We presented a high-sensitivity temperature detection using an implanted single Nitrogen-Vacancy center array in diamond. The high-order Thermal Carr-Purcell-Meiboom-Gill (TCPMG) method was performed on the implanted single nitrogen vacancy (NV) center in diamond in a static magnetic field. We demonstrated that under small detunings for the two driving microwave frequencies, the oscillation frequency of the induced fluorescence of the NV center equals approximately to the average of the detunings of the two driving fields. On basis of the conclusion, the zero-field splitting D for the NV center and the corresponding temperature could be determined. The experiment showed that the coherence time for the high-order TCPMG was effectively extended, particularly up to 108 µs for TCPMG-8, about 14 times of the value 7.7 µs for thermal Ramsey method. This coherence time corresponded to a thermal sensitivity of 10.1 mK/Hz 1/2 . We also detected the temperature distribution on the surface of a diamond chip in three different circumstances by using the implanted NV center array with the TCPMG-3 method. The experiment implies the feasibility for using implanted NV centers in high-quality diamonds to detect temperatures in biology, chemistry, material science and microelectronic system with high-sensitivity and nanoscale resolution.In recent years some thermal detection techniques have been developed to map temperature distribution with spatial resolution down to micrometer-nanometer range The NV center is a spin defect consisting of a substitutional nitrogen impurity adjacent to a carbon vacancy in diamond. It has increasingly attracted attention in recent years owing to its excellent properties, like photostability, biocompatibility, chemical inertness, and long spin coherence and relaxation times (∼ms in the isotopically pure diamond) at room temperature. These remarkable properties have been explored in many applications like quantum information processing, [12][13][14][15][16] metrologies such as magnetic field sensing, [17][18][19] electric field sensing, [20,21] force sensing, [22,23] thermal sensing, [8][9][10] single electron and nuclear spin sensing, [24][25][26] and external nuclear spin sensing. [27,28] In thermal sensing, Neumann et al. demonstrated the measurement of the temperature distribution on a glass coverslip using single NV center nanodiamonds as temperature sensors.[9] However, the thermal sensitivity was unsatisfactory due to the short coherence time. To address the short coherence time issue, Toyli et al. proposed the thermal Carr-Purcell-Meiboom-Gill (TCPMG) method and extended the spin coherence time up to 17 µs by TCPMG-2. [8] For further increasing the spin coherence time for the thermometry, in this work, we firstly studied the effects of the higher order TCPMG method applied on the implanted single NV centers in diamond at room temperature. In particular, a coherence time of 108 µs was obtained for TCPMG-8, about 14 times of the value 7.7 µs for Thermal Ramsey (T-Ramsey) method. This value corr...

We investigated the depth dependence of coherence times of nitrogen-vacancy (NV) centers through precisely depth controlling by a moderately oxidative at 580• C in air. By successive nanoscale etching, NV centers could be brought close to the diamond surface step by step, which enable us to trace the evolution of the number of NV centers remained in the chip and to study the depth dependence of coherence times of NV centers with the diamond etching. Our results showed that the coherence times of NV centers declined rapidly with the depth reduction in their last about 22 nm before they finally disappeared, revealing a critical depth for the influence of rapid fluctuating surface spin bath. By monitoring the coherence time variation with depth, we could make a shallow NV center with long coherence time for detecting external spins with high sensitivity.In recent years, shallow NV center has attracted increasing attention owing to its applications in nanoscale spin detection [1][2][3][4][5][6][7] and surface spin noise investigation [8][9][10][11]. Since the minimum detectable magnetic dipole moment scales as δµ ∝ r 3 / √ T 2 [9,12,13], where r is the NV-target spin distance and T 2 is the coherence times of the NV center, the nanoscale control of the NV center depth and the investigation of depth dependence of NV center coherence time are important.

In this work, we experimentally demonstrate energy transfer from a single negatively charged nitrogen-vacancy (NV) center in nanodiamond to a graphene monolayer. The mode values of lifetime and intensity of the fluorescence from the single NV center in nanodiamond on monolayer graphene are shorter and weaker than that on bare quartz substrate. The energy transfer efficiency is measured about 40%, consistent with our theoretical estimation.

We investigated the influence of spins on surface of nanodiamonds (NDs) to the longitudinal relaxation time (T1) and transverse relaxation time (T2) of nitrogen vacancy (NV) centers in ND. A spherical model of the NDs was suggested to account for the experimental results of T1 and T2, and the density of surface spins was roughly estimated based on the statistical analysis of experimental results of 72 NDs containing a single NV center. For NDs studied here, the T1 of NV center inside is highly dependent to the surface spins of the NDs. However, for the T2 of NV center, intrinsic contributions must be much pronounced than that by surface spins. In other words, T1 of an NV center in NDs is more sensitive to the change of the surface spin density than T2.

By choosing 2-pyridin-4-yl-4,5-imidazoledicarboxylic acid (H3PIDC) as the first ligand and sodium oxalate (OX) as the ancillary ligand, a series of mixed-lanthanide metal-organic frameworks (M'LnMOFs) [Tb1-xEux(HPIDC)(ox)1/2H2O]·3H2O (x = 0 1, 0.01 2a, 0.03 2b, 0.05 2c, 0.08 2d, 0.1 2e, 0.3 2f, 0.5 2g, 1 3) have been successfully synthesized via hydrothermal reactions. 2a-2f can serve as ratiometric luminescent sensors for detecting temperature. In this co-doped system, 2d shows an excellent linear response relationship with temperature from 303 to 473 K and exhibits a maximum relative sensitivity (Sr) of 0.60% K-1 at 473 K. Furthermore, powder X-ray diffraction (PXRD) experiments indicate that 2d has excellent chemical stability under simulated physiological conditions and alkali-acid solutions with pH ranging from 4 to 11, which makes it suitable to be applied in the physiological environment.

We make use of inherent vacancies and nitrogen substitutions in nanodiamonds to generate nitrogen-vacancy (NV) centers by high temperature annealing. After 800 °C annealing, low temperature photoluminescence intensity of nanodiamonds shows more than eight times improvement compared with that of unannealed samples. Confocal microscope images of well dispersed nanodiamonds indicate a dramatically increased proportion of nanodiamonds containing NV centers after annealing. Optically detected magnetic resonance spectrum of single NV center demonstrates that the resultant nanodiamonds are suitable for further application as magnetic field sensor. The annealing-oxidation method could be an attractive option for NV center generation in nanodiamonds.

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