Comprehensive characterization and optoelectronic significance of Ho3+ and Cr3+ Co-doped ZnAl2O4 spinels

The spinels ZnAl1.99-xHoxCr0.01O4 (with x = 0 and 0.001) were synthesized using a solid-state method, and various techniques were employed for their characterization. X-ray diffraction (XRD) analysis confirmed a cubic spinel structure with the Fdm space group for both spinels. The morphology and homogeneity of the chemical composition were determined using scanning electron microscopy (SEM) and energy dispersive X-ray analysis. Raman and infrared vibrational spectroscopy techniques were also employed for analysis. The optical band gap (E-g) was determined from UV/vis absorption spectra, and the direct transition behavior was confirmed by Tauc's law. The observed large disorder and defect concentration are attributed to the presence of Cr3+ and Ho3+ ions, explaining this behavior. The electron paramagnetic resonance (EPR) measurement presented different types of traps. Room temperature absorption spectra exhibited multiple peaks corresponding to the 3d-3d and 4f-4f transitions of Cr3+ and Ho3+ ions. The results obtained validate the significance of our compounds in optoelectronic device applications.