Effect of titania nano composite on structural and optical properties of Ho³⁺ doped silica glasses for green laser applications

Using sol–gel technique, we synthesized a novel series of titania-silicate glasses doped with Ho³⁺ ions, featuring a chemical composition (80-x) SiO₂ + 20TiO₂ + xHoCl₃ (where x varied from 0.5 to 3.5 mol%, and was referred to as Ho³⁺ ions concentrations). Subsequently, we conducted comprehensive characterization to investigate both the physical parameters and spectroscopic properties of these glasses. Structural analysis involved techniques such as X-ray diffraction (XRD), Fourier transform infrared spectroscopy (FTIR), and transmission electron microscopy (TEM) to elucidate their structural properties. Using the Debye–Scherrer equation, the average grain size of polymorphic anatase phase TiO₂ NPs was determined to be 14 nm. To comprehend the visible photoluminescence and lasing potentialities of titania-silicate glasses, spectroscopic studies including optical absorption and emission measurements were carried out. The bonding behavior of the Ho³⁺ ions and its surrounding ligand was studied using Judd–Ofelt (JO) intensity parameters (Ω_λ, λ = 2, 4, 6); Ω₂ > Ω₄ > Ω₆; regardless of Ω₂ or Ω₄ or Ω₆, they all initially rise and then decrease with Ho³⁺ ion concentration, reaching their maximum value at 1.5 mol%. There are five visible emissions in the glass photoluminescence spectrum: two red, one green, and one blue. The green emission has the maximum intensity, occurring at 549 nm from the ⁵S₂ → ⁵I₈ transition. Analysis involved employing calculations to ascertain various parameters including the spectroscopic quality factor (χ = Ω₄/Ω₆), color chromaticity coordinates (x, y), correlated color temperature (CCT), and color purity (CP). Its appropriateness for designing and developing visible green lasers is demonstrated by the strong visible emission, large stimulated emission cross-section (σ_se), and high branching ratio (β) achieved during the ⁵S₂ → ⁵I₈ (green) transition of titania-silicate glass doped with 1.5 mol% of Ho³⁺ ions.