Enhanced red emission in CaMoO₄:Bi³⁺,Eu³⁺

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 Bi ³⁺ 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 Y₂O ₃: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 Eu ³⁺ 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.