Enhanced red emission in Ca0.5La(MoO4)2:Eu3+ phosphors for UV LEDs

Abstract

La³⁺ was introduced into CaMoO₄ to form a novel compound with the chemical formula Ca_0.5La(MoO₄)₂ and Eu³⁺ activated the new compound was synthesized by a solid-state reaction method. An enhanced red emission at 615 nm originating from the ⁵D₀–⁷F₂ transition of Eu³⁺ was reported in the Ca_0.5La(MoO₄)₂:Eu³⁺ phosphor. XRD patterns indicate a structural similarity to CaMoO₄. The red emission intensity of the Ca_0.5La(MoO₄)₂:Eu³⁺ phosphor is 5.92 times higher than that of CaMoO₄:Eu³⁺. Photoluminescent spectra, diffuse reflection spectra and lifetime measurements indicate that the red emission enhancement is due to the increase of the ⁷F₀–⁵L₆ absorption intensity of Eu³⁺ in the distorted crystal field of the Ca_0.5La(MoO₄)₂:Eu³⁺ phosphor. Enhanced red emission, stronger ⁷F₀–⁵L₆ absorption intensity, and high color purity indicate that the Ca_0.5La(MoO₄)₂:Eu³⁺ phosphor is a promising red phosphor for UV LEDs. The luminescence properties of the Bi³⁺ co-doped Ca_0.5La(MoO₄)₂:Eu³⁺ phosphor was also investigated. Although Bi³⁺ co-doped into the Ca_0.5La(MoO₄)₂:Eu³⁺ phosphor broadens PLE spectra in the UV range and makes it more suitable for UV pumped LEDs, it decreases the distortion and induces a new quenching path, and thus makes the emission intensity decrease.