An efficient green-emitting α-Ca1.65Sr0.35SiO4:Eu2+ phosphor for UV/n-UV w-LEDs: synthesis, luminescence and thermal properties

Abstract

A series of Eu²⁺ singly doped α-Ca_1.65Sr_0.35SiO₄:Eu²⁺ phosphors have been synthesized via the high-temperature solid-state reaction method. X-ray diffraction (XRD), Fourier transform infrared (FT-IR) spectroscopy, scanning electron microscopy (SEM), diffuse reflectance spectroscopy and photoluminescence (PL) including temperature-dependent PL were used to characterize the as-prepared samples. The XRD patterns and Rietveld refinement of the presented sample show the pure phase of the as-prepared samples. All of the phosphors exhibit intense and broad absorption bands in the ultraviolet and near ultraviolet (n-UV) range, and produce bright green emission upon 365 nm UV radiation. The critical concentration of Eu²⁺ for the maximum intensity was determined to be about 1 mol% in α-Ca_1.65Sr_0.35SiO₄:Eu²⁺ after optimizing the composition. The energy transfer mechanism between Eu²⁺ was demonstrated to be dipole–dipole interaction. Besides, the fluorescence decay curves, the temperature dependent PL and CIE value of α-Ca_1.65Sr_0.35SiO₄:Eu²⁺ phosphors were investigated. It is reasonable that the decay times of samples decrease with increasing Eu²⁺ content. The CIE chromaticity coordinates shift from green (0.197, 0.395) to the border between the green and yellow (0.242, 0.547) region, which agree with the corresponding emission spectra. The maximum quantum yield is 69% for α-Ca_1.65Sr_0.345SiO₄:0.005Eu²⁺. The thermal stability of luminescence of selected α-Ca_1.65Sr_0.34SiO₄:0.01Eu²⁺ was also investigated and compared with that of the commercial green phosphor, which shows its good performance. The above results suggest that it is a good candidate for green-emitting phosphors applied in UV/n-UV pumped w-LEDs.