Tunable photoluminescence of apatite phosphor Ca_5.95−xSr_xLa₄(SiO₄)₂(PO₄)₄O₂:0.05Eu²⁺ and its application in light‐emitting diodes

Abstract

A series of new apatite phosphors Ca 5.95−x Sr x La 4 (SiO 4 ) 2 (PO 4 ) 4 O 2 :0.05Eu 2+ (x = 0-5.95) were prepared with the solid-state method. The variations of the occupation rate and cell parameters were investigated in detail, demonstrating that the phosphors are pure phases and that the different occupation rates of La 3+ , Ca 2+ , and Sr 2+ ions are due to the different electrostatic bond strengths. The reflectance and photoluminescence excitation spectra prove that the phosphors can be efficiently excited with near-ultraviolet (n-UV) light. The broad redshift (50 nm) in the photoluminescence spectra is attributed to the increase in the crystal field splitting when the Ca 2+ ion is replaced by the larger Sr 2+ ion. At 150°C, the obtained phosphors maintain an emission intensity of~67%-77% of that at room temperature (25°C), which indicates relatively the high performance of apatite phosphors in the temperature-dependence experiment. Because of the substitution of the small Ca 2+ ion by the large Sr 2+ ion, the emission color changes from green to yellow. Finally, a series of self-made light emitting diodes lamps were fabricated by coating the Ca 5.95−x Sr x La 4 (SiO 4 ) 2 (PO 4 ) 4 O 2 :0.05Eu 2+ phosphors with commercial blue and red phosphors on an n-UV chip (λ ex = 370 nm). The selfmade white-emitting lamps display a continuous changing correlated color temperature (4053-9353 K) or commission international de L'eclairgae (from [0.29, 0.28] to [0.38, 0.37]), implying that the series apatite phosphors have great potential to meet the different requirements of applications. K E Y W O R D Sapatite, cation substitution, LED lamp, luminescence, phosphor