How far into the infrared can a colour centre in diamond emit?

AbstractInfrared emission has been observed for the nitrogen-vacancy (NV −) colour centre in diamond, in addition to the characteristic red emission of this centre [1]. However, this infrared emission zero-phonon line at 1046 nm is about four orders of magnitude weaker than the red emission. This is somewhat surprising, as a third of the population is known to decay without the red emission and the infrared emission is considered to be associated with the alternative decay path. The most obvious explanation is a competing effcient non-radiative decay.There are few reports of diamond emitting at wavelengths longer than 1000 nm. Colour centres in diamond have strong electron-phonon coupling and, of course, the phonon energies in diamond are high. These properties suggest that non-radiative decay could dominate the transition whenever the electronic energy lies in the infrared. This would be a general phenomena and would account for the weak IR emission observed for this centre. It would also account for why there are so few reports of emission from diamond in the infrared

Time-averaging within the excited state of the nitrogen-vacancy centre in diamond

The emission intensity of diamond samples containing negatively charged nitrogen-vacancy centres are measured as a function of magnetic field along the 111 direction for various temperatures. At low temperatures the responses are sample and stress dependent and can be modelled in terms of the previous understanding of the 3E excited state fine structure which is strain dependent. At room temperature the responses are largely sample and stress independent, and modelling involves invoking a strain independent excited state with a single zero field spin-level splitting of 1.42 GHz. The change in behaviour is attributed to a temperature dependent averaging process over the components of the excited state orbital doublet. It decouples orbit and spin and at high temperature the spin levels become independent of any orbit splitting. One significant implication of this averaging is that it simplifies the development of room temperature applications

Singlet levels of the NV−^{-} centre in diamond

The characteristic transition of the NV- centre at 637 nm is between ${}^3\mathrm{A}_2$ and ${}^3\mathrm{E}$ triplet states. There are also intermediate ${}^1\mathrm{A}_1$ and ${}^1\mathrm{E}$ singlet states, and the infrared transition at 1042 nm between these singlets is studied here using uniaxial stress. The stress shift and splitting parameters are determined, and the physical interaction giving rise to the parameters is considered within the accepted electronic model of the centre. It is established that this interaction for the infrared transition is due to a modification of electron-electron Coulomb repulsion interaction. This is in contrast to the visible 637 nm transition where shifts and splittings arise from modification to the one-electron Coulomb interaction. It is also established that a dynamic Jahn-Teller interaction is associated with the singlet ${}^1\mathrm{E}$ state, which gives rise to a vibronic level 115 $\mathrm{cm}^{-1}$ above the ${}^1\mathrm{E}$ electronic state. Arguments associated with this level are used to provide experimental confirmation that the ${}^1\mathrm{A}_1$ is the upper singlet level and ${}^1\mathrm{E}$ is the lower singlet level.Comment: 19 pages, 6 figure

Observation of the dynamic Jahn-Teller effect in the excited states of nitrogen-vacancy centers in diamond

The optical transition linewidth and emission polarization of single nitrogen-vacancy (NV) centers are measured from 5 K to room temperature. Inter-excited state population relaxation is shown to broaden the zero-phonon line and both the relaxation and linewidth are found to follow a T^5 dependence for T up to 100 K. This dependence indicates that the dynamic Jahn-Teller effect is the dominant dephasing mechanism for the NV optical transitions at low temperatures

Driving Course Engagement Through Multimodal Strategic Technologies

This paper describes the development of a new second-year level undergraduate Physics course at the University of Newcastle, comprising three four-week modules (encompassing Special Relativity, Nuclear and Particle Physics) for a combined roster of both Newcastle and James Cook students. A series of multimodal digital learning technology platforms were employed to see if they could maximise student engagement. Specifically, a flipped classroom system was trialled whereby students were tasked with creating their own lecture notes from online videos (created using Lightboard and PowerPoint). This approach resulted in 90% of the class actively engaging with the lecture content. Weekly online tutorial workshops consistently achieved an attendance rate of approximately 85% and included an online quiz based on embedded questions within the lecture videos. In addition, innovative STEM laboratory workshops exploited active engagement strategies including purely online worksheets to blended and remote experiments. The inclusion of a Slack-based project management hub enabled students to work seamlessly under constantly changing COVID-19 restrictions while exposing them to planning, management and Python control coding, under the visage of “embracing technology and best practice to deliver the greatest possible student experience”. A review of students’ view of the Lightboard and PowerPoint lecture content was conducted with Lightboard being the student’s outright preference

UTILISING TECHNOLOGIES FOR POST-COVID MULTIMODAL COURSE ENGAGEMENT: AN INITIAL STUDY

In 2020, new undergraduate courses were developed, each with three 4-week modules. In particular, Modern Physics II was developed for a combined roster consisting of both Newcastle and James Cook University students and comprising Special Relativity, Nuclear and Particle Physics modules. To enable maximum engagement, a flipped classroom regime with no lecture notes, blended and remote laboratories and the inclusion of the SLACK project management hub was employed. Students were tasked with creating their own digital lecture notes from online videos resulting in 100% active engagement with the lecture content. All lecturettes contained embedded questions and a comparison of lightboard and PowerPoint was conducted. Weekly, online tutorial workshops using Zoom culminated with over 85% attendance rate consistently throughout the course. A weekly blackboard quiz was performed at a random time during these workshops and based on the embedded lecturette questions. New innovative STEM laboratory workshops were constructed in a variety of active engagement, from purely online worksheets, blended and remote experiments which were developed to work seamlessly under the changing COVID-19 restrictions. Students were exposed to planning, management and python control coding under the visage of “embracing technology and best practice to deliver the greatest possible student experience”

Nanodiamonds carrying quantum emitters with almost lifetime-limited linewidths

Nanodiamonds (NDs) hosting optically active defects are an important technical material for applications in quantum sensing, biological imaging, and quantum optics. The negatively charged silicon vacancy (SiV) defect is known to fluoresce in molecular sized NDs (1 to 6 nm) and its spectral properties depend on the quality of the surrounding host lattice. This defect is therefore a good probe to investigate the material properties of small NDs. Here we report unprecedented narrow optical transitions for SiV colour centers hosted in nanodiamonds produced using a novel high-pressure high-temperature (HPHT) technique. The SiV zero-phonon lines were measured to have an inhomogeneous distribution of 1.05 nm at 5 K across a sample of numerous NDs. Individual spectral lines as narrow as 354 MHz were measured for SiV centres in nanodiamonds smaller than 200 nm, which is four times narrower than the best SiV line previously reported for nanodiamonds. Correcting for apparent spectral diffusion yielded a homogeneous linewith of about 200 MHz, which is close to the width limit imposed by the radiative lifetime. These results demonstrate that the direct HPHT synthesis technique is capable of producing nanodiamonds with high crystal lattice quality, which are therefore a valuable technical material