Optical and structural properties of PbSe films obtained by ionic exchange of lead oxyhydroxicarbonate in a selenium-rongalite solution

In this work, starting from precursor films of Pb₁₀O(OH)₆(CO₃)₆, previously obtained by chemical bath deposition technique, we report the process to obtain PbSe films through ionic exchange. For this, after chemical deposition, several pieces of the precursor films were immersed in selenium ions solution in order to promote the transformation to PbSe films by ionic exchange. Instead using the conventional sodium selenium sulfite solution as the selenium ions solution, a new one is reported, which is based in rongalite (CH₃NaO₃S) and sodium citrate as reducing agents. Samples were removed after 30, 60 and 90 min to determine the effects of ionic exchange time on the phase transformation process. The complete set of samples was analyzed by X-ray diffraction, scanning electron microscopy and optical absorption measurements. The XRD results show a gradual crystalline transformation from the precursor phase to cubic PbSe crystalline phase. The gradual phase transformation is accompanied by surface morphologic changes as shown by SEM images. From the optical absorption spectrum of the PbSe films, it was calculated the energy band gap, being around 0.34 eV.