Preparation and luminescent properties of a novel orange-red phosphor Sr₂RE₈(SiO₄)₆O₂:Eu^(2+,3+) (RE = Y, Gd, La) for LEDs

Abstract

A series of novel orange-red Sr_1.9RE₈(SiO₄)₆O₂:0.1Eu^(2+,3+) (RE = Y, Gd, La) phosphors were synthesized by high-temperature solid-phase reaction method, all of which are apatite structure, belonging to hexagonal crystal system. The cell parameters (a, c) and cell volume (V) of Sr_1.9RE₈(SiO₄)₆O₂:0.1Eu^(2+,3+) decrease with the substitution of RE³⁺ by La³⁺, Gd³⁺ and Y³⁺, respectively, and the crystal size decreases from 64.8309 to 49.0382 nm. The excitation spectra of Sr_1.9RE₈(SiO₄)₆O₂:0.1Eu^(2+,3+) phosphors are a broadband in the range of 200–600 nm, which can be attributed to the CTS of Eu³⁺ and the d–f transition of Eu²⁺. When RE³⁺ in the matrix is replaced by La³⁺, Gd³⁺ and Y³⁺, respectively, the charge transfer band of Eu³⁺ generates bathochromic shift from 265 to 275 nm, and the broadband of the excitation spectrum of Eu²⁺ is red shifted from 320.5 to 336 nm. The emission spectra of Sr_1.9RE₈(SiO₄)₆O₂:0.1Eu^(2+,3+) phosphors in the range of 500–750 nm are a set of strong sharp line spectra, which are inconsistent with emission broadband spectrum of Eu²⁺ allowing electric dipole transition, mainly including the transition of ⁵D₀, ⁵D₁, ⁵D₂ → ⁷F_J from Eu³⁺. This result indicates that Eu²⁺ can efficiently transfer energy to Eu³⁺ and Sr_1.9La₈(SiO₄)₆O₂:0.1Eu^(2+,3+) exhibits the highest transfer efficiency. Importantly, the color coordinates of Sr_1.9RE₈(SiO₄)₆O₂:0.1Eu^(2+,3+)(RE = Y, Gd, La) are all in the orange-red light range, and the color temperature is lower than 1800 K with a high color rendering index (CRI ≥ 75), which is suitable for the phosphor of white LED excited by UV chip.