A novel series of intense red–green up-conversion (UC) phosphors SrO: Er3+/Yb3+, Gd3+, Lu3+, Bi3+ were obtained through a modified solid-state reaction. The obtained UC samples emitted dazzling red–green light. Their spectra were composed of strong red emission (4F9/2→4I15/2) and green emission (2H11/2, 4S3/2→4I15/2) with the excitation of a 980 nm near-infrared (NIR) laser diode (less than 90 mW/cm2). The dependence of UC spectra on dopant contents, concentration and pumping power were comprehensively analyzed. The possible UC mechanisms and processes were proposed. These studies provided an opportunity to adjust emission colors and design new types of materials with desired properties through referencing a given methodology. It is anticipated that these materials may have potential applications in the fields of authentication, display and photo-switching.

Although a variety of Bi3+-activated common luminescent materials have been investigated, few Bi3+-doped long afterglow phosphors have been discovered up to now. In this work, we developed a novel long afterglow material KGaGeO4:Bi3+ by solid-state reaction. The highlight of this work is the observation of bright cyan to blue color tunable long afterglow of KGaGeO4:Bi3+. The structural information of the samples was studied in detail using Rietveld refinement. Photoluminescence and phosphorescence properties of the phosphor were investigated systematically. The reason why the photoluminescence and phosphorescence color can be tuned has been discussed. A bright long afterglow could be observed by the naked eye for 3 hours in the dark after ultraviolet irradiation was ceased. Moreover, we have analyzed the reason why the KGaGeO4 host is suitable for Bi3+ to generate afterglow emission by exploring the nature of traps in KGaGeO4:Bi3+ with the help of thermoluminescence spectra. In this phosphor, Bi3+ ions doped in K+ sites behave as luminescence centers, while negatively charged defects serve as hole-trapping centers. In view of the experimental results, a feasible afterglow mechanism of KGaGeO4:Bi3+ was also proposed and discussed.

A novel dual-emitting temperature sensor, Sr1.7Zn0.3CeO4F0.2:Eu3+, is successfully synthesized via a ceramic reaction. Powder X-ray diffraction patterns and Rietveld refinement verify the phase purity of the sensor. Its photoluminescence spectrum exhibits a pronounced intrinsic dual emission, theoretically divided by the wavelength of 570 nm: one stems from Eu3+ and the other is derived from the Ce4+–O2− charge transfer state. The temperature-dependent luminescence spectra of the dual-emission thermophosphor demonstrate its superior sensitivity towards ambient temperature. Further studies illustrate that the intensity ratio between the aforementioned two parts, as a function of temperature, is perfectly linear over a broad temperature window, yielding a convenient and accurate approach to obtain the temperature of a target, measured using the noncontact self-referencing model. We also investigate the basis of the underlying mechanism of Sr1.7Zn0.3CeO4F0.2:Eu3+ as a dual-emission thermometric sensor. The research herein shows that the intrinsic dual-emission sensor, as a new-fashioned thermophosphor, displays potential for ratiometric intensity measurements in thermometry domains.

Infrared (IR) light-emitting materials have wide applications. However, variety and economical accesses to obtain IR materials and devices are still limited, because the IR-emitting materials are always suffering from two obstacles, namely, lower absorption and lower emission efficiency. In this work, using a modified high-temperature solid-state reaction an efficient short-wavelength IR luminescent material is successfully synthesized. On the basis of the excellent luminescent properties, a convenient IR light-emitting diode (LED) device is fabricated by combining the novel IR material with a commercial UV LED chip. Besides the anticipation that it may lead to a boost of the application of IR device in different fields, importantly, we also consider that the ingenious synthesis strategy may open a door for obtaining novel ions doped functional materials.

A novel dichromic luminescence probe SrO:Eu3+,Bi3+ for temperature sensing is achieved. The detailed luminescence properties, e.g., the excitation emission spectra, energy transfer efficiency, luminescence decay lifetimes and temperature dependent luminescence are comprehensively studied. The two dominant emissions 5D0 → 7F2 transition of Eu3+ and the 3P1 → 1S0 transition of Bi3+ display adjustable spectrum area. The interaction effect between Eu3+ and Bi3+ are proposed. The dichromic emissions are specifically responding to temperature with high sensitivity at ultra-wide range from 30 to 400 °C. Spatial and temporal temperature images on an aircraft surface have been successfully realized under excitation of commercial 365 nm light emitting diode (LED) by painting the SrO:Bi3+,Eu3+ phosphor on a plane model. Finally, the thermal quenching mechanism revealed by Arrhenius theory is employed to interpret the temperature sensitive luminescence behaviour.

A new orange-yellow-emitting Sr9Mg1.5(PO4)7:Eu2+ phosphor was prepared via high-temperature solid-state reaction. The structure and optical properties of it were studied systematically. Sr9Mg1.5(PO4)7:Eu2+ can be well-excited by 460 nm blue InGaN chips and exhibit a wide emission band covering from 470 to 850 nm with two main peaks centered at 523 and 620 nm, respectively, which originate from 5d–4f dipole-allowed transitions of Eu2+ in different crystallographic sites. The sites attribution, concentration quenching, fluorescence decay analysis, and temperature-dependent luminescence properties were investigated in detail. Furthermore, a warm white LED device was fabricated by combining a 460 nm blue InGaN chip with the optimized orange-yellow-emitting Sr9Mg1.5(PO4)7:Eu2+. The color coordinate, correlated color temperature and color rendering index of the fabricated LED device were (0.393, 0.352), 3437 K, and 86.07, respectively. Sr9Mg1.5(PO4)7:Eu2+ has great potential to serve as an attractive candidate in the application of blue light-excited warm white LEDs.Keywords: blue InGaN chips; orange-yellow-emitting phosphor; photoluminescence; Sr9Mg1.5(PO4)7:Eu2+; warm white LEDs

Adjusting and controlling an ion’s chemical state has always been a focus of researchers’ attention. Herein, an intense long-lasting phosphorescence of Eu2+ is obtained without any sacrificial reductant. The remarkable self-reducing process and the unique luminescence properties stem from a variation of the topological structure of the BO3 triangle.

A series of single-phase Ca9Sc(PO4)7:Eu2+,Tb3+,Mn2+ phosphors for UV excitations were synthesized by a high-temperature solid-state reaction. Energy transfer from Eu2+ → Tb3+ and Eu2+ → Mn2+ in a Ca9Sc(PO4)7 sample is a feasible route to realize color-tunable emission because Ca9Sc(PO4)7 single-doped Eu2+/Tb3+/Mn2+ emit blue, green and red light, respectively. Most of the white light region in the CIE chromaticity diagram has been realized in Ca9Sc(PO4)7:Eu2+,Tb3+,Mn2+ phosphors. Warm white light including the points of (0.337, 0.331), (0.353, 0.355) and (0.358, 0.327) close to day light (0.33, 0.33) with CCT of 5285 K, 4719 K and 4333 K is obtained, respectively.

Convenient, efficient synthesis methods that improve the emission intensity of rare earth ion doped phosphors are relatively rare. In this study, a simple modified solid-state reaction is proposed. This approach can greatly improve reaction temperature and overcome the requirement for harsh conditions. Its advantages come from the substitution of a solid–solid interface for a solid–gas interface. A novel Ce3+ doped SrO phosphor with an enhancive bright cyan emission is prepared and the photoluminescent properties of SrO:Ce3+ are first reported. This study will provide valuable clues for synthesizing many other ion doped functional materials besides rare earth ion doped luminescent materials.

In this article we synthesized a series of new reddish orange long-lasting phosphorescence phosphors by co-doping Li+ ions into Sm3+ activated α-Zn2P2O7, characterized their luminescence properties, and evaluated the effect of Li+ co-doping on both photoluminescence and Phosphorescence. The results showed that both the photoluminescence and Phosphorescence originated from characteristic reddish orange emissions of Sm3+ from its 4f–4f transitions of 4G5/2–6H5/2, 4G5/2–6H7/2 4G5/2–6H9/2 and 4G5/2–6H11/2. Besides markedly enhancing the photoluminescence intensity of Sm3+, the Li+ entering into the crystal lattice also promoted the long lasting phosphorescence performance via modifying the defect levels in the phosphors. The optimal long afterglow material was achieved when the Li+ concentration is 2 mol%. This phosphor shows bright reddish orange phosphorescence which could last for more than 3 hours in the dark. Four peaks appeared in its thermoluminescence curve, and the one at around 350 K was proved to be responsible for the occurrence of long lasting phosphorescence. The release of the captured electrons in the defect levels corresponding to this TL peak in room temperature to emission centers of Sm3+ underwent a tunneling process.

Novel red-emitting Eu3+, Sm3+ singly doped and co-doped Ca14Mg2(SiO4)8 phosphors were prepared by conventional solid- state reaction. Powder X-ray diffraction patterns were employed to confirm phase purity. Ca14Mg2(SiO4)8:Eu3+ phosphors exhibited intense red emission under 394 nm excitation and Ca14Mg2(SiO4)8:Sm3+ phosphors, excited at 405 nm, also showed strong red emitting at 602 nm. The concentration quenching mechanism of Ca14Mg2(SiO4)8:Eu3+ was dipole-dipole interaction, while that of Ca14Mg2(SiO4)8:Sm3+ was energy migration among nearest neighbor ions. The results indicated that Ca14Mg2(SiO4)8:Eu3+ and Ca14Mg2(SiO4)8:Sm3+ were promising red-emitting phosphors for WLEDs. Meanwhile, the effect of co-doping Sm3+ ions on photoluminescence properties of Ca14Mg2(SiO4)8:Eu3+ was studied and energy transfer from Sm3+ to Eu3+ was discovered in Eu3+, Sm3+ co-doped phosphors.(a) A schematic diagram of energy transfer model from Sm3+ to Eu3+ ions; (b) CIE chromaticity coordinates of (3) CMSO: 0.50Eu3+ (λex=390 nm), CMSO:0.08Sm3+ (1) and CMSO:0.08Sm3+,0.30Eu3+ (λex=405 nm) (2)

•A series of SC:0.01Eu3+ materials with different charge compensators were synthesized and further investigated by EDS, XPS, XRD and Rietveld refinements to verify the purity.•The effects of charge compensators on optical features were systematically studied via the reflectance and photoluminescence spectra.•The anionic charge compensators, especially F−, greatly enhanced photoluminescence properties, which may provide a novel method to synthesize and improve phosphors.Presently enormous interest in the modification of photoluminescence properties of Sr2CeO4:Eu3+ with charge compensators has been stimulated. Here we report the effect of charge compensators on optical characteristic of Sr2CeO4:Eu3+ synthesized by altering types of charge compensators and propose the possible explanation. The conclusion is made that anionic charge compensators, especially F−, may provide a novel approach to the development and improvement of the phosphors.

A series of novel red-emitting Sr1.7Zn0.3CeO4:Eu3+ phosphors were synthesized through conventional solid-state reactions. The powder X-ray diffraction patterns and Rietveld refinement verified the similar phase of Sr1.7Zn0.3CeO4:Eu3+ to that of Sr2CeO4. The photoluminescence spectrum exhibits that peak located at 614 nm (5D0–7F2) dominates the emission of Sr1.7Zn0.3CeO4:Eu3+ phosphors. Because there are two regions in the excitation spectrum originating from the overlap of the Ce4+–O2– and Eu3+–O2– charge-transfer state band from 200 to 440 nm, and from the intra-4f transitions at 395 and 467 nm, the Sr1.7Zn0.3CeO4:Eu3+ phosphors can be well excited by the near-UV light. The investigation of the concentration quenching behavior, luminescence decay curves, and lifetime implies that the dominant mechanism type leading to concentration quenching is the energy transfer among the nearest neighbor or next nearest neighbor activators. The discussion about the dependence of photoluminescence spectra on temperature shows the better thermal quenching properties of Sr1.7Zn0.3CeO4:0.3Eu3+ than that of Sr2CeO4:Eu3+. The experimental data indicates that Sr1.7Zn0.3CeO4:Eu3+ phosphors have the potential as red phosphors for white light-emitting diodes.Keywords: concentration quenching; photoluminescence; red-emitting phosphors; thermal quenching;

A series of new phosphors Zn2(0.97−x)P2O7:0.06Tm3+,2xMn2+ (0 ≤ x ≤ 0.05) were synthesized and their luminescence properties were investigated. The results showed that the defects in all the phosphors were related to Tm3+, and Mn2+ merely served as the emission centres. Tm3+ also acted as an emission centre and yielded blue phosphorescence corresponding to its characteristic f–f emissions in the phosphors where the Mn2+ concentration was low (x ≤ 0.001), while in the phosphors with high concentrations of Mn2+ it mainly served as a defect by forming Tm˙Zn. The electrons thermally released from defects selectively transferred to Mn2+ centres mainly through thermally-assisted tunnelling and this resulted in their red to near-infrared phosphorescence. By adjusting the ratio of Mn2+ to Tm3+ to control the spectral distribution, tunable long lasting phosphorescence from blue to near-infrared was achieved.

•The synthesized Sr2CeO4:Eu3+ phosphors were firstly probed by the Rietveld refinement.•The luminescence properties of Sr2CeO4:Eu3+ were systematically investigated.•The energy transfer from the Ce4+–O2− CTS to Eu3+ was discussed in detail based on the Inokuti–Hirayama theory.A series of color-tunable Sr2CeO4:Eu3+ phosphors have been successfully synthesized. The Rietveld refinement was firstly used to probe the phase purity and the structure of Sr2CeO4:Eu3+. The photoluminescence excitation spectra exhibit that the phosphors show a broad excitation band from 200 to 400 nm, which concurs well with the commercial near-UV LED. The photoluminescence spectra vary with the dopant content due to the energy transfer and the tunable blue-red color can be simply achieved by altering the doped Eu3+ ions concentrations. On the basis of the Inokuti–Hirayama theory, we obtained that the dipole-dipole interaction type takes charge for the energy transfer from the Ce4+–O2− charge-transfer state transition to Eu3+ ions and the schematic was plotted to illuminate the possible energy transfer process. The experimental results indicate that Sr2CeO4:Eu3+ phosphors may be potentially used as promising single-phased phosphors for near-UV white light-emitting diodes applications.

•Green long-lasting phosphorescence phosphor Ca14Mg2(SiO4)8:Eu2+, Dy3+ was prepared.•The luminescence and phosphorescence properties were investigated systematically.•Long-lasting phosphorescence mechanism of this phosphor was generally discussed.A novel silicate long-lasting phosphorescence phosphor Ca14Mg2(SiO4)8:Eu2+, Dy3+ was prepared by high-temperature solid state reaction. Its properties were investigated systematically by powder X-ray diffraction patterns, Rietveld refinements, photoluminescence spectra, long-lasting phosphorescence spectra, phosphorescence decay curves, and thermoluminescence spectra. Under the excitation of 400 nm, Ca14Mg2(SiO4)8:Eu2+, Dy3+ phosphor exhibits green light with the peak at 505 nm, which is attributed to the 4f65d1–4f7 electronic transition of Eu2+ ions. It is also found that Ca14Mg2(SiO4)8:Eu2+, Dy3+ phosphor can emit green persistent phosphorescence after the irradiation of ultraviolet or visible light is stopped. And for the optimal sample, the green persistent luminescence can last for about half an hour. The co-doping of Dy3+ ions greatly enhances the intensity and duration of the persistent luminescence in Ca14Mg2(SiO4)8:Eu2+, Dy3+ phosphor. However, the peak position of the long-lasting phosphorescence spectrum is red shift compared to that of the photoluminescence spectrum, and the possible reason was analyzed. Meanwhile, the long-lasting phosphorescence mechanism of this phosphor was also discussed.

•Bluish green long-lasting phosphorescence Ca9Bi(PO4)7:Eu2+,Dy3+ phosphor was synthesized for the first time.•The luminescence and phosphorescence properties of Ca9Bi(PO4)7:Eu2+,Dy3+ were systematically studied.•The corresponding afterglow mechanism of this phosphor was discussed.A new long-lasting phosphorescence phosphor Ca9Bi(PO4)7:Eu2+,Dy3+ was synthesized by solid state reaction and its long-lasting phosphorescence properties were investigated for the first time. The X-ray powder diffraction, photoluminescence, long-lasting phosphorescence spectra, decay curves and thermoluminescence curves were measured. The Ca9Bi(PO4)7:Eu2+,Dy3+ phosphor exhibits an asymmetric emission centered at 475 nm, which can be ascribed to the 4f65d1–4f7 electronic transition of Eu2+. For the optimized sample, the bright bluish green long-lasting phosphorescence could be observed for 5 h by naked eyes after the excitation source was removed. The long-lasting phosphorescence spectra show that the co-doping of Dy3+ ions greatly enhance the intensity of the long-lasting phosphorescence. Meanwhile, the long-lasting phosphorescence mechanism of this phosphor was discussed. Based on our study, Dy3+ ions are suggested to increase the density of electron or hole traps so as to improve the performance of the bluish green phosphorescence of Eu2+, including the intensity and persistent time.

A series of new phosphors Zn2(0.97−x)P2O7:0.06Tm3+,2xMn2+ (0 ≤ x ≤ 0.05) were synthesized and their luminescence properties were investigated. The results showed that the defects in all the phosphors were related to Tm3+, and Mn2+ merely served as the emission centres. Tm3+ also acted as an emission centre and yielded blue phosphorescence corresponding to its characteristic f–f emissions in the phosphors where the Mn2+ concentration was low (x ≤ 0.001), while in the phosphors with high concentrations of Mn2+ it mainly served as a defect by forming Tm˙Zn. The electrons thermally released from defects selectively transferred to Mn2+ centres mainly through thermally-assisted tunnelling and this resulted in their red to near-infrared phosphorescence. By adjusting the ratio of Mn2+ to Tm3+ to control the spectral distribution, tunable long lasting phosphorescence from blue to near-infrared was achieved.

A novel dichromic luminescence probe SrO:Eu3+,Bi3+ for temperature sensing is achieved. The detailed luminescence properties, e.g., the excitation emission spectra, energy transfer efficiency, luminescence decay lifetimes and temperature dependent luminescence are comprehensively studied. The two dominant emissions 5D0 → 7F2 transition of Eu3+ and the 3P1 → 1S0 transition of Bi3+ display adjustable spectrum area. The interaction effect between Eu3+ and Bi3+ are proposed. The dichromic emissions are specifically responding to temperature with high sensitivity at ultra-wide range from 30 to 400 °C. Spatial and temporal temperature images on an aircraft surface have been successfully realized under excitation of commercial 365 nm light emitting diode (LED) by painting the SrO:Bi3+,Eu3+ phosphor on a plane model. Finally, the thermal quenching mechanism revealed by Arrhenius theory is employed to interpret the temperature sensitive luminescence behaviour.

Although a variety of Bi3+-activated common luminescent materials have been investigated, few Bi3+-doped long afterglow phosphors have been discovered up to now. In this work, we developed a novel long afterglow material KGaGeO4:Bi3+ by solid-state reaction. The highlight of this work is the observation of bright cyan to blue color tunable long afterglow of KGaGeO4:Bi3+. The structural information of the samples was studied in detail using Rietveld refinement. Photoluminescence and phosphorescence properties of the phosphor were investigated systematically. The reason why the photoluminescence and phosphorescence color can be tuned has been discussed. A bright long afterglow could be observed by the naked eye for 3 hours in the dark after ultraviolet irradiation was ceased. Moreover, we have analyzed the reason why the KGaGeO4 host is suitable for Bi3+ to generate afterglow emission by exploring the nature of traps in KGaGeO4:Bi3+ with the help of thermoluminescence spectra. In this phosphor, Bi3+ ions doped in K+ sites behave as luminescence centers, while negatively charged defects serve as hole-trapping centers. In view of the experimental results, a feasible afterglow mechanism of KGaGeO4:Bi3+ was also proposed and discussed.

Adjusting and controlling an ion’s chemical state has always been a focus of researchers’ attention. Herein, an intense long-lasting phosphorescence of Eu2+ is obtained without any sacrificial reductant. The remarkable self-reducing process and the unique luminescence properties stem from a variation of the topological structure of the BO3 triangle.

A series of single-phase Ca9Sc(PO4)7:Eu2+,Tb3+,Mn2+ phosphors for UV excitations were synthesized by a high-temperature solid-state reaction. Energy transfer from Eu2+ → Tb3+ and Eu2+ → Mn2+ in a Ca9Sc(PO4)7 sample is a feasible route to realize color-tunable emission because Ca9Sc(PO4)7 single-doped Eu2+/Tb3+/Mn2+ emit blue, green and red light, respectively. Most of the white light region in the CIE chromaticity diagram has been realized in Ca9Sc(PO4)7:Eu2+,Tb3+,Mn2+ phosphors. Warm white light including the points of (0.337, 0.331), (0.353, 0.355) and (0.358, 0.327) close to day light (0.33, 0.33) with CCT of 5285 K, 4719 K and 4333 K is obtained, respectively.