Effect of Nd2O3 Concentration on Crystallization Mechanism and Third-Order Optical Nonlinearity of Lanthanide-Titanium-Tellurite Glass and Glass-Ceramics

Rare-earth (RE)-doped transparent tellurite glass-ceramics (GCs) embedded with “anti-glass” crystallites not only exhibit superior emission properties but can also be a potential medium for nonlinear optical (NLO) applications. Both of these properties depend on their transparency. Keeping this in view, we aimed to elucidate the effect of Nd³⁺ ion concentration (0.5–2 mol %) on the crystallization mechanism of lanthanum-gadolinium-titanium-tellurite (LGTT) glass in retaining the transparency and NLO properties. XRD reveals the precipitation of (La/Nd)₂T₆O₁₅ and Gd₂Te₆O₁₅ “anti-glass” crystallites upon ceramization of these glasses. Particle-size-dependent DSC confirms competition between the growth of these two crystalline phases at higher Nd³⁺ concentration that aids in controlling crystal growth. The FE-SEM microstructures demonstrate a change in morphology of the crystallites from rectangular (1.5 μm) to spherical (120 nm) with increasing Nd₂O₃ concentration from 0.5 to 2 mol % and thereby retaining optical transparency (12% → 55%) in GCs. Photoluminescence spectra reveal a maximum emission intensity for 1 mol % of Nd₂O₃-doped glass; however, the lifetime is maximum (156 μs) for 0.5% Nd₂O₃ doping. This study also discloses an enhancement of third-order NLO properties as a function of Nd₂O₃ concentration in LGTT glasses under femtosecond laser excitation at 800–1200 nm due to resonant nonlinearity. Emission intensity and NLO responses are increased in the GCs compared to their parent glasses. A maximum nonlinear absorption coefficient (α₂) of 4.986 × 10^–10 m/W and nonlinear refractive index (n₂) of 3.115× 10^–17 m²/W has been obtained from LGTT-Nd2(GC-36h) GCs at 800 nm. GCs exhibits an optical limiting threshold of 4.14 mJ/cm², suggesting its great potential for intense radiation shielding.