Rare earths (Ce, Eu) molar concentration-dependent of the structural and optical properties of CBD-CdS nanofilms

Abstract

It presents the characterization of rare earths (Eu,Ce)-doped CdS nanofilms that were synthesised by the growth technique chemical bath deposition (CBD) at the reservoir temperature of 70±2°C. The doping of CdS with rare earths is performed by varying the synthesis time from 60 to 135 min. The rare earths molar concentration was range from 0.0≤x≤3.5, which was determined by energy dispersive X-ray spectroscopy. X-ray diffraction (XRD) analysis and Raman scattering reveal that CdS nanofilms showed the zinc blende (ZB) crystalline phase. The CdS average nanocrystal size was ranged from 1.84 to 2.67 nm that was determined by the Debye–Scherrer equation from ZB (111) direction, which was confirmed by transmission electron microscopy. Raman scattering shows that the lattice dynamics is characteristic of bimodal behaviour and the multipeaks adjust of the first optical longitudinal mode for the (Eu,Ce)-doped CdS, which denotes the Raman shift of the characteristic peak about 305 cm⁻¹ of the CdS nanocrystals. The CdS nanofilms exhibit a direct bandgap that slightly decreases with increasing doping, from 2.50 to 2.42 eV, which was obtained by room temperature transmittance. The room-temperature photoluminescence of CdS shows the band-to-band transition at 2.88 eV, which is associated to quantum confinement and a dominant radiative band at 2.37 eV that is called the optical signature of interstitial oxygen. The Eu³⁺-doped CdS photoluminescence shows the dominant radiative band at 2.15 eV, which is associated to the intra-4f radiative transition of Eu³⁺ ions that corresponds to the magnetic dipole transition, (⁵D0→⁷F¹). For the Ce³⁺-doped CdS the dominant radiative transition, at 2.06 eV, is clearly redshifted, although the passivation of the CdS nanofilms by Ce was approximately by a factor about 21 for the best results.