Improvement of thermal stability and photoluminescence in Sr0.8Ca0.2Al2Si2O8:Eu2+ by the substitution of Si–Na # Al–Sr and Ca # Sr for structural modifications†
Blue emitting phosphor is urgently needed in commercial application of white light emitting diodes for the reason that the existing ones lack proper emission and have poor thermal stability. Herein, we report two methods for Sr0.8Ca0.2Al2Si2O8:Eu2+ phosphors that were performed to optimize the luminescence properties and thermal stability based on structural reconstruction. One is partial substitution of Al3+–Sr2+ by Si4+–Na+ forming Sr0.77−xNaxCa0.2Al2−xSi2+xO8:0.03Eu2+ (x = 0–0.7); the other is altering the proportion of Ca2+ and Sr2+, forming Sr0.97−yCayAl2Si2O8:0.03Eu2+ (y = 0–0.97) solid solution. The phosphor's structural evolution, variation of the Eu2+ local environment, luminescence and thermal quenching were explored in detail. As a result, for Sr0.77−xNaxCa0.2Al2−xSi2+xO8:0.03Eu2+ (x = 0–0.7) series, (Al/Si)O4 tetrahedrons are enlarged and Eu–O polyhedrons are compressed; the emission gets red-shifted from 418 nm to 428 nm under 350 nm excitation; the thermostability of Sr0.97−yCayAl2Si2O8:0.03Eu2+ is improved with the incorporation of Si4+–Na+ pair. For Sr0.97−yCayAl2Si2O8:0.03Eu2+ (y = 0–0.97) series, the emission peak shows a large shift from 420 nm to 440 nm, which is attributed to a comprehensive result of nephelauxetic effect and crystal field splitting. Furthermore, thermal stability is improved by the coexistence of Ca2+ and Sr2+. White light emitting diodes fabricated by combining the as-prepared phosphor with commercial phosphors exhibit an excellent color rendering index Ra of 90.1 and a temperature of 4459 K with CIE coordinates of (0.357, 0.356). These results indicate that the as-developed composition series are promising for commercial application.