Dual-Functional Material for Tunable Color Optical Thermometry: Er³⁺/Yb³⁺ Co-Doped Lu₂Ge₂O₇ Emitting Red and Green Light under 980 nm/1550 nm Excitation

While rare-earth ions have found extensive applications as dopants in up-conversion luminescent materials across various fields, empirical observations reveal distinct influences of different dopants on diverse substances. In light of this, we successfully synthesized dual-mode excitation Lu₂Ge₂O₇ up-conversion phosphors doped with Yb³⁺/Er³⁺ ions (Lu₂Ge₂O₇ : Yb³⁺/Er³⁺). These phosphors are designed to exhibit two distinct emission colors, green and red, under excitation at 980  or 1550 nm. Our research delves into a comprehensive analysis of the potential up-conversion mechanisms, considering different excitation sources at wavelengths of 980 and 1550 nm. Our results unambiguously demonstrate that doping with Er³⁺ and Yb³⁺ ions can alter the optical properties of Lu₂Ge₂O₇, resulting in the tunable color and optical thermometry capabilities. This material exhibits promising prospects in diverse fields such as fluorescent anti-counterfeiting and temperature sensing.