Microwave-assisted synthesis and luminescence properties of NaYb1-xErxGeO4, NaY1-yYb3y/4Ery/4GeO4 olivines

A new series of olivine-type NaYb1-xErxGeO4 (x ​= ​0.0–0.35), NaY1-yYb3y/4Ery/4GeO4 (y ​= ​0.0–0.6) germanates has been prepared by the liquid-phase precursor method with further microwave annealing for the first time. It has been found that synthesized samples yield upconversion luminescence in the range of 400–900 ​nm under 980 ​nm laser diode excitation The concentration and excitation power dependences of emission intensity have been investigated. The mechanisms of upconversion luminescence as well as concentration quenching have been proposed. In addition, the dependence of the ratio between luminescence peaks at 534 and 560 ​nm on temperature has been studied at 298–498 ​K. The absolute (Sa) and relative (Sr) sensitivities reach maximum values of 0.66% ​× ​K−1 at T = 473 K and 1.05% ​× ​K−1 at T ​= ​298 ​K, respectively. The obtained data indicate the perspectives of using of NaY0.8Yb0.15Er0.05GeO4 sample as an active optical component for non-contact thermometers.