Suellen Maria Valeriano Novais

X-ray-excited optical luminescence and X-ray absorption fine-structures studies of CdWO4 scintillator

X-ray-excited optical luminescence (XEOL) emission and excitation spectra as well as the EXAFS signal of CdWO(4) were measured in the energy region of the Cd and W absorption edges. From EXAFS refinement, structural parameters such as number of atoms, distance from the absorbing atom and width of coordination shells in the W neighborhood were determined. The role of W-O interactions on the intrinsic luminescence of CdWO(4) is discussed. The efficiencies of conversion, transfer and emission processes involved in the scintillation mechanism showed to be high when self-trapped excitons are formed locally by direct excitation of W ions. Annihilation of these excitons provides the characteristic scintillation of CdWO(4), a broad band emission with maximum at 500 nm. The presence of two energetically different O positions in the lattice gives rise to the composite structure of the luminescence band, and no influence of extrinsic defects was noticed. A mismatch between the X-ray absorption coefficient and the zero-order luminescence curves corroborates that the direct excitation of Cd ions induces secondary electronic excitations not very effective in transferring energy to the luminescent group, WO(6).

Synthesis and characterization of multicolour fluorescent nanoparticles for latent fingerprint detection

In this study, we successfully developed Y2O3 nanoparticles doped with Tb3+ and Eu3+ ions to generate fluorescent images of latent fingerprints. The optical and structural characterization of the nanoparticles was carried out and the fluorescence mechanisms are discussed. In our studies, the developed nanoparticles were effective in producing fluorescent images of latent fingerprints in shades of green, red and yellow with high-contrast colour under ultraviolet lighting.