Narrow Zero-phonon Lines Research Articles

Computational search for efficient single-photon emitters among the substitutional doping defects in two-dimensional GaSe

Single photon emitters (SPE) in the near-infrared (NIR) spectrum range are critical elements in quantum communication technology. We apply here computational methods to reveal local defects in the GaSe monolayer with properties favorable for such SPEs. Based on an educated guess, we selected twelve defects YX in GaSe, where the Y dopant substitutes the X host atom, X = Ga or Se, and Y = C, Si, Ge, N, P, or As. Our calculations show that two defects, NGa, and PGa, are dynamically unstable. For the remaining defects, we apply the linear response GW method and Bethe-Salpeter equation (BSE) to calculate the electronic structure and optical excitation spectra. Some defects are found to have two sharp peaks (occupied and unoccupied) of the density of the electronic states within the band gap. The NSe-, PSe-, and AsSe-defects have intense sharp an optical excitation peak at energies around 0.8 eV (λ = 1550 nm). Analysis of the formation of the BSE eigenstates associated with these peaks suggests that these excitations can cause a narrow zero-phonon line emission. We thus propose the NSe-, PSe-, and AsSe-defects in the GaSe monolayer as promising SPE in NIR region.

Theory of Photoluminescence Spectral Line Shapes of Semiconductor Nanocrystals.

Single-molecule photoluminescence (PL) spectroscopy of semiconductor nanocrystals (NCs) reveals the nature of exciton-phonon interactions in NCs. Understanding the homogeneous spectral line shapes and their temperature dependence remains an open problem. Here, we develop an atomistic model to describe the PL spectrum of NCs, accounting for excitonic effects, phonon dispersion relations, and exciton-phonon couplings. We validate our model using single-NC measurements on CdSe/CdS NCs from T = 4 to 290 K, and we find that the slightly asymmetric main peak at low temperatures is comprised of a narrow zero-phonon line (ZPL) and acoustic phonon sidebands. Furthermore, we identify the specific phonon modes that give rise to the optical phonon sidebands. At temperatures above 200 K, the spectral line width shows a stronger dependence upon the temperature, which we demonstrate to be correlated with higher order exciton-phonon couplings. We also identify the line width dependence upon reorganization energy, NC core sizes, and shell thicknesses.

Elastic Phonon Scattering Dominates Dephasing in Weakly Confined Cesium Lead Bromide Nanocrystals at Cryogenic Temperatures.

Cesium lead halide perovskite nanocrystals (PNCs) have emerged as a potential next-generation single quantum emitter (QE) material for quantum optics and quantum information science. Optical dephasing processes at cryogenic temperatures are critical to the quality of a QE, making a mechanistic understanding of coherence losses of fundamental interest. We use photon-correlation Fourier spectroscopy (PCFS) to obtain a lower bound to the optical coherence times of single PNCs as a function of temperature. We find that 20 nm CsPbBr3 PNCs emit nearly exclusively into a narrow zero-phonon line from 4 to 13 K. Remarkably, no spectral diffusion is observed at time scales of 10 μs to 5 ms. Our results suggest that exciton dephasing in this temperature range is dominated by elastic scattering from phonon modes with characteristic frequencies of 1-3 meV, while inelastic scattering is minimal due to weak exciton-phonon coupling.

Manganese Luminescent Centers of Different Valence in Yttrium Aluminum Borate Crystals.

We present an extensive study of the luminescence characteristics of Mn impurity ions in a YAl3(BO3)4:Mn crystal, in combination with X-ray fluorescence analysis and determination of the valence state of Mn by XANES (X-ray absorption near-edge structure) spectroscopy. The valences of manganese Mn2+(d5) and Mn3+(d4) were determined by the XANES and high-resolution optical spectroscopy methods shown to be complementary. We observe the R1 and R2 luminescence and absorption lines characteristic of the 2E ↔ 4A2 transitions in d3 ions (such as Mn4+ and Cr3+) and show that they arise due to uncontrolled admixture of Cr3+ ions. A broad luminescent band in the green part of the spectrum is attributed to transitions in Mn2+. Narrow zero-phonon infrared luminescence lines near 1060 nm (9400 cm-1) and 760 nm (13,160 cm-1) are associated with spin-forbidden transitions in Mn3+: 1T2 → 3T1 (between excited triplets) and 1T2 → 5E (to the ground state). Spin-allowed 5T2 → 5E Mn3+ transitions show up as a broad band in the orange region of the spectrum. Using the data of optical spectroscopy and Tanabe-Sugano diagrams we estimated the crystal-field parameter Dq and Racah parameter B for Mn3+ in YAB:Mn as Dq = 1785 cm-1 and B = 800 cm-1. Our work can serve as a basis for further study of YAB:Mn for the purposes of luminescent thermometry, as well as other applications.

Tin disulfide with bright near-IR luminescence centers obtained at high pressures

In this work, the high-pressure and high-temperature (HPHT) method was applied to obtain crystalline tin disulfide (${\mathrm{SnS}}_{2}$). The synthesis was performed in a sulfur-tin-carbon growth system by placing the reaction mixture of sulfur and tin in a graphite capsule. The synthesized ${\mathrm{SnS}}_{2}$ demonstrated to be a highly crystalline $2H$-polytypic form suitable for mechanical exfoliation of atomically thin films. The crystals reveal strong near-IR photoluminescence attributed to a new luminescence center in ${\mathrm{SnS}}_{2}$. At 5 K, this center is characterized by a narrow zero-phonon line at 885 nm and phonon sideband whose structure is governed by ${\mathrm{SnS}}_{2}$ phonon density of states. Based on $\mathit{ab}$ initio calculations, the center is attributed to carbon in the tin sublattice. The side product of the HPHT synthesis is the diamond phase containing optically active tin-vacancy centers (${\mathrm{SnV}}^{\ensuremath{-}}$).

Effect of boron doping on luminescent properties of silicon--vacancy and germanium--vacancy color centers in diamond particles obtained by chemical vapor deposition

The effect of doping with boron on the luminescent properties of diamond particles synthesized by Hot Filament Chemical Vapor Deposition technique with color centers embedded during the growth process has been studied. It is shown that at low boron doping level, the photoluminescence intensity of a narrow zero-phonon line of the silicon-vacancy color center (738.2 nm) demonstrates a strong dependence on the concentration of boron atoms at the sites of the diamond lattice. The dependence of the intensity of a broad photoluminescence band in the wavelength range 520-800 nm on the concentration of boron atoms in the gas mixture in the range from 14 to 64000 ppm has been analyzed. The Raman scattering spectra of the obtained particles have been studied. At the concentration of boron atoms in the gas mixture up to 1540 ppm, the Raman scattering spectra of diamond particles practically do not change when the boron concentration is varied. At high boron doping level, the diamond band in the Raman spectra exhibit a spectral response typical of the Fano resonance. Keywords: diamond particles, color centers, boron doping, photoluminescence, chemical vapor deposition.

Creation of silicon vacancy color centers with a narrow emission line in nanodiamonds by ion implantation

Nanodiamonds containing silicon-vacancy (SiV) centers with high brightness, high photo-stability, and a narrow zero phonon line (ZPL) have attracted attention for bioimaging, nanoscale thermometry, and quantum technologies. One method to create such nanodiamonds is the milling of diamond films synthesized by chemical vapor deposition (CVD). However, this requires post-processing such as acid treatment and centrifugation after the milling process. Therefore, the number of SiV center-containing nanodiamonds made from an initial CVD diamond is small. An alternative method without these problems is the implantation of Si ions into preselected nanodiamonds. This method, however, has an issue regarding the ZPL linewidths, which are more than twice as broad as those in nanodiamonds synthesized by CVD. In order to reduce the linewidth, we employed annealing treatment at high temperatures (up to 1100°C) and high vacuum after the implantation. For an ion fluence of 1013 ions/cm2, a ZPL with a linewidth of about 7 nm at room temperature was observed for a nanodiamond with a median size of 29.9 ± 16.0 nm. This was close to the linewidth for nanodiamonds created by CVD.

Spectral broadening and ultrafast dynamics of a nitrogen-vacancy center ensemble in diamond

Many applications of nitrogen-vacancy (NV) centers in diamond crucially rely on a spectrally narrow and stable optical zero-phonon line transition. Though many impressive proof-of-principle experiments have been demonstrated, much work remains in engineering NV centers with spectral properties that are sufficiently robust for practical implementation. To elucidate the mechanisms underlying their interactions with the environment, we apply multi-dimensional coherent spectroscopy to an NV center ensemble in bulk diamond at cryogenic temperatures. Our spectra reveal thermal dephasing due to quasi-localized vibrational modes as well as ultrafast spectral diffusion on the picosecond timescale. The intrinsic, ensemble-averaged homogeneous linewidth is found to be in the tens of GHz range by extrapolating to zero temperature. We also observe a temperature-dependent Stark splitting of the excited state manifold, relevant to NV sensing protocols.

Sources of Double-Wave Narrow-Band Emission Based on Diamond Nanoparticles with Simultaneously Introduced Germanium–Vacancy and Silicon–Vacancy Color Centers

The method of hot-filament chemical vapor deposition has been employed to synthesize diamond particles with germanium–vacancy and silicon–vacancy color centers. In the next stage, the reactive ion-plasma etching of the particles was performed. This, yielded diamond nanoparticles with photoluminescence spectra constituted by two narrow high-intensity zero-phonon lines of the centers introduced. These fluorescent diamond nanoparticles are promising for application as sources of double-wave narrow-band emission in luminescent nanothermometry.

Engineering telecom single-photon emitters in silicon for scalable quantum photonics.

We create and isolate single-photon emitters with a high brightness approaching 105 counts per second in commercial silicon-on-insulator (SOI) wafers. The emission occurs in the infrared spectral range with a spectrally narrow zero phonon line in the telecom O-band and shows a high photostability even after days of continuous operation. The origin of the emitters is attributed to one of the carbon-related color centers in silicon, the so-called G center, allowing purification with the 12C and 28Si isotopes. Furthermore, we envision a concept of a highly-coherent scalable quantum photonic platform, where single-photon sources, waveguides and detectors are integrated on an SOI chip. Our results provide a route towards the implementation of quantum processors, repeaters and sensors compatible with the present-day silicon technology.

Chemical stabilization of Eu2+ in LuPO4 and YPO4 hosts and its peculiar sharp line luminescence

The efficient 4f65d→4f7 (d-f) luminescence from Eu2+ is well-known for host lattices where Eu2+ is substituted on a divalent (e.g. Ca2+, Sr2+) or monovalent (e.g. Na+, K+) cation site. Only recently some studies appeared concerning d-f emission from Eu2+ on a trivalent cation site. The stable Eu2+ emission was observed in X-ray irradiated LuPO4:Eu3+ crystals where Eu2+ is produced through trapping of conduction band electrons generated by X-ray absorption. Here, we demonstrated that Eu2+ can also be chemically stabilized in YPO4 and LuPO4 through co-doping with a tetravalent charge compensator: Hf4+. In orthophosphate crystals doubly doped with Eu and Hf, the characteristic Eu2+ emission is observed at low temperatures without the need for X-ray irradiation. The excitation and emission spectra show strong and narrow zero-phonon lines and a rich vibronic structure. In the excitation spectra a multitude of zero-phonon transitions to individual crystal field components of 7FJ multiplets in the 4f6(7FJ)5d excited state was observed for Eu2+ in both LuPO4 and YPO4. Analysis of the spectra is consistent with a slightly larger crystal field splitting for Eu2+ on the smaller Lu3+ site (compared to Y3+). The observation of many 4f6(7FJ)5d electronic origins make these systems to be model compounds for testing the validity of theoretical models for energy level calculations of 4f65d states of Eu2+.

Источники двухволнового узкополосного излучения на основе алмазных наночастиц с введенными одновременно центрами окраски германий-вакансия и кремний-вакансия

Diamond particles with germanium-vacancy and silicon-vacancy color centers were synthesized by Hot Filament Chemical Vapor Deposition technique. The next step was the reactive ion-plasma etching of the particles. As a result, the diamond nanoparticles were obtained whose photoluminescence spectra consist of two narrow intense zero phonon lines of the embedded centers. Such fluorescent diamond nanoparticles are promising as dual-wavelength narrow-band light emitters for luminescent nanothermometry.

Energy Transfer from Perovskite Nanocrystals to Dye Molecules Does Not Occur by FRET.

Single formamidinium lead bromide (FAPbBr3) perovskite nanocubes, approximately 10 nm in size, have extinction cross sections orders of magnitude larger than single dye molecules and can therefore be used to photoexcite one single dye molecule within their immediate vicinity by means of excitation-energy transfer (EET). The rate of photon emission by the single dye molecule is increased by 2 orders of magnitude under excitation by EET compared to direct excitation at the same laser fluence. Because the dye cannot accommodate biexcitons, NC biexcitons are filtered out by EET, giving rise to up to an order-of-magnitude improvement in the fidelity of photon antibunching. We demonstrate here that, contrary to expectation, energy transfer from the nanocrystal to dye molecules does not depend on the spectral line widths of the donor and acceptor and is therefore not governed by Förster's theory of resonance energy transfer (FRET). Two different cyanine dye acceptors with substantially different spectral overlaps with the nanocrystal donor show a similar light-harvesting capability. Cooling the sample from room temperature to 5 K reduces the average transition line widths 25-fold but has no apparent effect on the number of molecules emitting, i.e., on the spatial density of single dye molecules being photoexcited by single nanocrystals. Narrow zero-phonon lines are identified for both donor and acceptor, with an energetic separation of over 40 times the line width, implying a complete absence of spectral overlap-even though EET is evident. Both donor and acceptor exhibit spectral fluctuations, but no correlation is apparent between the jitter, which controls spectral overlap, and the overall light harvesting. We conclude that the energy transfer process is fundamentally nonresonant, implying effective energy dissipation in the perovskite donor because of strong electron-phonon coupling of the carriers comprising the exciton. The work highlights the importance of performing cryogenic spectroscopy to reveal the underlying mechanisms of energy transfer in complex donor-acceptor systems.

High-pressure synthesis and characterization of Sn-doped single crystal diamond

Development of new routes for fabrication of diamond containing color centers with specific optical and magnetic properties is important for its employment in many innovative applications such as the emerging quantum technologies. Here we report a systematic study on the high-pressure synthesis of diamond from various tin-containing systems aimed at establishing growth conditions favorable for the incorporation of Sn atoms in crystallized diamonds with the formation of the tin-vacancy (SnV) color centers. Synthesis experiments are performed at 6.3–7.5 GPa and 1400–1900 °C using solvent-catalysts of three different types: FeSnAl, Sn-(Ti, Al, Zr) and SnMg. We established the main features of diamond crystallization from these catalysts and determined photoluminescence characteristics of the synthesized diamonds. It is found that over the range of the P-T conditions and catalyst compositions employed in the study, the SnMgC system is a most effective medium for growing Sn-doped single crystal diamond. We show that with the approach developed in the study it is possible to fabricate diamond single crystals with sizes from ∼50 μm to ∼1 mm containing high-quality SnV color centers with narrow zero-phonon lines.

Observation of Fourier transform limited lines in hexagonal boron nitride

Single defect centers in layered hexagonal boron nitride (hBN) are promising candidates as single photon sources for quantum optics and nanophotonics applications. However, until today spectral instability hinders many applications. Here, we perform resonant excitation measurements and observe Fourier-Transform limited (FL) linewidths down to $\approx 50$ MHz. We investigate optical properties of more than 600 quantum emitters (QE) in hBN. The QEs exhibit narrow zero-phonon lines (ZPL) distributed over a spectral range from 580 nm to 800 nm and with dipole-like emission with high polarization contrast. The emission frequencies can be divided into four main regions indicating distinct families or crystallographic structures of the QEs, in accord with ab-initio calculations. Finally, the emitters withstand transfer to a foreign photonic platform - namely a silver mirror, which makes them compatible with photonic devices such as optical resonators and paves the way to quantum photonics applications including quantum commmunications and quantum repeaters.

Wide-Range Spectral Diffusion in Single Mg-Tetraazaporphyrin Molecules in a Polymer Matrix at Cryogenic Temperatures

Zero-phonon spectral lines of single Mg-tetraazaporphyrin molecules in a polymer matrix and their spectral trails are recorded using cryogenic fluorescence nanoscopy at a temperature of 6 K. Spectral diffusion (stochastic jumps of zero-phonon lines) in an anomalously wide spectral range up to several tens of inverse centimeters is revealed. The structure of the vibronic band in the fluorescence excitation spectrum of single molecules, including both a narrow zero-phonon line and a broad phonon sideband, is directly observed.

Looking back on 28 years of cryogenic single-molecule experiments

Starting with the first single-molecule fluorescence experiments in 1990, the field of cryogenic single-molecule spectroscopy exploits the narrow zero-phonon lines of single molecules, usually in molecular crystals and glasses. Occasionally, similar experiments can also be done at room temperature, as illustrated by the case of the NV- center in diamond. In this review contribution, I shall illustrate the variety and scope of the experiments performed in the past 28 years, highlighting some important points and outlooks.

Coherence Properties and Quantum Control of Silicon Vacancy Color Centers in Diamond

Atomic‐scale impurity spins, also called color centers, in an otherwise spin‐free diamond host lattice have proven to be versatile tools for applications in solid‐state‐based quantum technologies ranging from quantum information processing (QIP) to quantum‐enhanced sensing and metrology. Due to its wide band gap, diamond can host hundreds of different color centers. However, their suitability for QIP or sensing applications has only been tested for a handful of these, with the nitrogen vacancy (NV) strongly dominating this field of research. Due to its limited optical properties, the success of the NV for QIP applications however strongly depends on the development of efficient photonic interfaces. In the past years the negatively charged silicon vacancy (SiV−) center received significant attention due to its highly favourable spectral properties such as narrow zero phonon line transitions and weak phonon sidebands. Here, the recent work investigating the SiV center's orbital and electron spin coherence properties is reviewed as well as techniques to coherently control its quantum state using microwave as well as optical fields. Also, potential future experimental directions to improve the SiV's coherence time scale and to develop it into a valuable tool for QIP applications are outlined.

Bright optical centre in diamond with narrow, highly polarised and nearly phonon-free fluorescence at room temperature

Using shallow implantation of ions and molecules with masses centred at 27 atomic mass units (amu) in diamond, a new artificial optical centre with unique properties has been created. The centre shows a linearly polarised fluorescence with a main narrow emission line mostly found at 582 nm, together with a weak vibronic sideband at room temperature. The fluorescence lifetime is ∼2 ns and the brightest centres are more than three times brighter than the nitrogen-vacancy centres. A majority of the centres shows stable fluorescence whereas some others present a blinking behaviour, at faster or slower rates. Furthermore, a second kind of optical centre has been simultaneously created in the same diamond sample, within the same ion implantation run. This centre has a narrow zero-phonon line (ZPL) at ∼546 nm and a broad phonon sideband at room temperature. Interestingly, optically detected magnetic resonance (ODMR) has been measured on several single 546 nm centres and two resonance peaks are found at 0.99 and 1.27 GHz. In view of their very similar ODMR and optical spectra, the 546 nm centre is likely to coincide with the ST1 centre, reported once (with a ZPL at 550 nm), but of still unknown nature. These new kinds of centres are promising for quantum information processing, sub-diffraction optical imaging or use as single-photon sources.

Bright and photostable single-photon emitter in silicon carbide

Single-photon sources are of paramount importance in quantum communication, quantum computation, and quantum metrology. In particular, there is great interest in realizing scalable solid-state platforms that can emit triggered photons on demand to achieve scalable nanophotonic networks. We report on a visible-spectrum single-photon emitter in 4H silicon carbide (SiC). The emitter is photostable at room and low temperatures, enabling photon counts per second in excess of 2$\times$10$^6$ from unpatterned bulk SiC. It exists in two orthogonally polarized states, which have parallel absorption and emission dipole orientations. Low-temperature measurements reveal a narrow zero phonon line (linewidth $<0.1~$nm) that accounts for $>30$% of the total photoluminescence spectrum.