Structural and optical studies of ZnAl₂O₄:x% Cu²⁺(0<x≤1.25) nanophosphors synthesized via citrate sol-gel route

Nanocrystalline ZnAl₂O₄:x% Cu²⁺(0<x≤1.25) phosphor powders were prepared via the citrate sol-gel technique. The pure-phase cubic structures in this systems were verified by the powder X-ray diffraction. Energy Dispersive x-ray Spectroscopy analysis confirmed the presence of the expected elements (Zn, Al, O and Cu). Scanning Electron Microscopy showed that the morphology of the phosphor was dependent on the concentration of Cu²⁺. High-Resolution Transmission Electron Microscopy confirmed that the Cu²⁺ concentration does not significantly influence the crystallites sizes of the phosphors. Ultraviolet–visible spectroscopy results showed that the Cu²⁺ concentration influenced the band gap of the host. Photoluminescence results showed that the emission intensity of the powder sample was dependent on the Cu²⁺ concentration. The emission from the host lattice was observed at 394 nm, while Cu²⁺ showed major emission at 405 and minor emission at 574 nm. The emission at 405 nm was due to the 3d⁸4s¹ → 3d⁹ transitions of Cu²⁺. The Commission on Illumination color coordinate evidently showed shifts from the bluewish to the greenish region with an increase in Cu²⁺ concentration.