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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 200 fs 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. [ABSTRACT FROM AUTHOR]

The semiconducting behavior of two-dimensional (2D) metal nanostructures has recently attracted much interest for their possible applications in optoelectronics and others. In particular, tuning the bandgap of such nanostructures can open up a new avenue for fabricating functional nano-devices. In the present article, we report the synthesis of 2D metallic Zn nanosheets at room temperature using a ball mill, which is capable of producing large-scale materials in a single run. Initially, nanoplates were formed for ball milling the octahedral-shaped Zn nanoparticles for the time of milling of 6 h. Subsequent ball milling for another 6 h leads these nanoplates to nearly uniform nanosheets. The thickness of these 2D nanostructures was found to decrease with an increase in the time of milling. Visible photoluminescence (PL) emissions centered at ∼3, ∼2.9, and ∼2.75 eV were observed from all the Zn particles showing semiconductor behavior. The origin of such semiconductor behavior was explained based on the radiative transition of electrons from the sp band to the upper states of the 3d band. This argument was confirmed through the studies of photoelectron spectroscopy and the first principle calculations employing density functional theory (DFT). Furthermore, excitation-dependent PL studies indicated that the bandgap of the 2D Zn nanostructures decreased with the increase in the ball milling time. Therefore, a redshift in the bandgap was observed with the increase in the ball milling time. Such changes in the bandgap with the thickness of 2D Zn nanostructures were also verified from the studies of DFT. Thus, the present study demonstrated that the bandgap of 2D metallic Zn nanostructures could be effectively tuned by reducing the thickness. [ABSTRACT FROM AUTHOR]

Relativistic coupled-cluster calculations of the ionization potential, dissociation energy, and excited electronic states under 35 000 cm−1 are presented for the actinium monofluoride (AcF) molecule. The ionization potential is calculated to be IPe = 48 866 cm−1, and the ground state is confirmed to be a closed-shell singlet and thus strongly sensitive to the T , P -violating nuclear Schiff moment of the Ac nucleus. Radiative properties and transition dipole moments from the ground state are identified for several excited states, achieving a mean uncertainty estimate of ∼450 cm−1 for the excitation energies. For higher-lying states that are not directly accessible from the ground state, possible two-step excitation pathways are proposed. The calculated branching ratios and Franck–Condon factors are used to investigate the suitability of AcF for direct laser cooling. The lifetime of the metastable (1)3Δ1 state, which can be used in experimental searches of the electric dipole moment of the electron, is estimated to be of order 1 ms. [ABSTRACT FROM AUTHOR]

A narrow-band green emitting K3Tb(PO4)2 phosphor has been synthesized by a novel single-crystal growth approach involving the application of an inert flux. Its structural and spectroscopic peculiarities have been systematically studied by means of single-crystal X-ray diffraction, scanning electron microscopy, energy-dispersive X-ray spectroscopy analysis, and diffuse reflectance, infrared and photoluminescence spectroscopy. The layered framework of the title compound is organized by linking together slightly distorted phosphate tetrahedra with non-condensed TbO7 polyhedra into [Tb(PO4)2]3− sheets interconnected by potassium cations. K3Tb(PO4)2 reveals an intense slow green photoluminescence (PL) (decay time constant τ is near 2.6 ms) under excitation in the range from VUV (100 nm) up to blue light (484 nm). Intensive narrow lines of the 5D4 → 7F6-0 (4f8 → 4f8) radiative transitions in Tb3+ ions form the PL spectra. Besides, fast violet PL (time constant τ < 20 ns) occurs under PL excitations in a narrow range from 250 to 325 nm. Dependencies of the PL quantum yield, and the green and violet PL decays on the excitation wavelength have been analyzed taking into account the multi-phonons, cross-relaxation processes and exciting light absorption by the inherent defects in the K3Tb(PO4)2 crystal lattice. The dependency of the complex characteristics of PL quantum yield on the excitation wavelength and violet photoluminescence is ascribed to the formation of Tb4+ ions. The color coordinates and color purity of the emission were estimated for the cases of PL excitation in the 160–371 nm spectral range. It has been shown that these characteristics are similar to or even better than those reported for conventional commercial green phosphors. The high values of correlated color temperature (T > 4863 K) of the emission indicates the potential use of K3Tb(PO4)2 for enhancing cold-light emitting devices. [ABSTRACT FROM AUTHOR]

The present study investigated the impact of incorporating copper nanoparticles (CuNPs) on the optical properties of erbium-doped borate glasses. Through melt-quenching and heat treatment techniques, glasses with varying Cu 2 O concentrations (x = 0–5 mol%) were synthesized. Physical and structural analyses revealed that Cu ions serve as effective network modifiers. They foster the formation of a greater proportion of BO 4 tetrahedra and thus enhancing glass homogeneity. Optical absorption spectra demonstrate a distinct modulation of Er3+ absorption bands with Cu 2 O embedding, indicating the formation of CuNPs, as validated by the emergence of surface plasmon resonance bands. This structural evolution results in a noticeable reduction in the bandgap energy, signifying improved semiconducting behavior. Judd-Ofelt analysis highlighted the profound influence of CuNPs on hypersensitive transitions, thereby affecting oscillator strength. Photoluminescence measurements revealed amplified emission in the visible red and near infrared (NIR) region, attributed to the synergistic effects of CuNPs and Er3+ ions, with 5 mol % Cu 2 O exhibiting the highest emission intensity. Analysis of the radiative properties validates the enhancement of the emission cross-section, gain bandwidth, optical gain and radiative transitions. These enhancements contribute to a notable increase in the branching ratio from 0.91 % to 5.41 % accompanied by an increase in the quantum efficiency from ∼79 % to ∼90 %. Moreover, decay analysis revealed a notable enhancement in lifetime from 3.03 ms to 15.74 ms, which is indicative of enhanced radiative transitions. Overall, the incorporation of CuNPs into erbium-doped borate glasses facilitates significant enhancements in physical, structural, and optical properties. This positions them as promising materials for a wide array of optoelectronic applications. This comprehensive study sheds light on the complex interplay between CuNPs and erbium-barium borate glasses, offering valuable insights for the development of advanced optoelectronic materials with enhanced performance and functionality. [Display omitted] [ABSTRACT FROM AUTHOR]

Temperature‐adaptive variable emissivity reflectors offer an electricity‐free and environmentally friendly cooling strategy, holding substantial potential to improve the global energy landscape. However, challenges associated with unoptimized solar absorptance can lead to overcooling or overheating when the modulation of infrared emittance is held constant, thereby increasing extra energy consumption. Herein, a temperature‐adaptive variable emissivity reflector based on W‐Mg co‐doped VO2 (W‐Mg‐VER) is proposed, engineered to optimize solar absorptance (αL = 0.40) while maintaining effective infrared emittance modulation (Δɛ = 0.69) near ambient temperature. To maximize year‐round energy savings in regions experiencing significant daily temperature fluctuations, W‐Mg co‐doped VO2 is employed to reduce solar absorptance by modifying electron occupancy in the V 3d orbital and expanding the optical bandgap. Outdoor experiments have validated the remarkable temperature management and energy‐saving capabilities of the W‐Mg‐VER, facilitated by its seamless transition between radiative cooling and heat‐retaining modes. Numerical simulation indicates that a W‐Mg‐VER roof covering 100 m2 would save 152.9 GJ of energy annually in locations with significant daily temperature variations. Moreover, W‐Mg‐VER demonstrates robust performance, exhibiting less than 1% degradation in emittance tunability and solar absorptance after 10 000 cycles. This approach provides valuable insights and practical guidance for significantly enhancing global energy savings. [ABSTRACT FROM AUTHOR]

Noncovalent spatial interaction has become an intriguing and important tool for constructing optoelectronic molecules. In this study, we linearly attached three conjugated units in a multi π‐stacked manner by using just one trident bridge based on indeno[2,1‐b]fluorene. To achieve this structure, we improved the synthetic approach through double C−H activation, significantly simplifying the preparation process. Due to the proximity of the C10, C11, and C12 sites in indeno[2,1‐b]fluorene, we derived two novel donor|acceptor|donor (D|A|D) type molecules, 2DMB and 2DMFB, which exhibited closely packed intramolecular stacking, enabling efficient through‐space charge transfer. This molecular construction is particularly suitable for developing high‐performance thermally activated delayed fluorescence materials. With donor(s) and acceptor(s) constrained and separated within this spatially rigid structure, elevated radiative transition rates, and high photoluminescence quantum yields were achieved. Organic light‐emitting diodes incorporating 2DMB and 2DMFB demonstrated superior efficiency, achieving maximum external quantum efficiencies of 28.6 % and 16.2 %, respectively. [ABSTRACT FROM AUTHOR]

Spectroscopic studies of Ho3+-doped SrF2 crystals were performed regarding applications in solid-state lasers. The crystal structure of the Ho:SrF2 crystal was investigated using single-crystal X-ray diffraction. SrF2 exists as a cubic structure with an Fm3m space group. A Raman shift of 288 cm–1 was observed for the Ho:SrF2 single crystal. SrF2 hosts with low-frequency vibrational modes are suitable for reducing nonradiative emissions while maximizing radiative emissions. The absorption spectrum was recorded in the visible region from 400 to 800 nm, yielding absorption lines at 416, 450, 468, 473, 484, 536, 638, and 643 nm. The fluorescence spectrum recorded at an excitation wavelength of 450 nm shows two emission bands at 546 and 656 nm, which correspond to green and red emission, respectively. The intensity parameters Ωλ (λ = 2, 4, and 6) were estimated using the Judd–Ofelt theory. For Ho:SrF2 single crystal, the calculated Ωλ are Ω2 = 0.14 × 10–20 cm2, Ω4 = 3.14 × 10–20 cm2, and Ω6 = 3.74 × 10–20 cm2. The radiative transition probabilities, radiative lifetimes, and branching ratios βR for Ho:SrF2 were determined using the Judd–Ofelt parameters. The 5S2 + 5F4 → 5I8 transition is more effective for population-building processes because of its lifetime (0.26 ms) and higher branching ratios (~82.86%). Ho:SrF2 is, therefore, a promising solid-state laser crystal for green and red spectral regions. [ABSTRACT FROM AUTHOR]

The effect of irradiation with different doses of 4-MeV electrons on radiative recombination of nonequilibrium charge carriers in Cu(In,Ga)(S,Se)2 thin films of solar cells was studied. Near-edge photoluminescence (PL) in the energy range ~0.9–1.2 eV in nonirradiated and irradiated direct-gap Cu(In,Ga)(S,Se)2 solid solutions was caused by optical interband transitions and radiative recombination through energy levels of acceptor- and donor-type structure defects in the presence of strong potential fluctuations. PL spectra measured in the temperature range 5–300 K exhibited energy shifts of the near-edge PL band maxima and redistributions of their intensities in thin films after irradiation with different doses of electrons. The activation energies of nonradiative recombination were determined from the quenching of PL band intensities. The possible nature of structural defects in nonirradiated and electron-irradiated Cu(In,Ga)(S,Se)2 solid solutions was discussed. [ABSTRACT FROM AUTHOR]

A glass composition using TeO2-K2TeO3-Nb2O5-BaF2 co-doped with Er2O3/Ho2O3 and Er2O3/Yb2O3 was successfully fabricated. Its thermal stability and physical parameters were studied, and luminescence spectroscopy of the fabricated glasses was conducted. The optical band gap, Eopt, decreased from 2.689 to 2.663 eV following the substitution of Ho2O3 with Yb2O3. The values of the refractive index, third-order nonlinear optical susceptibility (χ(3)), and nonlinear refractive index (n2) of the fabricated glasses were estimated. Furthermore, the Judd–Ofelt intensity parameters Ω t   (t = 2 , 4 , 6) , radiative properties such as transition probabilities (Aed), magnetic dipole-type transition probabilities (Amd), branching ratios (β), and radiative lifetime (τ) of the fabricated glasses were evaluated. The emission cross-section and FWHM of the 4I13/2→4I15/2 transition around 1.54 μm of the glass were reported, and the emission intensity of the visible signal was studied under 980 nm laser excitation. The material might be a useful candidate for solid lasers and nonlinear amplifier devices, especially in the communications bands. [ABSTRACT FROM AUTHOR]

Surface ligands crucially influence the structure and luminescence of metal nanoclusters (NCs). In this study, three [Ag25(SPhCl)16−xClx(DPPB)6]2+ (x = 0 for Ag25, x = 1 for Ag25‐Cl, and x = 4 for Ag25‐4Cl) featuring thiol and Cl ligand combinations are synthesized and investigated. Ag25‐4Cl, which has the smallest number of rigid thiol ligands, exhibits the strongest photoluminescence (PL) and chemiluminescence (CL), and its PL quantum yield is 73.43% higher than that of Ag25. Structural analysis indicates that Cl ligands, being smaller and less sterically hindering than thiols, compress the motif layer towards the core, reducing non‐radiative transitions and boosting radiative ones to enhance PL. All three NCs exhibit CL in the presence of singlet oxygen, demonstrating the ability of the NCs to react with radicals and scavenge them. CL and radical scavenging experiments show that Ag25‐4Cl exhibits the highest CL and the lowest radical reaction ability, indicating that CL intensity of an NC depends more on its intrinsic luminescence ability and less on its ability to react with radicals. The regulation of luminescence by ligands and the CL and radical‐scavenging behavior of NCs are expected to be extended to other NC systems and related applications. [ABSTRACT FROM AUTHOR]

A chiral shape‐persistent macrocyclic compound (Si‐[3]), designed by the C/Si substitution in the spiro‐atom of spirobifluorene in the cyclic trimer (C‐[3]), has been successfully synthesized in this study. The C/Si substitution made the spiro‐conjugation and energy levels of HOMO and LUMO decrease. Due to the silicon substitution, the macrocyclic compound Si‐[3] was able to be degraded by fluoride ions, but its reaction rate was slower than that of the unsubstituted spirosilabifluorene, showing the chemical stability of Si‐[3]. Furthermore, the chiroptical properties of Si‐[3] with D3‐symmetric macrocyclic structure were investigated, and (P,P,P)‐Si‐[3] showed a high emission quantum yield (Φf=80 %) and moderate dissymmetry factor of circularly polarized luminescence (CPL) (glum,exp=−1.2×10−3). According to the time‐dependent density‐functional theory (TD‐DFT) calculations using polarizable continuum model (PCM), the bright CPL from Si‐[3] was explained by a planarization of one bisilafluorenyl moiety at the excited state, which is responsible for the almost fully‐allowed radiative transition with a short emission lifetime of τf=1.89 ns. [ABSTRACT FROM AUTHOR]

Scintillators have been widely used for high‐energy radiation imaging. It is in great demand and challenge to develop scintillator materials with fast decay time, high scintillation light yield, and low detection limit for high‐resolution imaging applications such as time‐of‐flight positron emission tomography. However, it is still a challenge to develop the ultrafast carrier dynamics to achieve 100% ultrafast decay time with high scintillation light yield. To meet the demand, a series of component‐tunable Cs2ZnCl4: x%Zr single crystals as promising ultrafast scintillators is successfully developed. With 8% of Zr‐dopant (Cs2ZnCl4: 8%Zr), the single crystal exhibits high light yield (28000 photons MeV−1) and low detection limit (51 nGy s−1) under X‐ray excitation. Photo‐induced transient absorption signals on sub‐nanosecond and nanosecond scales ensure almost 100% fast decay time (≈3 ns) in nanoseconds under γ‐ray excitation. In particular, the different radiative transition processes are achieved under ultraviolet and high‐energy radiation due to the tunable carrier dynamics from the shallow trapped state to the self‐trapped exciton (STE) state. [ABSTRACT FROM AUTHOR]

The pursuit of energy‐saving materials and technologies has garnered significant attention for their pivotal role in mitigating both energy consumption and carbon emissions. In particular, thermochromic windows in buildings offer energy‐saving potential by adjusting the transmittance of solar irradiation in response to temperature changes. Radiative cooling (RC), radiating thermal heat from an object surface to the cold outer space, also offers a potential way for cooling without energy consumption. Accordingly, smart window and RC technologies based on thermochromic materials can play a crucial role in improving energy efficiency and reducing energy consumption in buildings in response to the surrounding temperature. Vanadium dioxide (VO2) is a promising thermochromic material for energy‐saving smart windows and RC due to its reversible metal‐to‐insulator transition, accompanying large changes in its optical properties. This review provides a brief summary of synthesis methods of VO2 nanostructures based on nanoparticles and thin films. Moreover, this review emphasizes and summarizes modulation strategies focusing on doping, thermal processing, and structure manipulation to improve and regulate the thermochromic and emissivity performance of VO2 for smart window and RC applications. In last, the challenges and recent advances of VO2‐based smart window and RC applications are briefly presented. [ABSTRACT FROM AUTHOR]

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. [ABSTRACT FROM AUTHOR]

We study the spectroscopy of an ensemble of negatively charged nitrogen-vacancy centers in diamond at high temperatures between room temperature and 700 K under high vacuum conditions. Spin resonances are studied using optical detection of magnetic resonance (ODMR), and optical spectroscopy is employed to study radiative transitions. Upon increasing the temperature, the intensity of radiative decay in visible and infrared decreased. In addition, the ODMR resonance frequencies were decreased, and the phonon line emission shifted to higher wavelengths. Density functional theory calculation of the zero-field splitting parameter (D) revealed that thermal expansion is not enough to explain the shift in the ODMR frequencies. Fitting the measured intensity of photo-luminescence with the theoretical predictions of the Mott–Seitz model yields the value of 0.22 eV for the energy barrier associated with nonradiative decay. [ABSTRACT FROM AUTHOR]

NIR‐II luminescent materials are the key enablers of smart spectroscopy‐based techniques, offering capabilities for nondestructive analysis and bio‐imaging. Here, a broadband NIR‐II luminescence with a recorded external quantum efficiency (EQE) of 76% in LiGa5O8 are demonstrated, using heavily doping Cr3+ ion (10%) as a light harvester and a controllable energy transfer (ET) from Cr3+ to Ni2+ (0.4%) ions. Even though the Cr3+ ion produces substantially weak luminescence due to concentration quenching, the introduction of Ni2+ ions effectively extract the excitation energy to generate NIR‐II luminescence. Complementary investigations using synchrotron‐based EXAFS fittings and structural refinement disclose a significant structural distortion in the LiGa5O8 compound, which facilitates the relaxation of the parity‐selection rules for Cr3+ and Ni2+ ions. Additionally, DFT calculations identify specific site occupations, which favor unidirectional ET from Cr3+ to Ni2+ ions. As a result, the significant absorption of excitation light by heavy‐doping Cr3+ ions and high radiative transition probability in Ni2+ ions synergistically result in a record high EQE. These findings provide pioneering insight into rational NIR‐II light generation by deliberated control of ET pathway in heavily doped systems, thereby with promising implications for NIR spectroscopy applications. [ABSTRACT FROM AUTHOR]

Energy levels, transition rates, and electron-impact ionization and excitation cross sections for W I are calculated by multi-configuration Dirac–Fock (MCDF) method using the MDFGME code which aims at improving the accuracies of the atomic data which has been crucial for spectroscopic diagnostics of erosion rate of W in plasma surface interaction. Particular attention has been paid to the core–core (CC) and core–valence (CV) electron correlation effects on the level energies and radiative transition rates. The inclusion of the CC and CV electron correlations significantly improves an agreement with the atomic structure data based on experiments. The electron-impact ionization and excitation cross sections are obtained employing binary-encounter Bethe model and scaled plane wave Born approximation, respectively, from the wave functions by the MCDF calculation The obtained collision cross sections and rate coefficients are compared with other available data, which has been used to determine the erosion rate of W with spectral lines in the range of 400–525 nm. [ABSTRACT FROM AUTHOR]

Ratiometric afterglow luminescent (AGL) probes are attractive for in vivo imaging due to their high sensitivity and signal self‐calibration function. However, there are currently few ratiometric AGL probes available for imaging enzymatic activity in living organisms. Here, we present an energy diversion (ED) strategy that enables the design of an enzyme‐activated ratiometric AGL probe (RAG‐RGD) for in vivo afterglow imaging. The ED process provides RAG‐RGD with a radiative transition for an 'always on' 520‐nm AGL signal (AGL520) and a cascade three‐step energy transfer (ET) process for an 'off‐on' 710‐nm AGL signal (AGL710) in response to a specific enzyme. Using matrix metalloproteinase‐2 (MMP‐2) as an example, RAG‐RGD shows a significant ~11‐fold increase in AGL710/AGL520 toward MMP‐2. This can sensitively detect U87MG brain tumors through ratiometric afterglow imaging of MMP‐2 activity, with a high signal‐to‐background ratio and deep imaging depth. Furthermore, by utilizing the self‐calibration effect of ratiometric imaging, RAG‐RGD demonstrated a strong negative correlation between the AGL710/AGL520 value and the size of orthotopic U87MG tumor, enabling accurate monitoring of orthotopic glioma growth in vivo. This ED process may be applied for the design of other enzyme‐activated ratiometric afterglow probes for sensitive afterglow imaging. [ABSTRACT FROM AUTHOR]

The melt quenching technique was used to prepare zinc tellurite glasses with composition of [(TeO2)0.7 (ZnO)0.3]1-x [Sm2O3]x, where x is the molar fraction. The glasses were synthesized at various x values of 0.01, 0.02, 0.03, 0.04, and 0.05. Xray diffraction patterns depict the absence of distinct absorption peaks, indicating its amorphous nature. The shear and longitudinal velocities of the samples were measured using 5 MHz of frequency at room temperature. Physical properties such as density ( ρ) , and molar volume ( V m) increases from 5.142 to 5.324 g/cm3 and 27.412 to 27.590 cm3/mol. Variations in ultrasonic velocity, elastic moduli, Debye temperature ( θ D ), Softening temperature ( T S ) and Poisson's ratio (σ) were discussed and correlated with the composition of the glass samples. Additionally, elastic moduli and Poisson's ratio were compared with the theoretically measured data using the four theoretical elastic models of Makishima and Mackenzie, Rocherulle, Bond compression and Ring Deformation models. The Judd-Offelt parameters ( Ω 2 , Ω 4 and Ω 6 ) are obtained using Judd-Ofelt theory. To determine the possible applications of the synthesized glasses, the spectroscopic parameters were calculated for each band: radiative transition probabilities [ A MD / A ED ], branching ratio β R , spectroscopic quality factor ( Ω 4 / Ω 6 ), gain bandwidth (Δλeff × σp) and the optical gain (σp × τ). The obtained higher values of gain bandwidth, optical gain, branching ratio, spectroscopic quality factor (1.550) and the radiative transition probabilities show that the glasses prepared are appropriate for laser applications. [ABSTRACT FROM AUTHOR]

The single crystals of CsI-Yb2+ were grown, and their spectroscopic studies were conducted. The observed luminescence in CsI-Yb2+ is due to 5d–4f transitions in Yb2+ ions. Using time-resolved spectroscopy, spin-allowed and spin-forbidden radiative transitions of ytterbium ions at room temperature were found. The excitation spectra of Yb2+ luminescence bands were obtained in the range of 3–45 eV. The mechanism of charge compensation of Yb2+ ions in a CsI crystal was also studied, the spectrum of the thermally stimulated depolarization current was measured, and the activation energies of the two observed peaks were calculated. These peaks belong to impurity–vacancy complexes in two different positions. The charge compensation of Yb2+ occurs via cation vacancies in the nearest-neighbor and next-nearest-neighbor positions.The Yb2+ ions are promising dopants for CsI scintillators and X-ray phosphors in combination with SiPM photodetectors. [ABSTRACT FROM AUTHOR]

Donor‐acceptor (D–A•) type luminescent organic radicals have received widespread attention as efficient doublet emitters. However, their generally low photoluminescence quantum efficiency (PLQE) and limited photostability restrict their various applications. Since unraveling the relationship between structure and properties of D–A• type luminescent radicals remains a challenge, here, a series of tri(2,4,6‐trichlorophenyl)methyl (TTM) radical derivatives, which differ by the location of their ring fusion sites and nature of their heteroatoms, is synthesized. The PLQE of isomers varies by ten times as a function of ring fusion sites. In particular, the PLQE of a radical undergoing ring fusion at the carbazole 3,4‐position is as high as 98.0%. Quantum‐chemical calculations show that in the case of overlapping holes and electrons, by increasing the effective distance between the D and A moieties, the radiative transition rates of the radicals increase. Also, decreasing the electronic coupling between the charge‐transfer and local‐excited states and avoiding large geometrical distortions between the ground state (D0)_and the first excited state (D1) can significantly reduce the nonradiative transition rates. This work offers a design strategy to obtain efficient and stable luminescent radicals by modifying the sites of ring fusion, which allows control of the radiative and nonradiative transition rates. [ABSTRACT FROM AUTHOR]

Organic radical luminescent materials have attracted worldwide attention because of their absolute spin‐allowed radiative transition and sensitivity to the environment, which give it multiple stimulus response properties. Nowadays, how to regulate and utilize the sensitivity of radicals has become a hot and difficult issue. Here, arylphosphonium bromide salts are introduced into the molecular backbone of naphthimide (NMI) using an intramolecular counterion strategy, and prepared a novel multifunctional stabilized radical luminescent: TPP‐o‐3OMe‐NMI‐Br. Interestingly, this molecule exhibits different assembly modes in different solvents, resulting in the generation of two crystals with different fluorescence (green: G‐C; orange–yellow: Y‐C), in which the Y‐C crystalline powder exhibits excellent stabilization properties for doublet and triplet excitons, which induce the emission of orange–yellow radical afterglow, and exhibits multi‐stimuli responsiveness to external pressure (P), temperature (T) and water (W). Moreover, interesting time‐dependent photoactivated colorful fluorescence and orange–yellow radical afterglow can be observed in TPP‐o‐3OMe‐NMI‐Br@PMMA films with different doping ratios and exhibit multi‐color tunability, multiple stimulus responses, multiple data encryption, and optical information erase/write behavior. This study not only broadens the types and applications of organic radical long afterglow materials but also provides new ideas for designing new organic "chameleon" luminescent materials in the field of smart luminescence materials. [ABSTRACT FROM AUTHOR]

Context. It is now well established that the neutron star (NS) merger is at the origin of the production of trans-iron heavy elements in the universe. These elements are therefore present in large quantities in the ejected matter, whose electromagnetic radiation, called kilonova, is characterized by a significant opacity due to the high density of spectral lines belonging to many heavy ions. Among these, the lanthanide ions play an essential role since, with their open 4f subshell, they have a considerable number of transitions that can absorb emitted light. The knowledge of the atomic structure and the radiative parameters of these ions as well as the determination of the corresponding opacities is therefore of paramount importance for the spectral analysis of kilonovae. Aims. The main goal of the present work is to determine the relative contributions of the different lanthanide elements to the opacity of the emission spectrum of a kilonova in its early phase, that is, a few hours after the NS merger, where the conditions are such that the temperature is between 25 000 and 40 000 K. At these temperatures, the lanthanide ions whose charge states are between V and VII are predominant. Methods. We used the pseudo-relativistic Hartree–Fock (HFR) method extensively to calculate the relevant atomic data (energy levels, wavelengths, and oscillator strengths) in La-Lu V-VII ions. The corresponding monochromatic opacities were estimated from the expansion formalism. Results. We calculated the spectroscopic parameters for a total of more than 800 million radiative transitions in all the ions considered. These data were used to estimate the expansion opacities and Planck mean opacities for all the lanthanide elements at early-phase kilonova conditions between 25 000 and 40 000 K, making it possible to deduce the respective contributions of each element as a function of temperature. Atomic calculations were also carried out with the fully relativistic Multiconfiguration Dirac-Hartree-Fock (MCDHF) method in the specific case of the Yb V ion, as the available experimental data had not yet been compared with the theoretical calculations in our previous studies on lanthanide ions. [ABSTRACT FROM AUTHOR]

A quantum memory is a crucial keystone for enabling large‐scale quantum networks. Applicable to the practical implementation, specific properties, i.e., long storage time, selective efficient coupling with other systems, and a high memory efficiency are desirable. Though many quantum memory systems are developed thus far, none of them can perfectly meet all requirements. This work herein proposes a quantum memory based on color centers in hexagonal boron nitride (hBN), where its performance is evaluated based on a simple theoretical model of suitable defects in a cavity. Employing density functional theory calculations, 257 triplet and 211 singlet spin electronic transitions are investigated. Among these defects, it is found that some defects inherit the Λ electronic structures desirable for a Raman‐type quantum memory and optical transitions can couple with other quantum systems. Further, the required quality factor and bandwidth are examined for each defect to achieve a 95% writing efficiency. Both parameters are influenced by the radiative transition rate in the defect state. In addition, inheriting triplet‐singlet spin multiplicity indicates the possibility of being a quantum sensing, in particular, optically detected magnetic resonance. This work therefore demonstrates the potential usage of hBN defects as a quantum memory in future quantum networks. [ABSTRACT FROM AUTHOR]

Naphthalocyanine-based agents exhibit huge potential in photodynamic therapy, yet their photodynamic performance is restricted by the penetration depth of the external laser. Herein, we employed 18F-FDG as an internal light source to excite silicon naphthalocyanine nanoparticles to simultaneously circumvent radiative transition and boost 1O2 generation for tumor suppression. [ABSTRACT FROM AUTHOR]

In purely organic room‐temperature phosphorescence (RTP) materials, fluorescence radiative transitions generally compete against inter‐system crossing (ISC) transitions to give fluorescence/phosphorescence dual emission. In order to achieve pure phosphorescence in RTP organic light‐emitting diodes (OLEDs), extended π‐conjugation is introduced into Se‐containing donors to suppress the fluorescence radiative transitions by the symmetry excited state orbitals in the introduced π–π* transitions that cancel the overlap of the orbitals, and two novel nonaromatic amine donor containing orange RTP emitters namely 2‐(benzo[c]phenoxaselenin‐10‐yl)‐4,6‐diphenyl‐1,3,5‐triazine (BPXSeDRZ) and 2‐(dibenzo[a,c]phenoxaselenin‐11‐yl)‐4,6‐diphenyl‐1,3,5‐triazine (DBPXSeDRZ) are developed, both of which exhibit efficient orange pure phosphorescence in doped films thanks to the sufficient ISC transitions. As a result, high external quantum efficiencies of 17.2% and 17.9% are respectively achieved for the orange RTP‐OLEDs based on BPXSeDRZ and DBPXSeDRZ for the first time, and they also exhibit stable pure electro‐phosphorescence spectra in a wide driving voltage. Moreover, by adopting DBPXSeDRZ as a sensitizer to harvest the triplet excitons and tetraphenyldibenzoperiflanthene as a conventional fluorescent emitter, the external quantum efficiency of the sensitized red fluorescent OLED can be elevated to 10.1%, which greatly expands the potential applications of the metal‐free phosphors in OLEDs. [ABSTRACT FROM AUTHOR]

Nowadays, the application scenarios of rare earth doped luminescent materials tend to be refined and complicated. The optical properties of rare earth doped materials are difficult to precisely control via the traditional design and synthesis methods, namely, changing doping concentration or preparative conditions. The aim of this study is to tune the optical transition properties of Er3+ in tungsto-molybdate NaY(Mo x W 1- x O 4) 2 (x = 0, 0.01, 0.1, 0.3, 0.5, 0.7, 0.9, 0.99 and 1.0) phosphors by changing the host matrix. The Er3+ doped continuous tungsto-molybdate solid solution NaY(Mo x W 1- x O 4) 2 phosphors were prepared via a solid state reaction technique at optimized calcination temperatures. The refractive indexes of the obtained solid solution samples were confirmed according to different models and compared. Subsequently, the optical transition intensity parameters, radiative transition rates and intrinsic radiative lifetimes of Er3+ in these solid solution phosphors were calculated in the framework of Judd-Ofelt theory. It was confirmed that the optical transition properties of Er3+ can be greatly tuned by the solid solution composition, and the tuning effects for different transitions are different. To validate the reliability of the Judd-Ofelt calculations, the temperature-dependent emission spectra of two green emissions of Er3+ for different solid solution samples were studied. It was found that the radiative transition rate ratios between two green emissions derived from theoretical calculations and experimental measurements are in reasonable agreement, thus proving that the optical transition calculations are reliable and the optical transition properties of Er3+ in the tungsto-molybdates can be tuned in a large range. This work reminds us of a new route for developing novel luminescence materials based on practical demands. [ABSTRACT FROM AUTHOR]

A series of Tb3+-doped Sr2YTaO6 double perovskite phosphors (SYT:Tb3+) were synthesized using a conventional solid-state reaction method. A strong green emission was observed in the SYT:Tb3+ phosphors, and the optimal doping concentration of Tb3+ was confirmed to be 5 mol%. The electric dipole-dipole interaction was ascribed to be the main mechanism for the luminescence concentration quenching. Analysis of the concentration-dependent fluorescence decay confirmed that the self-generated quenching model holds for the dynamic process of Tb3+ decays in SYT. Furthermore, the internal quantum efficiencies, non-radiative transition rates, and energy transfer rates of the 5D4 level for the SYT:Tb3+ samples were estimated, respectively. The luminescence thermal stability of the sample was also evaluated based on the Arrhenius model. The chromaticity shift of the SYT:5 mol% Tb3+ phosphor was examined to be 0.013 when the sample temperature was increased from 303 to 483 K, thus indicating excellent chromaticity shifting resistance under high temperature conditions. Moreover, the Judd-Ofelt parameters were calculated from the emission spectra of SYT:Tb3+ to be Ω2 = 0.29 × 10-20, Ω4 = 0.45 × 10-20, and &@937;6 = 0.72 × 10-20 cm², respectively. The fluorescence branching ratios and radiative transition rates for the 5D4 level were calculated based on the obtained Judd-Ofelt parameters. Finally, a white light-emitting diode (LED) prototype was assembled using a 310 nm LED chip combined with a prepared green SYT:Tb3+ phosphor and two other commercial blue and red phosphors. The obtained warm white light exhibits good chromaticity coordinates (0.32, 0.32) and a high color rendering index of 96.1. Based on the above results, it can be known that the prepared SYT:Tb3+ phosphors have a potential application as green emitting phosphors in white LEDs. [ABSTRACT FROM AUTHOR]

The broad emission bump in the electromagnetic spectra observed following the detection of gravitational waves created during the kilonova event of the merging of two neutron stars in August 2017, named GW170817, has been linked to the heavy elements of lanthanides (Z = 57–71) and a new understanding of the creation of heavy elements in the r-process. The initial spectral emission bump has a wavelength range of 3000–7000 Å, thus covering the region of ultraviolet (UV) to optical (O) wavelengths, and is similar to those seen for lanthanides. Most lanthanides have a large number of closely lying energy levels, which introduce extensive sets of radiative transitions that often form broad regions of lines of significant strength. The current study explores these broad features through the photoabsorption spectroscopy of 25 lanthanide ions, Ho I-III, Er I-IV, Tm I-V, Yb I-VI, and Lu I-VII. With excitation only to a few orbitals beyond the ground configurations, we find that most of these ions cover a large number of bound levels with open 4 f orbitals and produce tens to hundreds of thousands of lines that may form one or multiple broad features in the X-ray to UV, O, and infrared (IR) regions. The spectra of 25 ions are presented, indicating the presence, shapes, and wavelength regions of these features. The accuracy of the atomic data used to interpret the merger spectra is an ongoing problem. The present study aims at providing improved atomic data for the energies and transition parameters obtained using relativistic Breit–Pauli approximation implemented in the atomic structure code SUPERSTRUCTURE and predicting possible features. The present data have been benchmarked with available experimental data for the energies, transition parameters, and Ho II spectrum. The study finds that a number of ions under the present study are possible contributors to the emission bump of GW170817. All atomic data will be made available online in the NORAD-Atomic-Data database. [ABSTRACT FROM AUTHOR]

Exploiting emissive hydrophobic nanoclusters for hydrophilic applications remains a challenge because of photoluminescence (PL) quenching during phase transfer. In addition, the mechanism underlying PL quenching remains unclear. In this study, the PL‐quenching mechanism was examined by analyzing the atomically precise structures and optical properties of a surface‐engineered Ag29 nanocluster with an all‐around‐carboxyl‐functionalized surface. Specifically, phase‐transfer‐triggered PL quenching was justified as molecular decoupling, which directed an unfixed cluster surface and weakened the radiative transition. Furthermore, emission recovery of the quenched nanoclusters was accomplished by using a supramolecular recoupling approach through the glutathione‐addition‐induced aggregation of cluster molecules, wherein the restriction of intracluster motion and intercluster rotation strengthened the radiative transition of the clusters. The results of this work offer a new perspective on structure‐emission correlations for atomically precise nanoclusters and hopefully provide insight into the fabrication of highly emissive cluster‐based nanomaterials for downstream hydrophilic applications. [ABSTRACT FROM AUTHOR]

The Y-type compound 67dTPA-FQ combining 2-phenylfuro[2,3-b]quinoxaline (FQ) with triphenylamine (TPA) demonstrated to be a green fluorescence emitter (519 nm) with a ΔES1T1 of 0.40 eV. Herein, TPA units in 67dTPA-FQ were replaced with 10-phenyl-10H-phenoxazine (Ph-PXZ) units to shift the S1 energy to a lower direction to reduce ΔES1T1 and realize thermally-activated delayed fluorescence (TADF). Thus, Y-shaped (67dPXZ-FQ) and T-shaped (58dPXZ-FQ) compounds were synthesized. As the donor changed from TPA to PXZ, the emission bands of the Y- and T-shaped compounds in toluene shifted to 585 nm and 631 nm, respectively. As we expected, ΔES1T1 for Y- and T-shaped compounds decreased to 0.12 eV and 0.15 eV, respectively, well lower than 0.3 eV. Unfortunately, the TADF feature was not observed. Theoretical calculations revealed that the HOMO and LUMO orbitals of both compounds were completely located at one of the PXZ fragment and 2-phenylfuro[2,3-b]quinoxaline moiety, respectively, yielding a complete electron separation by phenylene bridges between the acceptor FQ and PXZ. As a result, the oscillator strength (f) of the S1 → S0 transition was only 0.0001–0.0002, leading to weak radiative transition capability of the S1 state. As a result, a low fluorescent yield of 25–36% was obtained. Moreover, the calculated spin–orbital coupling value between the S1 and T1 was only 0.13 cm−1 for both 67dPXZ-FQ and 58dPXZ-FQ, suggesting weak driving capability for the reverse intersystem crossing process. As such, the TADF features of the two compounds were not observed. [ABSTRACT FROM AUTHOR]

Embedding both boron and nitrogen into the backbone of acenes to generate their isoelectronic structures has significantly enriched the acene chemistry to offer appealing properties. However, only small BN‐heteroacenes have been extensively investigated, with BN‐heptacenes as the hitherto longest homologue. Herein, we report the synthesis of three new nonacene BN‐isosteres via incorporating a pair of antiaromatic B2C4 and N2C4 heterocycles, representing a new length record for BN‐heteroacenes. The distance between the B2C4 and N2C4 rings affects the contribution of the charge‐separated resonance forms, leading to tunable antiaromaticity of the two heterocycles. The adjusted local antiaromaticity manifests substantial influence on the molecular orbital arrangement, and consequently, the radiative transition rate of BN‐3 is greatly enhanced compared with BN‐1 and BN‐2, realizing a high fluorescence quantum yield of 92 %. This work provides a novel design concept of large acene BN‐isosteres and reveals the importance of BN/CC isosterism on their luminescent properties. [ABSTRACT FROM AUTHOR]

Organic room‐temperature phosphorescence (RTP) from triplet excitons has shown great potential for biological imaging and sensing, but these applications in aqueous environments are often limited by the moisture‐mediated phosphorescence quenching. Water‐induced enhancement of RTP can overcome this limitation, but the underlying mechanism remains unclear. This study focuses on two control prototypes CT and CTW, composed of trimesic acid (TMA, guest) and cyanuric acid (CA, host), while CTW introduces 20 wt.% water to CT, leading to enhanced RTP. Theoretical calculations demonstrate that the molecular conformation of TMA manipulated by intermolecular interactions governs the RTP property of aggregates. From CT to CTW, the TMA tends to a more coplanar geometry due to the decreased values in the span of deviation from plane. This conformational change not only increases the spin‐orbit coupling (SOC) of S1→Tn, thereby accelerating the intersystem crossing process and radiative transition for promoting RTP efficiency, but also reduces the SOC of T1→S0, suppressing the non‐radiative transition to prolong RTP lifetime. Exciton dynamics reproduce the prolonged RTP lifetime from CT to CTW in experiments, which is dominated by the SOC, rather than the electron‐vibration coupling. The findings offer novel insights for developing water‐doped materials with improved RTP performance. [ABSTRACT FROM AUTHOR]

Perylene diimides (PDIs) have received considerable attention as a versatile class of functional dyes owing to their flexible reaction sites and remarkable stability. Recent advances have enhanced our understanding of the fluorescence and photothermal conversion properties of PDI molecules. The interplay between radiative and nonradiative transitions controls the emission and heat generation processes in these molecules. This comprehensive overview summarizes the recent strategies for manipulating the structures of PDI molecules for fluorescence and photothermal conversion applications. Additionally, challenges and potential solutions associated with the usage of fluorescent and photothermal PDI molecules are discussed. [ABSTRACT FROM AUTHOR]

Herein we report the optical and spectroscopic properties of lithium–calcium–bismuth–borate (LCBB) glasses containing Eu3+ prepared via the melt-quenching method, and the prepared samples were systematically characterised through X-ray diffraction (XRD), Raman, ultraviolet–visible–near-infrared (UV–Vis-NIR) and photoluminescence (PL) spectroscopic techniques. The absence of XRD peaks evidenced the amorphous nature of glass. Different borate functional groups were identified from Raman spectra. Urbach energy and radiative properties were evaluated from the UV–Vis–NIR absorption spectra. The phonon energy of the glass samples was estimated by considering the energy differences between the zero-phonon level (ZPL) and phonon side bands (PSBs) present in excitation spectra. Judd–Ofelt (JO) parameters have been evaluated from the luminescence intensity ratios of 5D0 → 7FJ (J = 2, 4) to 5D0 → 7F1 transitions. These parameters have been used to derive radiative properties such as transition probabilities, branching ratios, radiative lifetimes and peak stimulated emission cross-sections for the 5D0 → 7FJ transitions. The JO results and the lifetime decay studies showed that LCBBEu2 glass exhibits higher stimulated cross-section (16.74 × 10–22 cm2) and quantum efficiency (67.80%), which is highest among the reported by other research groups. Also, the LCBB doped with Eu3+ glasses exhibit strong emission in the red region, making them potential candidates for photonic device applications. [ABSTRACT FROM AUTHOR]

Previously reported atomic data (spectral lines, wavelengths, energy levels, and transition probabilities) were collected and systematically analyzed for Cs VI. The present theoretical analysis was supported by extensive calculations made for Cs VI with a pseudo-relativistic Hartree–Fock (HFR) method together with the superposition of configuration interactions implemented in Cowan's codes. In this work, all previously reported energy levels and their (allowed) transition assignments were confirmed. A critically evaluated set of optimized energy levels with their uncertainties, observed and Ritz wavelengths along with their uncertainties, and theoretical transition probabilities with their estimated uncertainties were presented in the compilation. In addition to this, we determined the radiative transition parameters for several forbidden lines within the ground configuration 5 s 2 5 p 2 of Cs VI. [ABSTRACT FROM AUTHOR]

Full utilization of the excited species at both singlet states (1R*) and triplet states (3R*) is crucial to improving electrochemiluminescence (ECL) efficiency but is challenging for organic luminescent materials. Here, an aggregation‐induced delayed ECL (AIDECL) active organic dot (OD) containing a benzophenone acceptor and dimethylacridine donor is reported, which shows high ECL efficiency via reverse intersystem crossing (RISC) of non‐emissive 3R* to emissive 1R*, overcoming the spin‐forbidden radiative decay from 3R*. By introducing dual donor‐acceptor pairs into luminophores, it is found that nonradiative pathway could be further suppressed via enhanced intermolecular weak interactions, and multiple spin‐up conversion channels could be activated. As a consequence, the obtained OD enjoys a 6.8‐fold higher ECL efficiency relative to the control AIDECL‐active OD. Single‐crystal studies and theoretical calculations reveal that the enhanced AIDECL behaviors come from the acceleration of both radiative transition and RISC. This work represents a major step towards purely organic, high‐efficiency ECL dyes and a direction for the design of next‐generation ECL dyes at the molecular level. [ABSTRACT FROM AUTHOR]

Time-dependent density functional theory (TDDFT) based approaches have been developed in recent years to model the excited-state properties and transition processes of the molecules in the gas-phase and in a condensed medium, such as in a solution and protein microenvironment or near semiconductor and metal surfaces. In the latter case, usually, classical embedding models have been adopted to account for the molecular environmental effects, leading to the multi-scale approaches of TDDFT/polarizable continuum model (PCM) and TDDFT/molecular mechanics (MM), where a molecular system of interest is designated as the quantum mechanical region and treated with TDDFT, while the environment is usually described using either a PCM or (non-polarizable or polarizable) MM force fields. In this Perspective, we briefly review these TDDFT-related multi-scale models with a specific emphasis on the implementation of analytical energy derivatives, such as the energy gradient and Hessian, the nonadiabatic coupling, the spin–orbit coupling, and the transition dipole moment as well as their nuclear derivatives for various radiative and radiativeless transition processes among electronic states. Three variations of the TDDFT method, the Tamm–Dancoff approximation to TDDFT, spin–flip DFT, and spin-adiabatic TDDFT, are discussed. Moreover, using a model system (pyridine–Ag20 complex), we emphasize that caution is needed to properly account for system–environment interactions within the TDDFT/MM models. Specifically, one should appropriately damp the electrostatic embedding potential from MM atoms and carefully tune the van der Waals interaction potential between the system and the environment. We also highlight the lack of proper treatment of charge transfer between the quantum mechanics and MM regions as well as the need for accelerated TDDFT modelings and interpretability, which calls for new method developments. [ABSTRACT FROM AUTHOR]

The semiconductor–metal heteronanocrystals (HNCs) that possess a perfect epitaxial interface can accommodate novel and interesting physical phenomena owing to the strong interaction and coupling between the semiconductor excitons and metal plasmons at the interface. Here, we fabricate the pyramidal ZnO–Au HNCs and study their unique photophysical properties. Several Au nanospheres are perfectly epitaxially bound with a single ZnO NC owing to the small lattice mismatch between them and there are also ZnO–Au–ZnO sandwiched HNCs. There is a strong coupling between the green defect-associated recombination in the ZnO NC and the localized surface plasmon resonance (LSPR) of the Au nanosphere at the interface of the HNC. This leads to resonant defect recombination–LSPR energy transfer and resultant nearly complete quenching of the green defect luminescence of the ZnO NCs in the HNCs, leaving only the UV exciton luminescence. The lifetimes of both the green and UV emission bands decrease significantly in the ZnO–Au HNCs relative to that of the pure ZnO NCs owing to the combined effect of resonance energy transfer and surface plasmon enhanced radiative transition. The exponent of the luminescence intensity–excitation intensity power function for the green emission band is remarkably smaller than unity, and this suggests that the involved defects have an intermediate concentration. [ABSTRACT FROM AUTHOR]

Color tunability from red to orange to yellow has been demonstrated in GaN-based LED devices with Eu-doped GaN layers as the active region. Under current injection, this is achieved by varying the current density and the pulse conditions. The underlying mechanism behind this color tunability is a redistribution of energy among the 5DJ states of a Eu3+ ion. This energy shuffling is facilitated by a local defect that has been neglected in previous modeling work. Including this defect allows for a quantitative prediction of the relative time-averaged populations of the Eu3+ ion's 5D0 and 5D1 states. Extracting, from experimental results, the red and yellow/green emission spectra due to radiative transitions from the respective levels and mixing them allows the overall chromaticity of the emission to be determined for varied excitation conditions. In addition, the model allows us to determine the optimal injection conditions to maximize the gamut of color tunability while minimizing power consumption. These simulations pave the way for practical, systematic color tuning from a single-contact pixel. [ABSTRACT FROM AUTHOR]

Overcoming exciton quenching and improving electroluminescence (EL) performances continue to pose persistent challenges in the development of efficient deep blue thermally activated delayed fluorescence (TADF) emitters. Herein, an asymmetric multi‐donors strategy is employed that provides the potential of establishing multiple radiative transition channels for fluorescence emission and reverse intersystem crossing (RISC), while allowing flexible modulation of packing modes in single‐crystal state and optimization of morphology in films by modifying the substitution site of the donor units. As a result, intermolecular π–π interactions are effectively alleviated and a very smooth surface with a reduced defect density is simultaneously achieved, which can significantly reduce the density of triplet excitons, accelerate the charge transfer rate, and enhance carrier injection efficiency. Consequently, a super‐high photoluminescence quantum yield (PLQY) of 99% and fast kRISC of 1.1 × 105 s−1 are concurrently achieved for the proof‐of‐concept emitter 3,4‐Cz‐SF‐SFAC. The corresponding deep‐blue organic light‐emitting diode (OLED) demonstrates an exceptional external quantum efficiency (EQE) of 31.1%, accompanied by an emission peak at 457 nm, one of the preeminent TADF materials within the deep blue region, ranking among the most efficient OLEDs with an EL spectra below 460 nm on record. [ABSTRACT FROM AUTHOR]

The triatomic hydrogen ion $ \mathrm {H}_3^+ $ H 3 + is one of the most important species for the gas phase chemistry of the interstellar medium. Observations of $ \mathrm {H}_3^+ $ H 3 + are used to constrain important physical and chemical parameters of interstellar environments. However, the temperatures inferred from the two lowest rotational states of $ \mathrm {H}_3^+ $ H 3 + in diffuse lines of sight – typically the only ones observable – appear consistently lower than the temperatures derived from H $ _2 $ 2 observations in the same sightlines. All previous attempts at modelling the temperatures of $ \mathrm {H}_3^+ $ H 3 + in the diffuse interstellar medium failed to reproduce the observational results. Here we present new studies, comparing an independent master equation for H $ _3^+ $ 3 + level populations to results from the Meudon PDR code for photon dominated regions. We show that the populations of the lowest rotational states of $ \mathrm {H}_3^+ $ H 3 + are strongly affected by the formation reaction and that H $ _3^+ $ 3 + ions experience incomplete thermalisation before their destruction by free electrons. Furthermore, we find that for quantitative analysis more than two levels of H $ _3^+ $ 3 + have to be considered and that it is crucial to include radiative transitions as well as collisions with H2. Our models of typical diffuse interstellar sightlines show very good agreement with observational data, and thus they may finally resolve the perceived temperature difference attributed to these two fundamental species. [ABSTRACT FROM AUTHOR]

The capture times of holes to the shallow excited levels of neutral mercury vacancy via acoustic phonon emission are calculated for Hg1 –xCdxTe, as well as the transition times of holes from shallow localized levels to the continuum of the valence band at different temperatures. Due to the redistribution of carriers in the valence band with temperature, the time of carrier capture to the localized levels of the neutral vacancy increases, and the time of reionization to the continuum decreases. Based on the calculation results, a model is proposed to describe the temperature quenching of photoluminescence caused by radiative transitions between the localized states of holes on a neutral mercury vacancy. [ABSTRACT FROM AUTHOR]

We fabricated arrays of parallel nanowires. Each of the nanowires consists of two different magnetic metals. Using Raman spectrometry, we studied the spectra that appear when a heterojunction between metals is illuminated by a laser and studied the effect of an external magnetic field on the spectra. We also measured the dependence of the intensity of the spectra on the position of the laser spot (in the region of heterojunctions) and on the radiation intensity and we hypothesized the threshold nature of excitation. Near the contact of two metals, the symmetry of the crystal lattice is broken due to amorphization, and a nonzero orbital momentum of the electrons appears. As a result, another radiative transition of electrons become allowed without spin flip, which is sensitive to the magnetic field. [ABSTRACT FROM AUTHOR]

In this study, a comprehensive analysis of emission in erbium-doped and erbium and ytterbium co-doped fluoroindate glasses has been presented. The luminescence of the erbium transitions and the effect of ytterbium co-doping under 488, 808 and 976 nm laser excitation have been discussed. Optimization of rare-earth (RE) ions doping concentration and the energy transfer processes related to the sensibilization effect in Er3+/Yb3+ co-doped fluoroindate glasses focusing on the reciprocal distribution of radiative transitions, energy transfer parameters, and lifetimes have been analyzed. The luminescence consists of several bands in the visible (525, 546 and 660 nm) and the infrared (1550 and 2700 nm) spectral regions that correspond to characteristic radiative energy transitions within the erbium ions. In glasses co-doped with the Er3+/Yb3+ system, an augmentation in the emission intensity was observed in the visible and at 1550 nm, while a decrease was observed in the 2700 nm infrared band. The increase of the Yb3+: 2F 5/2 lifetime under 488, 808 and 976 nm excitation showed significant Er3+: 4I 11/2 → Yb3+: 2F 5/2 back energy transfer. Based on the analysis of the available literature, it can be concluded that energy transfer upconversion and cooperative energy upconversion play a significant role in modulating luminescence intensity values within the examined emission bands. This effect is likely enhanced due to the incorporation in a low phonon energy glass matrix. As a result of the above optimization, a glass optical fiber co-doped with 0.8 YbF 3 /1.4 ErF 3 (in mol%) was drawn and characterized, showing a strong emission at 2.77 μm. The optimized Er3+/Yb3+ co-doped fluoroindate glass and glass optical fiber confirmed their ability to be used in the visible and near-infrared spectral regions as efficient optical fiber sources. [ABSTRACT FROM AUTHOR]

Near‐infrared (NIR) fluorophores with pH‐responsive properties suggest merits in biological analyses. This work establishes a general and effective method to obtain pH‐responsive NIR emissive gold nanoclusters by introducing aliphatic tertiary amine (TA) groups into the ligands. Computational study suggests that the pH‐responsive NIR emission is associated with electronic structure change upon protonation and deprotonation of TA groups. Photo‐induced electron transfer between deprotonated TA groups and the surface Au‐S motifs of gold nanoclusters can disrupt the radiative transitions and thereby decrease the photoluminescence intensity in basic environments (pH=7–11). By contrast, protonated TA groups curb the electron transfer and restore the photoluminescence intensity in acidic environments (pH=4–7). The pH‐responsive NIR‐emitting gold nanoclusters serve as a specific and sensitive probe for the lysosomes in the cells, offering non‐invasive emissions without interferences from intracellular autofluorescence. [ABSTRACT FROM AUTHOR]

As an emerging 2D ultrawide bandgap semiconductor, hexagonal boron nitride (h‐BN) is gaining significant attention for its superior properties and wide applications. Although optical properties of h‐BN have been partially revealed by using h‐BN bulk single crystal, luminescence properties of the h‐BN few‐layer are rare due to its poor crystallinity. In this work, the h‐BN epilayers have been synthesized on sapphire substrates by the submicron‐spacing vapor deposition method. The crystalline quality of the h‐BN epilayer is improved with the increase of the growth temperature, and the full width at half‐maximum of the Raman peak is only ≈13 cm−1. The low temperature cathodoluminescence spectra of h‐BN epilayers exhibit two strong deep ultraviolet (DUV) luminescence peaks at 5.49 and 5.35 eV, as well as a weaker and broader defect‐related emission band at ≈4.0 eV. The DUV emission band is ascribed to the recombination of bound excitons and its phonon replica. Based on the theoretically predicted energy levels, the 4.0 eV emission band is tentatively attributed to the radiative transition from C impurities occupying the B sites to the B vacancies. Moreover, the h‐BN‐based DUV photodetectors exhibit an outstanding performance, making it a promising prospect for optoelectronic applications. [ABSTRACT FROM AUTHOR]

Thermal disturbance deteriorates the radiative transitions of up‐conversion phosphor, leading to decreased emission intensity at high operation temperatures. In this work, a thermal‐favored Yb3+/Nd3+ co‐doped KGaGeO4 up‐conversion phosphor with a negative thermal quenching behavior is explored. The as‐developed phosphor performs a one‐photon anti‐Stokes emission and exhibits a remarkable enhancement for the rise of ambient temperature reaching 653 K. It is demonstrated that the fascinating thermal behavior of the up‐conversion procedure is attributed to the enhanced energy transfer from the corresponding sensitizers to the activators by phonon assistance. Moreover, the microscopic dynamical process of phonon assistance and annihilation is revealed by introducing Er3+ ions as a probe. These results not only shed light on the phonon‐assisted strategy to build a highly efficient anti‐Stokes emission system but also open prospects for constructing phonon‐favored transitions with nonthermally coupled emissions to realize luminescence thermometry for their distinct thermal responsivity. [ABSTRACT FROM AUTHOR]

The combustion method was used to synthesize Ce3+ doped LaB 3 O 6 phosphors in a range of dopant concentrations. Both the un-doped and Ce3+ doped LaB 3 O 6 samples matched the required reference card, according to X-ray diffraction patterns. TL glow curves of Ce3+ doped LaB 3 O 6 samples at various dopant concentrations were examined by employing various optical detection filter combinations to define TL characteristics. LaB 3 O 6 :Ce3+ (1%) and IRSL-TL 565 nm were selected as the suitable sample and appropriate detection filter pairing. The TL maximum with a higher intensity was seen during preheating trials (with 2 °Cs−1) at around 270 °C. The experimental results showed feasible linearity (R2 = 0.998 and b = 1.054) between 5 and 1000 Gy for the dose response of LaB 3 O 6 :Ce3+ (1%). The short-term fading test was conducted at various time intervals up to a week. The findings showed that the dosimetric peak strength was almost constant for up to 5 days. However, an additional spurious maximum appeared at the higher temperature zone. Each sample showed an abnormal heating rate effect, which can be explained by localized electrons caught in the intermediate excited state, which is capable of radiative transitions via the conduction band. To find the overlapping peak numbers and determine the kinetic parameters of preheated LaB 3 O 6 :Ce3+ (1%), various heating rates, T M - T s , initial rise, and computerized glow curve deconvolution techniques were utilized. The results suggest that LaB 3 O 6 :Ce3+ may be an appropriate material for TL dosimetry applications due to its efficient TL characteristics. [ABSTRACT FROM AUTHOR]