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A series of terbium-doped strontium gallium germanate phosphors displaying persistent luminescence was synthesised using a high-temperature solid-state reaction method. Structural analysis confirmed the material structure, which exhibited a direct bandgap of 4.99 electronvolts. Under optical excitation, the material emits green light dominated by characteristic terbium transitions, with concentration quenching occurring through radiative reabsorption. The phosphor exhibits high thermal stability up to 675 Kelvin. Luminescence measurements revealed an afterglow persistence of up to 100 seconds alongside a persistent luminescence lifetime of around 7000 seconds. Analysis of thermoluminescence showed that doping generates interstitial and vacancy defects, which enhance the persistent emission alongside the material intrinsic defects. Tests confirmed the phosphor serves practical uses in latent fingerprint detection and anticounterfeiting measures.
Materials that glow long after an excitation source is removed are valuable for forensic and security tasks. This phosphor provides a durable green afterglow and high thermal stability. These traits allow investigators to reveal hidden fingerprints and help security specialists mark sensitive goods, improving reliability in challenging environments without needing continuous illumination.
The material targets forensic investigation and security labelling, specifically for latent fingerprint detection and anticounterfeiting. Potential users include law enforcement forensic teams and manufacturers seeking authentication markers. Because practical feasibility for both fingerprint detection and anticounterfeiting was demonstrated directly in the study, the technology appears to be applied and tested at a laboratory stage, requiring further engineering before industrial adoption.
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A series of Sr<sub>2-x</sub>Ga<sub>2</sub>GeO<sub>7</sub>: x Tb<sup>3+</sup> (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 4f<sub>8</sub> → 4f<sub>7</sub>5d<sub>1</sub> transition of the Tb<sup>3+</sup> 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 (<sup>5</sup>D<sub>3</sub>/<sup>5</sup>D<sub>4</sub>) to the ground-state levels (<sup>7</sup>F<sub>J</sub>). Among these transitions, the <sup>5</sup>D<sub>4</sub> → <sup>7</sup>F<sub>5</sub> 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.
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DOI: 10.1002/smll.202500285
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