Spectroscopic Characterization of Nanodiamond Solutions using Photothermal and Fluorescence Measurements
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Spectroscopic Characterization of Nanodiamond Solutions using Photothermal and Fluorescence Measurements Gour Pati, Z. Warren, M. J. Williams, A. Marcano and Renu Tripathi Department of Physics & Engineering, Delaware State University, Dover, DE – 19901, U.S.A. ABSTRACT Absorption, scattering and fluorescent properties of several different types of nanodiamond samples are measured to characterize them for various applications. Two different methods, spectrophotometry and photothermal spectroscopy were used to measure absorption properties of nanodiamonds suspended in aqueous solutions. Photothermal spectroscopy provides the advantage of measuring absorption of photoactive nanodiamonds with high-sensitivity. Spectral fluorescence properties of nanodiamond samples were studied using a commercial spectrofluorometer and a home-built inverted microscope integrated with a light-sensitive imaging spectrograph. Characteristic fluorescence spectrum of nitrogen-vacancy defects in single diamond nanocrystals was obtained using the light-sensitive instrument. INTRODUCTION Nitrogen-vacancy (NV) centers in nanodiamond (ND) have remarkable fluorescence properties which make them suitable for fluorescence microscopy and bioimaging applications [1]. NV centers emit bright and stable optical fluorescence when excited with visible light. NV centers also exhibit atom-like phenomena in their ground state with long coherence time. A single NV center in nanodiamond can exhibit spin polarization, optical read-out and quantum coherence effects at room temperature [2-4]. It can be probed coherently via optical or microwave radiation. There has been considerable interest in NV centers for quantum control of individual photons, electrons and nuclear spins [5]. For example, electron spin resonance in single NV center can be used to perform magnetic-field sensing with nanoscale spatial resolution [6]. Similarly, NV-based single photon source can be realized for quantum cryptography and communications [7]. In this work, we present results obtained in investigating the spectroscopic properties of nanodiamonds (size: 10 – 100 nm) containing NV defects. Several different types of ND samples are used in our studies. During synthesis, irradiation using electron (or ion) beam is used as a common procedure to activate and control NV centers in ND sample. We developed photothermal spectroscopy (PTS) [8] to measure absorption in ND samples by utilizing nonradiative relaxations in the photo-activated NV centers. Fluorescence spectrum of NV centers in ND was measured using a high-throughput, light-sensitive imaging spectrograph. EXPERIMENTAL DETAILS Nanodiamonds used in our studies were commercially obtained with particle sizes ranging from 10 nm to 100 nm. Some of these are synthetic (type-Ib) nano-powders (Microdiamant AG, MSY 0- 0.05; Van Moppes, SYP 0 – 0.05) with nominal size 25 nm. NV center naturally occurs in these nitrogen-rich samples with low probability even though they are not irradiated. Some of the other ND samples (Adamas Nanotechnologies, N
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