Samarium doped ZnAl₂O₄/ZnO mixed phase nanopowders fabricated by precipitation method for optoelectronic applications

This work reports on violet-orange light-emitting Sm3+ ions-doped ZnAl₂O₄/ZnO (referred to as ZZ) nanopowders fabricated via the precipitation method. A few studies have explored Sm3+ doped ZZ mixed phases, leaving their potential in visible light-emitting applications largely unexplored. This study explores the influence of varying Sm3+ concentrations on the structural, morphological, optical, and luminescent properties of ZZ mixed-phase nanopowders. X-ray diffraction revealed a combination of face-centred cubic ZnAl₂O₄ and hexagonal wurtzite ZnO. A phase transition was observed with the change in Sm3+ composition, resulting in a single-phase ZnO structure. Scanning electron microscopy revealed that the morphology had altered from clustered spherical shapes to aggregated, inhomogeneous structures. The average energy band gap values of the undoped and Sm3+ doped ZZ ranged between 3.2 eV and 3.3 eV. Photoluminescence studies indicated that the undoped ZZ emission peaks at 382, 501, 613, 681, 765, and 835 nm, which was reported for the first time. The emission peaks at 560, 610, 658, and 698 nm correspond to 4G_5/2 → 6H_5/2, 6H_7/2, 6H_9/2, and 6H_11/2 transitions of Sm3+. The Commission Internationale de l’Eclairage revealed that the Sm3+-doped ZZ nanopowders exhibited violet-red-orange colour. The colour rendering index (CRI) of the nanopowders was approximately above 70, indicating good colour performance and accuracy. Sm3+-doped ZZ nanopowders, thus, appear to be an excellent candidate for filling the violet-orange gap in visible light-emitting device applications.