Copper tungstate (CuWO) crystals were synthesized by the sonochemistry (SC) method, and then, heat treated in a conventional furnace at different temperatures for 1h. 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·2HO) with monoclinic structure), when the crystals are calcinated at 300°C have the presence of two phase (CuWO·2HO and CuWO), while the others heat treated at 400°C and 500°C have a single CuWO 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 1h, which have a mixture of CuWO·2HO and CuWO 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.

This paper consists of an experimental investigation on the effects of annealing temperature on the structural, surface and ozone gas-sensing properties of CuWO 4 nanoparticles prepared via a sonochemical route. X-ray diffraction patterns and X-ray absorption near-edge structure spectroscopy revealed that both long-and short-order structures increase with the annealing temperature. Electrical resistance measurements indicated that CuWO 4 samples were sensitive in the range of 15e1400 ppb, exhibiting a good reversibility and repeatability. The enhancement of the ozone gas-sensing properties was attributed to the reduction of hydroxyl species and the improvement of the crystallization degree. This study provides a versatile strategy for obtaining CuWO 4 nanoparticles for practical applications as an ozone gas sensor.