Chemically Tunable Aspect Ratio Control and Laser Refrigeration of Hexagonal Sodium Yttrium Fluoride Upconverting Materials

Abstract

Hexagonal sodium yttrium fluoride with Na 3x Y 2−x F 6 stoichiometry (β-NaYF) is a promising material for luminescence upconversion applications due to the narrow crystal field splitting of the Yb(III) ion's lower 2 F 7/2 manifold. However, growing single crystals of β-NaYF remains an outstanding challenge due to thermal expansion stresses that cause cracking during melt growth. In this paper, we demonstrate a novel hydrothermal synthesis of β-NaYF with the ability to tune the aspect ratio from microplatelets to microrods with aspect ratios that match computationally predicted cavity (Mie) resonances. These crystals have a rootmean-square roughness below 1 nm after calcination, which makes them ideal for optical cavities. The β-NaYF microcrystals are doped with 10% Yb(III) cations and are used to build optomechanical laser-refrigeration devices consisting of a hexagonal β-NaYF crystal located at the end of a cantilever. Laser refrigeration of these devices by >12.5 °C is observed using calibrated measurements of both the cantilever's fundamental eigenfrequency and a Boltzmann fit to crystal field luminescence from the Yb(III) ions.

Optical Trapping of High-Aspect-Ratio NaYF Hexagonal Prisms for kHz-MHz Gravitational Wave Detectors

“…Mode splitting is also often seen in levitated particles in the Rayleigh limit, caused by the asymmetric potential generated by polarisation dependent focusing of the beam [39]. Since our prisms are well into the Mie-Lorentz regime, separation between the modes results both from the polarization dependent focusing bias of the lens and geometry-dependent scattering resonances within the levitated particle [34].…”

“…By choosing such a material for the sensor, in the future laser refrigeration methods may enable higher trapping intensity and higher trap frequencies for gravitational wave searches approaching the several hundred kHz frequency range. To produce multi-µm-scale high-aspect ratio particles relevant for GW detectors, we recently developed a novel hydrothermal synthesis [34] to drive growth of the hexagonal beta NaYF into thin, wide plates that was not previously possible [30].…”

Upconversion as a spear carrier for tuning photovoltaic efficiency

“…30 Hexagonal (b phase) NaYF 4 is one of the most efficient and most studied host matrices for green and blue emission due to its narrow crystal field splitting. 21,31 Along with these properties, this matrix is safer to grow due to the high solubility of NaF in water as compared to other rare earth fluorides, like LiYF 4 , which require hazardous ammonium fluoride precursors. 32 Zhou et al synthesized the nanowire morphology of b-NaYF 4 that could be optically trapped and refrigerated using a near-IR laser having potential applications in localized optoelectronic device cooling and laser refrigeration.…”

Energy transfer characteristics of single-particle NaYF₄ core-shell structure

“…目前, 本课题组也针对Er 3+ 和Ho 3+ 离子掺杂的微 米核壳结构晶体的上转换发光特性进行了相关工 作, 并以单颗粒微米晶体为研究对象, 在NaErF 4 微米棒上包覆不同的惰性和活性壳层, 实现了单颗 粒微米棒红光发射增强 [19] . 同时, 通过构建NaYbF 4 : 2%Ho 3+ @NaYbF 4 @NaYF 4 核-壳-壳结构微米盘, 在980 nm激光激发下, 进一步提高了Ho 3+ 离子发 射的红绿比及红光发射强度 [20] . 然而, 对于具有不…”