Enhanced white light emission from a Tm3+/Yb3+/Ho3+ co-doped Na4ZnW3O12 nano-crystalline phosphor via Li+ doping

Abstract

This paper reports white light emission from a Tm³⁺/Yb³⁺/Ho³⁺ co-doped Na₄ZnW₃O₁₂ nano-crystalline phosphor synthesized through a solution combustion method. The structural measurements reveal the crystalline nature of the synthesized samples. The Tm³⁺/Yb³⁺ co-doped Na₄ZnW₃O₁₂ sample gives intense blue emission due to the ¹G₄ → ³H₆ transition whereas the Ho³⁺/Yb³⁺ co-doped Na₄ZnW₃O₁₂ sample gives intense green and red emissions due to the ⁵F₄/⁵S₂ → ⁵I₈ and ⁵F₅ → ⁵I₈ transitions, respectively, on excitation with 976 nm. When these three ions viz. Tm³⁺, Ho³⁺ and Yb³⁺; are co-doped in Na₄ZnW₃O₁₂ the sample gives intense upconverted white light. The as-synthesized sample emits larger emission intensity on annealing at higher temperature. Addition of Li⁺ in the co-doped phosphor further enhances the emission intensity of white light up to two times and the CIE coordinates of the white light are (0.30, 0.41), which is close to the standard white light (0.33, 0.33). The enhancement in the emission intensity has been discussed due to changes in the local crystal field and reduction in the optical quenching centers. Thus, this nano-crystalline phosphor can be a suitable candidate for white light in various optical applications.