Red Fluorescence Enhancement via Using the Charge Compensation and Co-doping WO3 in CaMoO4:Eu3+ Phosphor for Ultraviolet Converted LEDs

Abstract

Here we designed and synthesized the red NaxCa1−2xMoO4:Eux 3+ phosphors with fluorescence enhancement via high temperature solid state reaction. Phase purity analysis, which had been checked by the X-ray powder diffraction (XRD), showed that all the obtained samples crystallized in a scheelite structure with the space group of I41/a (No. 88). In these samples, we found that increasing the x value enabled shifting the XRD position to the low angle direction. For the photoluminescence (PL) properties, the charge transfer (CT) band as the x value increases exhibited an initial intensity increase followed by a subsequent decrease, and the optimal x value for the maximum CT band intensity was experimentally found to be 0.25. In sharp difference, directly exciting at the excitations of Eu3+, viz. 393 and 464 nm, allowed the Eu3+ emission to constantly increase the emission intensity. In order to further enhance the red fluorescence intensity, the WO3 was selected to co-dope into the NaxCa1−2xMoO4:Eux 3+ (x = 0.5) sample in order to form the Na0.50(MoO4)1−y(WO4)y:Eu0.50 3+ solid solution compounds. Upon excitation at 393 and 464 nm, the y value that corresponded to optimal Eu3+ fluorescence intensity was found to be 0.5. To illustrate our experimental observations, feasible mechanism profile was also given in this work. Our results have demonstrated that the Eu3+ fluorescence in CaMoO4 matrix could be enhanced by using the charge compensation and at the same time the WO3, which provided new insight into enhancing Eu3+ doped crystals for ultraviolet converted white-LEDs.