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.

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Phase and crystal structure of the Na 2 Y 2 B 2 O 7 :Tm 3+ -Yb 3+ inorganic phosphor prepared by solution combustion method has been identified by powder X-ray diffraction technique.Surface morphology and particle size has been examined by using the field emission scanning electron microscopy and high resolution transmission electron microscopy characterizations of the prepared materials. No absorption band around 980 nm has been observed in the Tm 3+ doped phosphors, whereas a broad band around 980 nm in the Tm 3+ -Yb 3+ codoped phosphors corresponding to the 2 F 7/2 ← 2 F 5/2 absorption transition of Yb 3+ ion has been detected. The upconversion emission bands have been observed in the UV, visible and NIR regions upon excitation with 980nm laser diode. The temperature sensing behaviour and the concept of nanoheater in the developed nanophosphor has been demonstrated by using the stark sublevels of the 1 G 4 level of Tm 3+ ion, which is responsible for the blue upconversion emission. The maximum sensor sensitivity of about 4.54×10 -3 K -1 at 300 K for the developed multifunctional nanophosphor has been determined. The temperature gain of about ~435 K has been observed at laser power density of 66.88 W/cm 2 and the colour coordinates do not change with the variation of pump power density. For localizing and heating the hyperthermia based cancer cells by using the NIR radiation a very low pump power density of about ~7.0 W/cm 2 has been established. The experimental observations prove the developed material to be used as a multifunctional nanomaterial in optical devices and biological applications.

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