Structural evolution, growth mechanism and photoluminescence properties of CuWO4 nanocrystals

Abstract Copper tungstate (CuWO 4 ) crystals were synthesized by the sonochemistry (SC) method, and then, heat treated in a conventional furnace at different temperatures for 1 h. The structural evolution, growth mechanism and photoluminescence (PL) properties of these crystals were thoroughly investigated. X-ray diffraction patterns, micro-Raman spectra and Fourier transformed infrared spectra indicated that crystals heat treated and 100 °C and 200 °C have water molecules in their lattice (copper tungstate dihydrate (CuWO 4 ·2H 2 O) with monoclinic structure), when the crystals are calcinated at 300 °C have the presence of two phase (CuWO 4 ·2H 2 O and CuWO 4 ), while the others heat treated at 400 °C and 500 °C have a single CuWO 4 triclinic structure. Field emission scanning electron microscopy revealed a change in the morphological features of these crystals with the increase of the heat treatment temperature. Transmission electron microscopy (TEM), high resolution-TEM images and selected area electron diffraction were employed to examine the shape, size and structure of these crystals. Ultraviolet–Visible spectra evidenced a decrease of band gap values with the increase of the temperature, which were correlated with the reduction of intermediary energy levels within the band gap. The intense photoluminescence (PL) emission was detected for the sample heat treat at 300 °C for 1 h, which have a mixture of CuWO 4 ·2H 2 O and CuWO 4 phases. Therefore, there is a synergic effect between the intermediary energy levels arising from these two phases during the electronic transitions responsible for PL emissions.