"Photo-physical, optical and forensic applications of Eu(III) complexes with chromone-based ligand"

Octa-coordinated Eu(III) complexes were synthesized via the solution precipitation method. The synthesized complexes were characterized through elemental analysis, UV analysis, XRD, SEM, FTIR, ¹H-NMR, TGA/DTA and photoluminescence analysis. IR and NMR analyses show that ligand coordinates through oxygen atom of aldehydic, oxygen atom of ketonic groups and nitrogen atom of ancillary ligand. The band gap energies obtained from reflectance measurements ranges (2.19-2.52 eV) and are in close agreement with computational analyses (2.20-2.54 eV). Photoluminescence spectroscopy conducted in both phases (solution and solid) shows red emission with five distinct emission peaks, among these ⁵D₀ → ⁷F₂ transition is the most intense transition. The J-O parameters, luminescence decay time, radiative and non-radiative decay rates, as well as quantum efficiencies, were calculated to elucidate the optical properties of complexes. Color purity (CP) values of complexes in solution ranges from 82.87% to 88.61%, while in solid phase range from 85.34% to 98.41%. The CCT values of complexes in solution range from 1715.12 to 1985.53 K and in solid phase ranges from 1795.20 to 3344.06 K, confirming their use in warm light-emitting material. These complexes were also utilized for developing latent fingerprints for various forensic applications. The E5 complex demonstrated excellent performance in latent fingerprint visualization under 365 nm UV illumination, revealing clear ridge patterns and minutiae including bifurcations, ridge endings, bridges, islands, and crossovers. These findings highlight the potential of the synthesized Eu(III) complexes as dual-functional materials for both photonic devices and forensic detection applications.