Transition Metal‐Involved Photon Upconversion

Upconversion (UC) luminescence of lanthanide ions (Ln3+) has been extensively investigated for several decades and is a constant research hotspot owing to its fundamental significance and widespread applications. In contrast to the multiple and fixed UC emissions of Ln3+, transition metal (TM) ions, e.g., Mn2+, usually possess a single broadband emission due to its 3d5 electronic configuration. Wavelength‐tuneable single UC emission can be achieved in some TM ion‐activated systems ascribed to the susceptibility of d electrons to the chemical environment, which is appealing in molecular sensing and lighting. Moreover, the UC emissions of Ln3+ can be modulated by TM ions (specifically d‐block element ions with unfilled d orbitals), which benefits from the specific metastable energy levels of Ln3+ owing to the well‐shielded 4f electrons and tuneable energy levels of the TM ions. The electric versatility of d0 ion‐containing hosts (d0 normally viewed as charged anion groups, such as MoO66‐ and TiO44‐) may also have a strong influence on the electric dipole transition of Ln3+, resulting in multifunctional properties of modulated UC emission and electrical behaviour, such as ferroelectricity and oxide‐ion conductivity. This review focuses on recent advances in the room temperature (RT) UC of TM ions, the UC of Ln3+ tuned by TM or d0 ions, and the UC of d0 ion‐centred groups, as well as their potential applications in bioimaging, solar cells and multifunctional devices. This review focuses on recent advances in the photon upconversion of transition metal ions with an emphasis on room temperature upconversion, the upconversion of Ln3+ tuned by TM or d0 ions (anion groups), and the upconversion of d0 ions (anion groups), as well as their potential applications in bioimaging, solar cells and multifunctional devices.