Properties of thin ZnS:Mn films sprayed by improved method: The role of Mn²⁺ ion concentration

Undoped and Mn-doped thin ZnS films were deposited on ordinary glass substrates at temperature of 450 °C by an improved spray pyrolysis (ISP) method. The ISP parameters, such as carrier gas flow rate, solution flow rate and substrate temperature, were controlled with accuracy ±0.25 Lpm, ±1 mL/h and ±1 °C, respectively. A pulse-spray mode of the method was used to spray the precursor solution. Thin film samples were prepared for Mn-doping with the concentrations of 0 at.%, 1 at.%, 3 at.%, 6 at.%, 8 at.% and 12 at.% relative to Zn in the spray solution. The Mn-doping concentration dependent chemical composition, surface morphology, and structural, optical and photoluminescence (PL) properties were studied. All the thin films were well adherent, nearly stoichiometric, dense, uniform, and possessed cubic crystal structure with preferential orientation along h〈1 1 1〉 direction. A slight enhancement in structural properties, an increase in band gap, and a decrease in refractive index and dielectric constant with Mn-doping concentration were observed. The PL spectra of Mn-doped thin ZnS films at room temperature exhibited both the 490 nm blue defect-related emission and the 590 nm yellow-orange Mn²⁺ ion related emission. The observed yellow-orange emission intensity was maximum for 3 at.% of Mn-doping concentration in the spray solution.