Strategic point defect engineering toward abnormal thermal quenching in Sm3+-doped Na-rich Na1.5La1.5TeO6 phosphors for LEDs applications

Thermal stability holds particular significance for phosphors intended for LEDs. Abnormal thermal quenching was successfully reached by strategic point defect engineering by inserting Frenkel defects and nonequivalent substitution defects in novel Sm3+ ions doped Na-rich distorted double perovskite Na1.5La1.5TeO6 phosphors. Its integral intensity at 420 K (115.03%) was far higher than that of room temperature. Besides, the phosphors exhibited a pronounced orange-red emission peak at 644 nm when excited at 404 nm, which was ascribed to the 4G5/2-6H9/2 transition of Sm3+ ions. The concentration quenching phenomenon resulting from dipole-dipole interactions was observed in the phosphors, and the optimal concentration of dopant Sm3+ was determined to be 1 mol%. After calculation, it was surprising that the color purity values of all phosphors were not less than 99.9%. Additionally, the internal quantum efficiency (IQE) reached 65.30%, and the activation energy (Ea) of Na1.5La1.5TeO6:1 mol%Sm3+ was 0.570 eV. Meanwhile, the emission spectrum of the produced orange-red light emitting diodes (LEDs) exhibited a close correspondence with the absorption curves of various plant pigments (chlorophyll b, allophycocyanin, phycocyanin, phytochrome red and far red (PR and PFR)). The prepared white light emitting diodes (WLEDs) possessed low correlated color temperature (CCT) of 4769 K and as high general color rendering index (CRI, Ra) value as 91. In summary, the phosphors presented promising options for plant-cultivating LEDs and high CRI WLEDs based on their superior optical and thermal properties.