Accuracy Estimation of All-Optical Thermometry Between 283–373 K using the NV^--Center Zero-Phonon Line Spectrum of Diamond Microparticles

The temperature dependences of the intensity, peak wavelength, and width of the zero-phonon line (ZPL) spectrum from diamond nanoparticles have been used for all-optical thermometry of microscale objects [1-3]. The method is especially effective when it is challenging to apply the thermometry using the optically detected magnetic resonance [4-5]. However, the ZPL spectrum shape varies particle-to-particle due to presumably the difference in the particle shape [3], which produces a different magnitude of the strain in the diamond lattice, and the variation requires calibration of the particle dependence of the three parameters mentioned above. To establish the calibration procedure and estimate the accuracy of the all-optical thermometry, we measured the particle-to-particle variation in the ZPL spectrum between 283–373 K.<br/>In the experiments, we used commercial diamond microparticles of 150 μm and 0.75 μm average diameters (Adamas Nanotechnologies). The microparticles were used instead of nanoparticles for the ease of particle-to-particle spectroscopy. Approximately 100 particles were dispersed on a silicon wafer mounted on a temperature-controlled stage of an epifluorescent microscope. 594 nm laser was used as an excitation light source, and the photoluminescence spectrum of each particle was measured using a spectrometer (1.5 nm resolution). In the measured spectra, a wavelength range near the ZPL was fitted using an analytical function based on the theoretical shapes of the ZPL and phonon side band spectra [6].<br/>The three parameters were evaluated from the fitting result, and we made histograms of them at every 10 K between 283–373 K. Among the three parameters, the peak wavelength has the smallest variance compared with the temperature dependence suggesting that better accuracy of the thermometry can be obtained by using the peak wavelength. We found that particles with close ZPL spectrum shape at 293 K have close temperature dependences of the peak wavelength between 283–373 K. Thus, the calibration could be done at one temperature condition by sorting particles having close ZPL spectrum shapes.<br/><br/>[1] T. Plakhotnik, <i>et al.</i>, <i>Nanotechnology</i> <b>26</b>, 245501 (2015).<br/>[2] P. C. Tsai, <i>et al.</i>, <i>Angew. Chem. Int. Ed.</i> <b>56</b>, 3025 (2017).<br/>[3] Y. Y. Hui, <i>et al., J. Phys. Chem. C</i> <b>123</b>, 15366 (2019).<br/>[4] M. Fukami, <i>et al., Phys. Rev. Appl.</i> <b>12</b>, 014042 (2019).<br/>[5] L. Ishikawa, <i>et al., Rev. Sci. Instrum.</i> <b>93</b>, 083705 (2022).<br/>[6] T. Shikama, <i>et al.,</i> <i>Jpn. J. Appl. Phys.</i> <b>60</b>, 012001 (2020).