Stark sublevels of Er3+-Yb3+ codoped Gd2(WO4)3 phosphor for enhancing the sensitivity of a luminescent thermometer

We report a strategy for enhancing the sensitivity of an optical thermometer by utilizing the Stark sublevels. Under 980 nm excitation, the upconversion emission originating from the Stark levels of Er3+(S-4(3/2(2))/S-4(3/2(1)) and F-4(9/2)/F-4(9/2(1))) is observed in a monoclinic phase Gd-2(WO4)(3): Er3+/Yb3+ phosphor, which is synthesized through the co-precipitation method. The temperature sensing behavior is studied over the range of 296-620 K based on thermal coupling levels H-2(11/2)/S-4(3/2(2)), H-2(11/2)/S-4(3/2), H-2(11/2)/S-4(3/2(1)), S-4(3/2(2))/S-4(3/2(1)) and F-4(9/2(2))/F-4(9/2(1)) using fluorescence intensity ratio (FIR) technology. The sensitivity based on Stark sublevels H-2(11/2)/S-4(3/2(2)) or H-2(11/2)/S-4(3/2(1)) is almost twice more than that based on the traditional H-2(11/2)/S-4(3/2) levels. The obtained maximum sensitivity of the optical thermometer is 16.5 x 10(-3) K-1 at 395 K (H-2(11/2)/S-4(3/2(2))). These results suggest that the use of Stark levels is a promising approach for enhancing the sensitivity of optical thermometers.