Modulating excitation light to alter temperature-dependence of two-photon upconversion luminescence in Yb3+/Tm3+ co-doped LuAG transparent ceramics

Abstract

A novel two-photon upconversion luminescence process was reported in Yb³⁺/Tm³⁺ co-doped LuAG transparent ceramics. Systematic photoluminescence measurements as a function of Tm³⁺ concentration reveal that an optimal doping level of 0.2 at% maximizes the upconversion efficiency. By tuning the excitation wavelength from 932 nm to 974 nm, temperature-dependent spectra acquired over 100–500 K exhibit distinct thermal behaviors that can be ascribed to phonon-assisted thermal activation. A physical model supports this interpretation, and an improved luminescence lifetime equation is introduced to account for the non-monotonic temperature dependence—characterized by an initial increase followed by a decrease in lifetime at higher temperatures. These insights not only deepen our understanding of two-photon upconversion luminescence mechanisms in co-doped ceramics but also suggest new strategies for tailoring vibronic luminescence in solid-state materials.