Photoluminescence properties and energy transfer in a novel Sr8ZnY(PO4)7:Tb3+,Eu3+ phosphor with high thermal stability and its great potential for application in warm white light emitting diodes

Abstract

Terbium and europium co-doped Sr₈ZnY(PO₄)₇ phosphors are successfully prepared through a high temperature solid-state reaction (SSR). The crystal structure of the as-prepared samples was identified to be Sr₈ZnY(PO₄)₇ (SZYP) pure phase by an X-ray powder diffraction technique. Under near-ultraviolet light excitation (378 nm), the SZYP:Tb³⁺ and SZYP:Eu³⁺ phosphors show green and red emission peaking at 545 and 618 nm, respectively. Moreover, an effective energy transfer process from Tb³⁺ to Eu³⁺ could be verified by the concentration dependence of emission intensity and lifetime. The energy transfer mechanism between Tb³⁺ and Eu³⁺ is determined to be governed by dipole–dipole interactions. The internal quantum efficiency (IQE) is evaluated to be as high as about 91%. The temperature-dependent spectra indicate that the SZYP:Tb³⁺,Eu³⁺ phosphor shows a high thermal stability. Furthermore, the as-fabricated white LED devices exhibit an excellent correlated color temperature (CCT) of 3223 K, a color rendering index (R_a) of 85.8 and a luminance efficiency of 37.4 lm W⁻¹. All results imply that the SZYP:Tb³⁺,Eu³⁺ phosphors have a great potential for application in white LEDs.