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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]

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]

A series of trivalent rare-earth element ions (europium, terbium, dysprosium) singly- and co-doped strontium yttrium borate phosphors was synthesized via the sol–gel method. The phase formation, luminescence properties, decay times, and energy transfer behaviors from terbium ions to europium ions, the thermal stability, and the Commission Internationale de L’Eclairage coordinates were investigated. Under the excitation of ultraviolet light, the singly doped phosphors exhibited green emission of terbium ions, white emission of dysprosium ions, and red emission of europium ions, respectively. For the terbium and europium ions co-doped strontium yttrium borate samples, a white emission can be realized by blending the doping concentration of terbium and europium ions. The critical distance between terbium and europium ions has been calculated to be about 14.52 Å and the energy transfer from terbium to europium occurred through the dipole–quadrupole interaction. At 150°C, the emission intensity of terbium and europium in the 12 mol% terbium and 14 mol% europium co-doped strontium yttrium borate sample was maintained at about 74% and 87% of their corresponding initial values, respectively, and the dysprosium ions singly doped strontium yttrium borate sample showed about 70% of its initial emission intensity at room temperature. The above results suggested that europium, terbium, dysprosium ions singly- and co-doped strontium yttrium borate phosphors have potential applications as ultraviolet-convertible phosphors. [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]

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]

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]

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]