Composition Screening in Blue-Emitting Li4Sr1+xCa0.97–x(SiO4)2:Ce3+ Phosphors for High Quantum Efficiency and Thermally Stable Photoluminescence

Photoluminescence quantum efficiency (QE) and thermal stability are important for phosphors used in phosphor-converted light-emitting diodes (pc-LEDs). Li 4 Sr 1+ x Ca 0.97– x (SiO 4 ) 2:0.03Ce 3+ (−0.7 ≤ x ≤ 1.0) phosphors were designed from the initial model of Li 4 SrCa(SiO 4 ) 2:Ce 3+, and their single-phased crystal structures were found to be located in the composition range of −0.4 ≤ x ≤ 0.7. Depending on the substitution of Sr 2+ for Ca 2+ ions, the absolute QE value of blue-emitting composition-optimized Li 4 Sr 1.4 Ca 0.57 (SiO 4 ) 2:0.03Ce 3+ reaches ∼94%, and the emission intensity at 200 °C remains 95% of that at room temperature. Rietveld refinements and Raman spectral analyses suggest the increase of crystal rigidity, increase of force constant in CeO 6, and decrease of vibrational frequency by increasing Sr 2+ content, which are responsible for the enhanced quantum efficiency and thermal stability. The present study points to a new strategy for future development of the pc-LEDs phosphors based on local structures correlation via composition screening.