The Optical Properties Of Color Centers In Single Crystal Diamond

In addition to its extremely high hardness and stability,diamond's excellent optical properties have attracted more and more attention.The wide band gap of the diamond makes it possible for the defect photoluminescence to be emitted without being absorbed,forming a series of defect-induced color center,the so-called“color centers”.These color centers have discrete levels like“single atoms”and are ideal for quantum information processing and quantum computing.The strong covalent bond structure of diamond provides a very stable lattice environment for the color centers,which makes the defect centers have stable optical properties and long spin coherence time,and has important application value in precision measurement.In addition,diamond has good biocompatibility and stability,and nanodiamond color center has great advantages in cell bioluminescent labeling,drug delivery and single-cell level temperature measurement in the field of biomedicine.At the same time,using mature micro-nano processing technology,diamond can be processed into high-quality optical microcavity and various optical waveguide structures,so that color-centered micro-nano photonic devices can be realized,which is important in integrating quantum optics and precision measurement on-chip.Application potential,and to achieve these important applications,the basic optical properties of diamond color centers,especially synthetic diamond single crystal cores,must be thoroughly studied.Spectral methods are important means of studying the physical properties of color centers,such as Raman spectroscopy,photoluminescence spectroscopy and optical absorption spectroscopy.Based on Raman spectroscopy and photoluminescence spectroscopy,we can study the electronic structure of the defect center,electron-phonon coupling and spin-orbit coupling.Because the defect is in the strong lattice structure,it will be modulated by the diamond host lattice.The photoluminescence spectrum can directly characterize the influence of the defect,so as to study its basic properties and broaden its application range.In this thesis,the optical properties of silicon-vacancy(SiV~-)center and nitrogen-vacancy(NV)center in single crystal diamond grown by MPCVD(microwave plasma chemical vapor deposition)are systematically studied by Raman spectroscopy and Photoluminescence spectroscopy,which include the fine structure spectrum of the SiV~-center and the phonon-assisted up-conversion of the SiV~-and NV color centers.The main research contents and results of this thesis are as follows:First,by measuring the PL spectrum of single crystal diamond grown by MPCVD method,a preliminary understanding of the crystal quality,defect type and defect concentration of single crystal diamond used in the experiment was obtained.The main defects in the CVD growth of single crystal diamond were found to be NV~0,NV~-and SiV~-color centers.At the same time,after the fluorescence scanning along the growth section,we found that the concentration of the three defects decreased with the increase of the growth thickness.The defect concentration in the initial growth sample was significantly higher than that at the end of growth,and the reason was explored.We believe that the introduction of N impurities mainly comes from the gas residue in the cavity or the diffusion of the HPHT diamond substrate.This preliminary study laid the foundation for subsequent research and also provided guidance for the control of defect concentrations in CVD grown single crystal diamonds.Second,by measuring the temperature dependent PL spectrum,we observed that the three main defects show different properties in low temperature.The fine structure of the spectrum appears in the SiV~-defect center.After comparing the fine structure spectra between the upper and lower surface,it is found that the upper surface fine structure spectrum has almost no difference in different sample sites,while the fine structure spectrum has a significant dependence on the position.At the same time,by means of high-resolution spectroscopy,it is found that the sub-peak composition of the fine structure spectrum is not derived from a single dipole transition.The polarization composition is confirmed by the polarization fluorescence measurement,and the cause of the splitting is determined from residual lattice stress in the growth process.The surface scanning of the fine structure of the lower surface shows that the SiV~-color center ground state and the excited state energy splitting can be widely adjusted with the position change.Our research can provide a channel for the regulation of the fine structure spectrum of SiV~-color center.By means of the residual stress in the growth process,the optical properties of the defect center are regulated and a qualitative judgment is made on the whether there is residual stress in the diamond.Third,through the measurement of the power dependence spectrum of the SiV~-color center of the upper and lower surfaces of the diamond,we confirmed that the fine structure spectrum of the color center has a very narrow line width at low temperature conditions,and can achieve sensitive detection of temperature.During the measurement of the fine structure spectrum of the lower surface under 4 K conditions,it was found the red shift of the spectrum was observed as the laser power increased,but no similar phenomenon was observed on the upper surface.By changing the excitation power to minimize the effects of the laser thermal effect,the intrinsic temperature dependence of the SiV~-color center is measured to infer the temperature rise of the sample local point.For the reason of the temperature rise,we conducted a heat conduction simulation on the experimental results,and it is considered that the temperature rise is caused by the lower thermal conductivity of the lower surface.The high defect concentration on the lower surface.The high defect concentration on the lower surface greatly reduces the thermal conductivity of the diamond.Through this experiment,it is possible to provide a reliable method for sensitive measurement of local site temperature and determination of diamond thermal conductivity under low temperature conditions.Fourth,by measuring the temperature dependence and power dependence of the SiV~-anti-Stokes fluorescence spectrum,we confirmed that the anti-Stokes fluorescence spectrum,we confirmed that the anti-Stokes fluorescence of SiV~-color center is derived from phonon-assisted rather than two-photon absorption.We experimentally observe the fluorescence up-conversion of SiV~-color centers.However Due to the defect concentration and total reflection of the diamond surface,no laser cooling was observed in the experiment,but our research provided experiment basis for laser cooling in diamond.Fifth,by studying the wavelength dependence of NV color center fluorescence with different charge state and the phonon-assisted fluorescence up-conversion of NV~0color center,we confirm that the phonon-assisted fluorescence up-conversion through that NV~0 color center can be used for different charge states of the NV color center.Experimentally,we observed that the fluorescence intensity of NV~-increase with increase of up-conversion,which confirms the rationality of the method and discusses its conversion mechanism in detail.Our research has a deeper understanding of the transformation mechanism of different charge states,and provides a direction for the regulation of defect concentration of negative charge state NV~-.