Crystal Growth and Characterization of Terbium-Based Borate Crystals of Sr₃Tb(BO₃)₃, Li₆Tb(BO₃)₃, and TbCa₄O(BO₃)₃: Color Centers, Spectroscopic Properties, and Optical Gain

Abstract

This work aims to evaluate the prospect for visible laser applications of three terbium-based borate single crystals, viz. Sr3Tb­(BO3)3 (STB), Li6Tb­(BO3)3 (LTB), and TbCa4O­(BO3)3 (TbCOB). Crystals with good optical quality were grown by the Czochralski technique. Formation of color centers was observed in the crystals grown in air atmosphere and was then circumvented by applying a reducing atmosphere during the growth process. The color centers were further studied by absorption and electron paramagnetic resonance spectroscopic characterization. Thermal properties that can impact laser operation, including thermal conductivity, specific heat capacity, and thermal expansion, were characterized using the as-grown crystals. The principal refractive indices of STB and LTB were measured experimentally. Cross sections of the 4f8 → 4f8 transitions of Tb3+ in these crystals were derived from the recorded absorption and emission spectra as well as the Judd–Ofelt calculations. The fluorescence decay curves from the 5D4 excited state were recorded to yield the fluorescence lifetimes. Experimental results and theoretical calculations indicate that these terbium-based crystals have minor nonradiative processes from the 5D4 manifold, and the transition cross sections in the visible spectra range are comparable to those of the previously reported gain media. Lastly, optical gain at 543 nm was measured in these crystals in a pump–probe scheme.

Spectroscopic properties of Tb3+ as an ion for visible lasers

“…In particular the recent reports on their efficient visible laser operation lead to a revival of spectroscopy on Tb 3+ doped materials. Just to name a few examples, phosphates [34], borates [35,36], garnets [37], perovskites [38], tungstates [39,40] and fluorides [16,17] were spectroscopically investigated in detail recently.…”

Defect Healing of Micro/Nanocrystals via the Coordination Competition of Rare Earth in Crystal Engineering

“…In the synthesis of complexes, the reaction of the same metal ion with an organic ligand often results in crystals with different colors depending on the reaction conditions. Similarly, although fluorescent ligands are introduced during the synthesis process, the final synthesized complex crystals do not fluoresce. ,− These phenomena are common in crystal synthesis, yet troubling. Thus, it is a great challenge to reveal the underlying mechanisms of these experimental phenomena.…”