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NANOSYSTEMS: PHYSICS, CHEMISTRY, MATHEMATICS, 2018, 9 (1), P. 55-57
Study of optical properties of the NV and SiV centres in diamond at high pressures
S.G. Lyapin1, I.D. Ilichev1, A.P. Novikov1, V.A. Davydov1, V.N. Agafonov2
XL. F. Vereshchagin Institute for High Pressure Physics, Russian Academy of Sciences, Troitsk, Moscow, Russia 2L.E.M.A., UMR CNRS-CEA 6157, University F. Rabelais, Tours, France
PACS 33.50.Dq, 62.50-p DOI 10.17586/2220-8054-2018-9-1-55-57
We report photoluminescence studies of micro- and nano-sized diamonds with NV0, NV- and SiV- centers under hydrostatic pressure up to 50 GPa. Diamonds have been obtained by high-pressure high-temperature (HPHT) treatment of metal-free growth systems based on mixtures of hydrocarbon, fluorocarbon, and silicone-containing organic compounds.
Keywords: diamond, colour centres, high pressures, DAC.
Received: 20 June 2017
Revised: 11 October 2017
1. Introduction
Color centers in diamond are considered now as an important basic element for different quantum-physical and biomedical applications. Although the properties of color centers in diamond have been studied very intensively for a long time, the pressure effect on photoluminescence is not well known. Knowledge of changes in the energy of the zero-phonon line (ZPL) with hydrostatic stress is crucial in analyzing temperature dependences [1,2], isotope shift [3] of ZPL. To our knowledge, the pressure coefficient was measured only for NV- centers [4,5].
Here, we report pressure effect on zero-phonon line in SiV-, NV0 and NV- centers under hydrostatic pressure up to 50 GPa.
2. Experimental
Homogeneous mixtures of naphthalene (C10H8), fluorographite (CF1.1) and tetrakis(trimethylsilyl)silane (C12H36Si5) were used as starting materials for synthesis of diamond with optically active SiV-, NV0 and NV- point defects. The synthesis was performed in a high-pressure apparatus of "Toroid" type [6]. Cylindrical samples of the initial mixtures (4 mm diameter and 5 mm height) obtained by cold pressing were put into graphite containers which were placed in the high-pressure apparatus. The experimental procedure consisted in loading the apparatus up to 8 GPa, heating up to the desired temperature 1200 °C) and short isothermal exposure under constant load for 5 - 10 s. The SEM images of the obtained products, which are mixtures of nano- and submicrometer-size fraction of diamond, show that the formation of diamond occurs with virtually 100 % yield.
Photoluminescence (PL) spectra were recorded using the 488 nm Ar+ laser line for excitation and a triplegrating spectrometer (Princeton Instruments TriVista 555) with a liquid-nitrogen-cooled CCD detector. Diamond samples, representing distinct agglomerates of micro- and nanoscale diamonds, were placed in a diamond-anvil cell (DAC) along with ruby crystal, serving as a pressure sensor. Helium was used as pressure-transmitting medium. For measurements at room temperature, a 50x objective (NA = 0.50) of a confocal microscope (Olympus BX51) was used to focus the laser beam and to collect the PL signal. To perform measurements at 80 K, the DAC was put into a He cryostat (Oxford Instruments OptistatSXM) and an achromatic lens was used for focusing the laser beam and collecting the signal. The laser spot on the sample inside the cryostat was ~ 5 ^m.
3. Results and discussion
Figure 1 shows typical photoluminescence spectra collected on diamonds doped with silicon of natural isotope composition. Because of unintentional doping of diamond with nitrogen occurred during synthesis, some of our samples contain nitrogen-vacancy defects (neutral NV0 and negatively charged NV-) detectable already at room temperature 296 K [6]. Two types of diamonds were used in pressure experiments i) with high concentration SiV-centers in order to track ZPL from SiV- centers; ii) with low concentration SiV- centers to allow detection of ZPL from NV centers. We were able to follow ZPL from SiV- and NV0 centers up to ~ 52 GPa (the maximum pressure achieved in our experiment). However, ZPL from NV0 centers became undetectable above ~ 40 GPa.
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E -*""/ \ 34.0
^ J \
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-jY V--26.6
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--- ^--i Dar
1.675 1.700 1.725 1.750 1.95 2.0C Energy (eV)
a) b)
Fig. 1. Normalized PL spectra of diamo
Study of optical properties of the NV and SiV centres in diamond at high pressures 57
Table 1. Pressure coefficients for ZPL in SiV-, NV- and NV0 centres at 296 and 80 K
E(P) = E0 + a • P + 0 • P2
296 K 80 K
Center Eo (eV) a (meV/GPa) 3 ■ 10-3 (meV/GPa2) Eo (eV) a (meV/GPa) 3■10-3 (meV/GPa2)
SiV- 1.680 1.09 -5.7 1.682 1.04 -5.3
NV- 1.943 5.81 -25 1.946 5.57 -19
NV0 2.156 2.14 0 2.156 2.21 0
Acknowledgements
The work was supported by the Russian Foundation for Basic Research (Grant No. 18-03-00936). References
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