Doping concentration-independent optical thermometric properties in Stark sublevels-based Er3+-activated BaGd2O4 luminescent thermometers

We reported a facile strategy to modify the sensor sensitivities of Er3+-doped BaGd2O4 phosphors by simultaneously modulating the dopant concentration and utilizing the proper Stark sublevels. Under the excitation of 377 nm, visible emissions originating from the Stark sublevels of Er3+ ions (2H11/2(1), 2H11/2(2), 4S3/2(1), 4S3/2(2), 4F9/2(1) and 4F9/2(2)) were detected in all the prepared samples. The optimal doping concentration for the Er3+ ions in the BaGd2O4 host lattice was 2 mol% and the electric dipole-dipole interaction can contribute to the concentration quenching mechanism. By utilizing the fluorescence intensity ratio technique, the optical thermometric properties of the obtained phosphors in the temperature range of 288-483 K were studied based on the thermally coupled levels of 2H11/2(1)/4S3/2(1), 2H11/2(2)/4S3/2(1), 2H11/2(1)/4S3/2(2), 2H11/2(2)/4S3/2(2) and 2H11/2/4S3/2. The maximum relative sensor sensitivities of the resultant compounds based on the Stark levels of 2H11/2(1)/4S3/2(2) were much higher than that based on the 2H11/2/4S3/2 ordinary thermally coupled levels. Furthermore, the relative sensor sensitivities of the synthesized phosphors were insensitive to the doping concentration and its maximum value was up to 0.0175 K−1 at 288 K. These characteristics demonstrated that the Er3+-doped BaGd2O4 material system was suitable for optical thermometers.