Gradient defects mediate negative thermal quenching in phosphors

Luminescent materials often suffer from thermal quenching (TQ), limiting the continuation of their applications under high temperatures up to 473 K. The formation of defect levels could suppress TQ, but rational synthesis and deep understanding of multiple defects-regulated luminescent materials working in such a wide temperature range still remain challenging. Here, we prepare a negative thermal quenching (NTQ) phosphor LiTaO3 : Tb3 + by introducing gradient defects VTa5−, TbLi2+, and ( VTaTbLi)3 − as identified by advanced experimental and theoretical studies. Its photoluminescence significantly becomes intense with rising temperatures and then slowly increases at 373 to 473 K. The mechanism studies reveal that gradient defects with varied trapping depths could act as energy buffer layers to effectively capture the carriers. Under thermal disturbance, the stored carriers could successively migrate to the activators in consecutive and wide temperature zones, compensating for TQ to enhance luminescence emission. This study initiates the synthesis of multi-defect NTQ phosphors for temperature-dependent applications.