Preparação de tunsgstatos cerâmicos do tipo scheelita com propriedades luminescentes

Abstract

The development of materiais with optical properties is of great technological importance. In crystalline form, AWO4 tungstates (A = Ca, Sr, Ba and Pb) are insulating materiais with high energy gap and great commercial interest due to their attractive luminescent properties. In this work, photoluminescence in these materiais in disordered State was observed. Compounds were synthesized at low temperatures as thin films and powders. Spin coating was used for film deposition on different substrates. Deposition conditions were optimized using glass substrates. Films were heat treated between 200 and 600 °C and powders between 300 and 700 °C. Materials’ characterization was done using X-ray difíraction (XRD), atomic force microscopy (AFM), UVvisible and raman spectroscopy. Monophasic materiais formation with tetragonal structure of scheelite type was observed. Optical characterization of films, using UV-visible spectroscopy, indicated that crystalline films presented a higher gap energy than amorphous ones. This is probably due to defects appearance in disordered structures, leading to optical absorption with smaller energies than crystalline materiais. Photoluminescence studies as a fiinction of calcination time and temperatura, as well as milling time, indicated that emission is present when the system has a disordered structure, not being due to organic residues originating from initial thermal treatment.