The role of thickness on the structural and luminescence properties of Y₂O₃:Ho³⁺, Yb³⁺ upconversion films

The structural, surface, and upconversion (UC) luminescence properties of Y₂O₃:Ho³⁺,Yb³⁺ films grown by pulsed laser deposition, for different numbers of laser pulses, were studied. The crystallinity, surface, and UC luminescence properties of the thin films were found to be highly dependent on the number of laser pulses. The X-ray powder diffraction analysis revealed that Y₂O₃:Ho³⁺,Yb³⁺ films were formed in a cubic structure phase with an Ia \(\overline{3 }\) $\overline{3}$ space group. The thicknesses of the films were estimated by using cross-sectional scanning electron microscopy, depth profiles using X-ray photoelectron spectroscopy (XPS), and the Swanepoel method. The high-resolution XPS was used to determine the chemical composition and oxidation states of the prepared films. The UC emissions were observed at 538, 550, 666, and 756 nm, assigned to the ⁵F₄ → ⁵I₈, ⁵S₂ → ⁵I₈, ⁵F₅ → ⁵I₈, and ⁵S₂ → ⁵I₇ transitions of the Ho³⁺ ions. The power dependence measurements confirmed the involvement of a two-photon process in the UC process. The color purity estimated from the Commission International de I’Eclairage coordinates confirmed strong green UC emission. The results suggested that the Y₂O₃:Ho³⁺,Yb³⁺ UC transparent films are good candidates for various applications, including solar cell applications.