Intrinsic optical bistability and frequency upconversion in Tm 3+ –Yb 3+ -codoped Y 2 WO 6 phosphor

The phase and crystal structure of Tm(3+)-Yb(3+) codoped Y2WO6 phosphor synthesized via the solid state reaction method was analysed by X-ray diffraction. The surface morphology and impurity content of the phosphor were analysed by field emission scanning electron microscopy (FE-SEM) and Fourier transform infrared (FTIR) spectroscopy, respectively. Upon excitation from a 980 nm diode laser, the developed phosphor shows three upconversion emission bands. Codoping with Yb(3+) ions in the Y2WO6:Tm(3+) phosphor significantly enhances the intensity of the frequency upconversion emission. The processes responsible for the UC emissions and their intensity variation upon codoping have been discussed with the help of pump power dependence, energy level diagrams and decay curve analysis. The intrinsic optical bistability and colour tunability are also reported for the developed phosphor.