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A series of Ce3+ and Tb3+ singly‐ and co‐doped NaBa4(AlB4O9)2Cl3 (NBAC) phosphors have been synthesized via high‐temperature solid state route. The crystal structure, morphology, photoluminescent properties, thermal properties and energy transfer process between Ce3+ and Tb3+ were systematically investigated. The structure refinements indicated that the phosphors based on NBAC crystallized in P42nm polar space group in monoclinic phase. The emission color could be tuned from blue (0.1595, 0.0955) to green (0.2689, 0.4334) via changing the ratio of Ce3+/Tb3+. The energy transfer mechanism of Ce3+/Tb3+ was verified to be dipole–quadrupole interaction via the examination of decay times of Ce3+ based on Dexter's theory. The good thermal stability showed the intensities of Ce3+ at 150°C were about 66.9% and 64.88% in NBAC:0.09Ce3+ and NBAC:0.09Ce3+, 0.07Tb3+ of that at room temperature, and the emission intensities of Tb3+ remained 102.41% in NBAC:0.11Tb3+ and 95.22% in NBAC:0.09Ce3+, 0.07Tb3+ due to the nephelauxetic shielding effect and the highly asymmetric rigid framework structure of NBAC. The maximum external quantum efficiency (EQE) of Ce3+ in NBAC:0.09Ce3+, yTb3+ phosphors could reach 43.38% at y = 0.13. Overall, all the results obtained suggested that NBAC:Ce3+, Tb3+ could be a promising option for n‐UV pumped phosphors. [ABSTRACT FROM AUTHOR]

The appearance of a cyan cavity is unavoidable in the 480–520 nm wavebands when combining n-UV LED chips (380–420 nm) with trichromatic phosphors to obtain white-light-emitting devices. Here, a concentration perturbation effect is proposed to improve the properties of phosphors via trace substitution of Mn2+, Mg2+ or Zn2+ cations for Ba2+ and Y3+ in Ba0.97Y2Si3O10:Eu. Based on local structure distortion or electron cloud interaction, the emission band corresponding to Eu2+ is broadened with a full width at half maximum (FWHM) more than 125 nm due to redistribution of Eu2+ and the emission color can be tuned to the cyan region. The coexistence of the above two effects on the photoluminescence can be further evidenced by the shifts of emission energy for the two sites in these systems. The quenching temperature for all the samples is observed over 473 K and even higher than that for the non-substituted Ba0.97Y2Si3O10:0.03Eu and it is discussed combined with Pauling's principles, average Uiso and the distortion degree of polyhedra, which could provide some references for improvement of thermal stability. Moreover, the valence mismatch between Mn2+/Mg2+/Zn2+ and Y3+ ions leads to the coexistence of Eu2+–Eu3+, which thus realizes color selective manipulation and even white light emission in Ba0.98−nMg0.02Y2Si3O10:nEu. Our results demonstrate that the concentration perturbation effect-assisted synthesis strategy has potential in improving the properties of phosphors for WLEDs, and it can also be extended to adjusting the coordination environment of activators whose properties are sensitive to local lattice variations and electronic surroundings. [ABSTRACT FROM AUTHOR]

Design of new hollow structure materials with high complexity in shell architecture and composition has been proven to be an efficient strategy to improve their properties in many applications. Herein we devise and demonstrate a general strategy to synthesize composite silicate with hierarchical hollow structure: (1) coating mesoporous silica on precursor; then (2) treated with proper solution on certain conditions, and then (3) thermal treatments. By using Y(OH)CO 3 submicrospheres as precursor, hollow composite silicate (Y 2 Si 2 O 7 @Zn 2 SiO 4 ) has been fabricated successfully. This Y 2 Si 2 O 7 @Zn 2 SiO 4 structure can accommodate multifold luminescent activator ions (Ce 3+ , Mn 2+ , Eu 3+ ) and realize full-color luminescence under a single wavelength excitation. Moreover, the emission of Ce 3+ , Eu 3+ and Mn 2+ in Y 2 Si 2 O 7 @Zn 2 SiO 4 structure exhibit excellent luminescence thermal stability due to the generation of defects at the interface and efficient energy transfer from the defect levels to activators at higher temperature. This novel fabrication methodology provides a feasible way to achieve multi-component hollow structure with multi-color emission for application in solid-state lighting, which is not limited to Y 2 Si 2 O 7 @Zn 2 SiO 4 material, but applying to other material systems. [ABSTRACT FROM AUTHOR]

Abstract: Charge compensation was the effective methods to enhance the luminescence properties of phosphors. In this paper, novel single‐phased orange light emitting Sr2Mg3P4O15:Eu3+ phosphors were prepared by solid state method. The phase purity and luminous characteristics were examined in detail. Meanwhile, three kinds of charge compensation methods (co‐doping the alkali metal R+ (R+ = Li, Na, and K), substituting Si4+ for P5+ and self‐compensation) were employed to solve the charge imbalance problem between Sr2+ and Eu3+. The results showed that emission intensity of Eu3+ was improved by 1.43 (Li+), 1.58 (Na+), 1.53 (K+), 1.61 (Si4+), and 1.30 (self) times than that of Sr1.6Mg3P4O15:0.40Eu3+, respectively, and there was no change in the emitting color simultaneously. Furthermore, as the temperature reached at 423 K, the emission intensity increased from 41.67% of Sr1.6Mg3P4O15:0.40Eu3+ to 55.69% (Li+), 61.62% (Na+), 58.98% (K+), 71.15% (Si4+), and 80.59% (self) of that at room temperature. The reasons of those phenomena were the reduction in ion vacancies caused by charge imbalance through the charge compensation process. The specific mechanisms were elaborated in detail. Overall, this research validated that the charge compensation strategies could be severed as the key method to improve the luminescence properties, especially the thermal stability of phosphor. [ABSTRACT FROM AUTHOR]

By substituting Sr or Ba for Ca ions, a series of single-phased K(Ca, M)Gd(PO):0.01Eu (M = Sr, Ba) phosphors have been successfully synthesized via the solid-state reaction. The phase formations, structures, photoluminescence (PL) properties and thermal stability of the two cation substituting K(Ca, M)Gd(PO):0.01Eu phosphors were studied in detail. The emission peaks showed blue-shift and the CIE coordinates changed from (0.2117, 0.3761) to (0.2096, 0.3195) and (0.1969, 0.2857) corresponding to the Sr or Ba substituting due to the weaker crystal field splitting of Eu. Further, the optimal substitution proportions of Sr, Ba for Ca were determined to be 0.40 and 0.08 mol, the thermal quenching luminescence properties were enhanced and the emission intensity of Sr or Ba substituting KCaGd(PO):0.01Eu was remained 58.88 or 66.86% of that measured at room temperature when the temperature increased to 423 K. All these properties predict that K(Ca, M)Gd(PO):0.01Eu (M = Sr, Ba) phosphors have potential applications in the field of phosphor-converted devices. [ABSTRACT FROM AUTHOR]

By substituting Gd 3+ for Ba 2+ ions in the single-phased Na 2 (Ba 5.99-2 m Eu 0.01 Gd m Na m )(Si 2 O 7 )(SiO 4 ) 2 (0 ≤ m ≤ 0.30) phosphors, the asymmetric emission peaks of three Eu luminescence centers monitored around 444, 494 and 552 nm varied accordingly under 365 nm excitation and caused the shift of CIE color coordinates from (0.1569, 0.2122) to (0.1697, 0.3082). Furthermore, the thermal stability and quantum yield of phosphors could be affected via the different cation substitution of Gd 3+ . Combined with the change tendencies of Ba-O bond lengths by Rietveld refinement, the possible mechanism of the luminescence transformation of Eu 2+ ion was the preferential occupancy at different crystallographic sites of Eu 2+ . Generally, this work sheds some new lights on the design and structure explanation of preferential occupancy at different crystallographic sites in phosphors. [ABSTRACT FROM AUTHOR]

A series of single-phased Na 2 Ba 5.99- x (Si 2 O 7 )(SiO 4 ) 2 :0.01Eu 2+ , x Mg 2+ and Na 2 Ba 5.99- y (Si 2 O 7 )(SiO 4 ) 2 :0.01Eu 2+ , y Zn 2+ phosphors have been successfully prepared via the solid-state reaction. Structural refinement, luminescence property, color tuning and thermally stability were systematically investigated. The as-prepared Na 2 Ba 6 (Si 2 O 7 )(SiO 4 ) 2 :0.01Eu 2+ phosphor showed broad excitation bands from 250 nm to 450 nm and presented wide emission bands under 365 nm excitation, which could be decomposed by Gaussian fitting into three peaks corresponding to different Eu luminous centers named Eu1, Eu2 and Eu3. By substituting Mg 2+ or Zn 2+ for Ba 2+ , the relative intensities of Eu1, Eu2 and Eu3 emission bands changed gradually. Combined with the variation tendencies of Ba O bond lengths by Rietveld refinement, the possible mechanism of the luminescence transformation of Eu 2+ ion was the preferential occupancy of Eu 2+ at different crystallographic sites. In addition, the introduction of Mg 2+ ion expressed more obvious improvement on the thermal quenching behaviors of Eu 2+ than Zn 2+ ion in this matrix. The emission intensities of Eu2 and Eu3 could be enhanced from 63.2% to 82.7% and 35.1%–46.8% at 373 K compared to the initial intensity when Mg 2+ concentration was 0.10. Generally, this work sheds some new lights on the design and structure explanation of preferential occupancy at different crystallographic sites in phosphors. [ABSTRACT FROM AUTHOR]

The bluish-green KBaY(BO):Eu phosphors were prepared by high-temperature solid state reaction method. The photoluminescence properties, concentration quenching and energy transfer as well as the luminescence decays were investigated. The emission spectrum showed a single intensive band centered at 500 nm, which correspond to the 4 f 5 d → 4 f transition of Eu. The optimal concentration for the luminescence of Eu in KBaY(BO):Eu was determined to be 0.03 mol. The critical energy transfer distance was calculated as 21.34 Å. The corresponding concentration quenching mechanism was verified to be a dipole-dipole interaction. And the blue-shift behavior of KBaY(BO):Eu with increasing temperature was analyzed by the configurational coordinate diagram. The results indicate that the KBaY(BO):Eu phosphors have potential applications as an ultraviolet-convertible phosphor due to its effective excitation in the ultraviolet rang. [ABSTRACT FROM AUTHOR]

Monodisperse mono-concave microsphere/microflower/nanosheet GdBO 3 :Eu 3+ samples have been successfully synthesized via hydrothermal method using Gd 0.99 Eu 0.01 (OH) 3 nanorods as sacrificial precursors. X-Ray diffraction (XRD), Fourier transform infrared spectroscopy (FT-IR), field scanning electron microscopy (FE-SEM) and fluorescence spectrometry were used to characterize the samples. The shape of these as-prepared GdBO 3 :Eu 3+ architectures can be tuned effectively by controlling the concentrations of NaOH (C NaOH ) of the precursor solution and the amounts of PEG (20000) surfactant. As a typical morphology, the possible formation mechanism for GdBO 3 :Eu 3+ monodisperse mono-concave microsphere was presented in detail. Under ultraviolet excitation, the as-obtained GdBO 3 :Eu 3+ samples showed strong characteristic orange and red emission of Eu 3+ . Compared with samples get by solid state reaction, the samples obtained by hydrothermal method possess higher red/orange (R/O) ratio attributed to 5 D 0 − 7 F 1 and 5 D 0 − 7 F 2 transitions. The influence of diversity morphology on the R/O ratio and emission intensity has been also investigated. This work sheds some light on the design of a well-defined complex structure, and the luminescent properties have potential applications in fluorescent lamps and field emission displays. [ABSTRACT FROM AUTHOR]

Utilizing energy transfer process, Ce, Tb co-doped BaZrSiO (BZS) phosphors have been successfully prepared via solid state reaction process. The phase structure, photoluminescence properties, decay curves, thermal stability, and the energy transfer mechanism were investigated in this paper. The critical distance calculated by quenching concentration method was 8.84 Å, and the energy transfer process from Ce to Tb in BZS:Ce/Tb phosphors had been demonstrated to be a resonant type via a dipole-quadrupole mechanism. The emission colors of the phosphors could be tuned from blue (0.1625, 0.1261) to green (0.2979, 0.5473) through the corresponding Ce to Tb energy transfer. Moreover, thermal quenching luminescence results revealed that BZS:Ce, Tb exhibited good thermal stability. The Tb intensity of BZS:0.04Ce, 0.02Tb sample showed about 60.88 % of its initial emission intensity at room temperature. The above results indicate that the phosphors may be potentially used as single-component blue-green emission phosphors for application in light emitting device. [ABSTRACT FROM AUTHOR]

A series of Eu2+ and Tb3+ singly-doped and co-doped Sr3Y2(Si3O9)2 (SYSO) phosphors have been synthesized via a conventional high-temperature solid-state reaction. The crystal structures, photoluminescence properties, fluorescence lifetimes, thermal properties and energy transfer of SYSO:Eu2+,Tb3+ were systematically investigated in detail. Rietveld structure refinement of the obtained phosphors indicated that the SYSO host crystallized in a monoclinic system with the space group C2/c (15) and there are three kinds of cation sites for the doped ions to occupy forming emission centers. The photoluminescence (PL) emission bands of SYSO:xEu2+ show a red-shift tendency with increasing Eu2+ content which should be attributed to more Eu2+ ions entering into Sr2/Y2 and Sr3/Y3 sites from the Sr1/Y1 site. For the co-doped SYSO:Eu2+,Tb3+ samples, tunable colors from cyan to green can be realized by varying the doping concentration of the Tb3+ ions. The intense green emission was realized in the SYSO:Eu2+,Tb3+ phosphors on the basis of the highly efficient energy transfer from Eu2+ to Tb3+ with an efficiency of over 89%. As a result, the emission intensity of SYSO:0.01Eu2+,0.21Tb3+ is about 2.5 times higher than that of SYSO:0.21Tb3+ under 340 nm UV excitation. The energy transfer mechanism from Eu2+ to Tb3+ in the SYSO host was ascribed to the quadrupole–quadrupole interactions. These results indicated that the SYSO:Eu2+,Tb3+ phosphors can act as single-phase green emitting phosphors for possible applications in ultraviolet light-based white light-emitting diodes (w-LEDs). [ABSTRACT FROM AUTHOR]

Eu doped KCaY(PO) (KCYP) phosphors with irregular, hemispherical and spherical morphologies are successfully synthesized via a sol-gel method. The crystalline structure, morphology and luminescence properties of these phosphors are characterized by powder X-ray diffraction, scanning electron microscopy and photoluminescence spectroscopy. Under the excitation wavelength of near-ultraviolet (n-UV) 392 nm, the as-prepared KCYP:0.03Eu phosphor exhibits an intense orange-red emission at 588 nm corresponding to D → F transition of Eu. The effect of synthesis conditions such as the dose of citric acid and pH of the precursor solution on the morphology and luminescence intensity of the phosphors is discussed in detail. The morphologies of KCYP:0.03Eu phosphors vary from a small amount of spheres to aggregated hemispheres and then to smooth spheres by increasing the molar ratio of citric acid to metal ions in the host. The highest emission intensity can be obtained at the molar ratio of citric acid to metal ions 2:1 and pH = 8.0, respectively. [ABSTRACT FROM AUTHOR]

The narrow‐band emitting phosphors have been extensively investigated in recent years, with the expectation that a wide color gamut of phosphor‐converted backlighting device could be fabricated. Due to the weak electric–phonon interaction and low structural relaxation caused by the high rigid crystal structure and symmetric coordination environment, Sr2MgAl22O36:Mn2+ (SMAO:Mn2+) shows a narrow full‐width at half‐maximum of 26 nm, a high color purity of 81.5%, and a low thermal quenching (82% at 473 K of the initial intensity at 298 K). Using K2SiF6:Mn4+ as the red phosphor, SMAO:Mn2+ as the green one, and GaN‐based chip as the blue component, the white light‐emitting diode exhibits a National Television Standard Committee value of 127%. All the results demonstrate that the SMAO:Mn2+ phosphor has a promising application in the field of advanced wide‐color‐gamut backlight display, and the establishment of the relationships between the narrow‐band emission and crystal structure can also be applied to design other novel narrow‐band phosphors for backlighting technologies. A novel narrow‐band green‐emitting phosphor Sr2MgAl22O36:Mn2+ with peak position at 518 nm, full‐width at half‐maximum of 26 nm, and a low thermal quenching at high temperature (82% of room temperature intensity at 498 K) under the excitation of blue light‐emitting diode chip is discovered. These good luminesce properties are benefited from the high rigid crystal structure and symmetric coordination environment. [ABSTRACT FROM AUTHOR]

Color-tunable and white-emitting Pr3+ and Tb3+ co-doped La 2 Ti 2 O 7 phosphors were prepared via a molten salt method. The as-synthesized samples were analyzed by X-ray diffraction (XRD), scanning electron microscopy (SEM), diffuse reflection spectra (DRS), photoluminescence spectra (PL), fluorescence decay curves and temperature-dependent photoluminescence spectra in detail. The La 2 Ti 2 O 7 :Pr3+, Tb3+ phosphors are uniform square-like nanobelt and the band gap of La 2 Ti 2 O 7 host is calculated to be 3.83 eV by DRS. Under 296 nm wavelength UV excitation, the La 2 Ti 2 O 7 :Pr3+ compounds show strong red emission with peaking at 612 nm. Four typical emission lines of Tb3+ ions are observed from the region of 480–650 nm in La 2 Ti 2 O 7 :Tb3+ phosphors, and the strongest green emission peak is located at 545 nm. What's more, the emission color of La 2 Ti 2 O 7 :0.001Pr3+, 0.010 Tb3+ can be tuned from white (0.3274, 0.3379) to pink (0.4777, 0.2890) upon the excitation from 290 to 348 nm and the emission color of La 2 Ti 2 O 7 :0.001Pr3+, x Tb3+ can be also tuned from white to green by changing the concentration of Tb3+. The La 2 Ti 2 O 7 :Pr3+, Tb3+ phosphors have the poor temperature dependence, resulting from the value of Δ R (the displacement between parabolas of the intervalence charge transfer states and ground states) for Tb3+ and Pr3+ both are larger. The results indicate that La 2 Ti 2 O 7 :Pr3+, Tb3+ phosphors could be a promising tunable and white light emission phosphor. Image 1 • The La 2 Ti 2 O 7 : Pr3+/Tb3+ nanostrips were successfully prepared by molten salt method. • Multi-color luminescence evolution was achieved. • A new single-phased white light emission was realized through Pr3+/Tb3+-codoping. [ABSTRACT FROM AUTHOR]

Abstract Exploring the process of structure evolution and mechanism of controllable luminescence in the solid solution phosphors is meaningful but still challenging. Herein, new solid solution phosphors of Ca 9 Al 1- x Y x (PO 4) 7 :Eu2+ were selected as examples to address the challenging via the construction of bi-directional relationships between structure evolution and photoluminescence property. In Ca 9 Al 1- x Y x (PO 4) 7 , the structure evolution caused the redistribution of Eu2+ in the multiple cationic sites, accompanied by the changes of emission color from blue (0.1828, 0.1192) to cyan (0.1723, 0.3305), which were investigated by Gaussian fitting, decay time, and bond energy theory. Conversely, the Gaussian fitting peaks displayed different blue or red shifts in the process of structure evolution, which could reversely reflect the specific changes of bond lengths in each cationic site and were helpful for exhaustive understanding the process of structure evolution in Ca 9 Al 1- x Y x (PO 4) 7. Besides, the thermal stability behaviors of Ca 8.95 Al 1- x Y x (PO 4) 7 :0.05Eu2+ exhibited that the decline rate of low energy bands were faster than that of high energy bands due to the thermally active phonon-assisted effect. The constructed bi-directional relationships pave a feasible way to investigate the variations of structure evolution and emission properties, which will be helpful for the design of new kinds of phosphors. Graphical abstract Image 1 Highlights • Bi-directional relationships between structure evolution and luminescence were built. • The structure evolution caused the redistribution of Eu2+ in various cationic sites. • The delicate information of structure was analyzed by the shifts of emission peaks. • The changes of thermal stabilities were detected and analyzed. [ABSTRACT FROM AUTHOR]

Abstract Novel single-phased and emission-tunable layered Bi 4 Ti 3 O 12 :Pr3+ nanosheets have been successfully synthesized via molten salt method. The as-prepared samples were characterized by X-ray diffraction and scanning electron microscopy to investigate their crystalline phases and morphologies. Furthermore, we explored the photoluminescence properties of the Bi 4 Ti 3 O 12 :Pr3+ phosphors, while the cross-relaxation processes between 1D 2 , 3P 0 emitting states and the Pr3+–Ti4+ intervalence charge transfer state, color tuning and thermally stability were discussed in detail. Besides, the emission hue of Bi 4 Ti 3 O 12 :Pr3+ could be adjusted from white-light (0.3059, 0.2731) to yellow (0.5167, 0.4792) by tuning the excitation wavelength, in which the ratio of 3P 0 →3H 4 and 1D 2 →3H 4 was changed. In addition, the increases in temperatures led to the cooperative effects of thermal-quenching behavior and the cross-relaxation processes, thus resulting in the significant decrease of 3P 0 →3H 4 emission in comparison to the 1D 2 →3H 4 emission. The results suggested that the Bi 4 Ti 3 O 12 :Pr3+ is an effective color-tuning phosphor. Graphical abstract Image 1 Highlights • The regular sheet-like Bi 4 Ti 3 O 12 :Pr3+ phosphors were successfully prepared by molten salt method. • The phosphors show color tuning emissions form near white to yellow. • The thermal stability of the 1D 2 emission is obviously better than that of 3P 0. [ABSTRACT FROM AUTHOR]

Investigating the relationships between luminescent properties and the energy positions of rare earth ions is helpful for the design of phosphors. Herein, (Ca 1- x Sr x ) 8 Mg 3 Al 2 Si 7 O 28 :Ce 3+ /Eu 2+ were synthesized by solid state reaction. The variations of energy positions of lowest 5d levels of Ce 3+ and Eu 2+ with the changes of centroid shift, crystal field splitting and stokes shifts were qualitatively calculated based on the empirical formulas. Substitution of Ca 2+ by Sr 2+ ions made the emission peaks of Eu 2+ in (Ca 1- x Sr x ) 8 Mg 3 Al 2 Si 7 O 28 shift from 527 to 469 nm and the full width at half-maximum of Ce 3+ in (Ca 1- x Sr x ) 8 Mg 3 Al 2 Si 7 O 28 widen from 55 to 66 nm. On the basis of calculated results, the variations of emission peaks of Eu 2+ were mainly ascribed to the elevating of lowest 5d levels caused by the weakened centroid shift and crystal field splitting, especially the declined energy of crystal field splitting (from 2.28 to 2.01 eV). The effects of decreased rigidity and increased disorder of lattice caused by Sr 2+ substituting Ca 2+ had a greater impact than that of the centroid shift and crystal field splitting on the luminescence properties of Ce 3+ in (Ca 1- x Sr x ) 8 Mg 3 Al 2 Si 7 O 28 . Serious thermal quenching behaviors occurred in the series phosphors due to the thermal ionization processes, which were proofed by the constructed host-referred binding energy and vacuum-referred binding energy diagrams according to the experimental and calculated results of (Ca 1- x Sr x ) 8 Mg 3 Al 2 Si 7 O 28 :Ce 3+ /Eu 2+ . [ABSTRACT FROM AUTHOR]

A series of monodisperse cruciate multilayer H 3 Sr 6 (PO 4 ) 5 ·2H 2 O:Eu 2+ microarchitectures assembled by crossed nanorods have been successfully synthesized via a facile surfactant-assisted hydrothermal route. XRD and FT-IR confirmed the existence of crystalline water in the phosphor. The FE-SEM images revealed that the phase and morphology of resulting samples were strongly depended on the optimization of the reaction conditions, especially the pH value and the molar ratio of citric acid (CA)/Cations. Furthermore, the possible growth mechanism of H 3 Sr 6 (PO 4 ) 5 ·2H 2 O:Eu 2+ microarchitectures was proposed in detail. Under near-ultraviolet excitation of 365 nm, the as-obtained H 3 Sr 6 (PO 4 ) 5 ·2H 2 O:0.05Eu 2+ sample exhibited intense wide characteristic blue emission of Eu 2+ , which could be decomposed by Gaussian fitting into two peaks corresponding to different Eu 2+ luminous centers. The present results demonstrated that the morphology-tunable H 3 Sr 6 (PO 4 ) 5 ·2H 2 O:Eu 2+ microarchitecture could be used as a potential candidate for future optoelectronic device applications. [ABSTRACT FROM AUTHOR]

Abstract: Charge compensation was the effective methods to enhance the luminescence properties of phosphors. In this paper, novel single‐phased orange light emitting Sr2Mg3P4O15:Eu3+ phosphors were prepared by solid state method. The phase purity and luminous characteristics were examined in detail. Meanwhile, three kinds of charge compensation methods (co‐doping the alkali metal R+ (R+ = Li, Na, and K), substituting Si4+ for P5+ and self‐compensation) were employed to solve the charge imbalance problem between Sr2+ and Eu3+. The results showed that emission intensity of Eu3+ was improved by 1.43 (Li+), 1.58 (Na+), 1.53 (K+), 1.61 (Si4+), and 1.30 (self) times than that of Sr1.6Mg3P4O15:0.40Eu3+, respectively, and there was no change in the emitting color simultaneously. Furthermore, as the temperature reached at 423 K, the emission intensity increased from 41.67% of Sr1.6Mg3P4O15:0.40Eu3+ to 55.69% (Li+), 61.62% (Na+), 58.98% (K+), 71.15% (Si4+), and 80.59% (self) of that at room temperature. The reasons of those phenomena were the reduction in ion vacancies caused by charge imbalance through the charge compensation process. The specific mechanisms were elaborated in detail. Overall, this research validated that the charge compensation strategies could be severed as the key method to improve the luminescence properties, especially the thermal stability of phosphor. [ABSTRACT FROM AUTHOR]

By substituting Ca 2+ or Sr 2+ for Ba 2+ and Yb 3+ or La 3+ for Y 3+ , in whole or in part, the single-phased Ba 0.97- x M x Y 2 Si 3 O 10 :0.03Eu 2+ and Ba 0.97 Y 2- y RE y Si 3 O 10 :0.03Eu 2+ phosphors (M = Sr 2+ or Ca 2+ , RE = La 3+ or Yb 3+ ) were synthesized successfully via high temperature solid-state reaction method. The introduction of different cations caused higher covalence and rigidity of the as-prepared samples and enhanced the interaction between electrons around Eu 2+ ions, leading to the variation of emission color from bluish violet to light blue or greenish blue upon optimum excitation wavelength. In addition, the effect of cation substituting level on thermal stability of BaY 2 Si 3 O 10 :0.03Eu 2+ was investigated in details. The emission intensities of Ba 0.97- x Y 2 Si 3 O 10 :0.03Eu 2+ , x Sr 2+ , Ba 0.97- x Y 2 Si 3 O 10 :0.03Eu 2+ , x Ca 2+ , Ba 0.97 Y 2- y Si 3 O 10 :0.03Eu 2+ , y Yb 3+ and Ba 0.97 Y 2- y Si 3 O 10 :0.03Eu 2+ , y La 3+ varied in the range of 68.09%–78.64%, 78.44%–81.00%, 67.38%–79.90% and 60.25%–79.84% at 423 K compared to the initial intensity at room temperature, respectively. Meanwhile, the crystal filed split effect (CFSE) and nephelauxetic effect (NE) mechanisms were also proposed to better explain the red shifts and the changes of thermal quenching behavior of above samples. This work shed some light on the design of phosphors with controllable emission colors and higher thermal stability for the applications in phosphor-converted devices. [ABSTRACT FROM AUTHOR]

The novel phosphors BaZrSi 3 O 9 :Ce 3+ (BZS:Ce 3+ ) have been successfully synthesized by the conventional solid-state reaction. The phase purity and crystal structure were obtained by X-ray diffraction (XRD) measurements and Rietveld refinement. The photoluminescence spectroscopy revealed that the as-prepared phosphors exhibited a bright blue emission under the excitation by near ultraviolet light and the PL emission peaks of BZS: x Ce 3+ showed a red-shift from 432 nm to 451 nm on the Ce 3+ concentration increasing. The corresponding red-shift mechanism has been discussed. The concentration quenching behavior was observed. The luminescence decay curves and lifetime values were analyzed. This phosphor exhibited high internal quantum efficiency. Thermal quenching luminescence properties showed that the emitting intensity was remained 44.60% of that measured at room temperature when the temperature increased to 398 K. The results indicate that the BaZrSi 3 O 9 :Ce phosphor is a promising blue-emitting phosphor for the application as an ultraviolet-convertible phosphor. [ABSTRACT FROM AUTHOR]

• Phosphors with full visible spectra were obtained in β -Ca 3 (PO 4) 2 solid solutions. • The nonlinear changes of phase evolutions and regulation of spectra were analyzed. • High quality WLEDs device with CRI = 95.1 and CCT = 3213 K was fabricated. • The R9 value of WLED reached 93.1 when Eu2+ and Mn2+ were co-doped into phosphor. Exploring the phosphors with full visible spectra emission in a single system to realize versatile color output is highly desired but still challenging for high quality phosphor converted white light emitting diodes (WLEDs). Here, inspired by the multiple crystallographic sites in β -Ca 3 (PO 4) 2 structures and facile crystal-site engineering method, full visible spectra emission was obtained via the design of two kinds Ca 9 Y(PO 4) 7 -Ca 10 Li(PO 4) 7 :Eu2+, Mn2+ and Ca 9 Y(PO 4) 7 -Ca 10 Na(PO 4) 7 :Eu2+, Mn2+ solid solution phosphors. The structure characteristics and photoluminescence properties were investigated by the Rietveld refinement on the basis of X-ray diffraction data, density functional theory, and low/room/high temperature spectra. The nonlinear phase evolutions introduced by the disappearances of vacancy, decreases of polyhedron number and changes of occupying atom in the different five cationic sites aroused the redistributions of Eu2+ among the cationic sites, which achieved full visible spectra emission and then enabled the fabricated WLEDs to exhibit high color rendering index (CRI = 81.5) and low correlated color temperature (CCT = 4087 K) under 365 nm chip excitation. Moreover, the R9 value was further enhanced from 24.6 to 93.1 with the help of construction of Eu2+-Mn2+ energy transfer in selected phosphors, which improved the qualities of device with higher CRI and lower CCT (CRI = 95.1 and CCT = 3213 K). The new kinds of solid solution phosphors reported here could not only manipulate the redistributions of Eu2+ among different cationic sites for full visible spectra emission, but also pave a way to develop phosphors for high quality WLEDs. [ABSTRACT FROM AUTHOR]

A series of Eu doped and charge compensated Sr 5 (PO 4) 3 Cl phosphors have been synthesized via a solid-state reaction in air atmosphere. The XRD patterns and the Rietveld refinement confirmed that the obtained samples were pure phases. The photoluminescence properties of Sr 5 (PO 4) 3 Cl:Eu phosphors exhibited that Eu3+ could be reduced to Eu2+ in an air atmosphere, and the corresponding mechanism of abnormal reduction of Eu3+ to Eu2+ had been discussed. Meanwhile, the enhancement in the PL intensity of red emission and the thermal stability of phosphors was observed upon co-doping via the charge balance strategies of (a) 2Sr2+ = Eu3+ + R+ (R = Li, Na and K), (b) Eu3+ + Si4+ = Sr2+ + P5+ and (c) 3Sr2+ = vacancy + 2Eu3+, among which Na+ ions had the optimized charge compensation effect. The mechanisms between different charge compensation methods and the improvement in PL intensities of Eu3+ were also analyzed. • Mixed-valence of Eu-doped Sr 5 (PO 4) 3 Cl was prepared in air atmosphere. • The reduction mechanism of Eu3+ to Eu2+ was explained detailedly. • The luminescent properties had been improved via charge compensation. • The thermal stability of phosphors had been enhanced by charge compensation. [ABSTRACT FROM AUTHOR]

The tunable blue-emitting KBa 1− x (Mg/Zn) x Y 0.95 (BO 3 ) 2 :0.05Ce 3+ and K 1− y Na y BaY 0.95 (BO 3 ) 2 :0.05Ce 3+ phosphors have been investigated via cation substitution of Mg 2+ /Zn 2+ for Ba 2+ and Na + for K + in KBaY(BO 3 ) 2 host. The crystal structures, photoluminescence properties, thermal stability and the effect of Mg 2+ /Zn 2+ /Na + concentration on the luminescence characteristics were investigated in detail. The XRD analysis implied that KBa 1− x (Mg/Zn) x Y(BO 3 ) 2 solid solutions were limited, while continuous solid solution was possible in K 1− y Na y BaY(BO 3 ) 2 system. Upon the excitation at 365 nm, the emission peaks of KBa 1− x (Mg/Zn) x Y 0.95 (BO 3 ) 2 :0.05Ce 3+ (0 ⩽ x ⩽ 0.6) blue-shifted from 435 to 424 nm, and K 1− y Na y BaY 0.95 (BO 3 ) 2 :0.05Ce 3+ (0 ⩽ y ⩽ 1) blue-shifted from 435 to 427 nm with the Mg 2+ /Zn 2+ /Na + doping concentration increase. The thermal stabilities of KBa 1− x (Mg/Zn) x Y 0.95 (BO 3 ) 2 :0.05Ce 3+ phosphors were enhanced from 20 °C to 200 °C by increasing the concentration of Mg 2+ and Zn 2+ . The substitution of Na + for K + led to a decrease in the proportion of 5 D- 2 F 5/2 and 5 D- 2 F 7/2 corresponding to the Gaussian fitting of Ce 3+ in K 1− y Na y BaY 0.95 (BO 3 ) 2 :0.05Ce 3+ phosphors. At the temperature increased, the full width at half maximum of photoluminescence band of K 0.8 Na 0.2 BaY 0.95 (BO 3 ) 2 :0.05Ce 3+ decreased. However, the decreasing trend of FWHM became less obvious with the increasing concentration of Na + in the temperature dependent photoluminescence spectra of K 1− y Na y BaY 0.95 (BO 3 ) 2 :0.05Ce 3+ phosphors. [ABSTRACT FROM AUTHOR]

A single-phased white emitting phosphor LaBSiO 5 :Dy 3+ was successfully synthesized via a solid state reaction. The X-ray diffraction results confirmed that the doped Dy 3+ ions did not change the lattice structure. Several strong excitation peaks of LaBSiO 5 :Dy 3+ were found around 300–450 nm. Under excitation of 350 nm, the LaBSiO 5 :Dy 3+ exhibited white emission by combining the two emission peaks at 478 and 574 nm corresponding to the typical 4 F 9/2 → 6 H 15/2 and 4 F 9/2 → 6 H 13/2 transitions. The optimal substitution proportions of Dy 3+ for La 3+ was determined to be 1 mol% and the critical distance of Dy 3+ was 25.9628 Å. Moreover, the CIE chromaticity coordinates of LaBSiO 5 :Dy 3+ phosphor was (0.3116, 0.3474) which is close to the ideal white light coordinates (0.333, 0.333), indicating that the phosphor has a potential application as a single component ultraviolet-convertible white light emitting phosphor. [ABSTRACT FROM AUTHOR]

• Double perovskite structured LMNO: Pr3+ thermometric phosphor with four FIR models were designed. • The high S a and S r could reach 0.0597 K−1 and 0.7250% K−1, respectively. • The sample possesses good repeatability and reversibility under temperature-cycling processes. Currently, non-contact fluorescence intensity ratio (FIR)-based luminescent thermometry has been extensively attracted great attention for its promising applications in electromagnetic field, micro-temperature field and thermally harsh environments. In this work, the double-perovskite LaMg 0.402 Nb 0.598 O 3 : Pr3+ (LMNO: Pr3+) thermometric phosphor is firstly designed and successfully synthesized via a high-temperature solid-state method. Under 450 nm excitation, the as-prepared samples simultaneously exhibit blue emission (3P 0 → 3H 4), green emission (3P 1 → 3H 4) and red emission (1D 2 → 3H 4 , 3P 0 → 3F 2) of Pr3+. They present different dependence on the temperature due to the intervalence charge transfer state (IVCT). Accordingly, the four FIR models between 3P 1 → 3H 4 and 3P 0 → 3H 4 (G/B), 3P 1 → 3H 4 and 3P 0 → 3F 2 (G/R2), 1D 2 → 3H 4 and 3P 0 → 3H 4 (R1/B) and 1D 2 → 3H 4 and 3P 0 → 3F 2 (R1/R2) are used as temperature detecting signal in the range of 298–523 K, and the maximum absolute and relative sensitivity of LaMg 0.402 Nb 0.598 O 3 : 1.2% Pr3+ sample reached 0.0597 K−1 at 523 K and 0.7250% K−1 at 473 K, respectively. Excellent temperature sensing features are also demonstrated in the LaMg 0.402 Nb 0.598 O 3 : 0.3% Pr3+ and LaMg 0.402 Nb 0.598 O 3 : 2.0% Pr3+ samples. Except for high sensitivity for temperature sensing, the designed Pr3+-doped double-perovskite materials also realize the self-calibration by simultaneous monitoring of four models of FIR. Moreover, after five cycles, the relative luminescence intensity of LaMg 0.402 Nb 0.598 O 3 : 1.2% Pr3+ sample remains stable. These results indicate that LaMg 0.402 Nb 0.598 O 3 : Pr3+ phosphors have great promising application as self-calibrated optical temperature sensors. [ABSTRACT FROM AUTHOR]