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 Gd 3 Sc 2 Al 3 O 12 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 266 nm, 355 nm, and 980 nm laser excitations , manifesting a dark blue appearance under 266 nm ultraviolet (UV) excitation and a green hue under 355 nm and 980 nm excitations. Specifically, under 355 nm 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 2 H 11/2 and 4 S 3/2 thermally coupled energy levels of Er 3+ . The obtained maximum relative sensitivities ( S R ) for the two fitted luminescence modes were found to be 101.80×10 −4 K −1 at 300 K (980 nm excitation) and 126.39×10 −4 K −1 at 300 K (355 nm excitation), respectively. The impressive S R values substantiate Yb,Er:GSAG crystal as highly promising candidates for optical temperature sensing applications.