Iype, M., Varghese, S., & Mathew, E. (2010). Determination of the Energy Band Gap and Absorption Coefficient of Thin Films of Chemically Deposited Lead Sulphide, Copper Sulphide and Multilayer Lead Sulphide-Copper Sulphide Thin Films . Asian Journal of Chemistry, 14(2), 927–933. Retrieved from https://asianpubs.org/index.php/ajchem/article/view/22186