Mixed valence effects in TbVO4: Y nanocrystals and diamagnetic materials: Structure, optical linear & nonlinear, magnetic and Faraday rotation properties

Highlights: • Diamagnetic Y³⁺ doped ~100 nm spherical magneto-optical TbVO₄ were synthesized, characterized. • Tb_0.7Y_0.3VO₄/Tb_0.6Y_0.4VO₄ show lower band gap, modified magnetization and zircon-scheelite structure. • Glasses/ceramic with different homogeneity, transparency and structure were obtained. • Multivalence of Tb and V in diamagnetic matrix contributed to linear and nonlinearity improvement. • TbVO₄:30%Y doped glass show giant magnetization and Verdet constant (0.2248 min/G.cm). -- Abstract: Diamagnetic Y³⁺ ions doped magneto-optical TbVO₄ nanocrystals were synthesized and characterized, the influence of mixed valence effect in TbVO₄: Y to structure and properties of diamagnetic glasses/ceramic was studied. 80–100 nm spherical TbVO₄ nanocrystals were hydrothermally synthesized. The doping of 30% and 40% Y³⁺ into TbVO₄ increased the grain size to 120–150 nm and transformed pure zircon-type to a combination of zircon- scheelite type structure. EDX, Raman and infrared spectra revealed that the Y³⁺ occupied the site of Tb³⁺ with chemical formula of Tb_0.7Y_0.3VO₄ and Tb_0.6Y_0.4VO₄ respectively. More than 40% Y³⁺ could not be incorporated into TbVO₄ lattice. Y doped TbVO₄ nanocrystals presented two absorption peaks at 266 nm and 301 nm and one broad emission peak centered at 468 nm. A quenching of emission was observed for 40%Y doped TbVO₄ due to the non-radiation energy transfer between Tb³⁺ and Y³⁺. Three nanocrystals displayed EPR resonance signal at g = 1.98 for V⁴⁺ ions due to the ion (oxygen) vacancies and structure deformation. VSM and XPS results indicated that the Y³⁺ doping changed paramagnetic to diamagnetic due to the increase concentration of diamagnetic Y³⁺, V⁵⁺ and Tb⁴⁺ ions. Three nanocrystals doped diamagnetic glass/ceramic presented different transparency, homogeneity and structures because of multivalence states of Tb and V in glasses/ceramic. Pure TbVO₄ and TbVO₄:30%Y doped glasses exhibited transition ⁷F₀→⁵D₂ of Tb³⁺ and ²B_{2 g}→²B_{1 g} of V⁴⁺ ions which resulted in the reduction of band gap energy and red-shifts of absorption edges. A quenching of ⁵D₄→⁷F_5–2 transition of Tb³⁺ was observed in Tb_0.6Y_0.4VO₄ doped ceramic. Closed and open-aperture Z-scan showed an enhancement of nonlinearity due to the increase of polarizability. The mixed valence states of Tb and V yielded different magnetization and magneto optical rotation performances in glasses/ceramic. TbVO₄:30%Y doped glass exhibited remarkable third nonlinear susceptibility (7.66 × 10⁻¹¹ esu), magnetization and Verdet constant (0.2248 min/G.cm) at 633 nm.