Biocompatible luminescent Ce3+-sensitized SrF2:Tb3+ for anticounterfeiting and forensic fingerprint detection

Ce³⁺-sensitized Tb³⁺-activated SrF₂ nanophosphors (NPs) were synthesized using the hydrothermal method. Crystallographic characterization using X-ray diffraction confirms the formation of cubic SrF₂ with space group Fmm 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 SrF₂:5% Tb³⁺, 5% Ce³⁺ at 541 nm increases by 50-fold than that of SrF₂:5% Tb³⁺. The resonance energy transfer between Ce³⁺ and Tb³⁺via multipolar interactions is observed. The energy transfer efficiency and spectral overlap integral are calculated. The absolute quantum yield of SrF₂:5% Tb³⁺, 5% Ce³⁺ is observed to be ∼12%. The NPs show excellent biocompatibility towards the HeLa cell line with 70% cell viability. Intercellular uptake of the SrF₂:5% Tb³⁺, 5% Ce³⁺ nanophosphor is fair, and its potential for anti-counterfeiting and forensic fingerprint applications is observed.