Exploring the Sr ₂ Ga ₂ GeO ₇ :Tb ³⁺ Long Persistent Luminescence Phosphor for Cutting‐Edge Forensic Solutions in Latent Fingerprint Detection and Anticounterfeiting Applications

A series of Sr_2-xGa₂GeO₇: x Tb³⁺ (0 mol% ≤ x ≤ 10 mol%) phosphors exhibiting persistent luminescence is synthesized via a high-temperature solid-state reaction. Structural analysis and phase identification are conducted using X-ray powder diffraction and Rietveld refinement. The reflectance spectra revealed that the synthesized phosphor exhibited a direct bandgap with a value of 4.99 eV. The photoluminescence excitation spectra displayed broad absorption bands corresponding to the 4f₈ → 4f₇5d₁ transition of the Tb³⁺ ion, along with narrow-band absorption peaks attributed to the 4f-4f transitions. The emission spectra featured peaks resulting from transitions from the excited energy-state (⁵D₃/⁵D₄) to the ground-state levels (⁷F_J). Among these transitions, the ⁵D₄ → ⁷F₅ transition is dominant, producing the green emission of the synthesized phosphor. Concentration quenching is observed, attributed to the radiative reabsorption process. Additionally, the synthesized phosphor demonstrated thermal stability up to 675 K. The kinetic scan and afterglow measurements showed that the persistent luminescence lifetime is ≈7000 s, and the afterglow persistence is up to 100 s. Thermoluminescence measurements revealed that besides the intrinsic defect, doping introduced the interstitial and vacancy defects that contributed to improving the persistent luminescence of the synthesized phosphor. The synthesized phosphor demonstrated a practical application for latent fingerprint detection and anticounterfeiting applications.