Hydrothermal Synthesis of Yb<sup>3+</sup>: LuLiF<sub>4</sub> Microcrystals and Laser Refrigeration of Yb<sup>3+</sup>: LuLiF<sub>4</sub>/Silicon‐Nitride Composite Nanostructures
Elena Dobretsova, Xiaojing Xia, Anupum Pant, Matthew B. Lim, Michael C. De Siena, К. Н. Болдырев, A. D. Molchanova, Н. Н. Новикова, С. А. Климин, М. Н. Попова, Yueyang Chen, Arka Majumdar, Daniel R. Gamelin, Peter J. Pauzauskie
Abstract
Abstract The hydrothermal synthesis and characterization of 10%Yb 3+ :LiLuF 4 (LLF) microcrystals are reported. A combination of X‐ray diffraction (XRD) analysis, analytical transmission electron microscopy (TEM), scanning TEM (STEM), energy‐dispersive X‐ray (EDX) spectroscopy), temperature‐dependent Fourier‐transform infrared (FTIR) spectroscopy, and photoluminescence (PL) measurements confirm a scheelite ( I 4 1 / a ) phase and substitutional doping of Yb 3+ within the microcrystals. Laser cooling to more than 20 K below room temperature in vacuum (10 −3 torr) is demonstrated when irradiating individual microcrystals using a near‐infrared pumping wavelength ( λ = 1020nm) at a laser power of 40 mW (irradiance of 0.85 MW cm −2 ). The use of these microcrystals is further demonstrated for solid‐state laser refrigeration of an electron‐transparent silicon‐nitride (Si 3 N 4 ) TEM window. A combination of internal luminescence thermometry, heat‐transfer modeling, and control measurements on lithographically patterned Si 3 N 4 optical cavities is used to demonstrate successful bulk laser cooling of Si 3 N 4 TEM windows by ≈15 K below room temperature, opening new opportunities for contactless in situ TEM refrigeration.