Bulk Growth, Thermal, and Polarized Spectral Characters of Nd3+-Doped Ca3(BO3)2 Single Crystals

Abstract

The growth, ion concentrations, powder X-ray diffraction, thermal properties, and optical spectroscopy of Nd³⁺-doped Ca₃(BO₃)₂ single crystals are investigated. The Nd³⁺-doped Ca₃(BO₃)₂ single crystals with 1.97 at.% Nd³⁺ are successfully grown using the Czochralski (Cz) technique. To address the chemical valence imbalance between Nd³⁺ and Ca²⁺ in the Ca₃(BO₃)₂ crystals, the Na⁺ ions are introduced. The concentrations of Nd³⁺ and Na⁺ ions in the as-grown crystals are measured using inductively coupled plasma atomic emission spectroscopy (ICP-AES), yielding concentrations of 1.97 at% (N₀ = 1.55 × 10²⁰ cm⁻³), 1.94 at% (N₀ = 1.52 × 10²⁰ cm⁻³), respectively. The thermal behavior of the Nd³⁺-doped Ca₃(BO₃)₂ crystals, including thermal expansion coefficients, specific heat, and thermogravimetric and differential thermal analysis (TG-DTA), is systematically investigated. At room temperature, the polarized absorption spectra, polarized fluorescence spectra, and fluorescence decay lifetimes are measured. Spectral parameters, including polarized absorption and stimulated emission cross-sections, intensity parameters, transition probabilities, radiative lifetime, and branching ratios are determined using the Judd-Ofelt (J-O) theory. The results indicate that Nd³⁺-doped Ca₃(BO₃)₂ crystals are promising materials for near-infrared lasers, offering advantages such as rapid growth, large size, high specific heat, strong emission, and environmental stability.