Spontaneous Emission Lifetime Research Articles

Spectroscopic properties and laser cooling feasibility with the X1∏21/2↔X2∏23/2 transition for the PbX (X = F, Cl, Br, and I) molecules

The highly diagonal Frank–Condon factors (FCFs) are necessary for the laser cooling scheme, which means that only the molecules with the appropriate ground and excited electronic states can become candidates. Here, the laser cooling feasibility of the PbX (X = F, Cl, Br, and I) molecules is explored through four-component relativistic calculations. The potential energy curves and transition dipole moments of five Ω states are calculated and used to solve the Schrödinger equation of nuclear motion to obtain the rovibrational energy levels, spectroscopic parameters, the Einstein coefficients, and FCFs. Using the X1 2Π1/2 ↔ X2 2Π3/2 transition with highly diagonal FCFs, we construct optical schemes that can provide 104 ∼ 105 scattering phonons with four pumping lasers for PbX. The Doppler/recoil temperatures of PbX are 419.05 / 57.55, 9.63 / 61.20, 4.95 / 49.98, and 0.71 / 40.17 nK, respectively. Since the 10−4 s of the long spontaneous emission lifetime, the temperatures below microkelvin orders of magnitude can be achieved only if the adequate pre-cooling temperature is satisfied.

Optical Transparency Induced by a Largely Purcell Enhanced Quantum Dot in a Polarization-Degenerate Cavity.

Optically active spin systems coupled to photonic cavities with high cooperativity can generate strong light-matter interactions, a key ingredient in quantum networks. However, obtaining high cooperativities for quantum information processing often involves the use of photonic crystal cavities that feature a poor optical access from the free space, especially to circularly polarized light required for the coherent control of the spin. Here, we demonstrate coupling with a cooperativity as high as 8 of an InAs/GaAs quantum dot to a fabricated bullseye cavity that provides nearly degenerate and Gaussian polarization modes for efficient optical accessing. We observe spontaneous emission lifetimes of the quantum dot as short as 80 ps (an ∼15 Purcell enhancement) and a ∼80% transparency of light reflected from the cavity. Leveraging the induced transparency for photon switching while coherently controlling the quantum dot spin could contribute to ongoing efforts of establishing quantum networks.

First-principles study of transition metal dopants as spin qubits

Defect centers in solid-state materials have played an important role in the development of quantum information science as spin qubits. In recent years, many studies using optically detected magnetic resonance (ODMR) to manipulate the ground state spin of transition metal dopants have been reported. In this work, the tetrahedral ${d}^{2}$ and the octahedral ${d}^{3}$ transition metal ion systems are considered for the potential spin qubits, based on the ligand field theory and the basic requirements of general $\mathrm{\ensuremath{\Lambda}}$-type spin qubits. Then a computational scheme based on density functional theory is performed on the transition metal ligand structures $M{X}_{n}(M=\mathrm{V},\mathrm{Cr},\mathrm{Mn},\mathrm{Fe};X=\mathrm{N},\mathrm{O},\mathrm{C};\phantom{\rule{4pt}{0ex}}n=4, 6)$ in several typical hosts to analyze quantitatively their feasibility. The results on the charge transition levels, excitation, and excited-state structure relaxation energies of $M{X}_{n}$ show that some of them have the proper valence states to form the required ${d}^{2}$ or ${d}^{3}$ electronic systems and the appropriate excited-state level structure with the spin-selective transition. The results on the spontaneous emission lifetime show that the ${\mathrm{MnO}}_{4}$ structure is mostly suitable for spin polarization due to the fastest optical transition rates among these systems considered. Finally, some suggestions on determining potentially feasible systems activated by transition metal ions in solids are given.

Quantum limits to resolution and discrimination of spontaneous emission lifetimes

In this work we investigate the quantum information theoretical limits to several tasks related to lifetime estimation and discrimination of a two-level spontaneous optical emitter. We focus in particular on the model problem of resolving two mutually incoherent exponential decays with highly overlapping temporal probability profiles. Mirroring recent work on quantum-inspired super-resolution of point emitters, we find that direct lifetime measurement suffers from an analogue of "Rayleigh's Curse" when the time constants of the two decay channels approach one another. We propose alternative measurement schemes that circumvent this limit, and also demonstrate superiority to direct measurement for a related binary hypothesis test. Our findings add to a growing list of examples in which a quantum analysis uncovers significant information gains for certain tasks in opto-molecular metrology that do not rely on multiphoton interference, but evidently do benefit from a more thorough exploitation of the coherence properties of single photons.

Analysis of the structure and luminescence properties of Zn2 GeO4 :Eu3+ according to Judd-Ofelt theory.

The preparation and characteristic of nanorod-like Zn2 GeO4 doped with Eu3+ or zinc germanate (ZGO):xEu3+ (x = 0 ÷ 0.05), which was synthesized using the hydrothermal method, are described. The influence of Eu3+ -doping ions on the structure and the optical properties of ZGO was also investigated. According to the photoluminescence spectra, ZGO:xEu3+ nanophosphors gave a red emission due to the 5 D0 →7 F2 emission of Eu3+ ions. In accordance with Judd-Ofelt theory, the intensity parameters for f-f transitions from the emission and absorption spectrum were determined. At the 5 D0 excited state of Eu3+ , total spontaneous emission probabilities (AR ), lifetimes (τR ), branching ratios (βR ), and quantum efficiency (η) were calculated. The ZGO:xEu3+ (x = 0.02, 0.03, 0.04) phosphor showed the branch ratio β (5 D0 →7 F2 ) > 60%, indicating that the phosphors prepared here have a promising potential as laser light. The sample with a concentration of 0.04Eu3+ achieved the highest quantum efficiency of 84%, suggesting that it has potential light-emitting diode applications.

Local and nonlocal Purcell factor control of an emitter in graphene under the modulation of a static magnetic field

Spontaneous emission control of emitters holds great promise for applications in photonics and quantum optics. As a definition of the spontaneous emission lifetime of an atom or molecule, the Purcell factor of an emitter coupled with graphene controlled by a static magnetic field was studied. The results show that the Purcell factor can be effectively enhanced by applying an external magnetic field to graphene at low terahertz frequency. By analyzing the dispersion relations of graphene and the Purcell factor of an emitter nearby it, we find that the emitter-graphene interactions are most influenced by nonlocal effects at the low frequency, especially at a short emitter-graphene distance. The coupling between the emitter and the magnetic biased graphene becomes stronger under nonlocal effects, leading to a strong enhancement of the emission of the emitter. More specifically, the nonlocal Purcell factor can increase by orders of magnitude when the applied magnetic field is 10 T compared to the local model at a very short distance. The bias of the applied magnetic field extends a new path for the realization of Purcell factor modulation based on graphene-emitter interaction, and it may provide a promising application value for the design of the photo-magnetic-based quantum devices.

Ultrafast Kinetics of Chlorinated Polymer Donors: A Faster Excitonic Dissociation Path.

Halogen-substituted donor/acceptor materials are widely regarded as a promising strategy toward improved power-conversion efficiencies (PCEs) in polymer solar cells (PSCs). A chlorinated polymer donor, PClBTA-PS, and its non-chlorinated analogue, PBTA-PS, are synthesized. The PClBTA-PS-based devices show significant enhancements in terms of open-circuit voltage (VOC = 0.82 V) and fill factor (FF = 76.20%). In addition, a PCE of 13.20% is obtained, which is significantly higher than that for the PBTA-PS-based devices (PCE = 7.63%). Grazing incident wide-angle X-ray scattering shows that the chlorinated polymer enables better π-π stacking in both pure and blend films. DFT and TD-DFT calculations as well as ultrafast photophysics measurements indicate that chlorinated PClBTA-PS has a smaller bonding energy and a longer spontaneous-emission lifetime. The results also reveal that the charge-transfer-state excitons in PClBTA-PS:IT4Cl blend films split into the charge-separated (CS) state via a faster dissociation path, which produces a higher yield of the CS state. Overall, this study provides a deeper understanding of how a halogen-substituted polymer can improve PSCs in the future.

Solid‐State Red Laser with a Single Longitudinal Mode from Carbon Dots

AbstractMiniaturized solid‐state lasers with a single longitudinal mode are vital for various photonic applications. Here we prepare red‐emissive carbon dots (CDs) with a photoluminescence quantum yield (PLQY) of 65.5 % by combining graphitic nitrogen doping and surface modification. High‐concentration doping alters the CDs’ emission from blue to red, while the electron‐donating groups and polymer coating on their surfaces improve the PLQY and photostability. The CDs exhibit excellent stimulated emission characteristics, with a low threshold of amplified spontaneous emission (ASE) and long gain lifetime. A planar microcavity with only one resonant mode, which fitted with the CDs’ ASE peak, was constructed. Combining the CDs and microcavity produced a solid‐state laser with a single longitudinal mode, a linewidth of 0.14 nm and a signal‐to‐noise ratio of 14.8 dB (Q∼4600). Our results will aid the development of colorful solid‐state micro/nano lasers with potential use in practical photonics.

Solid-State Red Laser with a Single Longitudinal Mode from Carbon Dots.

Miniaturized solid-state lasers with a single longitudinal mode are vital for various photonic applications. Here we prepare red-emissive carbon dots (CDs) with a photoluminescence quantum yield (PLQY) of 65.5 % by combining graphitic nitrogen doping and surface modification. High-concentration doping alters the CDs' emission from blue to red, while the electron-donating groups and polymer coating on their surfaces improve the PLQY and photostability. The CDs exhibit excellent stimulated emission characteristics, with a low threshold of amplified spontaneous emission (ASE) and long gain lifetime. A planar microcavity with only one resonant mode, which fitted with the CDs' ASE peak, was constructed. Combining the CDs and microcavity produced a solid-state laser with a single longitudinal mode, a linewidth of 0.14 nm and a signal-to-noise ratio of 14.8 dB (Q∼4600). Our results will aid the development of colorful solid-state micro/nano lasers with potential use in practical photonics.

Judd-Ofelt analysis and luminescence studies of Er3+ doped halogeno-antimonate glasses

This research paper emphasized on application of Judd-Ofelt's (JO) theory for low doped erbium (0.2 mol%) halogeno-antimonate based glasses with molar composition (90 –x) Sb 2 O 3 - x ZnBr 2 - 10 NaCl (where x = 10, 20, 30 and 40 mol%). 80 Sb 2 O 3 – 9.8 ZnBr 2 - 10 NaCl - 0.2 Er 2 O 3 glass sample has low phonon energy and high refractive index is a potential candidate for luminescence applications. Differential scanning calorimetry (DSC) measurements show good the thermal stability of the prepared glass samples and on the other hand density, expansion coefficient and elastic moduli were reported. Judd-Ofelt's (JO) parameter intensities Ω 2 = 3.27 × 10 −20 cm 2 , Ω 4 = 1.24 × 10 −20 cm 2 and Ω 6 = 1.88 × 10 −20 cm 2 were found and these were compared with the literature. Radiative parameters such as spontaneous emission rate, branching ratio and lifetime were calculated. We focused on a high branching ratio radiative transitions 2 H 11/2 → 4 I 15/2 (β = 0.94) and 4 F 9/2 → 4 I 15/2 (β = 0.901). The overlap between absorption and emission bands is partial and stokes type shifts were presented. The gain curves were determined after calculation of absorption and stimulated emission cross sections. The infrared transmission curve of the glass matrix was marked extrinsic absorption bands SiO and hydroxyl OH possessed high vibration energy played quenching effect for photoluminescence. • SZNE02 novel glass system was developed by the conventional melt quenching method. • Judd-Ofelt's (JO) parameter intensities were compared with the literature. • High branching ratio radiative transitions. • Optical gap energy (E p = 2.95 eV) and refractive index n = 2.25 • Stimulated emission gains as a function of wavelength for different states of population inversion.

The NV metamaterial: Tunable quantum hyperbolic metamaterial using nitrogen vacancy centers in diamond

We show that nitrogen-vacancy (NV) centers in diamond can produce a unique quantum hyperbolic metamaterial. We demonstrate that a hyperbolic dispersion relation in diamond with NV centers can be engineered and dynamically tuned by applying a magnetic field at 20 K. This quantum hyperbolic metamaterial with a tunable window for the negative refraction allows for the construction of a superlens beyond the diffraction limit. In addition to subwavelength imaging, this NV metamaterial can be used in spontaneous emission enhancement, heat transport, and acoustics, analog cosmology, and lifetime engineering. Therefore, our proposal interlinks the two hotspot fields, i.e., NV centers and metamaterials.

Forbidden rotational transitions and astrophysics

The theory of forbidden rotational transitions is reviewed and spontaneous emission rates and lifetimes of metastable levels of NH3, H3O+, H3+, and CH3CN are calculated. Rotational levels are classified into stable, metastable, and unstable levels. The importance of the forbidden rotational transitions in the thermalization of interstellar molecules is discussed.

Tuning radiative lifetimes in semiconductor quantum dots.

Photonic devices stand to benefit from the development of chromophores with tunable, precisely controlled spontaneous emission lifetimes. Here, we demonstrate a method to continuously tune the radiative emission lifetimes of a class of chromophores by varying the density of electronic states involved in the emission process. In particular, we examined the peculiar composition-dependent electronic structure of copper doped CdZnSe quantum dots. It is shown that the nature and density of electronic states involved with the emission process is a function of copper inclusion level, providing a very direct handle for controlling the spontaneous lifetimes. The spontaneous emission lifetimes are estimated by examining the ratios of emission lifetimes to absolute quantum yields and also measured directly by ultrafast luminescence upconversion experiments. We find excellent agreement between these classes of experiments. This scheme enables us to tune spontaneous emission lifetimes by three orders of magnitude from ∼15 ns to over ∼7 µs, which is unprecedented in existing lumophores.

Narrow-linewidth coherent population oscillation spectroscopy of room-temperature cesium atomic ensemble

Coherent population oscillations spectroscopy, which is based on the interaction between atoms and the phase locked laser, is a kind of atomic population modulation spectroscopy. When the laser frequency difference is less than natural width of energy level, the coherent oscillation of atomic population will be induced by laser intensity modulation so that the probe laser transmission with narrow bandwidth can be realized. For a closed two-level system (TLS), the spectral line-width is limited mainly by the spontaneous emission lifetime of the upper atomic energy level. As for a three-level atomic system of Λ configuration, the two linearly polarized beams with both σ+ and σ- polarization component, the laser-atom interaction satisfies the selection rule. The spectral line-width mainly depends on the ground-state relaxation time, and the dependence on the line-width of spontaneous radiation is eliminated. In this paper, the laser from a external-cavity diode laser has its frequency locked to Cesium <inline-formula><tex-math id="M1">\begin{document}$6{{\rm{S}}_{1/2}}\left( {F = 3} \right) \to 6{{\rm{P}}_{3/2}}\left( {F' = 3} \right)$\end{document}</tex-math><alternatives><graphic xmlns:xlink="http://www.w3.org/1999/xlink" xlink:href="16-20210405_M1.jpg"/><graphic xmlns:xlink="http://www.w3.org/1999/xlink" xlink:href="16-20210405_M1.png"/></alternatives></inline-formula> transition. The frequencies of the two beams are shifted down by two independent double-passed acousto-optic modulators (AOM) to nearly resonate to Cesium <inline-formula><tex-math id="M2">\begin{document}$6{{\rm{S}}_{1/2}}\left( {F = 3} \right) \to 6{{\rm{P}}_{3/2}}\left( {F' = 2} \right)$\end{document}</tex-math><alternatives><graphic xmlns:xlink="http://www.w3.org/1999/xlink" xlink:href="16-20210405_M2.jpg"/><graphic xmlns:xlink="http://www.w3.org/1999/xlink" xlink:href="16-20210405_M2.png"/></alternatives></inline-formula> transition. The probe beam and the coupling beam are superposed at polarization beam splitter (PBS) cube and transmitted through the magnetically shielded cesium vapor cell in the same direction. The two beams have approximately the same Gaussian diameter of 6.6 mm. The beams are separated by another PBS behind the vapor cell, and the probe beam is detected by a photodiode. We realize the coherent population oscillation spectroscopy through the Cesium vapor cell at room temperature without buffer gas. The spectral linewidth is typically less than 50 kHz which is far below the spontaneous radiation linewidth(~5.2 MHz). The linewidth of coherent population oscillation spectroscopy of the Λ-type atomic energy level structure depends only on the population associated with the oscillation of multiple degenerate level systems except phase correlations of atomic states. Coherent population oscillation is beneficial to the obtaining of the narrow linewidth spectroscopy through the Rydberg atomic system with long excited state lifetime. Considering the importance of electric field measurement using Rydberg atoms, the method of coherent population oscillation can be used to improve the sensitivity of precise measurements based on Rydberg atoms.

Visible emission and energy transfer in Tb3+/Dy3+ co‐doped phosphate glasses

AbstractIn this work, we systematically study the spectroscopic properties of Tb3+/Dy3+ co‐doped phosphate glasses in the visible spectral region and explore the sensitization role of Dy3+ in the enhancement of visible fluorescence of Tb3+ ions. Judd‐Ofelt parameters Ω2 and Ω4/Ω6 of the phosphate glass as host for Tb3+ are calculated as 21.60 × 10‐20 cm2 and 0.73, respectively, based on the measured spectral absorption. Multiple energy transfer (ET) routes from Dy3+ to Tb3+ and their efficiencies are characterized, and the enhanced fluorescence properties of Tb3+ are investigated, including the emission spectral strength and the spontaneous emission lifetime as functions of Dy3+ doping concentration. The efficient nonradiative ET processes between Dy3+ and Tb3+ allow a moderate concentration level of Tb3+ to achieve favorably stronger spectral absorption at blue and ultraviolet wavelengths. Tb3+/Dy3+ co‐doped phosphate glass shows promising potential for phosphors and lasing operation at visible wavelengths.

Accurate dependences of spontaneous emission factor, lifetime, and photon lifetime on threshold current

Using the rate equation, several optical methods of characterizing the threshold of a laser diode (LD) were analyzed. The thresholds determined by all methods are consistent if the spontaneous-emission-coefficient (β) is small. If β<0.05, the thresholds obtained by different methods are different. Especially, for micro-nano LDs with a large β, these methods are starting to become inaccurate. However, the d S/dH is a relatively accurate method to characterize threshold of these LDs compared to other methods. The effects of the spontaneous-emission-lifetime (τsp) and the photon-lifetime (τp) on thresholds were analyzed. The exact functions between the threshold and the β, τsp and τp were obtained.

Emission properties of Pr3+-doped aluminosilicate glasses at visible wavelengths

In this work, we explore emission properties of Pr3+ ion doped aluminosilicate glasses at visible wavelengths where alkaline earth oxide modifiers (Mg2+, Ca2+, Sr2+, Ba2+) are introduced for enhancement of the Stark splitting of Pr3+ in the silicate matrix. The Pr3+ ion doped aluminosilicate glasses present strong absorption at visible wavelengths between 440 and 500 nm which gives rise to intense emission in the visible spectrum from 570 to 660 nm. The visible luminescence spectra under excitation at different pump wavelengths and the lifetime of spontaneous emission are investigated as functions of Pr3+ doping concentration. We report a longest lifetime of 115 μs measured at 3P0 level in Pr3+ implying Pr3+ doped aluminosilicate glass may be a promising candidate for efficient visible fiber laser operated at 610 and 640 nm wavelength. The concentration-induced quenching and various energy transfer processes are also investigated.

Modification of the Near‐Infrared Spontaneous Emission in Er3+‐Activated Inverse Silica Opals

Ordered SiO2:Er3+ inverse opal films are fabricated by sol–gel technique in combination with a self‐assembly method to examine their potential as a suitable platform to tailor the spontaneous emission lifetime of Er3+ ions and its concentration quenching (CQ). Good ordering on long‐range scale is evidenced by means of scanning electron microscopy, whereas reflectance measurements display a green bright color, as it results from optical Bragg diffraction from the (111) crystal planes. Moreover, it is observed that the spontaneous decay rates (SDRs) of the inverse opals are suppressed, in contrast to the corresponding reference samples, due to the modulation of the effective refractive index (neff), in agreement with the virtual cavity model. At the same time, the reduced CQ of Er3+ is attributed to the periodic empty cavity of the inverse opals. These results demonstrate that inverse opals can provide a tool for the enhancement of near‐infrared (NIR) luminescence.

Singlet–Triplet Transition Rate Enhancement inside Hyperbolic Metamaterials

AbstractThe spontaneous emission process is known to be largely affected by the surrounding electromagnetic environment of emitters, which manifests itself via the Purcell enhancement of decay rates. This phenomenon has been extensively investigated in the case of dipolar transitions in quantum systems, commonly delivering fast decay rates in comparison to forbidden transitions such as high‐order multipolar transitions or spin‐forbidden, singlet–triplet phosphorescence processes. Here, a decay rate enhancement of almost 2750‐fold is demonstrated for a ruthenium‐based phosphorescent emitter located inside a plasmonic hyperbolic metamaterial. The standard electromagnetic local density of states description, typically employed for the Purcell factor analysis of dipolar transitions, is unable to account for a photoluminescence enhancement of this magnitude, which is attributed to the interplay between the local density of states and strongly inhomogeneous electromagnetic fields inside the metamaterial. The large available range of spontaneous emission lifetimes reported here enables application of phosphorescent emitters in novel, fast, and efficient light‐emitting sources, beneficial for optical communications, quantum information processing, spectroscopy, or bio‐imaging.

Collision-mediated ultrafast decay of N2 fluorescence during fs-laser-induced filamentation.

We investigate experimentally spatiotemporal characteristics of fluorescence emission from fs-laser-induced filaments in air. Emissions accompanying the transitions of N2 (C3Πu-B3Πg) and N2+ (B2Σu+-X2Σg+) are dominant. The decay dynamics of fluorescence from different radial positions and longitudinal sections of a filament column are obtained along with high resolution spectra. A decay curve contains two exponential components: a fast one (with a decay time constant ∼10s ps), and a slow one (∼sub-ns). The lifetime of the N2 fluorescence is about three orders shorter than its spontaneous emission lifetime, indicating that most of the N2 molecules in the excited state (C3Πu) are de-excited through collision. Different de-excitation mechanisms of N2 (C3Πu) molecules contributing to fluorescence decay constants, e.g., the e--N2, N2-N2, and O2-N2 collisions, are elucidated. We analyze the variations of decay constants together with corresponding fluorescence intensities, and obtain temperature distributions by fitting band spectra of N2 molecules and N2+ ions with a synthetic spectral model. Our results suggest that the fast and slow decay processes originate from the e--N2 and O2-N2 collisions, respectively.