Abstract
Discovery of materials with exceptional frequency-conversion efficiency remains a central challenge in optoelectronics. In the wide-bandgap regime (crucial for ultraviolet and high-power applications), only a handful of crystals, such as β-BaB₂O₄(BBO), CsB₃O₅(CBO), CsLiB₆O₁₀(CLBO), and KDP, are routinely employed, yet each suffers from limited stability, modest nonlinear susceptibility, or low laser-induced damage thresholds. We have recently discovered this high-entropy borate system that overcomes these constraints and exhibits two orders of magnitude increase in optical second-harmonic generation (SHG) relative to commercial BBO. Using configurational entropy as a tuning knob, we have obtained higher optical transparency and broadband photoluminescence in both the visible and near-infrared wavelength ranges, with emission bands at 605, 705, 813, 910, and 1030 nm. Coupled with high-resolution SHG microscopy for phase identification and discovery, we have explored the structural and crystallographic origins of this phase through high-resolution hard-x-ray nanoprobe and 4D-STEM analysis, which reveal a structural distortion that lowers the crystallographic symmetry and is responsible for this enhancement. This work illuminates the promise of a high entropy synthesis strategy for designing next-generation optoelectronic materials that combine increased transparency, strong broadband luminescence, and enhanced nonlinear response in a single platform.
*S.S., J.-P.M., S.S.I.A., and V.G. acknowledge the National Science Foundation Grant Number DMR- 2011839. Work performed at the Center for Nanoscale Materials and Advanced Photon Source, both U.S. Department of Energy Office of Science User Facilities, was supported by the U.S. DOE, Office of Basic Energy Sciences, under Contract No. DE-AC02-06CH11357. J.N. was supported by the Department of Energy Basic Energy Science Grant Number DE-SC0012375. H.S. acknowledges the National Science Foundation Grant Number DMR-2210933. X-ray instrumentation was purchased with grants from the National Institutes of Health under the award numbers 1S10OD028589-01 and 1S10RR023439-01 to the Pennsylvania State University X-ray diffraction core facility.
