High-contrast latent fingerprint detection using green-emitting Ca9–2xMgNa1+x(PO4)7:xTb3 + downshifting phosphors

Ca 9-2x MgNa 1+x (PO 4 ) 7 : x Tb 3+ (0.005 ≤ x ≤ 0.3) phosphors were synthesized via microwave-assisted hydrothermal synthesis. The charge balance of the phosphors was maintained by codoping monovalent Na + ions along with the trivalent Tb 3+ ions such that they substituted two divalent Ca 2+ ions in the host matrix. The X-ray powder diffraction studies confirmed the uniform single-phase formation of the phosphors, while the field-emission scanning electron microscopy confirmed the microcrystalline morphology of the phosphors. The diffuse reflectance spectra showed strong absorption in the UV region that overlapped with the emission of the mercury vapour lamp. The photoluminescence (PL) studies further validated that the ultraviolet (UV) radiation efficiently pumped the phosphors that produced strong and intense green fluorescence emissions. The optimum PL intensity was recorded for x = 0.2 Tb 3+ doping. The temperature-dependent PL studies showed an anomalous variation in their emission intensity that was thermally quenched only after reaching its optimum at 523 K. The applicability of the as-synthesized phosphor was demonstrated for latent fingerprint (LFP) detection using the powder-dusting method. The performance of the optimised phosphor was tested for the LFPs stained on different types of non-porous surfaces, for the LFPs donated by various donors, and for those LFPs aged for different periods. The phosphor exhibited high-contrast imaging of the LFPs owing to the intense green fluorescence under the UV lamp. Moreover, the minutiae details of the LFPs were quickly recognized and analysed from the images captured using a simple camera setup. The results confirmed that Ca 8.6 MgNa 1.2 (PO 4 ) 7 :0.2Tb 3+ phosphor would be a promising forensic tool for LFP detection in crime investigation and biometric identification.