Robust thermal performance of red-emitting phosphor composites for white light-emitting diodes: Energy transfer and oxygen-vacancy induced electronic localization

Ce³⁺ ion can effectively sensitize Sm³⁺ ion via energy transfer, and this phenomenon can led to the development of white light-emitting diodes (WLED). However, interestingly, high correlated color temperature (CCT), poor color-rending index (CRI), poor thermal stability, and low efficacy of available red phosphor still pose immense challenges. Herein, we undertook a combined analysis: X-ray diffraction (XRD), crystal refinement, electron spin resonance (ESR), transmission electron microscopy (TEM), scanning electron microscopy (SEM), and diffuse reflection spectroscopy (DRS). We also observed the optical properties of the resulting samples. The Ce³⁺ and Sm³⁺ dopants on the Sr²⁺ and La³⁺ sites in the mixed cation borate Sr₃LaAl₃B₄O₁₅ (SLAB) phosphors were quantitatively evaluated. A cerium ion merged as a sensitizer, improving the red emission intensity by enhancing it 3.9 times. The energy transfer (ET) between Ce³⁺ and Sm³⁺ was examined experimentally and with theoretical models as a function of Ce³⁺ concentrations at ambient temperatures. Several theoretical models were employed to simulate the luminescence decays of Ce³⁺ and Sm³⁺ doped samples at different doping levels and their transfer mechanisms were studied depending on forced electric dipole at each ion. Notably, the electronic sites created by the oxygen vacancies around the Ln³⁺ ions can effectively justify the highly efficient bluish-red phosphor. Additionally, the SL_0.95AB:0.02Ce³⁺,0.03Sm³⁺ exhibited outstanding thermal-quenching (TQ) resistance and has > 94.8% intensity at 425 K. WLEDs made with the use of SL_0.95AB:0.02Ce³⁺,0.03Sm³⁺ furnished an exceptional CRI exceeding 88 and low at CCT 4503 K. These results are superior to the parameters of commercial WLED containing Y₃Al₅O₁₂:Ce³⁺ phosphor and blue LED chip (CCT≈7746 K, CRI≈75), and they could be a cornerstone for the fabrication of warm WLEDs.