Influence of spinning speed on the structural, surface, and NIR emission properties of spin-coated Y2O3:Ho3+, Yb3+ thin films

At various spinning speeds, Y2O3:Ho3+, Yb3+ thin films were grown on quartz substrates through a sol-gel spin coating route. High-temperature treatment of the deposited films was further done at 1000 °C. The structural and surface properties of the films were explored using powder x-ray diffraction (PXRD) and x-ray photoelectron spectroscopy (XPS). The thicknesses of the thin films were estimated using XPS depth profiles and the Swanepoel method. The structural analysis revealed a mixture of SiO2 and Y2O3 phases. The XPS high-resolution scans and depth profiles confirmed that the extra SiO2 phase resulted from the diffusion of the quartz substrate’s elements into the prepared films due to high-temperature treatment. The films’ thicknesses decreased with increasing spinning speed. Upon 448 nm excitation, the films showed a dominant near-infrared emission at 1204 nm assigned to the 5I6 → 5I8 transition of the Ho3+ ion, with no trace of Yb3+ emission. The results revealed that the near-infrared (NIR) emission intensity of the films was dependent on the spinning speed. The spinning speed influenced surface roughness and film thickness, which, in turn, affected NIR emission via total internal reflection and excitation volume. The improved emission at 1204 nm indicates that the Y2O3:Ho3+, Yb3+ films are suitable for laser applications, among other fields.