Higher Excited States Research Articles

Dual and Panchromatic Emission from N-Aryl-phenanthridinones: Extension of the Seesaw Photophysical Model with a Slight Twist.

White-light emission from a single organic molecule, known as a single white-light emitter, is a rare phenomenon and desirable property for a class of materials with potential future applications in white lighting. Since N-aryl-naphthalimides (NANs) have been shown to follow excited state behavior and unique dual or panchromatic emission through a substituent pattern prescribed via a seesaw photophysical model, this study investigates the substituent effects on the fluorescence emission of structurally related N-aryl-phenanthridinones (NAPs) dyes. Following a similar placement prescription of an electron-releasing group (ERG) and electron-withdrawing group (EWG) at the phenanthridinone core and N-aryl moiety, we discovered from time-dependent density functional theory (TD-DFT) results that NAPs show a substitution pattern opposite to NANs in order to promote S2 and higher excited states. Interestingly, 2-methoxy-5-[4-nitro-3(trifluoromethyl)phenyl]phenanthridin-6(5H)-one 6e displayed a pronounced dual and panchromatic fluorescence dye depending on the solvent. For the six dyes included in the study, full spectral information in a variety of solvents, as well as fluorescence quantum yield and lifetime are reported. TD-DFT calculations support the predicted optical behavior via mixing of S2 and S6 excited states via anti-Kasha type of emission behavior.

High concentration quenching, improved PLQY and high color purity of novel Gd2TiO5:Eu3+ triggered by complete solubility of dopant

In the surge of new inorganic luminescent host for lanthanide ion for efficient solid-state lighting, Ln2TiO5 comes as a new class of materials with all optically suited properties. Triggered by very high solubility of Eu3+ ion in Gd2TiO5 with minimal lattice strain, negligible doping induced structural distortion and no charge compensating defects; Gd2TiO5:Eu3+ (GTOE) delivered an extraordinary credentials as novel phosphor material. GTOE demonstrated no concentration quenching up to 10 mol % doping; monotonic rise in emission intensity, higher excited state lifetime, high red color purity∼99% and PLQY∼ 14%. Luminescence lifetime spectroscopy suggested stabilization of Eu3+ in both GdO7 with distorted pentagonal bipyramid (DPB) and distorted hexagonal bipyramid (DHB) geometry having similar coordination and symmetry and is well supported by two stark components in 5D0→7F0 transitions. Positron annhilation lifetime spectroscopy (PALS) suggested that average positron lifetime remained constant in all the samples indicating no charge compensating defects formation further justifying occupancy of Eu3+ in isovalent Gd3+ site. Judd-Ofelt analysis suggested that local symmetry around Eu3+ ion and polarizability of Eu–O bonds in GTO host doesn't change throughout the concentration range. This work proposed an excellent candidate for red emitting materials towards phosphor converted white light emitting diodes (pcLEDs) having high dopant solubility, PLQY and color purity.

Excited State Photophysics of Curcumin and its Modulation in Alkaline Non-Aqueous Medium.

Curcumin, a well-known medicinal pigment, has seen limited applications in biology despite having great potential as a therapeutic drug. Deprotonation is one of the possible ways to enhance solubility of curcumin in polar solvent. Here, we have explored the effect of deprotonation on the ultrafast dynamics of this biomolecule with the help of the time-resolved fluorescence spectroscopic measurements using the femtosecond fluorescence upconversion technique. The excited state photophysics of fully deprotonated curcumin significantly differs from that of neutral curcumin. We have observed that the completely deprotonated curcumin not only has higher quantum yield, but also higher excited state lifetime and slower solvation dynamics in comparison to neutral curcumin. We propose solvation dynamics and intramolecular charge transfer as the excited state processes associated with the radiative decay of the completely deprotonated molecule, while ruling out the possibility of excited state proton exchange or proton transfer. Our results are well supported by time-dependent density-functional theory calculations. Lastly, we have also demonstrated the possibility of modulating the ultrafast dynamics of fully deprotonated curcumin using non-aqueous alkaline binary solvent mixtures. We believe our results will provide significant physical insight towards unveiling the excited state dynamics of this molecule.

Dissipation and dephasing of interacting photons in transmon arrays

Transmon arrays are one of the most promising platforms for quantum information science. Despite being often considered simply as qubits, transmons are inherently quantum mechanical multilevel systems. Being experimentally controllable with high fidelity, the higher excited states beyond the qubit subspace provide an important resource for hardware-efficient many-body quantum simulations, quantum error correction, and quantum information protocols. Alas, dissipation and dephasing phenomena generated by couplings to various uncontrollable environments yield a practical limiting factor to their utilization. To quantify this in detail, we present here the primary consequences of single-transmon dissipation and dephasing to the many-body dynamics of transmon arrays. We use analytical methods from perturbation theory and quantum trajectory approach together with numerical simulations, and deliberately consider the full Hilbert space, including the higher excited states. The three main nonunitary processes are many-body decoherence, many-body dissipation, and heating/cooling transitions between different anharmonicity manifolds. Of these, the many-body decoherence---being proportional to the squared distance between the many-body Fock states---gives the strictest limit for observing effective unitary dynamics. Considering experimentally relevant parameters, including also the inevitable site-to-site disorder, our results show that the state-of-the-art transmon arrays should be ready for the task of demonstrating coherent many-body dynamics using the higher excited states. However, the wider utilization of transmons for ternary-and-beyond quantum computing calls for improving their coherence properties.

Eu3+ as a spectroscopic probe to understand local site-luminescence correlation in novel Y2TiO5:Eu3+ phosphor

Red emitting phosphor materials play a very important role in improving the color rendering index and lighting efficiency of phosphor-converted white light-emitting diodes (pc-WLEDs). However, the research pertaining to design and development of the same has somehow saturated with real lack of novel compositions and functionalities. In this work, a sincere effort has been vested in designing relatively new compositions Y2TiO5:x%Eu3+(x = 1–10) using simple solid-state reactions for efficient, narrow and pure red emission. Europium is distributed at both Y(1) and Y(2) site with higher excited state lifetime. Under the optimal mid and near ultraviolet light excitation, Y2TiO5:5%Eu3+shows a strong red emission at 608 nm with a high color purity of 99.96% and a moderate internal quantum efficiency of 13%. Impressively, this red-emitting phosphor exhibits a concentration quenching at 5.0 mol%, internal QY of ∼34%, lower non-radiative channels and higher branching ratio. Trend in Judd-Ofelt parameter suggested that there is monotonic increase in degree of distortion and as the concentration increases Eu-O bond becomes highly polarizable. This work and the obtained results suggested that Y2TiO5:Eu3+ phosphor has great potential to serve as red emitting phosphor for pc-WLEDs, opening a new perspective for developing new titanate-based luminescent materials.

Organic All-Photonic Artificial Synapses Enabled by Anti-Stokes Photoluminescence.

All-photonic synaptic devices with the merits of visible signals and high spatiotemporal resolution are promising to break the Von Neumann bottleneck. Although organic synapses outperform their inorganic counterpart for easy molecular modulation and lower energy consumption, the organic all-photonic artificial synapse has never been reported. Here, all-photonic synaptic characteristics were unprecedentedly observed in an organic semiconductor, (3,6-dimethyl-9H-carbazol-9-yl)(thiophen-2-yl) methanone (S2OC), with anti-Stokes photoluminescence. Impressively, the intensity of fluorescence from the higher excited state (S3) exhibited synaptic performance, which constantly increased with irradiation time through a channel composed of intersystem crossing, triplet-triplet annihilation, and energy transfer. More importantly, the relationship between the molecular structure and synaptic performance was established. Based on the synaptic photoplasticity property, noncontacted multilevel anticounterfeiting and imaging recognition were realized in all-photonic synapse arrays. This work provides a universal strategy for tuning the performances of organic synapses upon regulating the molecular structures, which paves the way for the application of organic semiconductors in artificial intelligence.

Energies of the ground and excited states of confined two-electron atom in finite potential well

For the ground and excited configurations, we have carried out the energy eigenvalues and corresponding wavefunctions of two-electron atom enclosed by finite confining potential by using Quantum Genetic Algorithm (QGA) procedure and Hartree-Fock Roothaan (HFR) method. Besides, we have analysed in detail orbital energies and probabilities of finding electron for the configurations 1S (1s2), 3S (1s2s), 3P (1s2p), 3D (1s3d) and 3F (1s4f). The results reveal that the potential barrier height plays a significant role on average energies, state energies, orbital energies and probabilities of finding electrons in orbitals. As dot size is extremely small and extremely large, the energies for 1snl configurations are getting close to each other, but between these two extreme situations they are separating from each other. While going to higher excited states, singlet and triplet states are almost the same due to the weakening of the exchange energy.

Thermodynamic properties and effective mass of a weakly-interacting Bose gas using the static fluctuation approximation

The Static Fluctuation Approximation is used to investigate the thermodynamic properties and the single-particle effective mass of a weakly-interacting Bose gas. These properties include: the transition temperature, condensate fraction, energy spectrum, total energy, and specific heat capacity. The effects of the potential strength, number density, and temperature on these properties are studied. The transition temperature decreases as the potential strength increases, or the number density decreases. Also, the condensate fraction decreases drastically with increasing potential strength or decreasing density number. The total energy and specific heat indicate that the system is in the classical (quantum) regime at temperatures greater (less) than the transition temperature. The specific heat has a peak at the transition temperature. Regarding the effective mass: in higher excited states, it is close to the ‘bare’ mass, regardless of the potential strength and number density; but, in low-lying states, it is tangibly affected by these variables.

Holographic entanglement entropy and subregion complexity for excited states of holographic superconductors

We investigate the holographic entanglement entropy (HEE) and the holographic subregion complexity (HSC) for holographic superconductors, both in the Einstein and in the Einstein-Gauss-Bonnet gravitational theories. For both ground and excited states, we show that, in the Einstein gravity, the HSC decreases as the temperature increases and the normal phase has a smaller HSC than the superconducting phase, which is opposite to the behavior of the HEE. Moreover, we find out that, for a given temperature T in the superconducting phase, the higher excited state leads to a lager value of the HEE but a smaller value of the HSC. However, the Einstein-Gauss-Bonnet gravity has significantly different effect on the HSC, while the HEE always increases monotonously as the temperature increases and its value in the normal phase always larger than that in the superconducting phase. Our results indicate that the HEE and HSC provide richer physics in phase transitions and condensation of scalar hair for holographic superconductors with excited states.

Reaction dynamics of molecules in highly electronically excited states attained by multiphoton and multiple excitation methods

Abstract Multiphoton absorption and multiple excitation can lead to the formation of highly electronically excited states of molecules. We have been applying these excitation methods to explore specific photochemical reactions, which are rather difficult to attain by normal one-photon absorption processes. In the present review, we will introduce several examples of these photochemical responses specific to highly excited state in the condensed phase, such as two-photon-gated cycloreversion, one-color control of both reactions in photochromic systems and rapid capture of an electron ejected from the higher excited state leading to rapid generation of charge-separated states at the high energy level with a lifetime much longer than microseconds.

Ultrafast non-adiabatic dynamics of stilbene-based plant-derived sunscreens with cis–trans isomerization structures

In this work, we investigated the potential UV protection mechanism of the natural compounds hydroxy resveratrol and pterostilbene by combining theoretical calculations and femtosecond transient absorption spectra (FTAS). The UV absorption spectra showed that the two compounds exhibited strong absorption properties and high photostability. We found two molecules will reach the S1 state or an even higher excited state after UV exposure and molecules in S1 will cross a lower energy barrier to reach the conical intersection. The adiabatic trans–cis isomerization process happened and finally return to the ground. Meanwhile, FTAS clarified the time scale of trans–cis isomerization of two molecules was ∼ 10 ps, which also met the requirement of fast energy relaxation. This work also provides theoretical guidance for developing new sunscreen molecules from natural stilbene.

Predicting the Excitation Dynamics in Lanthanide Nanoparticles

AbstractWith their dipole‐forbidden 4f transitions, lanthanides doped in nanoparticles promise high excited state lifetimes and quantum yields that are required for applications such as composite lasers or nanoscale quantum memories. Quenching at the nanoparticle surface, however, severely reduces the lifetime and quantum yield and requires resource‐consuming experimental optimization that could not be replaced by simulations due to the limitations of existing approaches until now. Here, a versatile approach is presented that fully accounts for spatiotemporal dynamics and reliably predicts the lifetimes and quantum yields of lanthanide nanoparticles. LiYF4:Pr3+nanoparticles are synthesized as a model system, and the lifetimes of a concentration series (≈10 nm, 0.7−1.47 at%) are used to match the model parameters to the experimental conditions. Employing these parameters, the lifetimes and quantum yields of a size series (≈5 at%, 12−21 nm) are predicted with a maximum uncertainty of 12.6%. To demonstrate the potential of the model, a neutral shell is added around the core particles in the model which extends the lifetime by up to 44%. Furthermore, spatiotemporal analysis of single nanoparticles points toward a new type of energy trapping in lanthanide nanoparticles. Consequently, the numerical optimization brings applications such as efficient nanoparticle lasers or quantum memories within reach.

Strong-field ionization and AC-Stark shifted Rydberg states in OCS

We present theoretical results for intensity-dependent above-threshold ionization (ATI) spectra from oriented OCS molecules probed by intense femtosecond laser pulses with wavelengths of 800 and 400 nm. The calculations were performed using the time-dependent Schrödinger equation within the single-active-electron approximation and including multielectron polarization effects. The results capture some of the experimental findings (Yu et al 2017 J. Phys. B: At. Mol. Opt. Phys. 50 235602), in particular when considering the sensitivity of the ATI spectra on the molecular orientation. We identify characteristic features in the ATI spectra which correspond to resonant multiphoton ionization via highly-excited Rydberg states are captured by the theory.

An efficient and stable blue-emission OLED based on the A-π-A configuration by “hot exciton” strategy

The “hot exciton” channel, which effectively converts triplet excitons to singlet excitons from the high triplet excited state (Tn, n > 1) to the singlet excited state (Sm, m ≥ 1), can theoretically achieve 100% utilization efficiency (ηs) of the singlet excitons. In this work, two deep-blue “hot exciton”-based fluorescent emitters, IAM and TAM, with the asymmetric structure of acceptor(A)-π-acceptor(A) configuration, were designed and synthesized. Both compounds have excellent thermal stability with thermal decomposition temperatures of up to 505 and 486 °C, respectively. The outstanding thermal stability makes them easy to form amorphous films, during device vaporization, which is beneficial for luminescence. The optimized non-doped device based on IAM achieves a deep-blue emission centered at 452 nm with International Commission on Electron Emission (CIE) coordinates of (0.148, 0.145), and reaches a maximum external quantum efficiency (EQEmax) of 6.09% and a maximum luminance of 9197 cd m−2. The EQE maintains 5.1% at 1500 cd m−2, with a low efficiency roll-off, by virtue of the excellent carrier balance derived from the rational molecular regulation of IAM. The excellent deep-blue electroluminescent performance of IAM indicates that the “hot exciton” channel has unique advantages in achieving superior deep-blue emission. Meanwhile, the A-π-A design strategy is an effective way to realize the “hot exciton”, which sheds a light on the research on the “hot exciton” materials.

Valley-orbit splitting of lithium-related donors in silicon

The energy spectra of lithium-related donors in silicon are revisited by temperature-dependent infrared absorption spectroscopy. We determine the valley-orbit splitting of an interstitial isolated lithium donor and its complex with residual oxygen in float-zone grown crystals doped from the melt. Lithium-oxygen donors exhibit a temperature evolution of their absorption spectra similar to that of substitutional single-electron group-V donors, while its valley-orbit splitting is corrected upwards to +9.865(5) meV. For the lithium donor, the previously reported inverted valley-orbit splitting is not confirmed since the components of different symmetry are not spectrally resolved in our study. Instead, the chemical shift of the ground state of the donor, having a symmetry different from that of group-V donors, was corrected to a slightly larger value of 1.82(2) meV. Intracenter transitions from the split-off ground state of the Li donor exhibit an anomalous broadening. In addition, several Rydberg-like high excited states, up to $7{h}_{\ifmmode\pm\else\textpm\fi{}}$, of lithium-related centers were determined from absorption spectra of moderately doped samples.

Configurational entropy of black hole quantum cores

Two types of information entropy are studied for the quantum states of a model for the matter core inside a black hole geometry. A detailed description is first given of the quantum mechanical picture leading to a spectrum of bound states for a collapsing ball of dust in general relativity with a non-trivial ground state. Information entropies are then computed, shedding new light on the stability of the ground state and the spectrum of higher excited states.

Strategy for Modulating Dihedral Angle Distribution for Enhanced Anti-Kasha TADF Behavior

D–A type thermally activated delayed fluorescence (TADF) materials with aggregation-induced emission (AIE) have attracted extensive research interest for their intense emission and high quantum yield in aggregated state. Herein, TADF molecules with vertical twisted structures are achieved by the methylation strategy which effectively separated the highest occupied molecular orbital (HOMO) and the lowest unoccupied molecular orbital (LUMO). With the increase of the dihedral angle, 18 times enhancement of the photoluminescence quantum yield (PLQY) is realized in the aggregated state. The density functional theory (DFT) calculations demonstrate that these TADF molecules exhibit excellent photophysical properties in violation of Kasha’s rule: fluorescence originates from the higher energy electronic excited state (S2) rather than the S1 state.

Excitation Intensity-Dependent Quantum Yield of Semiconductor Nanocrystals

One of the key phenomena that determine the fluorescence of nanocrystals is the nonradiative Auger-Meitner recombination of excitons. This nonradiative rate affects the nanocrystals' fluorescence intensity, excited state lifetime, and quantum yield. Whereas most of the above properties can be directly measured, the quantum yield is the most difficult to assess. Here we place semiconductor nanocrystals inside a tunable plasmonic nanocavity with subwavelength spacing and modulate their radiative de-excitation rate by changing the cavity size. This allows us to determine absolute values of their fluorescence quantum yield under specific excitation conditions. Moreover, as expected considering the enhanced Auger-Meitner rate for higher multiple excited states, increasing the excitation rate reduces the quantum yield of the nanocrystals.

Photodissociation study of CO2 on the formation of state-correlated CO(X1Σ+, v) with O(3P2) photoproducts in the low energy band centered at 148 nm.

The spin-forbidden O(3P2) + CO(X1Σ+, v) channel formed from the photodissociation of CO2 in the low energy band centered at 148nm is investigated by using the time-sliced velocity-mapped ion imaging technique. The vibrational-resolved images of the O(3P2) photoproducts measured in the photolysis wavelength range of 144.62-150.45nm are analyzed to give the total kinetic energy releases (TKER) spectra, CO(X1Σ+) vibrational state distributions, and anisotropy parameters (β). The TKER spectra reveal the formation of correlated CO(X1Σ+) with well resolved v = 0-10 (or 11) vibrational bands. Several high vibrational bands that were observed in the low TKER region for each studied photolysis wavelength exhibit a bimodal structure. The CO(X1Σ+, v) vibrational distributions all present inverted characteristics, and the most populated vibrational state changes from a low vibrational state to a relatively higher vibrational state with a change in the photolysis wavelength from 150.45 to 144.62nm. However, the vibrational-state specific β-values for different photolysis wavelengths present a similar variation trend. The measured β-values show a significant bulge at the higher vibrational levels, in addition to the overall slow decreasing trend. The observed bimodal structures with mutational β-values for the high vibrational excited state CO(1Σ+) photoproducts suggest the existence of more than one nonadiabatic pathway with different anisotropies in the formation of O(3P2) + CO(X1Σ+, v) photoproducts across the low energy band.

Holographic p-Wave Superconductor with Excited States in 4D Einstein–Gauss–Bonnet Gravity

We construct a holographic p-wave superconductor with excited states in the 4D Einstein–Gauss–Bonnet gravity using the Maxwell complex vector field model. In the probe limit, we observe that, the higher curvature correction or the higher excited state can hinder the vector condensate to be formed in the full parameter space, which is different from the holographic s-wave superconductor. Regardless of the choice of the vector mass by selecting the value of m2L2 or m2Leff2, we note that the critical chemical potential becomes evenly spaced for the number of nodes and that the difference of the critical chemical potential between the consecutive states depends on the curvature correction. Moreover, we find that the higher curvature correction or the higher excited state will alter the universal relation of the gap frequency, and the pole and delta function of the conductivity for the excited states can be broadened into the peaks with the finite width as the curvature correction increases.