Blue-emitting Bi-doped double perovskite Gd2ZnTiO6 phosphor with near-ultraviolet excitation for warm white light-emitting diodes

Abstract

A series of Bi3+ ions activated blue-emitting phosphors Gd2-xZnTiO6:xBi3+ (0 ≤ x ≤ 0.015) were synthesized by high-temperature solid-state procedure. The Density Functional Theory (DFT) calculations demonstrated that the host lattice Gd2ZnTiO6 possessed a direct band gap of 3.07 eV which agreed well with the optical band gap of about 3.80 eV obtained from the diffuse reflection spectrum. Moreover, the Gd2-xZnTiO6:x Bi3+ crystallizes in a monoclinic space group P21/n (# 14) and the representative Gd1.9925ZnTiO6:0.0075Bi3+ phosphor presents an irregular crystal shape with smooth surface, clear edges and corner. All of them emit bright blue light with the emission peak at 419 nm under 375 nm excitation and the optimum Bi3+ ion doping concentration is 0.0075. In addition, the thermal quenching properties and PL decay test show that the Gd1.9925ZnTiO6:0.0075Bi3+ possess good thermal stability and an efficient energy transfer between Bi3+ ions. Finally, we explored the application of Gd1.9925ZnTiO6:0.0075Bi3+ phosphor by fabricating the warm pc-WLED device. Notably, the device presents good luminescence properties with the International Commission on Illumination (CIE) coordinates of (0.4485, 0.4222), a high color rendering index (CRI) of 89.4 and low corresponding color temperature (CCT) of 2956 K under 60 mA current.