A robust, multifunctional optical sensing platform operating under practical conditions

Abstract

This work presents a systematic investigation of Ho³⁺/Tm³⁺/Yb³⁺ tri-doped LiCaLa(MoO₄)₃ (LCLMO) phosphors as an optical platform for ratiometric thermometry. The LCLMO host lattice combines low phonon energy, high thermal stability, and a tunable crystal field environment, enabling efficient energy transfer among the incorporated lanthanide ions. Under continuous-wave excitation at 975 nm, Yb³⁺ ions act as effective sensitizers, transferring excitation energy non-radiatively to Ho³⁺ and Tm³⁺ activators and generating intense multicolor upconversion emissions spanning the visible and NIR spectral regions. Temperature sensing performance was evaluated using four optimized fluorescence intensity ratio (FIR) pairs, including one thermally coupled (FIR_700/795) and three non-thermally coupled channels (FIR_700/477, FIR_700/660, and FIR_700/550), providing redundant and reliable temperature readout. A high relative sensitivity of 3.22% K⁻¹ at 298 K was achieved, accompanied by excellent temperature resolution (ΔT = 0.8 K) over a broad operating range of 298–588 K. The combination of high thermometric sensitivity, multi-channel ratiometric reliability, extended temperature operability, and NIR excitation establishes LCLMO:Ho³⁺/Tm³⁺/Yb³⁺ phosphors as a promising multifunctional platform for advanced luminescent thermometry and optical sensing.