Optical sensing of temperature based on non-thermally coupled levels and upconverted white light emission of a Gd2(WO4)3 phosphor co-doped with in Ho(III), Tm(III), and Yb(III)

The authors describe a new phosphor of the composition Gd-2(WO4)(3):0.3%Ho/0.5%Tm/15%Yb that displays distinctly improved sensitivity to temperature (T) due to non-thermally coupled energy levels of Ho(III) and Tm(III) ions. Under 980 nm excitation, the upconverted blue (peaking at 473 nm), green (540 nm) and red (655 and 700 nm) fluorescences exhibit T-dependent luminescence in the 295 to 595 K range. The T sensing capability was investigated by using a ratiometric (2-wavelength) technique. The maximum sensitivity to T is found to be 26.14 x 10(-3) K-1 at 595 K based on the red [Tm(III)] and green [Ho(III)] emissions. The colors of the phosphor are located in the white region of the CIE diagram in the whole T-range which also makes it suitable for use in white displays.