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Structural and optical properties of as-grown cubic CdS polycrystalline films annealed in H 2 and air atmospheres are reported. The CdS films were grown onto glass substrates by chemical-bath deposition. The forbidden band-gap and the x-ray diffraction spectrum evolution as a function of the thermal annealing temperature, in H 2 and air ambients, were studied. Band-gap shift and changes in grain size, lattice parameter and crystalline structure were influenced by the type of atmosphere and the temperature of the thermal annealing. From these results, the dependence of the band-gap on the lattice parameter was determined.

Mixed WO 3 -CuWO 4 films have been prepared from aqueous solution of copper sulfate and polytungsten gel with molar ratio Cu/W from 0 to 100 %. These solutions were sprayed onto alumina substrates at 220 ºC. The obtained films were amorphous, and crystallized after an annealing at 300 ºC in air for 3 h. The annealed films were composed by a mixture of CuWO 4 and WO 3 phases. The film obtained from a solution with an equimolar ratio of Cu/W was a pure CuWO 4 . The pure WO 3 films obtained have a high surface "irregularities" (eventually the porosity). Those surface "irregularities" in the films were maintained or eventually increased as Cu/W molar ratio augments in the starting solution up to 10%. The gas sensitivities to butanol and ethanol vapors are also enhanced when the CuWO 4 phase increases in the film up to 7% -10%; further increments to this proportion the detection sensitivity decreases, so compromises are around 7% -10%. The gas sensitivity of pure CuWO 4 was lower than pure WO 3 .

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