High entropy engineering to enhance optical and functional properties of wide bandgap novel single crystals for efficient energy conversion applications

Efficient energy conversion from one laser frequency to another in the ultraviolet range is challenging due to the lack of available material systems with high nonlinear optical coefficients and laser damage thresholds. This study reports a new family of high entropy rare earth single crystals A⁵ & A⁶Ba₃(B₃O₆)₃ (A= Nd, Tb, Sm, Dy, Gd, Yb, and Er) with remarkable potential in nonlinear optical applications. Our anisotropic linear and nonlinear optical characterization reveals both type-I and type-II SHG phase matchability, with the highest effective phase-matched SHG coefficients of ~3.2 pm/V at 800nm fundamental wavelength, higher than the monolithic single crystals and commercially utilized β-BaB₂O₄. Through high entropy engineering in these rare earth borates, we have also observed a drastic enhancement in IR transparency and crystallinity compared to monolithic single crystals. The presence of rare-earth elements has enhanced the photoluminescence of these materials in both visible and IR regions. This study not only demonstrated the first experimental synthesis of such wide bandgap single-crystal high entropy systems with no observable phase segregation or intermixing but also enhanced the potential for optoelectronic properties.