All‐Optical Thermometry with Infrared Emitting Defects in Diamond

Abstract Diamond color centers (optically active defects) can be used for all‐optical thermometry for non‐invasive and localized temperature measurements. The visible to near‐infrared photoluminescence of these defects is greatly attenuated in optical fibres and biological samples and therefore limits their use. A color center in Si‐doped diamond with emission coinciding with the O‐band and a major biological transparency window has recently been reported. It has a zero phonon line (ZPL) at 1221 nm and well‐resolved phonon side‐band features. In this work, a strong temperature dependence above 150 K is observed, allowing for accurate temperature measurements up to approximately 420 K. The temperature can be determined via spectral shifts or thermal broadening of the ZPL and through the intensity ratio between the ZPL and the phonon side‐band to a maximum temperature resolution of 0.57 K/Hz. Thermometry using these micro‐diamonds is demonstrated for both electronic and biological applications highlighting their versatility. The potential for further enhancements in sensitivity is discussed.