Preparation and Optical Properties of Nd:Bi₂Ti₂O₇ Laser Crystal with Disordered Structure and Attractive...

Laser crystals with multiwavelength emission characteristics are potential light sources for terahertz radiation. Herein, the pure and Nd-doped Bi₂Ti₂O₇ (BTO) laser crystals with sizes up to 16 × 13 × 5 mm³ were successfully grown using the flux method in the KF-B₂O₃-CaBi₄Ti₄O₁₅ growth system. The crystal structure, ideal morphology, chemical, mechanical, and thermal properties, optical transmission and Raman spectra, refractive index, absorption, and fluorescence spectra, as well as fluorescence lifetimes, were systematically studied. Besides, the spectral parameters of Nd³⁺ ions in the BTO crystal were systematically calculated based on the Judd-Ofelt theory. The Nd:BTO crystal has a wide transmittance range (0.44-7.30 μm), a small coefficient of thermal expansion (5.80 × 10^-6 K^-1), and a large absorption full width at half-maximum (fwhm) (31.2 nm) at around ∼804 nm, making it more potential for use in high-power laser systems. Moreover, fluorescence spectra show four emission peaks at 1054, 1062, 1104, and 1112 nm. The strong multiwavelength emission property makes Nd:BTO a promising laser crystal, serving as a potential light source for terahertz radiation.