Synthesis and luminescence properties of Na+, Li+ compensated Er3+ doped CaAl4O7 phosphors

Abstract

Here the green-emitting highly luminescent Er³⁺ doped, Er³⁺-Li⁺ co-doped, Er³⁺-Na⁺ co-doped CaAl₄O₇ is synthesized by Pechini method at 1000^°C. Photoluminescence (PL) of CaAl₄O₇: Er³⁺ studies have been compared with Li⁺ co-doped CaAl₄O₇: Er³⁺ and Na⁺ co-doped CaAl₄O₇: Er³⁺. Na⁺ co-doped CaAl₄O₇:Er³⁺ shows increases in luminescence intensity compared to Li⁺ co-doped CaAl₄O₇: Er³⁺ and Er³⁺ doped CaAl₄O_7. The results suggest that CaAl₄O₇:Er³⁺ phosphor can be used as efficient green-emitting phosphor in white LED. The resultant phosphor emits green color peaking at 549 nm upon 378 nm excitation. Powder X-ray diffraction (PXRD) and photoluminescence (PL) techniques have been studied to characterize the synthesized microparticles. Further, this phosphor has good thermal stability that implies its potential to act as green phosphor in white light-emitting diodes. The effect of activator (Er³⁺), Na⁺ co-doped CaAl₄O₇:Er³⁺, and Li⁺ co-doped CaAl₄O₇:Er³⁺ phosphors luminescence spectra as well as photoluminescence life time studies were studied in detail. The results show that as the concentration of Er³⁺ in CaAl₄O₇ increases, the symmetry around the Er³⁺ ion decreases due to the creation of lattice defects in the crystal. Addition of Na⁺ and Li⁺ ions in CaAl₄O₇: Er³⁺leads to a small distortion in the local symmetry of Er³⁺ ions, thereby significantly enhancing its luminescence property. Analysis of photoluminescence life time studies of the prepared samples shows a smaller concentration quenching of Er³⁺ luminescence in charge compensated Na⁺ and Li⁺ CaAl₄O₇ phosphor.