Fig. 1.

Schematic representation of the radiative energy transfer upconversion (RETU) processes in all-inorganic CsPbX₃ perovskite quantum dots (PeQDs) through sensitization by lanthanide-doped nanoparticles (NPs). Lanthanide-doped NPs function as the energy donor to convert the NIR excitation light into the ultraviolet (UV) and visible emission light through successive photon absorption and energy transfer upconversion (ETU) processes within lanthanides. The emission light from the NPs is then reabsorbed by PeQDs to create electron–hole pairs (excitons) in the conduction band (CB) and valence band (VB), followed by photon emission through exciton recombination. The solid and dash lines represent the electronic transitions