Influence of Zn/Al molar ratio on the structural and photoluminescence performances of ZnxAl2O4:Cr3+ phosphors

Abstract Zn x Al 2 O 4 :Cr 3+ (0.8 ≤  x  ≤ 4) phosphors with spinel structure were prepared by using sol-gel method. The structure, morphology and photoluminescence properties were analyzed by using X-ray diffraction (XRD), scanning electron microscopy (SEM), transmission electron microscopy (TEM), electron paramagnetic resonance (EPR) and photoluminescence (PL). The spinel structure of ZnAl 2 O 4 was formed for all samples, and hexagonal structure of ZnO appeared in the powders with x  ≥ 1.1. The results of XRD, SEM and TEM showed that the crystallinity of Zn x Al 2 O 4 :Cr 3+ phosphors was improved with increasing the value of x . The PL spectra showed a series of sharp emission peaks ranging from 650 nm to 730 nm assigned to spin-forbidden 2 E g  →  4 A 2 g transition of Cr 3+ ions in spinel lattices. The most intense emission was observed in Zn 1.2 Al 2 O 4 :Cr 3+ powders, and the results of EPR showed that this enhancement resulted from the best dispersity of Cr 3+ ions in Zn x Al 2 O 4 lattices.