The effect of Ho doping on the microstructure and optical properties of Ba0.65Sr0.35TiO3 thin films

Ba0.65Sr0.35TiO3 (BST) thin films doped with holmium were prepared on silicon and fused quartz substrates by a modified sol–gel technique. The microstructures of BST films were characterized by atomic force microscopy (AFM) and X-ray diffraction (XRD). The results showed that 3 mol% Ho-doped BST has the largest grain size and surface root-mean square roughness. The transmission spectra of Ho-doped BST films were measured by spectrophotometer. The refractive index and thickness of 1 mol% Ho-doped BST film was calculated using envelope method from the transmission spectra. It showed that the refractive index increased from 1.94 to 2.09 as wavelength decreased from 700 nm to 400 nm, which was smaller than pure BST thin films we have reported. The average oscillator strength and wavelength were estimated using a Sellmeir-type dispersion equation. These results show the potential of using Ho-doped BST thin films as an electro-optical novel material.