Photoluminescence properties and energy transfer in a novel Sr ₈ ZnY(PO ₄ ) ₇ :Tb ³⁺ ,Eu ³⁺ phosphor with high thermal stability and its great potential for application in warm white light emitting diodes

Terbium and europium co-doped Sr ₈ ZnY(PO ₄ ) 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 Sr ₈ ZnY(PO ₄ ) ₇ (SZYP) pure phase by an X-ray powder diffraction technique. Under near-ultraviolet light excitation (378 nm), the SZYP:Tb ³⁺ and SZYP:Eu ³⁺ phosphors show green and red emission peaking at 545 and 618 nm, respectively. Moreover, an effective energy transfer process from Tb ³⁺ to Eu ³⁺ could be verified by the concentration dependence of emission intensity and lifetime. The energy transfer mechanism between Tb ³⁺ and Eu ³⁺ 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:Tb ³⁺ ,Eu ³⁺ 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:Tb ³⁺ ,Eu ³⁺ phosphors have a great potential for application in white LEDs.