Structural tuning of CdS nanoparticles with nucleation temperature and its reflection on the optical properties

Abstract

Structural tuning of CdS nanoparticles (NP) with the nucleation temperature and the reflection of changing the nucleation temperature on the optical properties were investigated. CdS NPs was synthesized by a simple chemical method at different nucleation temperatures; 150, 200, 300, 400, and 500 °C for different growth time. XRD analysis confirms the presence of two different phases with distinct structures; wurtzite and zinc blend with phase's percentage directly dependent on the nucleation temperature. Raising the nucleation temperature can improve the crystallinity a little but apparently reduces the lattice strain in CdS. The smallest grain size as well as the lowest microstrain were obtained at nucleation temperature of 200 °C. The maximum nucleation temperature is ≤300 °C, above this temperature CdS was dissociated forming cubic phase of CdO, as confirmed by XRD and FT-IR spectra. TEM image revealed that CdS particles have nearly spherical shape and the average particle size was estimated to be 13 nm. Rietveld analysis confirmed the biphasic nature of CdS NPs. The quantum size confinement and the tuning between the band gap and nucleation temperature were clearly readable in UV-Vis measurements. The calculated crystallite size values of CdS NPs are 8.34, 6.65 and 5.28 nm at 250, 200, and 150 °C respectively. The band gaps are found to decrease from 2.277 eV to 2.56 eV with the raising of nucleation temperature. The PL results show strong tuning between the nucleation temperature of CdS NPs and PL yield or emission intensity. The nucleation temperature at 200 °C is the optimum at which the nucleated CdS NPs display maximum fluorescence or emission intensity.