Reconfiguration of d-orbital states drives non-radiative energy dissipation in semiconductors

Abstract

Efficient photothermal conversion relies on the dissipation of energy from photoexcited charge carriers through non-radiative pathways. However, the fundamental electronic structure origins governing such processes in semiconductors remain poorly understood, limiting the rational design of photothermal materials. Here, using TiO₂ as a model system, we demonstrate that multi-transition-metal doping provides an effective strategy to simultaneously regulate electronic configurations and spin states, thereby governing carrier relaxation pathways. The incorporation of Fe, Co, and Mn into the TiO₂ matrix induces a redistribution of 3d-orbital defect states within the bandgap, giving rise to d–d interband transitions (IBTs), suppression of spin polarization, and accelerated non-radiative recombination. As a result, the optimized FeCoMn–TiO₂ exhibits broadband solar absorption and a near-unity photothermal conversion efficiency (97.9%), along with a high solar steam generation rate of 3.82 kg m⁻² h⁻¹ (91.2%). These findings establish a direct link between d-orbital electronic structure, spin characteristics, and non-radiative energy dissipation, providing a conceptual framework for designing photothermal semiconductors through electronic state engineering.