Near-Infrared Optical Thermometry of Nickel Color Centers in Diamond

We present an experimental study of temperature-dependent near-infrared fluorescence spectra of nickel color centers in diamond. The amplitude, the central wavelength, and the linewidth of the zero-phonon line (ZPL) in the fluorescence spectrum of these centers exhibit a strong temperature dependence, enabling highly sensitive temperature measurements. Due to the ZPL wavelength, falling within the biological transparency window, combined with a high-temperature sensitivity and low noise floor, as demonstrated by our experiments in practical thermometry settings, nickel color centers in diamond are ideally suited for all-optical temperature measurements, including thermometry of biological systems.