 30 min was observed after ceasing the excitation. The phosphorescence intensity decay obeyed a t−1 decay law, indicating a tunneling electron-hole recombination process in the phosphor. Four peaks appeared in the thermoluminescence curve and the ones at 322 and 370 K were thought to account for the long lasting phosphorescence at room temperature. The Ho3+ ion incorporated into the phosphor did not give any light but dramatically increased the intensities of both photoluminescence and phosphorescence via promoting defect levels in the phosphor.Three-dimension (3D) TL spectra of NaAlSiO4: Eu2+, Ho3+ measured from room temperature to 650 K with a heating rate of 3K per second

The temperature-dependent luminescence of Sr1.7Eu0.3MxCeO4.15+x/2 (M = Li+, Na+, K+, x = 0, 0.3) samples was investigated and discussed in the temperature range from 303 to 573 K. It is found that the thermal quenching temperature of samples decreases with Li+-/Na+-doping but increases with the incorporation of K+. We suggest that these observations are resulted from two factors. One is that the incorporation of Li+/Na+/K+ ions reduces the strength of potential field at the O2− sites, and then results in a red-shift of the Eu–O charge transfer band. The other is that Δr expands with Li+-/Na+-doping but shrinks with K+-doping. We consider that it is a feasible way to adjust the temperature-dependent luminescence properties of materials by introducing appropriate impurities.Research highlights► For Li+-doing, Na+-doping or K+-doping, the different substitution mechanisms are proposed and confirmed. ► The Eu–O CT band shifts to longer wavelength by doping with monovalent ions, Li+, Na+, K+. ► We explain it via two factors, i.e., ionic charge and electronegativity value. We propose that the influencing of the former is larger than the latter. ► An obvious thermal quenching behaviors for all red emitting samples are observed, providing for a possible application of the materials in thermometry. ► The thermal quenching temperatures vary with the addition of monovalent ions, Li+, Na+, K+. ► We interpret it via the shift of the excited Eu–O charge transfer state, consisting of its energy and Δr. ► We put forward a possible way to change thermal quenching luminescence properties of fluorescence materials by adding appropriate impurity ions, which is important for their applications in luminescence or thermometry.

Long-lasting phosphorescence (LLP) was observed in Pr3+-doped Y3Al5O12 (YAG:Pr) after it was excited by 240 or 290 nm light. The photoluminescence (PL) and LLP properties were studied. It is interesting that the PL and LLP spectra were different. In the PL emission spectra both the emissions of d–f and f–f transitions of Pr3+ ions were observed. However, in the LLP spectra of YAG:Pr the emissions of d–f transition were absent. It is deduced that the differences were due to the energy transfer process between traps and emission centers. On the other hand, significant differences were observed between the two LLP spectra after the sample was excited by 240 and 290 nm lights, respectively. The thermoluminescence (TL) properties were also studied. It is suggested that these studies will be significant for understanding the mechanism of LLP phenomenon.Highlights► Red LLP in Pr-doped Y3Al5O12 phosphor synthesized in reducing atmosphere. ► Difference between PL emission and LLP emission. ► Different LLP spectra excited by different wavelength light. ► Energy transfer between traps and emission center.

The room-temperature luminescent emission characteristics of Sr2CeO4:M+ and Sr2CeO4:Eu3+,M+ (M+ = Li+, Na+, K+) have been investigated under UV excitation. By introducing appropriate alkali metal cations dopants (Li+, Na+, K+) into the crystalline lattice, not only emission color of the blue-white-emitting Sr2CeO4 doped with low Eu3+ content can be tuned to green, but also the red emission intensity of Sr2CeO4 doped with high Eu3+ concentration is strengthened significantly. The relevant mechanisms have been elucidated in detail.

Tb3+ activated Sr4Al14O25 phosphors were synthesized by the high temperature solid-state reaction. For the sample, the color of the photoluminescence (PL) was green, but that of the afterglow was blue. The spectral results indicated that the photoluminescence was mainly due to the transitions from 5D4 to the ground energy levels of Tb3+ and obeyed the cross-relaxation mechanism; however, the afterglow was derived from the transitions from 5D3 and independent with the concentration of Tb3+. This difference was attributed to the reason that the energy transfer process of cross-relaxation was halted by the traps during the period of afterglow.

Polycrystalline powder sample of KSr4(BO3)3 was synthesized by high-temperature solid-state reaction. The influence of different rare earth dopants, i.e. Tb3+, Tm3+ and Ce3+, on thermoluminescence (TL) of KSr4(BO3)3 phosphor was discussed. The TL, photoluminescence (PL) and some dosimetric properties of Ce3+-activated KSr4(BO3)3 phosphor were studied. The effect of the concentration of Ce3+ on TL intensity was investigated and the result showed that the optimum Ce3+ concentration was 0.2 mol%. The TL kinetic parameters of KSr4(BO3)3:0.002 Ce3+ phosphor were calculated by computer glow curve deconvolution (CGCD) method. Characteristic emission peaking at about 407 and 383 nm due to the 4f05d1 → 2F(5/2, 7/2) transitions of Ce3+ ion were observed both in PL and three-dimensional (3D) TL spectra. The dose–response of KSr4(BO3)3:0.002 Ce3+ to γ-ray was linear in the range from 1 to 1000 mGy. In addition, the decay of the TL intensity of KSr4(BO3)3:0.002 Ce3+ was also investigated.

Phosphate long lasting phosphorescence (LLP) phosphors with composition of (Zn1−xTmx)2P2O7 were prepared by the high-temperature solid-state method. Their properties were systematically investigated utilizing XRD, photoluminescence, phosphorescence and thermoluminescence (TL) spectra. These phosphors emit blue light that is related to the characteristic emission due to the 1D2–3H6, 1D2–3H4 and 1G4–3H6 transitions of Tm3+. After the UV light excitation source was switched off, the bright blue long lasting phosphorescence can be observed which could last for more than 1 h in the limit of light perception of dark-adapted human eyes (0.32 mcd/m2). Two TL peaks at 336 K and 415 K appeared in the TL spectrum. By analyzing the TL curve the depths of traps were calculated to be 0.67 eV and 0.97 eV, respectively. Also, the mechanism was discussed in this report.

A new pyrophosphate long-lasting phosphor with composition of Ca1.96P2O7:0.02Eu2+, 0.02Y3+ is synthesized via the high-temperature solid-state reaction method. Its properties are systematically investigated utilizing XRD, photoluminescence, phosphorescence and thermoluminescence (TL) spectra. The phosphor emits blue light that is related to the characteristic emission of Eu2+ due to 5d–4f transitions. For the optimized sample, bright blue long-lasting phosphorescence (LLP) could be observed by naked eyes even 6 h after the excitation source is removed. The TL spectra show that the doping of Y3+ ions greatly enhanced intensity of 335 K peak and created new TL peak at about 373 K that is also responsible for the blue LLP. Based on our study, Y3+ ions are suggested to act as electron traps to improve the performance of the blue phosphorescence of Eu2+ such as intensity and persistent time.

By introducing the Y3+ into Sr2P2O7:Eu2+, we successfully prepared a kind of new phosphor with blue long-lasting phosphorescence by the high-temperature solid-state reaction method. In this paper, the properties of Sr2P2O7:Eu2+,Y3+ were investigated utilizing XRD, photoluminescence, luminescence decay, long-lasting phosphorescence and thermoluminescence (TL) spectra. The phosphor emitted blue light that was related to the 4f65d1–8S7/2 transition of Eu2+. The bright blue phosphorescence could be observed by naked eyes even 8 h after the excitation source was removed. Two TL peaks at 317 and 378 K related to two types of defects appeared in the TL spectrum. By analyzing the TL curve the depths of traps were calculated to be 0.61 and 0.66 eV. Also, the mechanism of LLP was discussed in this report.

RE3+-activated α- and β-CaAl2B2O7 (RE=Tb, Ce) were synthesized with the method of high-temperature solid-state reaction. Their VUV excitation and VUV-excited emission spectra are measured and discussed in the present article. The charge transfer band of Tb3+ and Ce3+ is respectively calculated to be at 151±2 and 159±3 nm. All the samples show an activator-independent excitation peak at about 175 nm and an emission peak at 350–360 nm ascribed to the host absorption and emission band, respectively.

Phosphors CaYBO4:RE3+ (RE=Eu, Gd, Tb, Ce) were synthesized with the method of solid-state reaction at high temperature, and their vacuum ultraviolet (VUV)–visible luminescent properties in VUV–visible region were studied at 20 K. In CaYBO4, it is confirmed that there are two types of lattice sites that can be substituted by rare-earth ions. The host excitation and emission peaks of undoped CaYBO4 are very weak, which locate at about 175 and 350–360 nm, respectively. The existence of Gd3+ can efficiently enhance the utilization of host absorption energy and result in a strong emission line at 314 nm. In CaYBO4, Eu3+ has typical red emission with the strongest peak at 610 nm; Tb3+ shows characteristic green emission, of which the maximum emission peak is located at 542 nm. The charge transfer band of CaYBO4:Eu3+ was observed at 228 nm; the co-doping of Gd3+ and Eu3+ can obviously sensitize the red emission of Eu3+. The fluorescent spectra of CaYBO4:Ce3+ is very weak due to photoionization; the co-addition of Ce3+–Tb3+ can obviously quench the luminescence of Tb3+.

Borates LiSr4(BO3)3 were synthesized by high-temperature solid-state reaction. The thermoluminescence (TL) and some of the dosimetric characteristics of Ce3+-activated LiSr4(BO3)3 were reported. The TL glow curve is composed of only one peak located at about 209 °C between room temperature and 500 °C. The optimum Ce3+ concentration is 1 mol% to obtain the highest TL intensity. The TL kinetic parameters of LiSr4(BO3)3:0.01Ce3+ were studied by the peak shape method. The TL dose response is linear in the protection dose ranging from 1 mGy to 1 Gy. The three-dimensional thermoluminescence emission spectra were also studied, peaking at 441 and 474 nm due to the characteristic transition of Ce3+.

The Sr2Mg(BO3)2 phosphors doped respectively with Tm3+, Tb3+ and Dy3+ as activator were prepared by high temperature solid-state reaction. All the thermoluminescence curves of the phosphors consisted of two isolated peaks and the Dy3+ activated sample exhibited the strongest thermoluminescence intensity. The kinetic parameters of the thermoluminescence of Sr2Mg(BO3)2 : 0.04 Dy were calculated employing the peak shape method and 3 dimensional thermoluminescent emission spectra were observed peaking at 480, 579, 662 and 755 nm due to the characteristic transition of Dy3+. In addition, the pre-irradiation heat-treatment and the thermoluminescence dose response of Sr2Mg(BO3)2 : 0.04 Dy were investigated.