Impact of size and defects on structure, optical and photoluminescence properties of Ni-doped SnO₂ nanoparticles co-doped with Cu

Single Ni-doped SnO₂ and Ni, Cu two elements simultaneously doped SnO₂ have been synthesized by simple chemical co-precipitation method. The structural (morphological) change-over from rod-like structure (Ni single doped) to mixture of spherical and hexagonal structure by dual doping was evidenced by the enhanced XRD intensity ratio of (110) and (101) planes and scanning electron microscopic (SEM) images. The reduced crystallite size from 13.2 nm (single doped) to 8.6 nm caused by Cu addition (Ni, Cu dual doping) was supported by the increase of micro-strain, shift of absorption edge towards and lower wavelength side and generation of defect states. The elevated band gap by Cu substitution was mainly due to the strong quantum size effect. The noticed infra-red (IR) peaks around 648–693 cm⁻¹ and the adjustment of its position and intensity confirmed the substitution of Cu in Sn–Ni–O network. The strong ultra-violet (UV) and visible emissions observed in Ni, Cu co-doped SnO₂ was discussed based on the conversion of electrons between the bands through defect states like oxygen vacancies.