Effect of Tb3+ concentration on the structure and optical properties of triply doped ZnAl2O4:1% Ce3+,1% Eu3+,x% Tb3+ nano-phosphors synthesized via citrate sol-gel method

Ce3+, Eu3+ and Tb3+ singly and triply doped ZnAl2O4 nano-powders were successfully synthesized via the citrate sol-gel method. X-ray diffraction (XRD) analysis showed that the powder samples consisted of the cubic crystalline phase. Energy dispersive X-ray spectroscopy (EDS) results confirmed the presence of all expected elements and the EDS map showed that the foreign ions were distributed homogeneously on the surface. Scanning electron microscopy (SEM) results revealed that the prepared powder morphology was influenced by doping. The transmission electron microscopy (TEM) results confirmed that the prepared powders were in the nano-scale region. The ultraviolet-visible (UV-vis) spectra showed that different dopants and varying the Tb3+ concentration influenced the effective band gap (Eg) of the host. The photoluminescence (PL) results showed that the emission at 395 nm was due to the defects emission within the host material. Ce3+ doped samples showed a broad emission peak centered at 425 nm which is attributed to the 5d → 4f transition of Ce3+ ions. The sample doped with Eu3+ showed two emission peaks at 592 and 616 nm ascribed to the 5D0 → 7F1 and 5D0 → 7F2 transitions of Eu3+ ions, respectively. Tb3+ singly-doped sample showed four peaks located at 489, 545, 587 and 616 nm, which were respectively ascribed to 5D4 → 7F6, 7F5, 7F4 and 7F3 transitions of Tb3+ ions. The Commission Internationale de l'Elcairage (CIE), or International Commission on Illumination, co-ordinates showed that the emission colour could be tuned by varying the Tb3+ concentration.