Biocompatible luminescent Ce 3+ -sensitized SrF 2 :Tb 3+ for anticounterfeiting and forensic fingerprint detection

Ce 3+ -sensitized Tb 3+ -activated SrF 2 nanophosphors (NPs) were synthesized using the hydrothermal method. Crystallographic characterization using X-ray diffraction confirms the formation of cubic SrF 2 with space group Fm 3̄ m for all samples. The FESEM image indicates spherical-shaped particles. Surface functionalization renders that the NPs are dispersible in water. The strong green emission of SrF 2 :5% Tb 3+ , 5% Ce 3+ at 541 nm increases by 50-fold than that of SrF 2 :5% Tb 3+ . The resonance energy transfer between Ce 3+ and Tb 3+ via multipolar interactions is observed. The energy transfer efficiency and spectral overlap integral are calculated. The absolute quantum yield of SrF 2 :5% Tb 3+ , 5% Ce 3+ is observed to be ∼12%. The NPs show excellent biocompatibility towards the HeLa cell line with 70% cell viability. Intercellular uptake of the SrF 2 :5% Tb 3+ , 5% Ce 3+ nanophosphor is fair, and its potential for anti-counterfeiting and forensic fingerprint applications is observed.