All-inorganic CsPbX3 (X = Cl, Br, and I) perovskite quantum dots (PeQDs) have shown great promise in optoelectronics and photovoltaics owing to their outstanding linear optical properties; however, nonlinear upconversion is limited by the small cross-section of multiphoton absorption, necessitating high power density excitation. Herein, we report a convenient and versatile strategy to fine tuning the upconversion luminescence in CsPbX3 PeQDs through sensitization by lanthanide-doped nanoparticles. Full-color emission with wavelengths beyond the availability of lanthanides is achieved through tailoring of the PeQDs bandgap, in parallel with the inherent high conversion efficiency of energy transfer upconversion under low power density excitation. Importantly, the luminescent lifetimes of the excitons can be enormously lengthened from the intrinsic nanosecond scale to milliseconds depending on the lifetimes of lanthanide ions. These findings provide a general approach to stimulate photon upconversion in PeQDs, thereby opening up a new avenue for exploring novel and versatile applications of PeQDs.

K2TiF6:Mn4+ is a highly efficient narrow‐band emission red phosphor with promising applications in white light‐emitting diodes (LEDs) and wide‐gamut displays. Nevertheless, the poor moisture‐resistant properties of this material hinder commercialization. A convenient reverse cation‐exchange strategy is introduced for constructing a core–shell‐structured K2TiF6:Mn4+@K2TiF6 phosphor. The outer K2TiF6 shell acts as a shield for preventing moisture in the air from hydrolyzing the internal MnF62− group, while effectively cutting off the path of energy migration to surface defects, thereby increasing the emission efficiency (especially for the phosphors doped with high concentrations of Mn4+). Employed as a red phosphor, the packaged white LED exhibits an extraordinarily high luminous efficacy of 162 lm W−1, a correlated color temperature (CCT) of 3510 K, and a color rendering index of 93 (Ra). Aging tests performed on this device at 85 °C and 85 % humidity for 480 h retain up to 89 % luminous efficacy. The findings could facilitate commercial application of K2TiF6:Mn4+@K2TiF6 phosphor.

. By means of temperature-dependent steady-state and transient UC spectroscopy, we unraveled the dominant mechanisms of phonon-assisted cooperative energy transfer (T > 100 K) and sequential dimer ground-state absorption/excited-state absorption (T < 100 K) for the CSU process in LiYbF 4 :Tb 3+ UCNPs.