Structural, magnetic and neutron diffraction studies on TbFe2TbAl2, TbCo2TbAl2 and HoCo2HoAl2

Abstract

The present investigation aims at the luminescence properties of Ca9Y(VO4)7:Eu3+, Bi3+ red phosphor materials. The red emission at 613 nm originating from 5D0–7F2 transition of Eu3+ in Ca9Y(VO4)7 is enhanced strongly with Bi3+–V5+ couple as the sensitizer, under excitation either into the 5L6 state or the 5D2 state. The energy transfer from Bi3+–V5+ to Eu3+ is discussed. For a fixed Eu3+ concentration, there is an optimal Bi3+ concentration with 15 mol%, at which the maximum luminescence intensity of Eu3+ is achieved. The red emission of Ca9Y(VO4)7:0.8Eu3+, 0.15Bi3+ (under 395 nm and 465 nm excitations) is stronger than that of commercial Y2O3:Eu3+ phosphor (under 395 nm and 467 nm excitations). Based on the ratios of the red emission at 613 nm to orange one at 592 nm, it is considered that the symmetry of Eu3+ site decreases with doping of Bi3+, leading to more opposite parity components. Lifetime and diffuse reflection spectra measurements indicate that the red emission enhancement is due to the enhanced transition probabilities from the ground state to 5L6 and 5D2 states of Eu3+ in the distorted crystal field. Therefore the present material is a promising red-emitting phosphor for white-light diodes with near-ultraviolet/blue GaN-based chips.