Structural and optical investigations of ZnS quantum dots: influence of pH value

ZnS quantum dots were successfully synthesized with different pH conditions by using the co-precipitation method. XRD spectra were recorded for all the as-synthesized and calcined samples. The calculated and observed patterns obtained from the Rietveld refinement indicate the virtues of reliability parameters and confirm that the compound crystallizes into cubic symmetry with the space group F-43 m. The calculated crystallite sizes revealed the reduction of sizes with increasing pH value. The functional groups present in all the obtained samples were identified from the observed FTIR spectra. The optical transmittance has been reduced due to the increase of pH at ZnS samples. The calculated band gap values for the calcined samples vividly decreased with increasing pH value. This would be attributed to the quantum confinement effect due to the reduction of the crystallite sizes of the samples. The PL emission peaks received in the UV region and the blue region were suppressed due to the pH variation. Thus, pH condition is one of the key factors in the synthesis and properties of ZnS quantum dots. (author)