Bright LaF₃:Eu@Ir Phosphors Combining Two‐Photon Excitation, d → f Energy Transfer and Tunable Time‐Gated Chromaticity for Multicolor Cell Imaging

Abstract In order to advance the practical applications of photoluminescence lanthanide‐based nanoparticles (LnNPs), it is essential to minimize quenching by surface defects and to enhance the efficiency of lanthanide excitation. Surface functionalization with organic antennas has proven effective in preparing dye‐sensitized LnNPs with enhanced photoluminescence performance. Nevertheless, the limited chemical and photochemical stability of the organic dyes hinders the practical applications of these composites. This report presents Eu‐doped LaF 3 submicron particles ( EuLa SMDs ) and analogue small nanoparticles ( EuLa NPs ) functionalized with a robust Ir III complex ( Ir1 ) as antenna. The EuLa SMDs @Ir1 and EuLa NPs @Ir1 hybrids exhibit a combination of short‐lived Ir‐based (yellow) and long‐lived Eu‐based (red) emissions, which can be selectively detected by time‐gated detection. Following Ir1 ‐sensitization, the Eu‐based emission is amplified, reaching up to 307‐fold (for EuLa SMDs @Ir1 ) and 188‐fold (for EuLa NPs @Ir1 ), compared to that exhibited by pristine phosphors. Efficient Ir1 ‐sensitized Eu III ‐based emission can also be achieved using NIR excitation, as Ir1 exhibits a moderate cross‐section of σ 2 = 4.6 ± 0.6 GM at λ = 800 nm. Both hybrids demonstrate effective internalization in HEK‐293 cells with no observed toxicity at concentrations relevant to biomedical applications. Cells are imaged by TG‐imaging and PLIM microscopy. Following UV–vis (λ exc = 375 nm) or NIR (λ exc = 800 nm) excitation, overlapped Ir1‐ and Eu‐based emissions are detected.