Thermally enhanced upconversion luminescence of Cr3+ in Er3+-Yb3+-Cr3+ tri-doped garnet phosphors for sensitive optical thermometry

Luminescence thermometry is strongly desired in many fields due to the capability of remote temperature measurement with fast response and high spatial resolution. For developing excellent luminescence thermometer, we systematically investigated the upconversion (UC) emissions from Er3+-Yb3+-Cr3+ tri-doped garnet-structured phosphors under the excitation of 980 nm laser. The influence of Ga3+/Al3+ dopant ratio in Y3Al5-xGaxO12 on the UC luminescence was studied in detail by the X-ray diffraction patterns, Raman spectra, FT-IR spectra and Judd-Ofelt theory. Research revealed that the increase of Ga3+ doping content could reduce the symmetry of rare earth (RE) ions site and simultaneously weaken the nonradiative relaxations, favoring the RE luminescence and the subsequent energy transfer (ET) from RE to Cr3+. More importantly, because of the thermally strengthened ET from Er3+ ions, about 27-fold enhancement in Cr3+ UC luminescence was successfully achieved within Er3+-Yb3+-Cr3+ tri-doped Y3Ga5O12 as temperature ascended from 303 to 873 K, which consequently leaded to the emission color switching in response to temperature change. These advances in the as-prepared garnet phosphors provide potential opportunity for vision-guided temperature sensing with high sensitivity (∼ 4.38% K−1) and low measurement uncertainty (∼ 0.29 K).