Photon management in lanthanide hybrid materials: Upconversion and quantum cutting for broadband light harvesting

The near-infrared (NIR) spectral region plays a pivotal role in modern photonics and optoelectronics, yet most conventional semiconductors and molecular materials fail to utilize low-energy photons efficiently. Lanthanide (Ln)-based luminescent systems offer a unique means to overcome this limitation through two complementary photon conversion mechanisms—downconversion (or quantum cutting, QC) and upconversion (UC). In QC processes, a single high-energy photon is converted into two or more lower-energy photons via cooperative energy transfer between neighboring Ln ions (Ln 3+ ), leading to photon multiplication and enhanced light-harvesting efficiency. Recent advances in QC-active materials, including Gd 3+ , Tb 3+ , and Yb 3+ -codoped oxides and fluorides, as well as emerging Ln 3+ -doped perovskite hosts, have demonstrated efficient UV/visible-to-NIR photon conversion, expanding the spectral coverage for photovoltaic and light-emitting device applications. In contrast, UC processes enable the stepwise absorption of multiple NIR photons to generate higher-energy visible or UV emission. To address the intrinsically weak absorption cross-sections of Ln ions, molecularly sensitized hybrid systems have been developed, where organic dyes act as broadband NIR antennae to mediate efficient energy transfer to Ln 3+ centers. Additionally, core-shell and inorganic-passivated nanostructures have been engineered to suppress nonradiative quenching by controlling lattice phonons and surface states. The integration of Ln 3+ -based UC materials with halide perovskites further enables synergistic photon management, allowing sub-bandgap NIR photons to be utilized in solar cells and photodetectors. These developments illustrate a unified strategy for bidirectional photon conversion through QC and UV, paving the way toward next-generation energy-harvesting and photonic devices.