Enhanced photoluminescence in Tm3+, Yb3+, Mg2+ tri-doped ZnWO4 phosphor: Three photon upconversion, laser induced optical heating and temperature sensing

Three photon upconversion photoluminescence has been observed in Tm3+, Yb3+ co-doped ZnWO4 phosphor synthesized through solid state reaction method. The structural measurements reveal an increase in crystallinity and particles size on Mg2+ incorporation. The EDS spectrum shows the presence of Zn, W, Tm, Yb, Mg and O elements in the phosphor. The UV-vis-NIR absorption spectra contain CTB and 4f-4f transitions due to Tm3+ and Yb3+ ions, respectively. The Tm3+, Yb3+ co-doped phosphor gives intense blue and NIR emissions alongwith a weak red emission due to (1)G(4)-> H-3(6), H-3(4)-> H-3(6) and (1)G(4)-> F-3(4) transitions, respectively upon 976 nm excitation. The emission intensity of the phosphor is found optimum at 2 mol% concentration of Yb3+ ion. When the Mg2+ ion is incorporated in the co-doped phosphor, the emission intensity enhances upto two times. This may be due to improved crystal structure and an increase in the intensity of absorption bands. The FIR analysis in the Stark components of (1)G(4) level suggests an efficient optical heating and temperature sensing ability. The temperature sensing sensitivity is found to be 34 x 10(-4) degrees K-1 at 300 K. Thus, the Tm3+, Yb3+, Mg2+ tri-doped ZnWO4 phosphor may be used in photonic devices, NIR source, as an optical heater and temperature sensor purposes.