Optical temperature sensing of Yb,Er:GSAG single crystal in both upconversion and downconversion dual-mode luminescence

Fluorescence intensity ratio thermometry represents a novel non-contact approach for rapid and precise temperature measurements. In this study, a Yb,Er co-doped Gd3Sc2Al3O12 single crystal (Yb,Er:GSAG) was investigated, exploiting the dual-mode luminescence of upconversion and downconversion for optical temperature sensing applications. The crystal exhibited distinct luminescence behaviors when subjected to 266nm, 355nm, and 980nm laser excitations, manifesting a dark blue appearance under 266nm ultraviolet (UV) excitation and a green hue under 355nm and 980nm excitations. Specifically, under 355nm excitation, the crystal demonstrated a predominantly pure green upconversion, with a green-to-red ratio of 38. For the first time, we propose an investigation into the temperature sensing behavior under dual-mode luminescence in the same crystal, utilizing the fluorescence intensity ratio of the 2H11/2 and 4S3/2 thermally coupled energy levels of Er3+. The obtained maximum relative sensitivities (SR) for the two fitted luminescence modes were found to be 101.80×10-4 K-1 at 300K (980nm excitation) and 126.39×10-4 K-1 at 300K (355nm excitation), respectively. The impressive SR values substantiate Yb,Er:GSAG crystal as highly promising candidates for optical temperature sensing applications.