Phonon Sidebands Research Articles

Novel reddish-orange emitting BaBPO5:Eu3+ phosphor for n-UV warm white-LEDs: Synthesis and study of structural and spectroscopic investigations

A novel reddish-orange emitting 2Ba2-xO-B2O3-P2O5:xEu3+ (x= 0.04, 0.06, 0.08, 0.10, 0.12 and 0.14 mol%) phosphor with different concentrations of Eu3+ ions were synthesized through high temperature solid-state reaction technique. The crystal structure has been studied by X-ray diffraction technique for all the concentrations of Eu3+ ions. The morphology and elemental analysis of the optimal ∼0.1 mol% concentration was examined by the SEM-EDS images. The functional groups were analysed by the FTIR characterization technique. The thermal properties were studied by the TGA-DSC analysis. The energy band gap of all the samples were analysed by using UV–VIS DRS technique. The photoluminescence properties of BaBPO5:Eu3+ phosphor with different concentrations of Eu3+ ions were investigated at λem = 611 nm and λex = 394 nm. Variation in emission intensity with Eu3+ ion concentrations, phonon side bands, multi-phonon relaxation rate and energy transfer mechanisms were studied. The BaBPO5:Eu3+ phosphors exhibit characteristic emission peaks corresponding to 5D0 → 7FJ (J = 0, 1, 2, 3, 4) transitions of Eu3+ ions under n-UV excitation. Among all the transitions, 5D0 → 7F1 (593 nm) transition shows higher intensity and asymmetric ratio (R21) for all concentrations of Eu3+ ions were calculated. The lifetimes of 5D0 level of Eu3+ ions in BaBPO5: Eu3+ phosphor were calculated by using fluorescent decay curve analysis. The CIE color coordinates reveal, reddish-orange emission in the low CCT range. These findings imply that BaBPO5: 0.1Eu3+ phosphor is a promising candidate for solid-state lighting applications as well as phosphor-converted warm w-LEDs.

Photoluminescence Spectra of Helium Ion-Implanted Diamond

Ion implantation in diamond crystals is widely used both for producing conducting microstructures in the bulk of the material and for creating isolated photon emitters in quantum optics, photonics, cryptography, and biosensorics. The photoluminescence (PL) spectra of helium ion-implanted diamonds are dominated by two sharp emission lines, HR1 and HR2 (from Helium-Related), at ~536 and 560 nm. Here, we report on PL studies of helium-related optical centers in diamonds. Experiments have been carried out on a (110) plate of natural single-crystal type IIa diamonds. The uniform distribution of radiation defects in a 700 nm-thick layer was obtained by ten cycles of multiple-energy (from 24 to 350 kV) helium ion implantation with a total dose of 5 × 1016 cm−2. The diamonds were annealed in steps in a vacuum oven at temperatures from 200 to 1040 °C. It is demonstrated that helium ion implantation in diamonds followed by annealing gives rise to more than a dozen various centers that are observed in the PL spectra in the range of 530–630 nm. The transformations of the PL spectra due to annealing are investigated in detail. The spectral shapes of phonon sidebands are determined for the HR1, HR2, and HR3 bands with ZPLs at ~536, 560, and 577 nm, respectively, and it is shown that these bands are attributed to interstitial-related centers in diamonds. The reported results are important for understanding the structure and properties of helium-related defects in diamonds.

Circumventing the polariton bottleneck via dark excitons in 2D semiconductors

Efficient scattering into the exciton polariton ground state is a key prerequisite for generating Bose–Einstein condensates and low-threshold polariton lasing. However, this can be challenging to achieve at low densities due to the polariton bottleneck effect that impedes phonon-driven scattering into low-momentum polariton states. The rich exciton landscape of transition metal dichalcogenides (TMDs) provides potential intervalley scattering pathways via dark excitons to rapidly populate these polaritons. Here, we present a theoretical and fully microscopic study exploring the time- and momentum-resolved relaxation of exciton polaritons supported by a MoSe2 monolayer integrated within a Fabry–Perot cavity. By exploiting phonon-assisted transitions between momentum-dark excitons and the lower polariton branch, we demonstrate that it is possible to circumvent the bottleneck region and efficiently populate the polariton ground state. Furthermore, this intervalley pathway is predicted to give rise to, yet unobserved, angle-resolved phonon sidebands in low-temperature photoluminescence spectra that are associated with momentum-dark excitons. This represents a distinct signature for efficient phonon-mediated polariton-dark-exciton interactions.

Ultracoherent Gigahertz Diamond Spin-Mechanical Lamb Wave Resonators.

We report the development of an all-optical approach that excites the fundamental compression mode in a diamond Lamb wave resonator with an optical gradient force and detects the induced vibrations via strain coupling to a silicon vacancy center, specifically, via phonon sidebands in the optical excitation spectrum of the silicon vacancy. Sideband optical interferometry has also been used for the detection of in-plane mechanical vibrations, for which conventional optical interferometry is not effective. These experiments demonstrate a gigahertz fundamental compression mode with a Q factor of >107 at temperatures near 7 K, providing a promising platform for reaching the quantum regime of spin mechanics, especially phononic cavity quantum electrodynamics of electron spins.

Design principles for >90% efficiency and >99% indistinguishability broadband quantum dot cavities

Abstract Quantum dots have the potential to be one of the brightest deterministic single photon sources with high end applications in quantum computing and cluster state generation. In this work, we re-examine the design of simple micropillars by meticulously examining the structural effects of the decay into leaky channels beyond an atom-like cavity estimation. We show that precise control of the side losses with the diameter and avoidance of propagating Bloch modes in the distributed Bragg reflectors can result in easy-to-manufacture broadband (Q≈ 750 − 2500) micropillars, allowing for broad optical coherent control pulses necessary for high single photon purity (> 99.2 − 99.99% achievable) while simultaneously demonstrating extremely high efficiency out the top (90.5% − 96.4%). We also demonstrate that such cavities naturally decouple from the phonon sideband, with the phonon sideband reducing by a factor of 5 − 33 allowing us to predict that the photons should show 98.5% − 99.8% indistinguishability without the need for filtering.

Near-pure red emission of highly thermally stable Eu3+ doped multi-component transparent oxyfluoride aluminosilicate glass-ceramic for red lasers and trichromatic WLEDs

In this paper, Eu3+ doped multi-component transparent aluminosilicate and oxyfluoride aluminosilicate glasses were fabricated by the melt-quenching procedure, and the glass-ceramics containing LiAlSi2O6 microcrystals (LAS glass-ceramics) were produced by a two-step heat treatment process. The XRD, SEM, and EDS data demonstrate that spherical single-phase LiAlSi2O6 microcrystals have precipitated from the glass matrices. The microhardness and flexural strength of the glass-ceramics vary in 6.27–6.66 GPa and 89.18–155.75 MPa, respectively. Phonon sideband analysis reveals that the phonon energies for both fluorine-containing and fluorine-free LAS glass-ceramics are approximately 971 cm−1, and the multiphonon relaxation rates (Wmp/W0) of the former are lower than those of the latter. Given its lower Wmp/W0 values, the fluorine-containing LAS glass-ceramic exhibits a higher emission intensity and a longer lifetime. Under 394 nm excitation, the fluorine-containing LAS glass-ceramic presents a warm and nearly pure red emission, characterized by a correlated color temperature of less than 3300 K and a color purity approaching 100 %. Time-resolved emission spectra support the photoluminescent stability of the Eu3+ ions. According to the Judd-Ofelt theory and spectral results, the fluorine-containing LAS glass-ceramic possesses lower Ω2/Ω4 and asymmetry ratios, leading to a more symmetrical local environment for the Eu3+ ions. Benefiting from its enhanced red emission, the 5D0→7F2 transition in the fluorine-containing LAS glass-ceramic exhibits a higher branching ratio (69.28 % > 50 %), emission cross-section (8.94 × 10−22 cm2), and gain bandwidth (12.12 × 10−28 cm3). Additionally, temperature-dependent photoluminescence spectra substantiate the excellent thermal stability of the Eu3+ doped fluorine-containing LAS glass-ceramic. Specifically, the intensity of the 5D0→7F2 transition at 150 °C remains 80 % of the initial intensity. Therefore, the Eu3+ doped multi-component transparent oxyfluoride aluminosilicate glass-ceramic has a significant competitive advantage in the field of red lasers and trichromatic WLEDs.

Impact of Fe-impurity centers on phonon subsystem of wurtzite-type ZnO

The paper addresses the question of the structural and vibrational properties of Fe-doped ZnO in the wurtzite structure with a lattice without an inversion center. The ZnO crystals containing Fe impurities in different charged states are studied by means of density functional theory (DFT) and potential-based methods. A first-principles simulation is performed to determine the local atomic configurations near the considered defects. The DFT results are compared with those obtained using the shell model. Both approaches give a similar pattern of lattice distortion around the Fe-impurity centers occupying cation sites in the isoelectronic charge state Fe2＋ and single-positive-charge state Fe3＋. The phonon local symmetrized densities of states projected onto the displacement of ions surrounding the defects are calculated by a well-established recursion method. The frequencies of defect vibrations of various symmetry types induced by Fe impurities are determined. The calculations made it possible to interpret the structure of the phonon sideband accompanying the zero-phonon line in polarized emission spectra attributed to the Fe3＋ intracenter transitions, as well as to estimate the role of Fe ions in the formation of observed peaks.

Large-Scale Statistical Analysis of Defect Emission in hBN: Revealing Spectral Families and Influence of Flake Morphology.

Quantum emitters in two-dimensional layered hexagonal boron nitride are quickly emerging as a highly promising platform for next-generation quantum technologies. However, the precise identification and control of defects are key parameters to achieve the next step in their development. We conducted a comprehensive study by analyzing over 10,000 photoluminescence emission lines from liquid exfoliated hBN nanoflake samples, revealing 11 narrow sets of defect families within the 1.6 to 2.2 eV energy range. This challenges hypotheses of a random energy distribution. We also reported averaged defect parameters, including emission line widths, spatial density, phonon side bands, and Franck-Condon-related factors. These findings provide valuable insights into deciphering the microscopic origin of emitters in hBN hosts. We also explored the influence of the hBN host morphology on defect family formation, demonstrating its crucial impact. By tuning the flake size and arrangement, we achieve selective control of defect types while maintaining high spatial density. This offers a scalable approach to defect emission control, diverging from costly engineering methods. It emphasizes the significance of the morphological aspects of hBN hosts for gaining insights into defect origins and expanding their spectral control.

Isolated single-photon emitters with low Huang–Rhys factor in hexagonal boron nitride at room temperature

The development of stable room-temperature bright single-photon emitters using atomic defects in hexagonal boron nitride flakes (h-BN) provides significant promise for quantum technologies. However, an outstanding challenge in h-BN is the creation and detection of isolated, stable single-photon emitters with high emission rates and with very low Huang–Rhys (HR) factor. Here, we discuss the quantum photonic properties of a single, isolated, stable quantum emitter that emits single photons with a high emission rate and a low HR value of 0.6 ± 0.2 at room temperature. A scanning confocal image confirms the presence of a deserted, single-quantum emitter with a prominent zero-phonon line at ∼578 nm with a well-separated phonon sideband at 626 nm. The second-order intensity-intensity correlation measurement shows an anti-bunching dip of ∼0.25 with an emission lifetime of 2.46 ± 0.1 ns, reinforcing distinct features of the single-photon emitter. The importance of low-energy electron beam irradiation and subsequent annealing is emphasized to achieve stable, reproducible single-photon emitters.

Mg doping induced enhancement of persistent luminescence of ZGGO: Cr3+ nanoparticles for time-gate optical encryption

Herein, ZMGGO:Cr3+ nanoparticles were prepared by incorporating Mg2+ ions into Cr3+-doped zinc gallogermenate nanoparticles through a hydrothermal path in combination with a vacuum heating. The average size of ZMGGO:Cr3+ nanoparticles minishes from 59 to 12 nm with growing Mg2+ concentration. Meanwhile their luminescence intensity at 696 nm of ZMGGO:Cr3+ nanoparticles was only decreased by less than half of that of the undoped nanoparticles due to the decreased particle size after Mg doping. Meanwhile, the integral luminescence intensity of their entire emission band shows an increasing trend with increasing temperature due to the enhanced phonon sideband luminescence at high temperature. More important, it is found that the formation energies associated with Mg′Ga-GaoZn and Zn′Ga-GaoZn defects are −1.2 and 1.69 eV, respectively, suggesting the enhanced afterglow intensity of ZMGGO:Cr3+ can be ascribed to Mg doping leading to the increased number of these anti-site traps. Finally, the dual-level time-gate optical encryption was demonstrated using phosphorescent inks containing ZMGGO:Cr3+ nanoparticles with different afterglow intensities.

Photo and X˗ray induced luminescences of Eu3+˗doped sodium alumino boro˗tellurite oxyfluoride scintillating glass for X˗ray detecting material

The spectroscopy features of sodium alumino boro˗tellurite oxyfluoride glasses doped with various molar fractions of Eu2O3 ions (TBANEu) are studied through absorbance, excitation, emission, and decay curves. The excitation data are used following phonon side band spectroscopy to evaluate the phonon energy (1326 cm-1) of the glass host. The densities, molar volumes, and refractive indices, including the Ω2,4,6 parameters of fabricated glasses are studied. The magnitudes of laser properties like effective line widths, branching ratios, and emission cross˗sections obtained for the Eu3+:5D0→7F2 transition could be useful for reddish-orange lighting devices application. Additionally the quantum efficiency estimated from experimental and calculated lifetimes is about ˃ 70% for the 5D0 level luminescence of TBANEu glasses. Upon 395 nm radiation, the current glass system can exhibit color coordinates close to (0.647, 0.351) for reddish˗orange light as performed by the CIE1931 chromaticity diagram. The integral scintillation intensities of TBANEu glasses were determined using the X˗ray excitation and observed that the TBANEu20 glass showed a highest scintillation efficiency of 39%, resulting in scintillator and X˗ray sensing device applications.

Theory of phonon sidebands in the absorption spectra of moiré exciton–polaritons

Excitons in twisted bilayers of transition metal dichalcogenides have strongly modified dispersion relations due to the formation of periodic moiré potentials. The strong coupling to a light field in an optical cavity leads to the appearance of moiré polaritons. In this paper, we derive a theoretical model for the linear absorption spectrum of the coupled moiré polariton–phonon system based on the time-convolutionless (TCL) approach. Results obtained by numerically solving the TCL equation are compared to those obtained in the Markovian limit and from a perturbative treatment of non-Markovian corrections. A key quantity for the interpretation of the findings is the generalized phonon spectral density. We discuss the phonon impact on the spectrum for realistic moiré exciton dispersions by varying twist angle and temperature. Key features introduced by the coupling to phonons are broadenings and energy shifts of the upper and lower polariton peak and the appearance of phonon sidebands between them. We analyze these features with respect to the role of Markovian and non-Markovian effects and find that they strongly depend on the twist angle. We can distinguish between the regimes of large, small, and intermediate twist angles. In the latter phonon effects are particularly pronounced due to dominating phonon transitions into regions which are characterized by van Hove singularities in the density of states.

Engineering the Impact of Phonon Dephasing on the Coherence of a WSe_{2} Single-Photon Source via Cavity Quantum Electrodynamics.

Emitter dephasing is one of the key issues in the performance of solid-state single-photon sources. Among the various sources of dephasing, acoustic phonons play a central role in adding decoherence to the single-photon emission. Here, we demonstrate that it is possible to tune and engineer the coherence of photons emitted from a single WSe_{2} monolayer quantum dot via selectively coupling it to a spectral cavity resonance. We utilize an open cavity to demonstrate spectral enhancement, leveling, and suppression of the highly asymmetric phonon sideband, finding excellent agreement with a microscopic description of the exciton-phonon dephasing in a truly two-dimensional system. Moreover, the impact of cavity tuning on the dephasing is directly assessed via optical interferometry, which points out the capability to utilize light-matter coupling to steer and design dephasing and coherence of quantum emitters in atomically thin crystals.

Synthesis of eco-friendly borosilicate glass with Eu3+ dopants: Harnessing recovered silica gel waste for reddish-orange emission materials

In this study, recovered silica gel waste (RSGW) is used as a key raw material to create borosilicate glass doped with Eu3+ ions in a new and environmentally friendly way. The glass compositions were fabricated using the melt quenching method, with different amounts of RSGW and a constant 1.0 mol% Eu3+ doping concentration. The study shows that increasing the doping concentration of RSGW improves the glass density and rigidity while reducing the molar volume, indicating enhanced glass stability. Photoluminescence and X-ray luminescence analyses confirm that the optimal composition with 50 mol% RSGW exhibits the strongest emission. Based on the phonon sideband analysis, the host glasses have a phonon energy of 966.53 cm− 1. An X-ray absorption near-edge structure (XANES) analysis showed that most of the europium ions were in the 3+ oxidation state. The CIE 1931 chromaticity investigation shows the x,y color coordinates at (0.645, 0.351) in the reddish-orange region. To optimize the doping concentration of Eu2O3, it was determined that a fixed concentration of 50 mol% RSGW created the most suitable mixture. Both luminescence emission spectra exhibit strong luminescence, with a peak emission wavelength of 615 nm (⁵D0→⁷F2), confirming concentration quenching in both photoluminescence and x-ray luminescence at a concentration of 1.0 mol%. The study explores potential applications of this novel material in photonics and suggests that this eco-friendly synthesis approach holds great promise for sustainable and efficient production of reddish-orange emission materials.

Judd‐Ofelt analysis and optical properties of Eu3+‐doped GdPO4 phosphors synthesized by combustion method

AbstractThe Eu3+‐doped GdPO4 nanoparticles were prepared via a straightforward combustion method using urea as fuel and nitrates as a precursor. X‐ray powder diffraction patterns, infrared spectrum (IR), HR‐TEM, photoluminescence (PL), phonon sideband and photoluminescence excitation (PLE) were researched. There is a phase transition from the hexagonal phase into the monoclinic phase when the calcined temperature is over 700 °C. All of phosphors have similar morphology and the average diameters for nanoparticles are 20–30 nm. Under the excitation at 273 nm, GdPO4:Eu3+ powders showed red emission bands originating from the 5D0–7FJ (J = 1, 2, 3 and 4) transitions of Eu3+. The orange‐red emission (5D0–7F1 transition) is dominated because the Eu3+ ions exist with inversion symmetry in the lattice. The study suggests that the optimal Eu3+ ions concentration is 5 mol%. In addition, the second order crystal field parameter (B20) and the influence of concentration of Eu3+ ions on decay time are also mentioned, the intensity parameters (Ω2,4,6) and quantum efficiency were determined based on Judd‐Ofelt theory.

Experimental Generation of Spin-Photon Entanglement in Silicon Carbide.

A solid-state approach for quantum networks is advantageous, as it allows the integration of nanophotonics to enhance the photon emission and the utilization of weakly coupled nuclear spins for long-lived storage. Silicon carbide, specifically point defects within it, shows great promise in this regard due to the easy of availability and well-established nanofabrication techniques. Despite of remarkable progresses made, achieving spin-photon entanglement remains a crucial aspect to be realized. In this Letter, we experimentally generate entanglement between a silicon vacancy defect in silicon carbide and a scattered single photon in the zero-phonon line. The spin state is measured by detecting photons scattered in the phonon sideband. The photonic qubit is encoded in the time-bin degree of freedom and measured using an unbalanced Mach-Zehnder interferometer. Photonic correlations not only reveal the quality of the entanglement but also verify the deterministic nature of the entanglement creation process. By harnessing two pairs of such spin-photon entanglement, it becomes straightforward to entangle remote quantum nodes at long distance.

Quantum dot coupled to a suspended-beam mechanical resonator: From the unresolved- to the resolved-sideband regime

We present experiments in which self-assembled InAs quantum dots are coupled to a thin, suspended-beam GaAs resonator. The quantum dots are driven resonantly and the resonance fluorescence is detected. The narrow quantum dot linewidths, just a factor of 3 larger than the transform limit, result in a high sensitivity to the mechanical motion. We show that one quantum dot couples to eight mechanical modes spanning a frequency range from 30 to 600 MHz: one quantum dot provides an extensive characterization of the mechanical resonator. The coupling spans the unresolved-sideband to the resolved-sideband regimes. Finally, we present the first detection of thermally driven phonon sidebands (at 4.2 K) in the resonance-fluoresence spectrum. Published by the American Physical Society 2024

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

Nanodiamonds that contain germanium-vacancy centers (GeV-NDs) exhibit significant potential for biomedical and quantum science applications. GeV-NDs with an average particle size of 9 nm were recently fabricated through a detonation process that enables the practical-scale production of detonation NDs (DNDs). However, the optical properties of the GeV centers in the DNDs have not been studied thoroughly. In particular, the luminescence spectrum of these GeV-DNDs had an unassigned peak at 1.98 eV. Here, we investigate the optical properties of GeV-DNDs under various conditions. Although the GeV-DNDs exhibit a zero-phonon line (ZPL) with similar excitation energy dependence and photostability to their bulk counterparts, the ZPL linewidth is broader. The 1.98 eV-peak is attributed to a composite phonon sideband peak. The unique properties of the GeV centers in these small DNDs are explained by enhanced electron–phonon coupling.

Empirical asymmetric phonon sideband due to phonons in the protein matrix present in photosynthetic complexes: Time-domain response theory

The phonon spectral density plays a key role in probing the dynamical and spectral behavior of molecular aggregates. One may utilize the intimate connection between the one-phonon profile and the phonon spectral density to extract a plausible form of the spectral density of media with rich structure using advanced optical spectroscopy. The excitonic transition is normally accompanied by a broad, asymmetric phonon-side band due to the coupling to the phonons in the surrounding protein matrix present in photosynthetic complexes. The asymmetry in the one-phonon profile of a homogeneous absorption spectrum and other experiments performed on photosynthetic bacterial reaction centers (BRCs) led the Small group to employ a half-Gaussian distribution function on the red side and half-Lorentzian distribution function on the blue side of the absorption lineshape to account for the one-phonon profile asymmetrical shape and relaxation effects contributing to spectroscopy and dynamics of BRCs at hand. Different research groups successfully employed the theory of Small to simulate their photosynthetic spectral data so they could calculate the homogeneous absorption and hole-burned spectra of photosynthetic complexes. Although this report does not directly use the formulae of homogeneous absorption, hole-burning, and fluorescence line-narrowed spectra of BRCs, and photosynthetic complexes, developed by Hayes-Small, it builds on their idea of the phonon sideband asymmetric shape in deriving an accurate and computationally efficient linear electronic transition dipole moment time correlation function. Besides the compelling tractability and efficiency of this correlation function, it accounts for excitonic coupling and eliminates all the inconsistencies arising in the Hayes-Small theory.

First-principles theory of the nitrogen interstitial in hBN: a plausible model for the blue emitter.

Color centers in hexagonal boron nitride (hBN) have attracted considerable attention due to their remarkable optical properties enabling robust room temperature photonics and quantum optics applications in the visible spectral range. On the other hand, identification of the microscopic origin of color centers in hBN has turned out to be a great challenge that hinders the in-depth theoretical characterization, on-demand fabrication, and development of integrated photonic devices. This is also true for the blue emitter, which is a result of irradiation damage in hBN, emitting at 436 nm wavelength with desirable properties. Here, we propose the negatively charged nitrogen split interstitial defect in hBN as a plausible microscopic model for the blue emitter. To this end, we carried out a comprehensive first-principles theoretical study of the nitrogen interstitial. We carefully analyzed the accuracy of first-principles methods and showed that the commonly used HSE hybrid exchange-correlation functional fails to describe the electronic structure of this defect. Using the generalized Koopman's theorem, we fine-tuned the functional and obtained a zero-phonon photoluminescence (ZPL) energy in the blue spectral range. We showed that the defect exhibits a high emission rate in the ZPL line and features a characteristic phonon side band that resembles the blue emitter's spectrum. Furthermore, we studied the electric field dependence of the ZPL and numerically showed that the defect exhibits a quadratic Stark shift that is perpendicular to plane electric fields, making the emitter insensitive to electric field fluctuations in the first order. Our work emphasizes the need for assessing the accuracy of common first-principles methods in hBN and exemplifies a workaround methodology. Furthermore, our work is a step towards understanding the structure of the blue emitter and utilizing it in photonics applications.