Growth and Correlated Structural–Mechanical–Optical Study of Yb³⁺-activated Y_0.7Gd_0.3VO­₄ Single Crystal

Disordered laser host materials have attracted significant attention due to their favorable spectroscopic properties, making them promising candidates for ultrafast laser gain medium applications [1,2]. In particular, disordered rare-earth orthovanadates provide an effective route for tailoring structural and optical properties through controlled cation substitution [2]. In this work, a 2.5 at% Yb³⁺-doped Y_0.7Gd_0.3VO₄ single crystal was grown along the [100] direction using the optical floating zone technique. Its structural, mechanical, and optical properties were systematically investigated and correlated. The selected composition introduces controlled Y/Gd substitutional disorder while preserving the structural stability of the zircon-type lattice.

Powder XRD confirm single-phase crystallization in the tetragonal structure (space group I4₁/amd) with refined lattice parameters a = b = 7.143 Å and c = 6.306 Å. High-resolution rocking-curve analysis of the (200) plane shows a narrow FWHM of 63.7 arc-sec, corresponding to a threading dislocation density of approximately 4.2 × 10⁶ cm^-2, indicating excellent crystalline perfection. Williamson–Hall analysis reveals microstrain of the order of 10^-4, attributed to ionic radius mismatch and substitution-induced lattice distortion. Vickers microhardness measurements demonstrate good mechanical robustness, with a hardness of about 4.8 Mohs, suitable for post-growth processing.

Polarized UV-Vis-NIR spectroscopy confirms strong optical anisotropy in the tetragonal zircon structure. The estimated optical bandgap is about 3.53 eV for π-polarization and 3.60 eV for σ-polarization. The absorption coefficient reaches ~16.47 cm^-1 under π-polarization compared to ~5.56 cm^-1 under σ polarization, with corresponding absorption cross-sections of ~5.47 × 10^-20 cm² (π) and ~1.82 × 10^-20 cm² (σ), confirming dominant π-oriented transitions. Photoluminescence spectra shows broad emission near 1020 nm under 985 nm excitation, corresponding to the ²F_5/2 → ²F_7/2 transition of Yb³⁺.

Overall, the Yb_0.025Y_0.7Gd_0.275VO₄ combines high crystalline quality with disorder-induced spectral broadening, highlighting the novelty of disorder-engineered orthovanadate hosts for broadband ultrafast solid-state laser gain media.