Enhanced Red Emission in CaMoO₄:Bi³⁺,Eu³⁺

Abstract

We report the observation of enhanced red emission at 613 nm originating from 5D0 → 7F2 transition of Eu3+-doped CaMoO4 with Bi3+ as an additive, under excitation either into the 5L6 state with 395 nm or the 5D2 state with 465 nm. The luminescence properties as a function of Bi3+ and Eu3+ concentrations are studied. Strongly enhanced red emission of Eu3+ is obtained by adding Bi3+ instead of increasing the Eu3+ concentration. For a fixed Eu3+ concentration, there is an optimal Bi3+ concentration, at which the maximum luminescence intensity is achieved. The red emission of CaMoO4:0.05Eu3+ is enhanced by a factor of 3 as 0.2 Bi3+ is co-doped into the system, stronger than that of commercial Y2O2S:Eu3+ and Y2O3:Eu3+ phosphors. 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 in which it is considered that more odd-rank crystal field components are induced by crystal structural distortion and symmetry decreasing with the addition of Bi3+, leading to more opposite parity components, for example, 4f55d states, mixed into the 4f6 transitional levels of Eu3+. The energy transfer from Bi3+ to Eu3+ also occurs and is discussed. The present material is a promising red-emitting phosphor for white light diodes with near-UV/blue GaN-based chips.