Molybdenum-Activated Halide Perovskites as Emerging Luminescent Materials: Advances and Challenges

Mo-activated halide perovskites are emerging as a distinctive class of transition-metal-activated luminescent materials. Octahedral Mo3+ centers give sharp near-infrared spin-flip and upconversion photoluminescence (PL), whereas emissive centers associated with higher-valence Mo can produce broadband near-infrared PL. These properties are attractive for photophysics and optoelectronics but depend sensitively on the Mo oxidation state, first-shell coordination, ligand-field strength, and oxygen incorporation. This review critically assesses recent progress in Mo-activated halide perovskites. We summarize the electronic structure and selection rules of Mo3+ and analyze Mo3+-centered downconversion and upconversion PL. We then examine broadband PL from halide and oxyhalide perovskites containing higher-valence Mo, highlighting both the evidence for Mo-related emission and the remaining ambiguity in emissive-center assignment. We finally discuss future directions for target-specific host selection, controlled enhancement of Mo3+ radiative transitions and sensitized excitation, quantitative performance evaluation, and predictive materials design, with the aim of moving Mo-activated halide perovskites from spectroscopic observations toward rationally designed luminescent materials.