The Energy Transfer and Thermal Stability of a Blue‐Green Color Tunable K2CaP2O7:Ce3+,Tb3+ Phosphor

Novel blue‐green emitting Ce³⁺‐ and Tb³⁺‐activated K₂CaP₂O₇ (KCPO) luminescent materials were synthesized via a solid‐state reaction method. X‐ray diffraction, luminescence spectroscopy, decay time, and fluorescent thermal stability tests have been used to characterize the prepared samples. The KCPO:Ce³⁺,Tb³⁺ luminescence spectra show broad band of Ce³⁺ ions and characteristic line of Tb³⁺ ion transition (⁵D₄–⁷F₅). The color variation in the light emitting from blue to green under UV excitation can be obtained by tailoring the Tb³⁺ content in KCPO:Ce³⁺. Besides, Ce³⁺ ions obviously intensify Tb³⁺ ion emission through an effective energy transfer process, which was confirmed from decay curves. The energy transfer efficiency was determined to be 82.51%. A resonant type mechanism via the dipole–quadrupole interaction can be proposed for energy transfer. As a whole, the KCPO:Ce³⁺,Tb³⁺ phosphor exhibits excellent performance in the range from 77 to 673 K, indicating the phosphors are highly potential candidates for solid‐state lighting.     

Luminescence Properties and Energy Transfer of Ce3+,Tb3+‐Coactivatedβ‐SiAlON Phosphors

Using the solid‐state reaction method, Ce³⁺,Tb³⁺‐coactivated Si₅AlON₇ (Si_6?zAl_zO_zN_8?z, z = 1) phosphors were successfully synthesized. The obtained phosphors exhibit high absorption and strong excitation bands in the wavelength range of 240–440 nm, matching well with the light emitting‐diode (LED) chip. The ET from Ce³⁺ to Tb³⁺ ions in Si₅AlON₇:Ce³⁺,Tb³⁺ has been studied and demonstrated by the luminescence spectra and decay curves. Moreover, the phosphors show tunable emissions from blue to green by tuning the relative ratio of the Ce³⁺ to Tb³⁺ ions. Thermal quenching properties of Si₅AlON₇:Ce³⁺,Tb³⁺ had also been investigated and the quenching temperature is ~190°C. These results show that Si₅AlON₇:Ce³⁺,Tb³⁺ could be a promising candidate for a single‐phased color‐tunable phosphor applied in UV‐chip pumped LEDs.     

Tuning the Color Emission of Sr2P2O7: Tb3+, Eu3+ Phosphors Based on Energy Transfer

A series of color tunable Tb³⁺‐ and Eu³⁺‐activated Sr₂P₂O₇ phosphors were synthesized by a traditional solid‐state reaction method in air atmosphere. The crystal structure, photoluminescence (PL) properties, energy transfer, thermal stability, and luminous efficiency were investigated. A series of characteristic emission of Tb³⁺ and Eu³⁺ were observed in the PL spectra and the variation in the emission intensities of the three emission peaks at around 416 nm (blue), 545 nm (green), and 593 nm (orange‐red) induced the multicolor emission evolution by tuning the Tb³⁺/Eu³⁺ content ratio. The energy‐transfer mechanism from Tb³⁺ to Eu³⁺ ion was determined to be dipole–dipole interaction, and the energy‐transfer efficiency was about 90%. The novel phosphors have excellent thermal stability in the temperature range of 77–473 K and the Commission International De L'Eclairage 1931 chromaticity coordinates of Sr₂P₂O₇: Tb³⁺, Eu³⁺ (λ_ex = 378 nm) move toward the ideal white light coordinates.     

New apatite-type phosphor Ca9La(PO4)5(SiO4)F2:Tb3+,Dy3+ with improved color rendering index

Ca₉La(PO₄)₅(SiO₄)F₂:Tb³⁺,Dy³⁺ (CLPSF:Tb³⁺,Dy³⁺) phosphors were successfully prepared using the traditional solid-state technique. The crystal structure was refined and the luminescence properties have been examined in detail. The band gap and electronic structure of Ca₉La(PO₄)₅(SiO₄)F₂ were performed by the periodic density functional theory (DFT) calculation. The spectral and fluorescence decay dynamics of CLPSF:Tb³⁺,Dy³⁺ show that the energy transfer behavior between Tb³⁺ and Dy³⁺ ions is observed. The CLPSF:Tb³⁺,Dy³⁺ phosphors can be efficiently excitable at the wavelengths range from 300 to 500 nm. The emission spectrum covers the whole visible part of the spectra with the sharp emission bands in red, green, and blue regions. The correlated color temperature (CCT) and color rendering index (CRI) of white light emission could be improved by the fine-tuning of the Tb³⁺ and Dy³⁺ ions ration in accordance with the energy transfer behavior. Thus, the CLPSF:Tb³⁺,Dy³⁺ phosphor could be used as a material for the near-ultraviolet (n-UV) and white light-emitting diodes (w-LEDs).     

A Single‐Phase Phosphor NaLa9 (GeO4)6O2: Tm3+, Dy3+ for Near Ultraviolet‐White LED and Field‐Emission Display

Single‐phase white‐light‐emitting phosphors NaLa_9(1?x?y) (GeO₄)₆O₂: xTm³⁺, yDy³⁺ (NLGO: xTm³⁺, yDy³⁺) have been synthesized by a traditional solid‐state reaction method. The powder X‐ray diffraction (XRD), photoluminescence (PL), PL excitation (PLE) spectra, fluorescence decay curves, chromaticity coordinates, correlated color temperature (CCT), and the cathodoluminescence (CL) properties of the obtained phosphors are measured and discussed in detail. It is discovered that the series samples could be color‐tunable (from blue to yellow) by tuning the doping content of Dy³⁺ with a fixed Tm³⁺ content excited at 357 nm and white light (0.341, 0.324) could be obtained with the CCT of 5079 K. A NLGO: 0.01Tm³⁺, 0.02Dy³⁺ is studied carefully as representative. The main emissions of Tm³⁺ (453 nm, ¹D₂–³F₄) and Dy³⁺ (478 nm, ⁴F_9/2–⁶H_15/2; 572 nm, ⁴F_9/2–⁶H_13/2) make it emit white light with good thermal stability (67% of the initial till 523 K). The energy transfer from Tm³⁺ to Dy³⁺ is noticed and further research has been done to explain the enhancement of Dy³⁺ emission and the excellent thermal stability. It also keeps stable under continuous electron bombardment with high intensity. All of these indicate that it could be a suitable candidate for white‐emitting phosphor applied for near ultraviolet‐white light‐emitting diode (NUV‐WLED) and field‐emission display (FED).     

Bright White‐Emitting Phosphors Ba2Gd(BO3)2Cl: Dy3+/Dy3+‐Tm3+ for Hg‐Free Lamps and White LEDs Applications

Spectroscopic properties of Ba₂Gd(BO₃)₂Cl: Dy³⁺ and Ba₂Gd(BO₃)₂Cl: Dy³⁺, Tm³⁺ under vacuum ultraviolet (VUV) and ultraviolet (UV) light excitations were investigated. Dy³⁺ single‐doped Ba₂Gd(BO₃)₂Cl showed broad absorption band in the VUV region, and bright warm white light with chromaticity coordinates (CIE) of (0.340, 0.381) upon VUV excitation at 172 nm, demonstrating this phosphor's applicability in mercury free lamps. Upon direct excitation Tm³⁺ from its ⁶F₆ level to ¹D₂ level, the decrease of emission intensity and lifetime of Tm^{3+ 1}D₂–³F₄ emission with increasing concentration of Dy³⁺ in Ba₂Gd(BO₃)₂Cl: Dy³⁺, Tm³⁺ confirmed the occurrence of energy transfer from Tm³⁺ to Dy³⁺. In addition, Ba₂Gd(BO₃)₂Cl: Dy³⁺, Tm³⁺ could be efficiently excited by 358 nm UV light and its emission color could be tuned from blue to yellow by codoping Tm³⁺. When 1% Tm³⁺ and 5% Dy³⁺ were codoped in the Ba₂Gd(BO₃)₂Cl, intensive white‐emitting light with CIE of (0.352, 0.328) and correlated color temperature of 4589 K was achieved upon 358 nm excitation, revealing the potential application of Ba₂Gd(BO₃)₂Cl: Dy³⁺, Tm³⁺ for white light‐emitting diodes (LEDs).     

Tunable luminescence and energy transfer properties of MgY4Si3O13: Ce3+, Tb3+, Eu3+ phosphors

The tricolor-emitting MgY₄Si₃O₁₃: Ce³⁺, Tb³⁺, Eu³⁺ phosphors for ultraviolet-LED have been prepared via a high-temperature solid-state method. X-ray diffraction, photoluminescence emission, excitation spectra and fluorescence lifetime were utilized to characterize the structure and the properties of synthesized samples. Two different lattice sites for Ce³⁺ are occupied from the host structure and the normalized PL and PLE spectra. The emissions of single-doped Ce³⁺/Tb³⁺/Eu³⁺ are located in blue, green and red region, respectively. The energy transfer from Ce³⁺ to Tb³⁺ and from Tb³⁺ to Eu³⁺ has been validated by spectra and decay curves and the energy transfer mode from Tb³⁺ to Eu³⁺ was calculated to be electric dipole-dipole interactions. By adjusting the content of Tb³⁺ and Eu³⁺ in MgY₄Si₃O₁₃: Ce³⁺, Tb³⁺, Eu³⁺, the CIE coordinates can be changed from blue to green and eventually generate white light under UV excitation. All the results indicate that the MgY₄Si₃O₁₃: Ce³⁺, Tb³⁺, Eu³⁺ phosphors are potential candidates in the application of UV-WLEDs.     

Comprehensive study on structural,thermal, morphological and luminescence (RL,PL, TL) properties of CaLa2(WO4)4: Tb3+, Dy3+ phosphors synthesized via sol-gel method

Tb³⁺/Dy³⁺ co-doped CaLa₂(WO₄)₄ (CLW: Tb³⁺/Dy³⁺) and its derivatives were synthesized by the sol-gel method. The morphology, thermal, structure and luminescent-optical properties the as-prepared light-emitting phosphors were characterized by utilizing scanning electron microscopy (SEM), differential thermal analysis (DTA)-thermogravimetric analysis (TG), X-ray diffraction (XRD) and radioluminescence (RL or X-ray luminescence) - photoluminescence (PL) –thermoluminescence (TL or TSL) - optical absorption spectrometry. The Tb³⁺ and Dy³⁺ ions were singly or doubly doped and the results were examined in detail. Moreover, for these phosphors, the energy transfer mechanisms which depend on RL and PL spectra were determined. The samples excited by X-ray demonstrate characteristic luminescence peaks of Dy³⁺ (422, 480, 575, 663 and 747 nm) and Tb³⁺ (489, 544, 586, 620, 652 and 675 nm). These emissions are similar for RL and PL measurements. It could be said that the energy transfer efficiency of the host material is perfect for rare-earth ions. The synthesized phosphors exhibit various colors from yellow to blue under UV excitation. The optical band gaps of host CLW, CLW: Tb³⁺, CLW: Dy³⁺ and co-doped CLW: Tb³⁺/Dy³⁺ were calculated at values 3.83 eV, 3.44 eV, 3.64 eV and 3.52 eV, respectively. From the results obtained, the CaLa₂(WO₄)₄: Tb³⁺, Dy³⁺phosphors may be one of the potential candidates for light-emitting diode.     

Eu‐, Tb‐, and Dy‐Doped Oxyfluoride Silicate Glasses for LED Applications

Luminescence glass is a potential candidate for the light‐emitting diodes (LEDs) applications. Here, we study the structural and optical properties of the Eu‐, Tb‐, and Dy‐doped oxyfluoride silicate glasses for LEDs by means of X‐ray diffraction, photoluminescence spectra, Commission Internationale de L'Eclairage (CIE) chromaticity coordinates, and correlated color temperatures (CCTs). The results show that the white light emission can be achieved in Eu/Tb/Dy codoped oxyfluoride silicate glasses under excitation by near‐ultraviolet light due to the simultaneous generation of blue, green, yellow, and red‐light wavelengths from Tb, Dy, and Eu ions. The optical performances can be tuned by varying the glass composition and excitation wavelength. Furthermore, we observed a remarkable emission spectral change for the Tb³⁺ single‐doped oxyfluoride silicate glasses. The ⁵D₃ emission of Tb³⁺ can be suppressed by introducing B₂O₃ into the glass. The conversion of Eu³⁺ to Eu²⁺ takes place in Eu single‐doped oxyfluoride aluminosilicate glasses. The creation of CaF₂ crystals enhances the conversion efficiency. In addition, energy transfers from Dy³⁺ to Tb³⁺ and Tb³⁺ to Eu³⁺ ions occurred in Eu/Tb/Dy codoped glasses, which can be confirmed by analyzing fluorescence spectra and energy level diagrams.     

Photoluminescence Mechanism and Thermal Stability of Tb3+‐Doped Y4Si2O7N2 Green‐Emitting Phosphors

With solid‐state reaction method, series of Y₄Si₂O₇N₂:Tb³⁺ phosphors were prepared under the high‐temperature and high‐pressure conditions. The photoluminescence properties at room and high temperature were investigated. Two groups of emission lines have been observed, which are corresponding to Tb^{3+ 5}D₃ → ⁷F_J (J = 6, 5, 4, 3, 2) and ⁵D₄ → ⁷F_J (J = 6, 5, 4, 3) transitions. The physical mechanisms for excitation, emission, concentration quenching, and thermal quenching were investigated. The cross‐relaxation mechanism between the ⁵D₃ and ⁵D₄ emission was investigated and discussed. The Tb–Tb critical distance for cross‐relaxation was calculated to be ~13 Å. The optimum Tb³⁺ concentration in this phosphor is 15 mol%. The quadrupole–quadrupole interaction dominates the non‐radiative energy transfer between the Tb³⁺ luminescence centers and causes the concentration quenching. This phosphor shows high thermal stabilities that at 150°C the intensity remains 92% compared with that measured at room temperature. The present work suggests that this Tb³⁺‐doped Y₄Si₂O₇N₂ material is a kind of potential green‐emitting phosphor.     

White‐emitting phosphor Ba2B2O5:Ce3+, Tb3+, Sm3+: Luminescence,energy transfer,and thermal stability

A series of Ba₂B₂O₅: RE (RE=Ce³⁺/Tb³⁺/Sm³⁺) phosphors were synthesized using high‐temperature solid‐state reaction. The X‐ray diffraction (XRD), luminescent properties, and decay lifetimes are utilized to characterize the properties of the phosphors. The obtained phosphors can emit blue, green, and orange‐red light when single‐doped Ce³⁺, Tb³⁺, and Sm³⁺. The energy can transfer from Ce³⁺ to Tb³⁺ and Tb³⁺ to Sm³⁺ in Ba₂B₂O₅, but not from Ce³⁺ to Sm³⁺ in Ce³⁺ and Sm³⁺ codoped in Ba₂B₂O₅. However, the energy can transfer from Ce³⁺ to Sm³⁺ through the bridge role of Tb³⁺. We obtain white emission based on energy transfer of Ce³⁺→Tb³⁺→Sm³⁺ ions. These results reveal that Ce³⁺/Tb³⁺/Sm³⁺ can interact with each other in Ba₂B₂O₅, and Ba₂B₂O₅ may be a potential candidate host for white‐light‐emitting phosphors.     

Preparation,luminescence properties and energy transfer of Ca9Y(PO4)7: Eu2+‐Tb3+ phosphors

Tb³⁺‐doped and Eu²⁺, Tb³⁺ co‐doped Ca₉Y(PO₄)₇ phosphors were synthesized by conventional solid‐state method. Additionally, the luminescence properties, decay behavior and energy transfer mechanism have already been investigated in detail. The green emission intensity of Tb³⁺ ions under NUV excitation is weak due to its spin‐forbidden f‐f transition. While Eu²⁺ can efficiently absorb NUV light and yield broad blue emission, most of which can be absorbed by Tb³⁺ ions. Thus, the emission color can be easily tuned from cyan to green through the energy transfer of Eu²⁺→Tb³⁺ in Ca₉Y(PO₄)₇:Eu²⁺,Tb³⁺ phosphor. In this work, the phenomenon of cross‐relaxation between ⁵D₃ and ⁵D₄ are also mentioned. The energy transfer is confirmed to be resulted from a quadrupole‐quadrupole mechanism.     

Trap engineering in ZnGa2O4:Tb3+ through Bi3+ doping for multi-modal luminescence and advanced anti-counterfeiting strategy

Optical information encryption based on luminescence materials have received much attention recently. However, the single luminescence mode of the luminescence materials greatly limits its anti-counterfeiting application with high safety level. Here, a series of luminescence materials of Tb³⁺ and Bi³⁺ co-doped ZnGa₂O₄ phosphors with great correspondence in photoluminescence (PL), persistent luminescence (PersL), and thermoluminescence (TL) modes was synthesized by the conventional solid-phase method for the application in multi-modal anti-counterfeiting fields. Under the excitation of 254 nm, ZnGa_1.99O₄:0.01 Tb³⁺, yBi³⁺ (y = 0.001,0.002) sample exhibited a broad blue emission band (the transition from [GaO₆]) at 440 nm and the characteristic emission peaks of Tb³⁺ at 495 nm, 550 nm, 591 nm and 625 nm, corresponding to the transitions of ⁵D₄-⁷F_n (n = 6, 5, 4, 3), respectively. Interestingly, the co-doping of Bi³⁺ ions improve the crystallinity and particle size of the phosphor, subsequently enhanced the PL intensity of Tb³⁺ to 6 times that of Tb³⁺ singly doped ZnGa₂O₄ phosphor. Further, the flexible films with multi-modal luminescence properties have been fabricated through the unique TL and PersL characteristics of ZnGa₂O₄: Tb³⁺, Bi³⁺ phosphors, including “Optical information storage film”, “snowflake and characters” and “QR code”. Moreover, a set of optical information encryption is obtained by combining ZnGa₂O₄:Tb³⁺, Bi³⁺ phosphor and red emitting phosphor. The results indicate that ZnGa₂O₄:Tb³⁺, Bi³⁺ phosphor with multi-modal stimulus response can be expected to be potentially used in the applications of optical information storage and anti-counterfeiting fields.     

Order-disorder structural transition in Pr3+-doped Ba3Ga2O6 for rewritable and write-once-read-many optical data storage

The emerging challenges of the big data era, both in storage density and security, require the development of the next-generation optical data storage materials. Here, we report for the first time a photo-stimulated luminescence (PSL) material, Ba₃Ga₂O₆: Pr³⁺, for rewritable optical storage and write-once-read-many data preservation. Ba₃Ga₂O₆: Pr³⁺, with an isolated deep trap depth in the range 1.26–1.53eV, has been used for data encoding/decoding under the excitation of 254 nm UV light and by the simulation of an 808 nm NIR laser. Meanwhile, the phosphor allows for high-security write-once-read-many optical memory by taking advantage of the irreversible change of the photoluminescence (PL) color from blue to green (a binary blue ‘0’ and green ‘1’ code) irradiated by 365 nm UV light. The comprehensive investigations indicate that the irreversible PL switching is as a result of the order-disorder structural transition by thermal treatment. The new persistent luminescence material not only exhibits promising applications in sustainable rewritable data storage, but also paves the way for write-once-read-many optical information storage with a high level of security.     

Tunable white light and energy transfer of Dy3+ and Eu3+ doped Y2Mo4O15 phosphors

A series of Dy³⁺ or/and Eu³⁺ doped Y₂Mo₄O₁₅ phosphors were successfully synthesized at a low temperature of 600 °C via solid state reaction. The as-prepared phosphors were characterized by X-ray powder diffraction (XRD), scanning electronic microscope (SEM), photoluminescence (PL) excitation, emission spectra and PL decay curves. XRD results demonstrate that Y₂Mo₄O₁₅: Dy³⁺, Eu³⁺ has the monoclinic structure with the space group of p21/C(14). Under the excitation of ultraviolet (UV) or near-UV light, the Dy³⁺ and Eu³⁺ ions activated Y₂Mo₄O₁₅ phosphors exhibit their characteristic emissions in the blue, yellow and red regions. The emitting light color of the Y₂Mo₄O₁₅: 0.08Dy³⁺, yEu³⁺ phosphors can be adjusted by varying the concentration ratio of Dy³⁺ to Eu³⁺ ions and a white light is achieved when the doping concentration of Eu³⁺ is 5%. In addition, the energy transfer from Dy³⁺ to Eu³⁺ is also confirmed based on the luminescence spectra and decay curves.     

Luminescence Properties and Energy‐Transfer Behavior of a Novel and Color‐Tunable LaMgAl11O19:Tm3+, Dy3+ Phosphor for White Light‐Emitting Diodes

Novel LaMgAl₁₁O₁₉:Tm³⁺, Dy³⁺ phosphors were prepared utilizing a high‐temperature solid‐state reaction method. The phase formation, luminescence properties, energy‐transfer mechanism from the Tm³⁺ to the Dy³⁺ ions, the thermal stability, and CIE coordinates were investigated. When excited at 359 nm, the LaMgAl₁₁O₁₉: xTm³⁺ phosphors exhibit strong blue emission bands at 455 nm. After codoping with Dy³⁺ and excitation at 359 nm, the LaMgAl₁₁O₁₉:0.03Tm³⁺, yDy³⁺ phosphors emitted white light consisting of the characteristic emission peaks of Tm³⁺ and Dy³⁺. The Dy³⁺ emission intensity increased with the Dy³⁺ concentration due to the energy transfer from Tm³⁺ to Dy³⁺, and concentration quenching due to the high Dy³⁺ doping concentration (y = 0.1 mol) did not occur. The calculation of the CIE coordinates of the LaMgAl₁₁O₁₉:Tm³⁺, yDy³⁺ phosphors revealed the tunability of the emission color from blue to bluish‐white and to white by changing the excitation wavelength and the doping concentration. An energy transfer from Tm³⁺ to Dy³⁺ by dipole–dipole interaction was confirmed by the decay curve, lifetime, and energy‐transfer efficiency measurements. When excited at 359 nm, the LaMgAl₁₁O₁₉:Tm³⁺, Dy³⁺ phosphor also showed good thermal stability, suggesting that it can be used in white LEDs excited by a GaN‐based ultraviolet LED.     

Synthesis,structural and luminescence properties of near white light emitting Dy-doped Y2CaZnO5 nanophosphor for solid state lighting

Novel near white light emitting Y₂CaZnO₅ (YCZ) nanocrystalline powders doped with Dy³⁺ ions were synthesized via the citrate gel combustion method. The structure of the compound is found to be triclinic with a particle size in the range of 20–30 nm. Luminescence properties have been characterized using photoluminescence (PL), excitation spectra and decay time measurements. The PL spectra have shown a broad blue band due to ⁴F_9/2→⁶H_15/2 transition and sharp yellow band corresponding to ⁴F_9/2→⁶H_13/2 transition of Dy³⁺ ions. From the concentration dependent PL studies, the optimum concentration of Dy³⁺ ions in YCZ is found to be 1.0 mol%, where intense near white light emission was observed. The Dy³⁺:YCZ nanophosphor has shown relatively better white color properties than the reported Dy³⁺:Y₂O₃ nanophosphor. The yellow to blue intensity ratios, CIE chromaticity coordinates and correlated color temperature studies have shown the possibility of using this compound for white light emission.     

Highly photoemissive polymer–transition metal complexes based on poly(2‐hydroxyethyl) methacrylate

The paper presents several new polymer complexes based on poly(2‐hydroxyethyl) methacrylate (P‐HEMA) and transition metals including Y³⁺, Eu³⁺, Tb³⁺ and Dy³⁺. Red‐, green‐, blue‐ and yellow‐emitting polymer complexes with remarkable photoluminescent (PL) properties, high degree of transparency and excellent processability both in bulk and in thin film were prepared and investigated. In the case of the prepared P‐HEMA–Eu³⁺ and P‐HEMA–Tb³⁺ polymer complexes, divinylbenzene was used as a crosslinker resulting a markedly enhanced PL emission, most probably due to the presence of the benzene rings which improve the efficiency of the energy transfer to the cation emissive centres. The prepared polymer complexes were structurally investigated through Fourier transform infrared and X‐ray photoelectron spectroscopies while atomic force microscopy was used to study the morphology of the prepared thin films. Steady‐state fluorescence spectroscopy and absolute PL quantum yield were used for the investigation of the luminescent properties. The impressive PL emission and the convenience of preparation in bulk or thin films could be important arguments for a wide area of applications ranging from photonic conversion materials in optoelectronic devices (light‐emitting diodes, flat‐panel displays) to full‐colour watermarks on special‐purpose papers or PL inks and coatings. © 2019 Society of Chemical Industry     

White‐Light and Yellow/Blue Photoluminescence Emission Based on Dy3+‐Doped SiO2–Gd2O3 Composites

This work attempts to obtain Dy³⁺‐doped SiO₂–Gd₂O₃ by sol–gel process_, with a molar ratio of 70Si⁴⁺–30Gd³⁺ and Dy³⁺ concentrations of 0.1, 0.3, 0.5, and 1 mol%. Heat treatment at temperatures of 1000°C, 1100°C, 1200°C, and 1300°C have been performed. From XRD, the Gd₂O₃ cubic phase was observed at 1000°C and 1100°C, at 1200°C also were observed Gd₂O₃ monoclinic phase, predominant at 1300°C. The band‐gap values vary between 4.4 and 5.3 eV, showing dependence on the crystalline phase. Under UV excitation, emission spectra show bands assigned to the Dy³⁺ transitions: ⁴F_9/2→⁶H_15/2 (484 nm), ⁴F_9/2→⁶H_13/2 (572 nm), and ⁴F_9/2→⁶H_11/2 (668 nm). The excitation at 275 nm has shown more effective. The ratio between the most intense emission bands (yellow/blue) show values around 0.84 and 1.63. CIE chromaticity diagrams show color coordinates at blue, yellow, and white regions, as a function of Dy³⁺ concentration and heat treatment. The lifetime values of excited state ⁴F_9/2 were around 0.20 and 0.69 ms. The morphology of particles changed from spherical to coral‐like shape as a function of heat treatment are observed. The sol–gel process showed to be an interesting route to obtain Dy³⁺‐doped binary system materials.     

Photostimulated and Long Persistent Luminescence Properties from Different Crystallographic Sites of β‐Sr2SiO4: Eu2+, R3+ (R = Tm,Gd)

Sintered ceramics of β‐Sr₂SiO₄: Eu²⁺, R³⁺(R=Tm, Gd) were prepared and their spectroscopic properties were evaluated. A large enhancement of green photostimulated luminescence (PSL) was observed from β‐Sr₂SiO₄:Eu²⁺ codoping with Tm³⁺ at a recognizable intensity level, and the most efficient PSL was obtained when the codoping concentration of Tm³⁺ was 0.002. It was proved that the introduction of Tm³⁺ created a large number of oxygen vacancies which serve as traps for electrons excited by UV irradiation. In addition, a distinguishable difference between the photoluminescence (PL) and PSL spectra of β‐Sr₂SiO₄: Eu²⁺, Tm³⁺ was observed, namely the PSL spectrum exhibits only a symmetric emission band peaked at about 540 nm while both 470 and 540 nm peaks were detected in the PL spectrum. It is safe to say that PSL only derives from one emission center of Eu2 in the crystallographic Sr2 sites, which could be ascribed to the different distribution of trap centers for two crystallographic Sr sites .