Synthesis and thermometry of NV- nanodiamond alpha-NaYF4 composite nanostructures

Negatively charged nitrogen-vacancy (NV^-) centers in diamond have a plethora of potential applications in quantum systems, including sensing and computing^1-3. Photothermal heating can limit the utility of NV^- center nanodiamonds, especially under high laser irradiances^4-6. A composite of nanodiamonds with NV^- defects and ytterbium-doped cubic sodium yttrium fluoride (Yb:α-NaYF₄ or NaYF) could offset the photothermal heating of nanodiamonds by the anti-Stokes fluorescence cooling of Yb³⁺ ions⁷. We present a novel preparation method for generating a NV^- diamond NaYF composite material based on a hydrothermal synthesis approach. Particle size was determined to be 230 ± 90 nm by SEM, and DLS data show a permanent connection between nanodiamonds and NaYF. Nanodiamonds are observed on the surfaces of NaYF materials. Nanodiamonds may also be incorporated within the body of individual NaYF grains, however the question of whether nanodiamonds are fully incorporated into the host NaYF material remains to be answered. The temperatures of host material and NV^- defects are accessed using mean fluorescence wavelength shifts and Debye-Waller factor thermometry respectively. The obtained temperature changes with increasing 1020 nm irradiance show good agreement. Two data sets showed photothermal heating of around 10 and 13 K at 6.3 MW/cm². Increased particle smoothness and sizes could lead to coolable composite materials.