Potential Laser Crystal of Zn4B6O13:Mn2+ with Low Thermal Expansion and High Thermal Conductivity: Single-Crystal Growth and Characterization

Abstract

Laser crystals, serving as the laser gain medium, are key materials in all-solid-state lasers. Due to considerable thermal expansion and low thermal conductivity, the performance of conventional laser crystals strongly depends on thermal management systems to improve the laser quality and power, which inevitably restricts the development of laser technology. In this work, a new potential laser crystal of Mn²⁺-doped Zn₄B₆O₁₃ (ZBO) with a low thermal expansion and high thermal conductivity was grown and characterized. The strong luminescence emission at 539 nm in ZBO:Mn²⁺ was observed, with a long lifetime of 16.20(7) ms, and the corresponding absorption bands in the range of 410–460 nm fall within the spectra of GaN- or InGaN-based laser diodes. In variable-temperature fluorescence spectra, promoted by relaxation on the parity-forbidden ⁴T₁-to-⁶A₁ transition from the increased phonon number, an abnormal negative thermal quenching was manifested below 140 K, with the lifetime consistently greater than 10 ms over the whole temperature range of 80–500 K. Meanwhile, ZBO:Mn²⁺ manifests very low thermal expansion (3.1 MK^–1) and high thermal conductivity (27.44(6) W/(m·K)) at room temperature (300 K). These excellent thermal properties, combined with good optical properties, make ZBO:Mn²⁺ an outstanding gain medium for green laser generation. Our study confirms that ZBO is a promising laser matrix crystal.