Effect of Particle Size on the Optical Properties of Silicon‐Vacancy Centers in Nanodiamonds Fabricated by a Detonation Process

Abstract

Nanodiamonds containing silicon‐vacancy centers (SiV‐NDs) are attracting attention as promising fluorescent markers. Recently, the preparation of single‐digit‐nanometer‐sized SiV‐NDs by a detonation process, which can be carried out on a practical scale, has been demonstrated. However, little is known about the effect of these extremely small diamonds fabricated by a detonation process on the electronic state of the SiV centers. In the present study, SiV‐NDs prepared by the detonation process are investigated spectroscopically. It is reported that the extremely small particle size, ≈10 nm, causes an increase of the nonradiative transition probability and an enhancement of the electron–phonon coupling compared with those of typical SiV centers. Because of their electronic states, SiV‐NDs also exhibit a short luminescence lifetime (≈0.56 ns) and a large linewidth (≈14.4 nm) at room temperature. Nevertheless, the fundamental properties of the SiV center, such as the photostability, do not change, irrespective of the particle size.

Optical properties of color centers in nanodiamonds fabricated by detonation process

“…Daicel fabricated the DNDs containing SiV − and GeV − centers used in this study according to the procedure described in the references [4,5]. These two types of DNDs were air-oxidized at 570 ºC [6]. The samples for optical measurements were prepared by dropping 100 μL of 10 wt% aqueous suspensions of each DND onto a glass substrate and drying it (drop-cast sample).…”

“…Therefore, SiV − and GeV − centers-containing NDs (SiV-and GeV-NDs, respectively) have been expected to be outstanding fluorescent markers for bioimaging and biosensing. In 2021 and 2022, our group succeeded in the straightforward synthesis of ~10 nm-sized SiV-and GeV-NDs using a detonation process that produces nanodiamonds (NDs) through the detonation of explosives such as a mixture of 2,4,6-trinitrotoluene and 1,3,5-trinitro-1,3,5-triazacyclohexane [4,5,6]. This achievement could lead to practical applications in the biomedical field, as the simplicity of the process allows for mass production.…”

Optical properties of negatively charged germanium-vacancy centers in detonation nanodiamonds with an average single-digit nanometer particle size

“…To evaluate the photostability of the GeV − centers in the DNDs, a 1 wt% GeV-DNDs-water colloidal solution sealed in a glass capillary was employed, following the methodology reported by Reineck et al 39) Our previous report on the photostability evaluation of SiV − centers in DNDs describes the process for preparing the colloidal solution. 37) The PL intensity of the colloidal sample was monitored over time using a similar optical system shown in Fig. 1, except that the excitation source was substituted with a continuouswave (CW) laser of 2.33 eV (LCX-532S, Oxxius).…”

“…Such broadening has also been observed in SiV-DNDs synthesized directly by the detonation process. 37) The wider homogeneous broadening could originate from an enhancement of electron-phonon coupling in the internal GeV − centers in DNDs due to the extremely small DND particle size effect. The inhomogeneous broadening most likely originates from the detonation process.…”

“…35,36) According to optical property evaluation of the SiV − centers in DNDs, the linewidth was slightly broader (32 meV), the DWF was smaller (0.47), and the luminescence lifetime was shorter (0.56 ns) than those of typical SiV − centers in bulk-sized diamonds. 37) The reason for these changes was explained by the average 10 nm particle size of the DNDs. The extremely small particle size distorted the SiV − structure and enhanced its electron-phonon interactions.…”