Synthesis and Optimum Luminescence of CaWO4-Based Red Phosphors with Codoping of EU3+ and Na+

Scheelite nanostructures Ca1-2x(Eu,Na)(2x)WO4 (0 < x <= 0.135) were prepared from 5 nm Ca-0.968(Eu,Na)(0.032))WO4 by hydrothermal treatment. The preparation of 5 nm Ca-0.968(Eu,Na)(0.032)WO4 at room temperature and subsequent hydrothermal treatment allow control over chemical compositions and particle size of CaWO4-based red phosphors that has not yetpossible when using traditional preparation methods. By careful structural and electronic characterization, it is shown that simulationeous substitutions of Eu3+ and Na+ at Ca2+ sutes were possible using this methodology, which aoolws one to vary the local symmmetry surrounding Eu3+ and moreover the energy transfer from O2- to Eu3+ and tungstate groups to Eu3+ for optimum luminescence. As a consequence, the obtained CaWO4-based nanocrystals displayed excellent luminescence properties as demonstrated by luminescence lifetimes of milliseconds, abnormally narrowed emissions, and maximum quantum efficiencies of 92%. The results reported in this work show that it is possible to control chemical composition of oxide nanostructures for structural decoration and luminescence property tailoring via codoping aliovalent ions.