Radiative Transitions Research Articles

Search for the radiative transition χc1(3872)→γψ2(3823)

Using 9.0 fb−1 of e+e− collision data collected at center-of-mass energies from 4.178 to 4.278 GeV with the BESIII detector at the BEPCII collider, we perform the first search for the radiative transition χc1(3872)→γψ2(3823). No signal is observed and the upper limit on the ratio of branching fractions B(χc1(3872)→γψ2(3823),ψ2(3823)→γχc1)/B(χc1(3872)→π+π−J/ψ) is set at 0.075 at the 90% confidence level. Our result contradicts theoretical predictions under the assumption that the χc1(3872) is the pure charmonium state χc1(2P). Published by the American Physical Society 2024

Computational insights into the underlying mechanism of zinc ion-specificity of the fluorescent probe, BDA-1

Ion specificity is crucial for developing fluorescence probes. Using a recently reported optical sensor (BDA-1) of Zn2+ as a representative, we carried out extensive quantum chemical calculations on its photophysical properties using density function theory. According to the calculated optimized geometries, excitation energies and transition oscillator strengths, the weak fluorescence of BDA-1 observed in experiments is attributed to the suppression of fluorescence emission by efficient internal conversion, rather than the previously proposed photoinduced electron transfer (PET) mechanism. With the addition of Zn2+ or Cd2+ ions, the tetradentate chelates [M:BDA-1-H+]+ (M=Zn, Cd) are produced. According to frontier molecular orbital and interfragment charge transfer analyses of these complexes, PET is preferentially confirmed to occur upon photo-excitation. Notably, as one coordination bond in the excited [Cd:BDA-1-H+]+ complex is significantly weakened in comparison to that of [Zn:BDA-1-H+]+, their molecular orbital compositions in the S1 state are completely different. As a result, absorption and radiation transitions of [Zn:BDA-1-H+]+ both have considerable oscillator strength, while fluorescence radiation from the excited [Cd:BDA-1-H+]+ is doubly suppressed. This difference causes that the fluorescence intensity of BDA-1 is sensitive to the addition of metal ions, and exhibits the zinc ion-specificity.

Spectroscopic properties of Pr3+-doped Titania-Silicate glass ceramic for photonic applications

Silicate-Titania (SiTi) glass-ceramics doped with Pr3+ (0.6, 1.6, 2.4 and 3.6 mol%) ions were prepared by sol-gel technique. The materials were characterized by powder XRD, FTIR, TEM, EDX, Optical absorption and Photoluminescence spectroscopy. The identification of non-bridging oxygen (NBO) formation and the removal of OH groups are validated through analysis of the FTIR spectra. Additionally, measurements using XRD and TEM showed that the samples contain nano-sized crystallites. The three phenomenological Judd–Ofelt (J–O) intensity parameters Ω2, Ω4, and Ω6 were obtained and used to analyze different radiative characteristics for the fluorescence levels of Pr3+ in the glass ceramic, including radiative lifetime, branching ratio, radiative transition probability and stimulated emission cross-section. Several emissions were observed in the visible region, among which the 1D2→3H4 in the orange-red region is the most intense. All of these reported branching ratios, stimulated emission cross-sections, and visible emission spectra point to the possibility of employing them as red region lasers. The CIE chromaticity coordinates from all of the emission spectra were also assessed to determine if these materials are suitable for orange-red phosphors. According to CIE chromaticity investigations, 1.6 mol% of Pr3+ ion concentration is ideal for SiTiPr glass-ceramic for use as red phosphors and possibly red lasers.

Blue-green emitting ZnS0.75O0.25:Ce3+,x%Tb3+ phosphor with tunable fluorescence lifetime

A series of ZnS0.75O0.25:0.1%Ce3+,x%Tb3+ phosphors were prepared by high temperature solid state reaction method. These phosphors exhibited two mixed phases consisting of hexagonal phase ZnS and hexagonal phase ZnO with the average particle size of 13.83 μm and emitted blue-green light. The luminescence mechanism consisted of Zn vacancy defects, the 5d1 → 2F5/2 radiative transitions of Ce3+, the 5D4 → 7F5 and 5D4 → 7F6 radiative transition of Tb3+ induced by the energy transfer of Ce3+ → Tb3+. An equation for the variation of the fluorescence lifetime of ZnS0.75O0.25:0.1%Ce3+,x%Tb3+ phosphors with concentration of Tb3+ fraction was obtained by exponential fitting. The short fluorescence lifetime could be tuned within the range of 113 μs to 550 μs with the increase of Tb3+ concentration, and the color was tunable from blue to blue-green, which is of important application in the field of high-energy particle detection.

Revealing the three-dimensional structure of microbunched plasma-wakefield-accelerated electron beams

Plasma wakefield accelerators use tabletop equipment to produce relativistic femtosecond electron bunches. Optical and X-ray diagnostics have established that their charge concentrates within a micrometre-sized volume, but its sub-micrometre internal distribution, which critically influences gain in free-electron lasers or particle yield in colliders, has proven elusive to characterize. Here, by simultaneously imaging different wavelengths of coherent optical transition radiation that a laser-wakefield-accelerated electron bunch generates when exiting a metal foil, we reveal the structure of the coherently radiating component of bunch charge. The key features of the images are shown to uniquely correlate with how plasma electrons injected into the wake: by a plasma-density discontinuity, by ionizing high-Z gas-target dopants or by uncontrolled laser–plasma dynamics. With additional input from the electron spectra, spatially averaged coherent optical transition radiation spectra and particle-in-cell simulations, we reconstruct coherent three-dimensional charge structures. The results demonstrate an essential metrology for next-generation compact X-ray free-electron lasers driven by plasma-based accelerators.

Photon Emission by an Electron in a Constant Background Field Modeling a Lorentz-Noninvariant Vacuum

Abstract We considered the radiative transition of an electron due to its spin-flip in a constant background field of the quasielectric type, which models the Lorentz-noninvariant vacuum. The power and probability of radiation and the degree of its linear polarization are calculated. It is shown that this radiative transition leads to the complete polarization of the initially unpolarized electron beam. The investigated effects increase with increasing electron energy.

Recent Progress in Solid-State Room Temperature Afterglow Based on Pure Organic Small Molecules.

Organic room temperature afterglow (ORTA) can be categorized into two key mechanisms: continuous thermally activated delayed fluorescence (TADF) and room-temperature phosphorescence (RTP), both of which involve a triplet excited state. However, triplet excited states are easily quenched by non-radiative transitions due to oxygen and molecular vibrations. Solid-phase systems provide a conducive environment for triplet excitons due to constrained molecular motion and limited oxygen permeation within closely packed molecules. The stimulated triplet state tends to release energy through radiative transitions. Despite numerous reports on RTP in solid-phase systems in recent years, the complexity of these systems precludes the formulation of a universal theory to elucidate the underlying principles. Several strategies for achieving ORTA luminescence in the solid phase have been developed, encompassing crystallization, polymer host-guest doping, and small molecule host-guest doping. Many of these systems exhibit luminescent responses to various physical stimuli, including light stimulation, mechanical stimuli, and solvent vapor exposure. The appearance of these intriguing luminescent phenomena in solid-phase systems underscores their significant potential applications in areas such as light sensing, biological imaging, and information security.

Radiative and electron-impact transitions of W I for spectroscopic diagnostics

Radiative and electron-impact transitions of W I for spectroscopic diagnostics

On the effective vibrational temperature of the source using (2)3∏ - X3∏ system of GeC molecule

In this work, the experimental potential energy curves for (2)3Π and X3Π electronic states of GeC molecule have been constructed by using Rydberg-Klein-Rees (RKR) method. The radiative transition parameters viz., Franck-Condon (FC) factor, r-centroid, electronic transition moment, band strength, relative band strength, Einstein coefficients, radiative lifetime and oscillator strength for the (2)3Π−X3Π system of GeC molecule have been estimated for the experimentally observed vibrational levels from Rydberg-Klein-Rees (RKR) potential and the estimated values are tabulated. The estimated effective vibrational temperature found as 5628 K for the (2)3Π−X3Π system of GeC molecule. The radiative transition parameters and effective vibrational temperature are evident that the possible presence of GeC molecule in solar and sunspots atmosphere. Further, these parameters are employed in rationalizations of astrochemical and astrophysical observations.

Coherent X-ray radiation excited by a relativistic electron in a periodic layered medium

The work is devoted to the development of the theory of coherent X-ray radiation near the direction of Bragg scattering of a beam of relativistic electrons crossing a target with a periodic layered structure with three different amorphous layers per period. The coherent X-ray radiation is considered within the two-wave approximation of the dynamic theory of diffraction as a sum of parametric X-ray radiation and diffracted transition radiation excited in the target by a relativistic electron. Expressions describing the spectral-angular and angular densities of PXR and DTR have been obtained and studied.

B-O-O-B Impurity Induces Ultralong Room-Temperature Phosphorescence of Boric Acid.

Organic materials that can emit ultralong room-temperature phosphorescence (RTP) have attracted a great deal of interest. Whether the pure boric acid (BA) solid can emit RTP and the origin of the RTP in BA caused a debate recently. Herein, our first-principles calculations and experimental measurements suggest that RTP of BA originates from the B-O-O-B group in a (H2BO3)2 species, which can be formed by polymerization of two dehydrogenated BA molecules under light irradiation. The calculated absorption, fluorescence, and phosphorescence spectra of B-O-O-B match well with the experiments. Experimental X-ray photoelectron and X-ray absorption spectra evidence the existence of B-O-O-B in BA. The O-O bond in B-O-O-B can break upon optical excitation, creating two B-O radicals. Radiative transition from localized dangling orbitals of the B-O radicals to the delocalized orbitals of the crystal bulk leads to the observed RTP. Our calculated phosphorescence lifetime is ∼1 s, which agrees well with the experiment.

Temperature-dependent law of transition probability associated with main emission states in YVO4:Re3+ (Re3+=Sm3+, Dy3+ and Eu3+)

The understanding of how radiative transition probabilities change with temperature is crucial for comprehending the relationship between fluorescence behavior and temperature. However, although various models have been proposed to explain the patterns of transition probabilities (A) with temperature changes, they lack consistency due to their derivation from distinct microscopic perspectives. In this study, the macroscopic law of the temperature-dependent A for the 4G5/2, 4F9/2, and 5D0 energy states in YVO4:Re3+(Re3+=Sm3+, Dy3+ and Eu3+) was obtained. Three rare earth ions (Re3+) were identified for each with unique energy level properties conducive to validating the general rules of A. These ions share a common characteristic: in the visible spectrum, their main emissions originate from the radiative transitions from the same higher energy level (4G5/2 in Sm3+, 4F9/2 in Dy3+, and 5D0 in Eu3+) to lower energy levels, respectively. The A of the main emission levels, varying with T, were obtained by fitting the fluorescence decay curves. The exponential law governing non-radiative transitions was revealed after separating the radiative transition rate (WR) from A. The macroscopic law of temperature-dependent transition probabilities of 4G5/2, 4F9/2, and 5D0 energy states in YVO4:Ln3+ (Ln3+ = Sm3+, Dy3+ and Eu3+) has been found to follow the Boltzmann distribution. The results indicate that the non-radiative transitions of the main emission levels of the rare-earth ions are processes from the excited state to adjacent lower energy levels. This macroscopic pattern may serve as a foundational rule for understanding the impact of microscopic factors on A.

Ultrafast excited state intramolecular proton transfer and isomerization of long-chain linked Schiff bases.

The ultrafast proton transfer and the following dynamics for aromatic Schiff bases N,N'-bis(salicylidene)ethylenediamine (salen) and N,N'-bis(salicylidene)-1,4-butylenediamine (salbn) were investigated with experimental and theoretical methods. A dual emission property with a large Stokes shift in salen and salbn indicates that excited state intramolecular proton transfer occurs with photoexcitation. An efficient single proton transfer was confirmed within 200fs for both molecules. Subsequently, a fast twisted motion of the keto moiety carries cis-keto to a relaxed stable geometry in the S1 state. Following the twisted motion, the phenol ring at keto moiety further rotates to a conical intersection with the ground state and a cis-trans isomerization occurs. The isomerization rate is high, which dominates the competition with the radiative transition, resulting in weak emission intensity. It is confirmed that the length of alkyl chain affects the direction of phenol ring twisting and rotation during the whole subsequent relaxation of excited cis-keto tautomer. Compared with polar solvent acetonitrile, the barrier of isomerization is higher and the hydrogen bond on keto moiety is stronger in nonpolar solvent toluene. It makes fluorescence radiation channels competing with isomerism more likely to occur, contributing to the observed difference of enol/keto emission ratios of salen and salbn in toluene and acetonitrile.

Efficient near-infrared organic light-emitting diodes with emission from spin doublet excitons

The development of luminescent organic radicals has resulted in materials with excellent optical properties for near-infrared emission. Applications of light generation in this range span from bioimaging to surveillance. Although the unpaired electron arrangements of radicals enable efficient radiative transitions within the doublet-spin manifold in organic light-emitting diodes, their performance is limited by non-radiative pathways introduced in electroluminescence. Here we present a host–guest design for organic light-emitting diodes that exploits energy transfer with up to 9.6% external quantum efficiency for 800 nm emission. The tris(2,4,6-trichlorophenyl)methyl-triphenyl-amine radical guest is energy-matched to the triplet state in a charge-transporting anthracene-derivative host. We show from optical spectroscopy and quantum-chemical modelling that reversible host–guest triplet–doublet energy transfer allows efficient harvesting of host triplet excitons.

The effect of the outer-sphere cations on the photophysical and magnetic properties of rare earth complexes with 2,2,2-trichloro-N-(diphenylphosphoryl)acetamide

Two series of rare earth coordination compounds have been synthesized (Na[RE(L4)] (labeled as 1RE) and PPh4[RE(L4)] (labeled as 2RE), where RE = Y3+, Eu3+, Tb3+, L = 2,2,2-trichloro-N-(diphenylphosphoryl)acetamide) to determine the possibility of modifying their photophysical and magnetical properties by changing the counterion. The crystal structure of 1RE was determined based on the single-crystal X-ray diffraction and the crystal structure of 2RE was determined based on quantum chemistry computational procedures. Characterization of the physicochemical properties of the compounds was carried out using differential scanning calorimetry (DSC), thermogravimetric analysis (TGA), 1H and 31P NMR spectroscopy as well as FT-IR, absorption and luminescence spectroscopy in the temperature range of 300 - 77 K. The rate constants of radiative (Arad) and non-radiative (Anrad) transitions, intrinsic (QLnLn) and overall (QLnL) emission quantum yields, sensitization efficiency (ηsens), the experimental and theoretical intensity parameters (Ωλ), the forward (WS, WT) and backward (WbS, WbT) intramolecular energy transfer (IET) rates were determined. Magnetic properties of Tb3+ compounds were studied in a constant field of 0.5 T in the temperature range of 1.8–300 K. Dynamic AC magnetic susceptibility measurements were carried out as a function of temperature and frequency for 1Tb and 2Tb. Only in the case of 2Tb, in the presence of an external DC field, a slight temperature dependence of in-phase χ′ and out-of-phase χ'' susceptibility was recorded. Based on experimental and theoretical results, the significant effect of counterion on the photophysical and magnetic properties of RE chelates has been demonstrated and clarified, providing valuable guidance for the design of bifunctional electromagnetic radiation converters.

Extraction method for superimposed coherent transition radiation using Fresnel reflection in a ring-type resonator

To generate terahertz pulses with a high peak power, a pulse train of coherent transition radiation (CTR) is superimposed by circulating it in a ring-type resonator at an L-band electron linear accelerator facility at the Kyoto University Institute for Integrated Radiation and Nuclear Science. By extracting the superimposed CTR pulses from the ring-type resonator via Fresnel reflection on a low-loss parallel substrate, we show that the cavity loss can be suppressed without being affected by the wavenumber of the CTR pulses. The power of the superimposed CTR pulse is increased to approximately four times that of a CTR generated by plane mirrors in the resonator at a wavenumber of 8.5cm−1, where the diffraction loss of the resonator is lower. Using shorter electron bunches to generate CTR pulses with higher wavenumbers increases the amplification factor caused by superposition and allows CTR pulses with a higher peak power to be generated.

Symmetry Molecular Design Strategy for Highly Efficient Blue Electroluminescence with Hot Exciton Mechanisms

AbstractEmitters with a hot exciton mechanism are regarded as one of the most promising candidates for organic light‐emitting diodes (OLEDs). In this study, a deep‐blue emitter with the hot exciton mechanism is reported, namely 2An‐PCz, by integrating a pair of carbazole groups with a 9,9′‐bi‐anthracene nucleus. Owing to the symmetric molecular architecture and intrinsic local excited state character, multiple high‐lying reverse intersystem cross (hRISC) channels and large overlaps of frontier molecular orbits (FMOs) can be formed, facilitating rapid hRISC processes as well as enhancement of radiative transition rates simultaneously. Combined with the strong luminescence properties brought by the unique X‐packing mode, a high photoluminescence quantum yield of 60.5% is achieved in the non‐doped state. Strikingly, non‐doped deep‐blue OLEDs exhibited a maximum external quantum efficiency (EQE) of 10.50% with minimal efficient roll‐off, which is one of the highest values for deep‐blue organic light‐emitting devices based on hot exciton emitters thus far. The magneto‐electroluminescence (MEL) experiment and transient electroluminescence measurements corroborated that both the high EQE and suppressed efficiency roll‐off are attributable to the rapid “hot exciton” channels.

Newly Designed Quasi-intrinsic Photosensitizers for Fluorescence Image-Guided Two-Photon Photodynamic Therapy with Type I/II Photoreactions.

In this work, a set of quasi-intrinsic photosensitizers are theoretically proposed based on the 2-amino-8-(1'-β-d-2'-deoxyribofuranosyl)-imidazo[1,2-α]-1,3,5-triazin-4(8H)-one (P), which could pair with the 6-amino-5-nitro-3-(1'-β-d-2'-deoxyribofuranosyl)-2(1H)-pyridone (Z) and keep the essential structural characters of nucleic acid. It is revealed that the ring expansion and electron-donating/electron-withdrawing substitution bring enhanced two-photon absorption and bright photoluminescence of these monomers, thereby facilitating the selective excitation and tumor localization through fluorescence imaging. However, instead of undergoing radiative transition (S1 → S0), the base pairing induced fluorescence quenching and rapid intersystem crossing (S1 → Tn) are observed and characterized by the reduced singlet-triplet energy gaps and large spin-orbit coupling values. To ensure the phototherapeutic properties of the considered base pairs in long-lived T1 state, we examined the vertical electron affinity as well as vertical ionization potential for production of superoxide anions via Type I photoreaction, and their required T1 energy (0.98 eV) to generate singlet oxygen 1O2 via Type II mechanism.

Light emission from ion-implanted SiGe quantum dots grown on Si substrates

We report on electroluminescence spectroscopy experiments demonstrating room-temperature light emission from heavily alloyed SiGe quantum dots, for which the light emission properties are enhanced by incorporated split-[110] self-interstitials. The quantum dots are formed during molecular beam epitaxy deposition of Si0.6Ge0.4 alloys on n-doped silicon-on-insulator substrates. To create the split-[110] self-interstitials the quantum dots were co-implantated in-situ using Si and Ge ions. The hybrid emitters were further embedded into the intrinsic region of a p-i-n diode structure to enable electrical pumping. Similar to previous theoretical results on unstrained Ge-based quantum dots containing these defects, radiative direct transitions are possible for these SiGe light emitters. However, in SiGe dots these transitions are not at the Brillouin zone center. Instead, first-principles calculations indicate that the presence of the split-[110] self-interstitial defect in strained and unstrained SiGe can lead to optically direct transitions in momentum space in the X-direction of the Brillouin zone.

Continuous tuning of optical transition properties and phonon spectrum in Er3+ doped germano-tellurite glass system

With the development of science and the progress of technology, novel and advanced rare earth ions doped luminescent materials with higher performance are demanded in the both emerging and traditional applications. Understanding the rules for tuning the spectroscopic properties of these materials is crucial for their development. However, achieving precise control over the optical properties of rare earth doped materials using traditional design and synthesis methods, such as altering dopants and their concentrations or modifying the preparative conditions, still remains challenging. This work aims to adjust the optical transition characteristics of Er3+ doped germano-tellurite glasses by changing the glass components. First, the Er3+ doped germano-tellurite glass series were synthesized using a high-temperature melt-quenching method at optimized melting temperatures. The tuning of band gap energy and refractive index of the glasses were revealed, and it was found that both of them can be monotonically and continuously tuned by changing the glass composition. The optical transition intensity parameters of Er3+ in the glasses were calculated in the framework of traditional three-parameterized Judd-Ofelt theory using the absorption spectra, and furthermore the corresponding optical transition parameters including radiative transition rates and intrinsic lifetimes for some interested levels were alsoconfirmed. The results demonstrated that the optical transition parameters could be efficiently modulated by changing the glass composition, indicating that the spectral properties of Er3+ doped germano-tellurite glasses can be tuned for the practical applications. The reliability of the deduced tuning rule was validated by comparing the theoretical and experimental transition rate ratios of 2H11/2 → 4I15/2 to 4S3/2 → 4I15/2. Furthermore, the tuning regulation of the phonon spectra in relation to the glass composition was discovered, showing a concordance between theoretical predictions and experimental results. From the above facts, it can be concluded that the optical transition properties of Er3+ in germano-tellurite glasses can be substantially adjusted by modifying the glass composition. This work provides a new perspective for designing and developing novel luminescent materials to meet specific application needs.