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The optical excitation of nitrogen-vacancy (NV) color centers in diamonds mostly results in fluorescence emission. During this process, a portion of the incident energy is transferred to phonon vibration, which heats the diamond crystal. For single NV color centers, the heat generated by the optical cycle is negligible, while for an ensemble of NV defects, the generated heat accumulates rapidly and heats the diamond. The temperature rise is rapid due to the high thermal conductivity of the diamond. In addition to the ability to be heated by light, the NV defect's unique properties also allow for the precise measurement of temperature using optically detected magnetic resonance. Here, we experimentally demonstrate that microcrystalline diamond containing NV center ensembles can be used as a self-gauged microheater. We attached a microcrystal diamond to an optical fiber in an endoscope configuration, evaluated its performance as a self-gauged heater under varied biologically relevant environments, and discussed its potential applications. In addition to the aforementioned capabilities, the NV defect enables the precise measurement of local magnetic fields. This provides a unique multimodal sensor to probe temperature-controlled magnetic phenomena at microscopic scales. [ABSTRACT FROM AUTHOR]

Electron–photon temporal correlations in electron energy loss spectroscopy (EELS) and cathodoluminescence (CL) spectroscopies have recently been used to measure the relative quantum efficiency of materials. This combined spectroscopy, named cathodoluminescence excitation (CLE) spectroscopy, allows for the identification of excitation and decay channels, which are hidden in average measurements. Here, we demonstrate that CLE can also be used to measure excitations' decay time. In addition, the decay time as a function of the excitation energy is measured, as the energy for each electron–photon pair is probed. We used two well-known insulating materials to characterize this technique, nanodiamonds with NV0 defects and hexagonal boron nitride (h-BN) with 4.1 eV defects. Both also exhibit marked transition radiations, whose extremely short decay times can be used to characterize the instrumental response function. It is found to be typically 2 ns, in agreement with the expected limit of the EELS detector temporal resolution. The measured lifetimes of NV0 centers in diamond nanoparticles (20–40 ns) and 4.1 eV defect in h-BN flakes (<2 ns) match those reported previously. [ABSTRACT FROM AUTHOR]