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.