Bandgap engineering—Influence of the evolution of (Zn/Mg)Al2O4:Cr3+ spinel phosphors on the photoluminescence properties

Abstract As a luminescent center ion in materials for deep red and near‐infrared light, Cr 3+ has been extensively studied in octahedral host materials. In this study, using zinc aluminate (ZnAl 2 O 4 ) and magnesium aluminate (MgAl 2 O 4 ) spinels with abundant octahedra as substrates, a series of Zn 1− x Mg x Al 2 O 4 :0.5%Cr 3+ ( x = 0, 0.2, 0.4, 0.6, 0.8, and 1) fluorescent powders were first prepared via a high‐temperature solid‐state method. The influence of different Mg/Zn ratios on (Zn/Mg)Al 2 O 4 :0.5%Cr 3+ optical properties was thoroughly explored. Experimental results show that an increase in the Mg/Zn ratio reduces the crystal field strength ( D q ) and leads to distortion of the [AlO 6 ] octahedra, resulting in broadening of the photoluminescence emission spectrum. Furthermore, the addition of Mg gradually reduces the formation of inverse spinel. An appropriate Mg/Zn ratio can improve luminescent intensity and quantum efficiency. In summary, this paper, through bandgap engineering by adjusting the Mg/Zn ratio, provides a detailed account of the changes in optical properties and the underlying mechanisms during the transition from ZnAl 2 O 4 :0.5%Cr 3+ to MgAl 2 O 4 :0.5%Cr 3+ spinels. It offers valuable insights for further research on the practical applications of Cr 3+ in areas such as lighting displays and bioimaging.