All-Optical Quantum Thermometry with Germanium and Nickel Color Centers in Diamonds

Accurate temperature sensing at the nanoscale is essential for advancing quantum technologies and probing thermal processes in condensed matter and biological systems. Here, we present an experimental study of the temperature-dependent fluorescence spectra of germanium and nickel color centers in diamonds. The zero-phonon line position, linewidth, and intensity exhibit a pronounced and systematic dependence on temperature across the investigated range, enabling highly sensitive thermometric readout with a low noise floor under purely optical excitation and detection. The germanium color center emits in the visible range, while the nickel color center emits in the near-infrared, providing complementary spectral characteristics that enable noninvasive thermal mapping across diverse environments. These results establish germanium and nickel color centers as promising platforms for high-resolution, all-optical quantum thermometry.