Engineering charge-transfer interactions for red-emitting SrLa(Sc,Ga)O4:Ce3+ phosphor with improved thermal stability

Blue-light-excitable red-emitting phosphors with high thermal stability are essential for fabricating white light-emitting diodes (WLEDs). Herein, Ce3+-doped SrLaScO4 (SLO:Ce3+) phosphor is discovered to have an abnormal red emission band centered at 640 nm when excited at 440 nm. Spectroscopy and structural analyses confirm that Ce3+ ions occupy the [LaO8] polyhedrons competitively, generating a strong crystal field splitting and a large Stokes shift to produce a red emission. To further restrict the thermal quenching of SLO:Ce3+, charge-transfer engineering is implemented by incorporating a large electronegative Ga3+ in the Sc3+ site, which can attract more charges from nearby coordinating groups to decrease the electronic occupation at the bottom of the conduction band and thereby enlarge the band gap. Sc/Ga substitution in SrLa(Sc,Ga)O4:Ce3+ enhances the thermal stability by increasing the intensity ratio from 15% to 31% at 150°C compared with 20°C. This is attributed to the efficient suppression of the thermally stimulated ionization process. This study presents a general design principle for discovering novel Ce3+-doped red phosphors with good thermal stability for WLED applications.