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

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 (1)G(4) -> H-3(6) transition whereas the Ho3+/Yb3+ co-doped Na4ZnW3O12 sample gives intense green and red emissions due to the F-5(4)/S-5(2) -> I-5(8) and F-5(5) -> I-5(8) 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.