Comparative thermometric properties of bi-functional Er³⁺–Yb³⁺ doped rare earth (RE = Y, Gd and La) molybdates

The molybdate compounds as luminescent medium have received great attention of recent research due to their excellent intrinsic optical properties. Therefore, the investigation on the optical thermometry and nanoheating effect in Er³⁺–Yb³⁺ doped molybdates of yttrium (EYYMO), gadolinium (EYGMO) and lanthanum (EYLMO) nanophosphors is reported herein. The temperature dependent fluorescence intensity ratio of green (525 and 548 nm) emission bands of Er³⁺ ions were analyzed within 300–500 K temperature range to determine the thermal behavior. The comparative temperature sensitivity of the materials has been found to depend on the phonon energy of their own. The thermal sensitivity is higher in the materials with low phonon energy. The intensity ratio of the green emission bands has been found to alter with the laser excitation density, which can be used to estimate the induced temperature in the materials. Furthermore, the photothermal conversion efficiency is calculated in the water dispersed samples and the maximum photothermal conversion efficiency of 49.6% is achieved for EYGMO nanophosphor. Comparative experimental results explore unequal thermal sensing and induced optical heating in the three rare earth molybdates. The optical properties of the green emitting molybdates are interesting for temperature sensing and optical heating applications. (paper)