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We report on the unusually large blue shift of the electroluminescence spectrum with an increase of the drive current at 77 K in a double-barrier nanoheterostructure with a deep AlSb/InAs0.83Sb0.17/AlSb quantum well grown by metal-organic vapor phase epitaxy on the n-GaSb:Te substrate. The rise of the drive current from 20 mA to 220 mA led to a shift of the electroluminescence spectrum maximum toward higher photon energies by 100 meV. It was shown that this effect is due to indirect (tunneling) radiative transitions between electrons in InAsSb quantum well and heavy holes localized near the AlSb/p-GaSb heterointerface. The energy of radiative transition was linearly dependent on the applied voltage. In the drive current range of 50–220 mA, an electroluminescence blue shift was accompanied by spectrum narrowing by 40 meV and a noticeable change of the spectrum shape. With a rise in the drive current, a superlinear increase of the electroluminescence intensity caused by the nonlinear dependence of tunneling radiative recombination rate on transition energy was observed at 300 K and 77 K. [ABSTRACT FROM AUTHOR]

We design thermal emitters based on gold micrograting structures with VO2-filled slots for enhanced far-field thermal rectification. We numerically calculate the thermal rectification ratio for two different approaches, peak extinction and peak shift. In peak extinction, the VO2 phase transition switches the radiative coupling of the surface plasmon on and off. In peak shift, the phase transition shifts the wavelength of the radiatively-coupled surface plasmon. We vary the extinction coefficient of VO2 to determine the effect on rectification for each approach. In both cases, the rectification ratio can be increased by increasing the VO2 loss in the metallic state. This suggests that highly efficient, microstructured thermal rectifiers can be achieved via suitable manipulation of the optical properties of VO2. [ABSTRACT FROM AUTHOR]

Wide‐coverage near infrared (NIR) phosphor‐converted LEDs possess promising potential for practical applications, but little is developed towards the efficient and wide‐coverage NIR phosphors. Here, we report the single‐component lanthanide (Ln3+) ions doped Cs2M(In0.95Sb0.05)Cl6 (M=alkali metal) nanocrystals (NCs), exhibiting emission from 850 to 1650 nm with high photoluminescence quantum yield of 20.3 %, which is accomplished by shaping the multiple metal halide octahedra of double perovskite via the simple alkali metal substitution. From Judd‐Ofelt theoretical calculation and spectroscopic investigations, the shaping of metal halide octahedra in Cs2M(In1−xSbx)Cl6 NCs can break the forbidden of f‐f transition of Ln3+, thus increasing their radiative transition rates and simultaneously boosting the energy transfer efficiency from host to Ln3+. Finally, the wide‐coverage NIR LEDs based on Sm3+, Nd3+, Er3+‐tridoped Cs2K0.5Rb0.5(In0.95Sb0.05)Cl6 NCs are fabricated and employed in the multiplex gas sensing and night‐vision application. [ABSTRACT FROM AUTHOR]

Wide‐coverage near infrared (NIR) phosphor‐converted LEDs possess promising potential for practical applications, but little is developed towards the efficient and wide‐coverage NIR phosphors. Here, we report the single‐component lanthanide (Ln3+) ions doped Cs2M(In0.95Sb0.05)Cl6 (M=alkali metal) nanocrystals (NCs), exhibiting emission from 850 to 1650 nm with high photoluminescence quantum yield of 20.3 %, which is accomplished by shaping the multiple metal halide octahedra of double perovskite via the simple alkali metal substitution. From Judd‐Ofelt theoretical calculation and spectroscopic investigations, the shaping of metal halide octahedra in Cs2M(In1−xSbx)Cl6 NCs can break the forbidden of f‐f transition of Ln3+, thus increasing their radiative transition rates and simultaneously boosting the energy transfer efficiency from host to Ln3+. Finally, the wide‐coverage NIR LEDs based on Sm3+, Nd3+, Er3+‐tridoped Cs2K0.5Rb0.5(In0.95Sb0.05)Cl6 NCs are fabricated and employed in the multiplex gas sensing and night‐vision application. [ABSTRACT FROM AUTHOR]

In this work, we report a novel pyrene tethered unsymmetrical monosubstituted salicylaldehyde azine based organic functional molecule named 4-chloro-2-((E)-((E)-(pyren-1-ylmethylene)hydrazono)methyl)phenol (PHCS) and we performed comprehensive photophysical investigations on variable states of the fluorophore through extensive experimental and theoretical techniques. This luminophore possesses diverse multifaceted photophysics in different microenvironments, resulting in altered multifluorescence emission behaviors of the same molecule in different states. This state-dependent photophysical behavior of PHCS is attributed to the combinatorial (or tuning) effect of different photophysical mechanisms. The solution photophysics is dominated solely by the photo-induced electron transfer (PET) process that quenches the emission through non-radiative channels. Moreover, the dynamic rotation through single bonds (in a solvated state) act in synergy with PET in consuming energy efficiently via radiationless pathways offering weak emission attributes of PHCS molecules that have not interacted. On the contrary, we rationalized a prevalence of the synergistic effect of aggregation-induced emission enhancement (AIEE) and excited state intramolecular proton transfer (ESIPT) along with the suppression of PET and intramolecular motions in the PHCS molecular system at extremely high water concentrations compared to organic solutions with low to moderate water concentrations. Non-solvent addition provides a rapid transition of the excited-state population from well-dispersed monomers to organized self-assembled nano-aggregates. This apparent reversal in the excited-state population is perspicuous with the observations of remarkable 'level-off' tails in the UV-vis absorption spectra, a noteworthy fluorescence enhancement (18-fold), a significant increase in the amplitude and rotational relaxation time of the longer decay components associated with aggregates, as well as the large hydrodynamic diameters of the formed spherical nano-aggregates at high water concentrations. These results inevitably suggest the opening of the excited-state radiative transitions, discernible with the observed high radiative decay rate and the simultaneous closure of the radiationless annihilations reflected from the reduced non-radiative and electron transfer decay rates. Quite expectedly, the interaction of bovine serum albumin (BSA) with the PHCS luminogen also indicated a similar 'light up' emission response that contrasted the amplitudes of the faster (unbound) and longer (protein-bound) photoexcited species, with a distinct fluorescence enhancement (1.4-fold). In addition, there were increased amplitude average fluorescence lifetimes (2.7-fold) and rotational relaxation times (2.1-fold) of bound fluorophores in the protein microenvironment owing to the predominant RIM effects in the hydrophobic domains of BSA. Thus, the present investigation provides a new insight into how the multifaceted photodynamics of the AIEEgen underwent striking changes in variable microenvironments, which can provide a guidance to judiciously modulate the external microenvironment to harvest optimal optical responses of small organic functional molecules. [ABSTRACT FROM AUTHOR]

The ceramics based on cubic (Zr0.82–xHfxY0.17Eu0.01)O0.91 with different contents of hafnium were studied. In the work, the elemental composition of the samples was obtained, the cathodoluminescence (CL) spectra and decay kinetics of europium luminescence were studied. The researched showed increase in the content of hafnium doesn't affect the position and number of observed bands in the luminescence spectrum. The electric dipole and magnetic dipole radiative transitions ratio was estimated for all samples. It's demonstrated that a decrease in the local symmetry of the europium ion associated with an increase in the hafnium content. It's shown the 5D0–1F1 transition Eu3+ decay time doesn't depend on the hafnium content, but v-aries significantly in different regions of the sample, which can be attributed to the influence of grain bou-ndaries. [ABSTRACT FROM AUTHOR]

A series of Eu3+ and Eu3+/Gd3+ co-doped barium-bismuth-borate (Ba–Bi–B) glasses were prepared by melt-quench technique. And deliberated the physical, structural, and spectroscopic properties of all glasses and explored the energy transfer process from Gd3+ to Eu3+ ions. The density of glasses increased with increasing of Gd3+ concentration in co-doped glasses. Characteristics of steady-state and time-resolved photoluminescence (PL) of Eu-doped and Eu3+-Gd3+ co-doped glasses under different excitation wavelengths suggested the prospects of the investigated glass system for display device applications. PL spectrum displays a strong red emission peak centered at 612 nm due to the Eu3+: 5D 0 → 7F 2 transition. Less intense emissions centered at 577 nm (7F 0), 590 nm (7F 1), 651 nm (7F 3) and 700 nm (7F 4) are also observed from the radiative transitions of the excited state 5D 0 of Eu3+ions. The values of radiative parameters such as transition probability, branching ratios, and stimulated emission cross-sections were obtained from Judd–Ofelt theory analysis and indicated the aptness of the Ba–Bi–B glasses for optical devices. A 5-fold enhancement in the PL intensity was observed in 1.0 mol% Eu3+ and 3.0 mol% Gd3+ co-doped glass under λ Exci. = 394 nm excitation. The calculated commission Internationale de l'eclairage color coordinates and correlated color temperature values show that the Ba–Bi–B glasses are useful for red-laser and display device applications. [ABSTRACT FROM AUTHOR]

A photoluminescence (PL) method to characterize phase transition processes of Li+/Er3+:BaTiO3 (BLET) ferroelectric ceramics by infrared fluorescence intensities has been proposed. The fluorescence intensities are applied to detect the phase transition of BLET ceramics in multiple phase transition regions. It proves that the change in fluorescence intensities at the phase transition is due to a variation in the radiative transition probability of the 4I13/2 level. A physical mechanism is elucidated considering the relationship between fluorescence properties and the phase structure. Our research benefits an in-depth understanding of the relationship between the PL characteristics and the phase structure of ferroelectric materials and further develops the application potential of PL methods in ferroelectric phase transition detection. [ABSTRACT FROM AUTHOR]

The carrier collection efficiencies of InGaAs/GaAsP superlattice (SL) photovoltaic structures were optimized by choosing adequate manufacturing parameters, such as the composition and thickness of the quantum wells (QWs) and barrier layers. However, no insights have been observed from the viewpoint of the nonradiative transition of photoexcited carriers. In this study, piezoelectric photothermal (PPT) and photoluminescence (PL) measurements were performed as a function of temperature from 100 to 340 K. Using a piezoelectric transducer, the PPT signal detected the heat generated by nonradiative recombination (NR). The indium composition of the QW layer was fixed at 0.3, and the phosphorus composition x[P] in the barrier layer was changed from 0.4 to 0.6. The observed temperature dependences of the PPT and PL signal intensities were analyzed using a rate equation for the photoexcited carriers in e1 and hh1 quantized levels. Four carrier dissipating processes, namely, radiative recombination, NR, thermal escape from the QW thermal excitation (TE), and tunneling after thermal excitation (TATE), were considered for both electrons and holes. Thermal activation energies were included in the NR, TE, and TATE processes. Because nonradiative and radiative transition components cause PPT and PL signals, curve fitting of the temperature behavior enabled us to determine the activation energies. We then found that the activation energy of the NR process reached a maximum at x[P] = 0.45. No such maxima were observed for the TE and TATE process. This result was explained by a trade-off between the strain valance condition over the entire range of the SL structure and the local residual strain at the interfaces between the QW, interlayer, and barrier layer when x[P] increased. Because no software can theoretically calculate the activation energy of the NR process, we demonstrated the usefulness of the present PPT experimental methodology for investigating carrier transport properties. [ABSTRACT FROM AUTHOR]

Electromagnetically induced slow-light medium is a promising system for quantum memory devices, but controlling its noise level remains a major challenge to overcome. This work considers the simplest model for such medium, comprised of three-level Λ-systems interacting with bosonic bath, and provides a new fundamental trade-off relation in light–matter interaction between the group velocity of light and the Fano factor of photon current due to radiative transitions. Considering the steady state limits of a newly derived Lindblad-type equation, we find that the Fano factor of the photon current maximizes to 3 at the minimal group velocity of light, which holds true universally regardless of detailed values of parameters characterizing the medium. [ABSTRACT FROM AUTHOR]

We theoretically study a fairly universal effect of screening the quantum states of an optical field from interaction with the system as a result of excitation of the modes initially being in the ground (vacuum) state. The cases of two-level and harmonic perturbing subsystems are considered. In the case of a sufficiently large number of "screening" modes, the formation of the corresponding dark state occurs with a relatively weak modification of the initial state. Therefore, an ensemble of resonators with the fields in the vacuum state is able to screen an arbitrary (including entangled) quantum state of a relatively small group of excited resonators from interaction with a dissipative subsystem. [ABSTRACT FROM AUTHOR]

Dye lasers are commonly used in optical investigation because their solutions in organic solvents deliver tunable, coherent emissions. They exhibit intense fluorescence owing to some specific spectroscopic characteristics. One drawback of the laser dyes is that it shows excessive triplet-state losses (TSLs.) The lack of theoretical predictions of fluorescence rates, intersystem crossing (ISC), and phosphorescence in laser dyes prompted us to report on the predicted rates of radiative and nonradiative transitions of some laser dyes. Structural engineering by some substituents influencing the simulated rates of coumarin laser dye derivatives for an efficient operation was investigated. The NH2 functional group renders the coumarin 120 more fluorescents with reduced TLS than the other investigated materials. Tailoring new efficient laser dyes can be achieved guided by the calculated rates of emission and nonradiative processes. [ABSTRACT FROM AUTHOR]

An energy-efficient, cost-effective, versatile, and eco-friendly solution combustion scheme was adopted for preparing a series of down-converted Ca9Al(PO4)7:xTb3+ (x = 10–80 mol%) nanoparticles with green emanation. Ca9Al0.40Tb0.60(PO4)7 phosphor was subjected to phase purity and crystallographic analysis using the XRD-based Rietveld refinement technique, which revealed trigonal crystallization with R3c(161) phase group. The synthesized samples underwent EDX and TEM analysis for the elemental composition and morphological behavior. The optical energy band gaps for the host (Ca9Al(PO4)7) and the optimized matrix (Ca9Al0.40Tb0.60(PO4)7) were obtained from diffuse reflectance spectral studies as 4.37 eV and 4.28 eV, respectively. UV light can effectively stimulate the nanocrystalline phosphor, resulting in substantial luminous attributes credited to 5D4 → 7FJ (J = 6,5,4,3) radiative relaxation. The PL decay curves were regressed into a mono-exponential decay function. The Auzel Model determined the radiative lifetime, non-radiative rates, and quantum efficiency for the best sample as 0.255 ms, 1572.94 s−1, and 0.714, respectively. The electric-dipole radiative probabilities of transition (derived from overall radiative rates, which include magnetic and electric-dipole) were utilized to compute the intensity parameters Ωλ (λ = 2,4,6) = 32.68 × 10−20, 9.78 × 10−20 & 22.49 × 10−20 cm2 of Tb3+ ions in Ca9Al(PO4)7 host lattice. Advanced photometric properties such as CIE coordinates (0.253, 0.558) and CCT (7136 K) further supported green glow asserting a brilliant cool green-emitting contender for manufacturing WLEDs and photonic applications. [ABSTRACT FROM AUTHOR]

Mn4+-doped fluoride red light phosphors are widely utilized in various fields, and their luminous performance is influenced by their stability in high humidity and temperature environments. By incorporating TEOAH+ (TEOAH+ = (HOCH2CH2)3NH+) into the Na2TiF6 matrix, Na3HTiF8:Mn4+,TEOAH+ with improved thermal stability and water resistance was synthesized. Enhancement in the luminescence thermal stability is supported by its strong negative thermal quenching (NTQ) effect, which is attributed to the phonon-induced mechanism wherein the probability of radiative transitions increases much faster than the probability of non-radiative transitions. Additionally, the integrated emission intensity of the optimal sample Na3HTiF8:Mn4+,0.15TEOAH+ was maintained at 70.1% after being immersed in water for 360 min, which may be attributed to the addition of TEOAH+ cations in the structure, thus increasing its structural rigidity. The prototype light-emitting diode (LED) has a narrow emission band, 88.6% color gamut, and 83.1 lm W−1 light efficiency, according to the National Television Standards Committee (NTSC). The qualities of the phosphor make it an ideal candidate for back-lighting devices. [ABSTRACT FROM AUTHOR]

The photoluminescence of Au(I) complexes is generally characterized by long radiative lifetimes owing to the large spin-orbital coupling constant of the Au(I) ion. Herein, we report three brightly emissive Au(I) coordination compounds, 1, 2a, and 2b, that reveal unexpectedly short emission lifetimes of 10–20 ns. Polymorphs 2a and 2b exclusively exhibit fluorescence, which is quite rare for Au(I) compounds, while compound 1 reveals fluorescence as the major radiative pathway, and a minor contribution of a microsecond-scale component. The fluorescent behaviour for 1–2 is rationalized by means of quantum chemical (TD)-DFT calculations, which reveal the following: (1) S0–S1 and S0–T1 transitions mainly exhibit an intraligand nature. (2) The calculated spin-orbital coupling (SOC) between the states is small, which is a consequence of overall small metal contribution to the frontier orbitals. (3) The T1 state features much lower energy than the S1 state (by ca. 7000 cm−1), which hinders the SOC between the states. Thus, the S1 state decays in the form of fluorescence, rather than couples with T1. In the specific case of complex 1, the potential energy surfaces for the S1 and T2 states intersect, while the vibrationally resolved S1–S0 and T2–S0 calculated radiative transitions show substantial overlap. Thus, the microsecond-scale component for complex 1 can stem from the coupling between the S1 and T2 states. [ABSTRACT FROM AUTHOR]

Passive mode-locking in quantum cascade lasers (QCLs) remains one of the huge challenges because of the fast relaxation time of the excited carriers which is typically in the range of sub-picoseconds. The use of conventional techniques such as the semiconductor saturable absorber mirror is inefficient because the spatial hole burning effect dominates the carrier dynamics. To overcome this effect, longitudinal transition structures with relaxation time around 50 ps were proposed. However, mode-locking is assured with an external modulation at a cavity roundtrip frequency. In this paper, we demonstrate that a single-layer graphene used as a saturable absorber permits to generate stable pulses in such structures. The graphene is integrated with a highly reflective mirror to increase the internal electric field and achieve the saturation intensity. The dynamic of the QCL is modeled with Maxwell-Bloch equations while Maxwell-Ampere equation is used for the graphene layer by considering a nonlinear conductivity. This system of equations is solved using the one-dimensional Finite-Difference Time-Domain (FDTD) method. To model the single-layer graphene of a 0.33 nm thickness, a specific sub-cell is implemented based on Maloney method. Simulation results of a 6.2 μ m QCL with a diagonal radiative transition show a generation of isolated pulses with a peak electric field of 80 MV. m - 1 and a duration of 51 fs . The mode-locking remains stable for QCLs with a vertical transition having a relaxation time below 5 ps . [ABSTRACT FROM AUTHOR]

ZnO–P 2 O 5 glasses activated with Ag m n + clusters and Mn2+ ions were successfully synthetized by the melt-quenching method. X-ray diffraction patterns confirmed the glassy nature for doping concentrations up to 3.0 and 5.0 mol% of Ag+ and Mn2+ ions, respectively, whereas the Raman spectra in all cases displayed δ(P–O–P), ν s (P–O–P), ν s (PO 2) and ν as (PO 2) vibrational modes, typical of a phosphate glass network. The emission spectra under 345 nm (Ag m n + : S 0 → S 1 and Mn2+: 6A 1 (S) → 4T 1 (P) + 4E(D)), 385 nm (Ag m n + : S 0 → S 1) and 407 nm (Mn2+: 6A 1 (S) → 4A 1 (G) + 4E(G) and Ag m n + : S 0 → S 1) excitations, showed the broad band related to the superimposed Ag m n + cluster: S 1 → S 0 , T 2 → S 0 and T 1 → S 0 radiative transitions along with the Mn2+: 4T 1 (G) → 6A 1 (S) one. Under 385 nm excitation, the Mn2+ emission transition is attained by energy transfer from Ag m n + clusters. Such excitations lead to emission tonalities in the bluish white to cold white (345 and 385 nm) and cold white to reddish orange (407 nm) ranges, with correlated color temperature (CCT) values in the 10,095-5371 K (345 nm), 14,768-6862 K (385 nm) and 8592-1633 K (407 nm) ranges. Purplish pink emissions upon 345 nm excitation were obtained as well. The white color tonalities together with the color rendering index (CRI) and absolute quantum yield (QY, external) values up to 95 Ra and 35%, respectively, revealed promissory features for rare-earth-free white light emitting diode applications. The Ag m n + cluster: S 1 → S 0 emission fitting by the Burstein model suggested that the non-radiative energy transfer is mainly mediated by an electric dipole-dipole interaction. [ABSTRACT FROM AUTHOR]

Novel ternary fluoro-germano-tellurite (GTS) glasses doped with Er3+ ions with 0.5 mol% and 1.0 mol% were fabricated by a conventional melt and quenching method and investigated using methods of optical spectroscopy. The room-temperature absorption spectrum was recorded and analyzed to determine radiative transition rates, radiative lifetimes, and branching ratios of Er3+ luminescence. Decay curves of Er3+ luminesccence were recorded and analyzed. Temperature dependences of emission spectra and absorption spectra in the region from RT (room-temperature) up to 675 K were studied in detail. The contribution of competing radiative and nonradiative processes to the relaxation of luminescent levels of Er3+ was assessed. Absolute and relative sensitivity were established utilizing the comprehensive model based on thermally coupled 2H11/2/4S3/2 excited states of erbium. The high quantum efficiency of the first erbium-excited state and value of gain coefficient indicate that GTS:Er glass system can be considered as conceivable NIR (near infrared) laser material as well. [ABSTRACT FROM AUTHOR]

Purely organic fluorescence emitters with ultrahigh exciton utilization, such as thermally‐activated delayed fluorescence (TADF) materials, are pursued as the cornerstone of the new‐generation organic light‐emitting diodes (OLEDs). However, most TADF emitters suffer from the dilemma of the aggregation‐caused fluorescence quenching effects, severely limiting their applications. Excitingly, the recently proposed aggregation‐induced delayed fluorescence (AIDF) strategy holds the potential to tackle this problem thoroughly. Here, the recently reported AIDF emitters CP‐BP‐PXZ and its halogenated counterparts, 3‐CCP‐BP‐PXZ and 3‐BCP‐BP‐PXZ, are investigated with a united theoretical and experimental insight. Based on first‐principles calculations combined with the polarizable continuum model (PCM) and the quantum mechanics/molecular mechanics (QM/MM) model, the photophysical mechanisms of these novel materials are proposed. It is found that both reverse intersystem crossing (RISC) and the subsequent radiative transition of CP‐BP‐PXZ are promoted via aggregation, owing to the increased effective RISC channels and boosted oscillator strength. Meanwhile, the unfavorable internal conversion rate is greatly slumped, ascribed to the suppressed Duschinsky rotation effect (DRE). The unique heavy‐atom effect is disclosed in 3‐CCP‐BP‐PXZ and 3‐BCP‐BP‐PXZ that the halogens act as steric blockers in crystal, rather than spin–orbit coupling enhancers. It is hoped that this work can shed new light on the designation of high‐efficient solid‐state fluorescence emitters. [ABSTRACT FROM AUTHOR]

In the optical energy gap, visible and near-IR emission of halide phosphate glasses with a composition of 40P2O5-30ZnO-20LiCl-10BaF2 in mol% doped with 3.5 × 104 ppm Pr2O3, referred to as PZLBPr, were synthesized. The UV-VIS-NIR and spectroscopic properties of these glasses were also predicted. The current glasses had broadband emission photoluminescence covering a wavelength range of 1250 to 1700 nm when excited at 455 nm. These bands for near-infrared emission luminescence relate to the transitions 1G4 → 3H5, 1D2 → 1G4, and 3H4 → 3F3, 3F4 in the optical telecommunication window. The significant PL emission wideband was caused by the radiative transition from Pr3+: 1D2 to 1G4. At 445 nm excitation, these glasses exhibited emission bands that corresponded to blue/reddish orange spectral ranges in visible ranges. The prepared glass has a high lasing quality factor (Ω4/Ω6 = 0.9), high optical energy (4.72 eV), and quantum efficiency = 87.3% with FWHM = 156 nm of transition emission from the 1D2 → 1G4 level. As a result, broadband near infrared optical amplifiers can be fabricated from the prepared glasses. [ABSTRACT FROM AUTHOR]

The role is considered of all known potential sources of excitation of the 1D term of atomic oxygen in auroras and the value of their relative contributions to the emission intensity of 630.0-nm emission in the height interval of 100−300 km. The main attention is paid to the role of weak excitation sources of 1D terms, such as collisional interactions between the components of atmospheric gases N(2D) + O, N(2D) + O2,N(2P) + O2, and N+ + O2; direct electron impact O2 + e*; and the radiative transition O(1S) → O(1D) + hν557.7. It is shown that, despite the small partial contributions of these sources to the intensity of the 630.0-nm emission, their total contribution can be quite significant. The total efficiency of these sources varies from 66 to 6% with an increase in altitude from 100 to 300 km and is significant at altitudes below 200 km. It is shown that the influence of the decontamination process leads to the fact that, in the region of heights of ∼110−150 km, the set of reactions of collisional interactions of ionospheric plasma components N(2D) + O, N(2D) + O2,N(2P) + O2, and N+ + O2 becomes the second most efficient source contributing to the intensity of the 630.0-nm emission. [ABSTRACT FROM AUTHOR]

A series of ultrapure‐blue thermally activated delayed fluorescence (TADF) emitters featuring through‐space charge transfer (TSCT) have been constructed by close stacking between the donor and acceptor moieties in rigid heteroaromatic compounds. The obviously accelerated radiative transition of singlet excitons, the diminished vibrionic relaxation of ground and excited states, and the consequent reduced Stokes shift and the narrow emission are evident. The corresponding organic light‐emitting diodes (OLEDs) based on AC‐BO realize the best performance among all deep‐blue TSCT‐TADF emitters, with an external quantum efficiency (EQEmax) of 19.3 %. Furthermore, the OLEDs based on QAC‐BO display an EQEmax of 15.8 %, and achieve the first high‐efficiency ultrapure‐blue TSCT‐TADF material with an excellent Commission Internationale de L'Eclairage coordinate (CIE) of (0.145, 0.076) which perfectly matches the ultrapure‐blue CIE requirements (0.14, 0.08) defined by the National Television System Committee. [ABSTRACT FROM AUTHOR]

A series of ultrapure‐blue thermally activated delayed fluorescence (TADF) emitters featuring through‐space charge transfer (TSCT) have been constructed by close stacking between the donor and acceptor moieties in rigid heteroaromatic compounds. The obviously accelerated radiative transition of singlet excitons, the diminished vibrionic relaxation of ground and excited states, and the consequent reduced Stokes shift and the narrow emission are evident. The corresponding organic light‐emitting diodes (OLEDs) based on AC‐BO realize the best performance among all deep‐blue TSCT‐TADF emitters, with an external quantum efficiency (EQEmax) of 19.3 %. Furthermore, the OLEDs based on QAC‐BO display an EQEmax of 15.8 %, and achieve the first high‐efficiency ultrapure‐blue TSCT‐TADF material with an excellent Commission Internationale de L'Eclairage coordinate (CIE) of (0.145, 0.076) which perfectly matches the ultrapure‐blue CIE requirements (0.14, 0.08) defined by the National Television System Committee. [ABSTRACT FROM AUTHOR]

Tetraphenylpyrazine (TPP) is a conspicuous heterocyclic fluorophore with an aggregation-enhanced emission (AEE) character. In general, the TPP building block is considered either a molecular rotor or an electron acceptor in the construction of its derivatives. Therefore, a faint-blue emission is expected in its solution. Herein, we concentrated on a series of unusual DTPP-A type analogues, where two TPP units (DTPP) were connected using the electron-accepting group (A), i.e., benzodiazine (BQ), benzothiadiazole (BZ), thienyldioxide (TO), naphthothiadiazole (NZ) and benzobisthiadiazole (B2Z). The excited-state properties of two experimentally available compounds (DTPP-BZ and DTPP-TO) and three theoretically designed molecules (DTPP-BQ, DTPP-NZ and DTPP-B2Z) were studied by employing time-dependent density functional theory coupled with thermal vibration correlation function formalism. The tetrahydrofuran solvent environment was mimicked through the polarizable continuum model. It was found that the TPP components turned into electronic donors in these DTPP-A type systems, and the emission color widened from blue to red and even to near-infrared upon increasing the electron-accepting ability of the central bridge. The excitons localized on the central "acceptor" bridge offer sufficient orbital overlaps and contribute to the effective radiative transition. The rotation behaviors of the phenyls in the TPP components are also restricted upon such linkage, which could reduce the relaxation energy and give rise to a much slower non-radiative decay process. Thus, the emission of the bridged systems is boosted in solution though TPP itself is an AEE element. The present study provides a valuable strategy for the molecular design of heterocycle-containing emitters with whole visible light and near-infrared emission. [ABSTRACT FROM AUTHOR]

Two new heteroleptic cationic Ir(III) complexes bearing benzothiazole and pyridine motifs on fluorene groups were synthesized and characterized. Complexes Ir1 and Ir2 exhibit 1π,π* transitions below 430 nm, with broad but weak metal-to-ligand and ligand-to-ligand charge transfer absorption bands above 430 nm. Both complexes possess long-lived emissions (τem = 0.37 μs for Ir1, τem = 5.41 μs for Ir2) and triplet excited states (τTA = 0.14 μs for Ir1, τTA = 6.06 μs for Ir2). Their optical properties in solution and aggregated states were also investigated. Both Ir(III) complexes exhibit aggregation-induced phosphorescence emission behavior in an acetonitrile–water mixture. As the water content increased to 90%, the emission intensities of complexes Ir1 and Ir2 increased nearly 3 times and 2.8 times, respectively. Moreover, nonlinear transmittance experiments were performed in CH3CN and a CH3CN–H2O mixture (fw = 90%), and the strength of the reverse saturable absorption (RSA) at 532 nm followed the trend: Ir2 (CH3CN) ≥ Ir1 (CH3CN) > Ir2 (CH3CN–H2O) > Ir1 (CH3CN–H2O). Abundant triplet state excitons participated in the radiative transition progress, which inhibited the RSA process. These results indicate that the fluorene-decorated Ir(III) complexes are suitable for aggregation emission and optical power limiting applications. [ABSTRACT FROM AUTHOR]

Ram pressure stripping (RPS) is a process that removes the interstellar medium (ISM) quickly, playing a vital role in galaxy evolution. Previous RPS studies have treated the ISM as single-phase or lack the resolution and physical processes to properly capture the full multiphase ISM. To improve this simplification, we introduce an inflowing, hot intracluster medium (ICM) into a self-consistently modeled ISM in a local patch of star-forming galactic disks using the TIGRESS framework. Our simulations reveal that the workings of RPS are not only direct acceleration of the ISM by ICM ram pressure but also mixing-driven momentum transfer involving significant phase transition and radiative cooling. The hot ICM passes through the low-density channels of the porous, multiphase ISM; shreds the cool ISM; and creates mixing layers. The ICM momentum is transferred through the mixing layers while populating the intermediate-temperature gas and radiating thermal energy away. The mixed gas extends beyond galactic disks and forms stripped tails that cool back unless the ICM fluxes are large enough to prevent cooling until they escape the simulation domain. The mixing-driven momentum transfer predicts that the more ICM mixes in, the faster the ISM moves, resulting in the anticorrelation of outflow velocity and gas metallicity of the stripped ISM. The compression of the ISM disks due to the ICM ram pressure enhances star formation rates up to 50% compared to the model without ICM. With the ICM ram pressure higher than the disk anchoring pressure, star formation is quenched within ∼100 Myr. [ABSTRACT FROM AUTHOR]

We report a comparative study of coordination behaviour of 2-(2-aminophenyl)benzothiazole (NH2-pbt) and its phosphorus-containing derivative, α-aminophosphine oxide (PCNH-pbt), towards zinc halides. The corresponding coordination compounds [Zn(L)2Hal2] (L = PCNH-pbt, Hal = Cl, 1 and Hal = Br, 2) and [Zn(L')Hal2] (L' = NH2-pbt, Hal = Cl, 3 and Hal = Br, 4) were obtained as single phases. As evidenced by single-crystal X-ray diffraction analysis, L' ligand coordinates to Zn in a chelate manner via two N atoms. Despite a similar coordination mode in complexes 3 and 4, the spatial geometry of the ligand differs notably, which implies a relatively high flexibility of NH2-pbt. The L ligand exhibits another coordination mode, binding with Zn only via the oxygen of the P=O group. The differences in the structures of NH2-pbt, 3 and 4, and their counterparts, PCNH-pbt, 1 and 2, induce differences in their solid-state photoluminescence properties. The former group of the compounds exhibits conventional single-band emission, while the latter group reveals two bands. The minor band at 450 nm is ascribed to a radiative transition for the regular amine species, while the major band at 520–550 nm can be associated either with the proton-transferred imine species (ESIPT mechanism) or with a charge transfer state (TICT) with a different geometry. [ABSTRACT FROM AUTHOR]

The main physical premises of the quantum Zeno effect in the problem of stopping the spontaneous radiative decay of excited atoms and nuclei are considered. It is shown for the first time that such an effect can be realized only for low-frequency radiative transitions (not higher than the microwave range), which correspond to the selective interaction of a quantum system with one or several discretely arranged modes of a quantized electromagnetic field in the volume of experimental setups. It is shown that this process occurs at the initial stage of the reversible Rabi precession and is formally unrelated to the true irreversible spontaneous decay. It is also shown that the effect of deceleration of radiative decay in the case of a quasi-continuous distribution of field modes is fundamentally impossible, which explains its absence for quantum sources of visible and shorter-wavelength radiation. In this case, the law of spontaneous radiative decay both at the beginning of the process and after a long time is described by the same standard exponential law. It has been shown for the first time that the quantum Zeno effect and stopping of spontaneous decay are possible in the infrared and visible ranges, provided that there are controlled sources inside the optical microresonators. These results can be used to create high-performance microlasers and to create optical systems for storing and processing information. [ABSTRACT FROM AUTHOR]

Herein, Mn4+‐doped alkaline‐germanate phosphors are synthesized by using starting chemicals of alkaline (K, Rb) carbonates, GeO2 and MnO2. The compounds exhibit bright red photoluminescence (PL) under ultraviolet and blue excitation. X‐ray diffraction (XRD) and Raman investigation show the formation of solid solutions of trigonal KxRb2−xGe4O9. The potassium content dependence of the red PL shows the intensity maximized at x = 0.5 and 1.5. This behavior is well matched with the absorption of Mn4+ ions. PL quantum efficiencies (QEs) are also estimated and compared with a previous result for germanates synthesized with Mn carbonates as a starting material. The radiative and nonradiative transition probabilities are also estimated to understand the reason for the observed PL properties, revealing the higher nonradiative transition probability resulting from concentration quenching due to the starting chemical of MnO2. Ab initio calculations are also performed on the electronic structure of the host crystals of the end members of the obtained compounds, K2Ge4O9 and Rb2Ge4O9. The optical bandgap calculated varies between K and Rb, while the observed ones are not sensitive to the K content x. Nevertheless, they are high enough for the optimal red emission of Mn4+ ions via an excitation of 4A2g–4T1g or 4T2g. [ABSTRACT FROM AUTHOR]

The rate of annihilation delayed fluorescence of organic molecules localized on the surface of a layered spherical nanoparticle is calculated based on an original mathematical model on the assumption that one of the molecules remains stationary, while the other diffusively moves over the particle surface. A composite nanoparticle consists of a ferromagnetic (cobalt, nickel, or magnetite) core and a metal (Au or Ag) plasmon shell. Not only is the external uniform magnetic field into which the particle was placed taken into account, but also a nonuniform anisotropic magnetic field, formed by the ferromagnetic core of the composite, in the outer surface region of the particle. The predominant influence of the structural and geometric parameters of the system (the ratio of core radius to shell thickness) on the delayed fluorescence rate of molecules as a result of a plasmon increase/decrease in the radiative transition probability (more than 30%) is shown. The manifestation of the magnetic factor in the rate of the triplet–triplet annihilation reaction is less pronounced (about 10%). The obtained delayed fluorescence spectra of the layered ferroplasmonic nanocomposite with silver and gold shells demonstrate a clear dependence of the signal amplitude on the shell material and thickness. [ABSTRACT FROM AUTHOR]

Results of experimental and theoretical investigations into the electron-impact excitation of the resonance 6 s 6 p 1 P 1 ° â†' 6 s 21 S 0 (132.2 nm), as well as the cascade 6 s 7 s 1 S 0 â†' 6 s 6 p 1 P 1 ° (309.2 nm) and 6 p 21 D 2 â†' 6 s 6 p 1 P 1 ° (150.8 nm) spectral transitions from the ground 6 s 21 S 0 level in the thallium ion, are presented. Crossed beams of electrons and Tl+ ions in combination with a spectroscopic method were used in the experiment. Measured cross sections have a distinct resonance structure arising mainly from the electron decay of atomic 5 d 96 s 26 p 2, 5 d 106 s 7 s (1 S) np (n â©ľ 7), 5 d 106 s 6 d (1 D) np (n â©ľ 6), 5 d 106 s 6 d (1 D) nd (n â©ľ 6) and ionic 5 d 96 s 2 np, 5 d 96 s 2 nd, 5 d 96 snp (n â©ľ 6) autoionizing levels, as well as radiative transitions from the higher 6 s 7 s 1 S 0, 6 s 6 d 1 D 2, and 6 p 21 D 2, 1 S 0 ionic levels. Relativistic distorted wave (RDW) calculations are performed to obtain the effective cross sections for the above transitions. The absolute values of the cross sections are found to be 1.39 Ă— 10âˆ'16 cm2 at 300 eV for the λ 132.2 nm resonance line, and 0.11 Ă— 10âˆ'16 cm2 and 0.56 Ă— 10âˆ'16 cm2 at 100 eV for the λ 309.2 nm and λ 150.8 nm lines, respectively. The contribution of the cascade transitions being studied to the effective cross section of the λ 132.2 nm resonance line at the energy of 100 eV is about 30%. A calculation using the semi-empirical Van Regemorter formula is also performed to obtain the effective cross section of the resonance λ 132.2 nm line. The absolute value of the cross section at 300 eV is found to be nearly the same as that given by the RDW calculation. [ABSTRACT FROM AUTHOR]

A high-luminescent, blue-light excitable europium(III) coordination complex, [Eu(µ2-OC2H5)(btfa)(NO3)(phen)]2phen (1) {btfa = benzoyl trifluoroacetone, phen = 1,10-phenantroline}, has been synthesized and investigated. The complex was characterized by infrared (IR) and photoluminescence (PL) spectroscopy. The PL emission spectra of powder samples registered in a range of 10.7–300 K exhibit characteristic metal-centered luminescence bands, assigned to internal radiative transitions of the Eu3+ ion, 5D1→7Fj and 5D0→7Fj (j = 0–4). The high-resolution spectrum of the transition 5D0→7F0 shows that it consists of two narrow components, separated by 0.96 meV, which indicates the presence in the matrix of two different sites of the Eu3+ ion. The splitting pattern of 5D0→7Fj (j = 0–4) transitions indicates that europium ions are located in a low-symmetry environment. The absolute quantum yield and the sensitization efficiency were determined to be 49.2% and 89.3%, respectively. The complex can be excited with low-cost lasers at around 405 nm and is attractive for potential applications in optoelectronics and biochemistry. [ABSTRACT FROM AUTHOR]

Here we report a new strategy to tune both excitation and emission peaks of upconversion nanoparticles (UCNPs) into the first infrared biowindow (NIR‐I, 650–900 nm) with high NIR‐I‐to‐NIR‐I upconversion efficiency. By introducing the sensitizer Nd3+, activator Er3+, energy migrator Yb3+ and energy manipulator Mn2+ into specific region to construct proposed energy migration processes in the designed core–shell–shell nanoarchitecture, back energy transfer (BET) from activator to sensitizer or migrator can be greatly blocked and the NIR‐to‐red upconversion emission can be efficiently promoted. Consequently, BET‐induced photon quenching and the undesired green‐emitting radiative transition are entirely eliminated, leading to high‐efficiency single‐band red upconversion emission upon 808 nm NIR‐I laser excitation. Our findings provide insights into fundamental lanthanide interactions and advance the development of UCNPs for bioapplications with techniques that overturn traditional limitations. [ABSTRACT FROM AUTHOR]

Here we report a new strategy to tune both excitation and emission peaks of upconversion nanoparticles (UCNPs) into the first infrared biowindow (NIR‐I, 650–900 nm) with high NIR‐I‐to‐NIR‐I upconversion efficiency. By introducing the sensitizer Nd3+, activator Er3+, energy migrator Yb3+ and energy manipulator Mn2+ into specific region to construct proposed energy migration processes in the designed core–shell–shell nanoarchitecture, back energy transfer (BET) from activator to sensitizer or migrator can be greatly blocked and the NIR‐to‐red upconversion emission can be efficiently promoted. Consequently, BET‐induced photon quenching and the undesired green‐emitting radiative transition are entirely eliminated, leading to high‐efficiency single‐band red upconversion emission upon 808 nm NIR‐I laser excitation. Our findings provide insights into fundamental lanthanide interactions and advance the development of UCNPs for bioapplications with techniques that overturn traditional limitations. [ABSTRACT FROM AUTHOR]

Radiative transition decay width for χ c 1 → J / ψ γ has been calculated on N f = 2 twisted mass gauge configurations. In this simulation, twisted boundary conditions are applied to compute corresponding correlation functions. It helps us obtain form factors with more low four transfer momentum that benefit fitting the decay width more accurately. The calculated decay width for χ c 1 → J / ψ γ is smaller than the experiment data in particle data group (PDG). [ABSTRACT FROM AUTHOR]

Solution-processed polymer light emitting devices (PLEDs) using high-quality thermally activated delayed fluorescence (TADF) polymers as the emitting layers are attractive, however, high-efficiency white-light TADF polymers are very rare because of the complicated radiative transition channels. In this study, a series of hyperbranched TADF conjugated polymers were designed and synthesized which adopted the linear D-A-type TADF emitter of 1,8-naphthalimide-acridine as red chromophores, conjugated poly(fluorene-carbazole) as the blue backbone and triphenylamine as the hyperbranched cores. By adjusting the appropriate feed ratios of monomers, energy transfer process from the blue backbone to the red chromophores could be regulated and HR0.8 film had the highest photoluminescent quantum yield of 24 %. Consequently, its doped electroluminescent device showed the cold-white emission with the CIE color coordinates of (0.35, 0.23) and the maximum EQE of 6.82 %. By simply raising the concentration of the red chromophore in the polymers, the rapid reverse intersystem crossing (RISC) process and the enlarged energy gap between S 1 and T 1 were achievable. [Display omitted] • A series of hyperbranched conjugated polymers with excellent TADF character were designed and synthesized. • By raising the concentration of red chromophores, the reverse intersystem crossing rates was improved. • All polymers had flat and smooth film morphologies. • HR0.8 devices showed the best white light with a CIE coordinate of (0.35, 0.23) and the maximum EQE of 6.82%. [ABSTRACT FROM AUTHOR]

Based on the local surface plasmon resonance effect of Ag nanolayer, the luminescence enhancement in the visible light range of multilayer thin film has been investigated combined with metal/spacer molecule/photoluminescence material structure. The luminescence enhancement effect of multilayer thin films can be improved by adjusting the spin-coating number of Ag nanolayer and SiO 2 spacer in the multilayer structure. At the same time, the mechanism of enhanced luminescence has been analyzed according to the change in fluorescence lifetime. The effect of the coupling between Ag nanolayer and luminescence layer on the radiative transition rate and fluorescence quantum yield have been discussed. The up-conversion luminescence intensity of the noble metal-modified multilayer thin film can be further improved by combining the multilayer structure with sensitized layer. • The emission intensity of thin films are improved via the LSPR effect of Ag nanolayer. • On the basis of Ag@Tm/Yb structure, SiO 2 spacer layer is introduced to further enhance the upconversion luminescence. • The mechanisms of luminescence enhancement in the multilayer thin films are analyzed. • More than 20 times emission enhancement is achieved in the Ag@SiO 2 @Tm/Yb@Yb multilayer thin films. [ABSTRACT FROM AUTHOR]

• Quenching, transition probabilities, frequency dependent parameters, thermochromic shift method. • Intercrossing system. • Radiative and non-radiative transition probabilities. • Fluorescence lifetime. • Activation Energy. Steady state method is employed to study the effect of temperature on the absorption and emission characteristics of 3-(1H-benzo[ d ]imidazol-2-yl)-7-(diethylamino)-2H-chromen-2-one(3HBI-7D-2HChromen-2-one) laser dye in glycerol solvent. Temperature induces thermal effect on maxima absorption, emission wavelength, fluorescence intensity etc. Radiative and non-radiative transition probabilities mechanism, fluorescence lifetime, frequency assisted parameters decay rate constants, and activation energy is estimated. Advance thermochromic shift method is adopted to determine the ground and excited state dipole moments. [Display omitted] [ABSTRACT FROM AUTHOR]

Herein, a new electrochemiluminescence (ECL) biosensor was constructed with highly efficient polymerized carbon dots (PCDs) as ECL emitter and the improved localized catalytic hairpin assembly (L-CHA) as signal amplifier for ultrasensitive detection of microRNA-222 (miRNA-222). Impressively, compared to the traditional carbon dots with inefficient blue region ECL emission, PCDs with N, O co-dope and large conjugated π-system showed high electrical conductivity, narrow band gap and strong radiative transition, which could exhibit high ECL efficiency to improve the sensitivity of detection and long wavelength ECL emission to achieve deep tissue penetration for reducing biological damage. Furthermore, the trace target miRNA-222 could be efficiently converted into large amounts of output DNA labelled with the quencher dopamine (S-DA) through the L-CHA reaction to significantly enhance the target amplification efficiency for further improving the sensitivity of detection. Thus, the ECL biosensor could achieve the ultrasensitive detection of miRNA-222 from 100 aM to 100 pM with the detection limit of 76 aM. Therefore, this work proposed a novel CDs with high ECL efficiency and long wavelength ECL emission, which not only was used to build an ultrasensitive biosensor for biomolecules detection in clinical diagnosis, but also served as a potential emitter for ECL bioimaging. [ABSTRACT FROM AUTHOR]

[Display omitted] • QY was improved without changing the fluorescence wavelength by catalysis of MnSO 4. • The C = N and pyridine N could suppress k NR , leading to the QY increasement. • Warm white LED with excellent performance was constructed by using muticolor CDs. Multicolor carbon dots (CDs) possess tremendous potential applications, especially in optoelectronic devices. However, further applications in warm white LED have been constrained due to the extremely low quantum yield (QY) of multicolor CDs. In this work, fluorescence enhancement multicolor CDs (o-CDs(cat.) (emitted yellow, Em = 550 nm, QY = 85.4 %), m-CDs(cat.) (emitted blue, Em = 440 nm, QY = 35.7 %), p-CDs(cat.) (emitted red, Em = 610 nm, QY = 73.8 %)) with almost 15 % QY improvement, without changing the fluorescence emission wavelength, was successfully achieved by introducing MnSO 4 into the reaction system. The relevant mechanism may be the catalytic effect of MnSO 4 , which leads to the increased content of C = N and pyridine N, further suppressing non radiative transitions, leading to the increasement of QY. Finally, the obtained high QY multicolor CDs were applied to warm white LED with the color coordinates (CIE) of (0.33,0.36), color rendering index (CRI) of 90, correlated color temperature (CCT) of 3473 K. Laying the foundation for the research methods and mechanisms of metal ion caused high QY of CDs. [ABSTRACT FROM AUTHOR]

An explicit realistic model featuring a supercooled phase transition, which allows us to explain the background of gravitational waves recently detected by pulsar timing arrays, is constructed. In this model the phase transition corresponds to radiative symmetry breaking (and mass generation) in a dark sector featuring a dark photon associated with the broken symmetry. The completion of the transition is ensured by a non-minimal coupling between gravity and the order parameter and fast reheating occurs thanks to a preheating phase. Finally, it is also shown that the model leads to primordial black hole production. [ABSTRACT FROM AUTHOR]

Optical properties of cesium bismuth germanate Cs 2 Bi 2 O(Ge 2 O 7) (CBGO) nonlinear single crystal doped with trivalent europium (Eu3+) ions grown from melt were investigated. Strong Eu3+ emission lines in the orange-red range centered at 576, 596, and 617 nm originating from the 5D 0 to 7F 0,1,2 transitions, respectively, were observed. Judd-Ofelt intensity parameters describing f-f transitions were calculated from the room temperature emission and excitation spectra and were used to determine spectroscopic parameters such as radiative lifetimes, transition probabilities and branching ratios3 for 5D 0 level of Eu3+. The values obtained by using Judd-Ofelt approach were compared with experimental results for the 5D 0 excited state. The measurement of the 5D 0 fluorescence decay of Eu3+ ions in the Cs 2 Bi 2 O(Ge 2 O 7) matrix (0.5 at.% in the alloy) confirmed its exponential nature, with a time constant of 0.82 ms at 300 K. The high-resolution laser spectroscopy of CBGO Eu3+ performed at 10 K confirmed the Eu3+ distribution into two distinct sites. Based on both the results of optical spectroscopy and structural analysis, the allocation of sites for Eu3+ ions was discussed. • Cs 2 Bi 2 O(Ge 2 O 7):Eu3+ crystals have been grown from stoichiometric melts under conditions of low temperature gradient. • Judd-Ofelt intensity parameters for f-f transitions in CGBO:Eu3+ have been determined. • The Eu3+ distribution into two distinct sites in CBGO host has been experimentally confirmed. • The values of transition probability and radiative lifetime of the 5D 0 level of Eu3+ in CBGO crystal have been determined. [ABSTRACT FROM AUTHOR]

Photoluminescence characteristics of Gd 2 O 3 :Bi are studied in the 4.2–800 K temperature range by the time-resolved spectroscopy methods. Purely cubic structure of Gd 2 O 3 :Bi is confirmed by XRD. The luminescence of Bi3+(S 6) and Bi3+(C 2) centers is found to arise from the electron transitions from the emitting level of the triplet excited state of Bi3+, corresponding to the 3P 1 → 1S 0 transitions of the free Bi3+ ion. Relaxation processes in the triplet excited state of Bi3+ ions do not result in the population of the lowest-energy metastable level. The absence of the radiative transitions, corresponding to the 3P 0 → 1S 0 transitions of the free Bi3+ ion, explains the short (0.3–2.0 μs) decay time of the triplet emission of Bi3+ even at 4.2 K. The conclusion is made that the fast luminescence decay cannot be caused by the mixing of the metastable and emitting levels of the triplet excited state of Bi3+ by the magnetic field created at the Bi3+ site by the magnetically ordered Gd3+ sublattice. The electron transfer and recombination processes, resulting in the appearance of the photo- and thermally stimulated electron recombination luminescence of Bi3+(S 6) and Bi3+(C 2) centers under excitation in the E exc > 4.3 eV energy region, are also discussed. The energy level positions of the Bi3+(S 6) and Bi3+(C 2) centers in the band gap of Gd 2 O 3 are estimated. [Display omitted] • Photo- and thermoluminescence and XRD are studied for Gd 2 O 3 :Bi3+ powder. • Luminescence arises only from the 3P 1.→ 1S 0 transitions of Bi3+(S 6) and Bi3+(C 2) • This explains a short (∼10−6 s) decay time of the triplet luminescence at 4.2 K. • Fast decay cannot be caused by the magnetic field created at Bi3+ site by Gd3+ sublattice. • Electron transfer processes take place under excitation of Bi3+ with E exc >4.3 eV. [ABSTRACT FROM AUTHOR]

In order to investigate the effect of positional isomerization on the photoelectric properties of thermally activated delayed fluorescence (TADF) emitters, thereby fully stimulating the potential of the molecular backbone, herein, two red TADF isomers, oTPA-PPP and mTPA-PPP, were developed and synthesized by linking triphenylamine (TPA) donor into different positions of the pyrido [2′,3′:5,6] pyrazino [2,3-f] [1,10] phenanthroline (PPP). Their photoluminescent quantum yields (PLQYs) and external quantum efficiencies (EQEs) were significantly different by manipulating the substitution position of the donor. Compared with mTPA-PPP, oTPA-PPP exhibited higher PLQY benefiting from intramolecular hydrogen bonding and larger fluorescence radiative decay rate, as confirmed by both theoretical and experimental analyses. As a result, oTPA-PPP-based organic light-emitting diode (OLED) realized high EQE max of 19.2 % with red emission at 603 nm, whereas mTPA-PPP achieves an EQE max of 7.9 % at 596 nm. This work provides a simple and feasible molecular design strategy to design and select red TADF emitters with excellent properties. [Display omitted] • Two emitters' photophysical properties can be finely regulated and their molecular skeleton potential is excited. • Multi-nitrogen atom receptors promote RISC and radiative transition processes. • High k r of 5.29 × 107 s−1 for oTPA-PPP suppressed the non-radiative decay and enhanced PLQY to 92.8 %. • OTPA-PPP-based OLED realized high EQE of 19.2 % with red emission peaked at 603 nm. [ABSTRACT FROM AUTHOR]

• Zn2+ containing samarium strontium borate glasses are prepared by the standard melt quenching approach. • The Judd–Ofelt theorem is used to investigate the radiative transitions of Sm3+ ions from the 6H 5/2 level to higher levels. • The PL emission spectra exhibit four bands corresponding to the transitions 4G 5/2 → 6H 5/2 , 6H 7/2 , 6H 9/2 , and 6H 11/2. • The chromaticity coordinates fallin the reddish orange zone, with colour correlated temperatures lower than the warm limit. • The prepared glasses are well-suited for warm reddish orange emission-based laser and photonic applications. Sm 2 O 3 –SrO–B 2 O 3 glasses containing ascending ratios of ZnO were created via the standard melt quenching approach. The optical and luminescent properties were assessed by analysing absorption, reflectance, excitation, and emission spectra obtained from measurements. The density, molar volume, metallization criterion, optical basicity, optical bandgap, Urbach energy, and dispersion parameters were evaluated and discussed. The spectral radiative transitions of the Sm3+ ion in different excited states were investigated using the Judd–Ofelt (J–O) theorem. The least square fit method was used to evaluate the J–O intensity parameters, which were subsequently utilized to determine radiative characteristics including transition probability, branching ratio, and lifetime. For all glasses, the reddish orange transition 4G 5/2 → 6H 7/2 demonstrated the highest strength and had the maximum values for stimulated emission cross section, radiative transition probability, and gain bandwidth. The chromaticity coordinates fell within the reddish orange region and the colour correlated temperatures ranged from 1840 to 1935 K, suggesting the suitability of the glasses for warm reddish orange emission-based laser and photonic applications. [Display omitted] PL emission spectra of Zn2+ containing samarium strontium borate glasses. CIE chromaticity diagram of Zn2+ containing samarium strontium borate glasses. [ABSTRACT FROM AUTHOR]

Tantalum (Z = 73) is an element that is produced in the neutron-induced transmutation of tungsten (Z = 74) which in turn will compose the divertors in Tokamaks. As a consequence, their sputtering may generate ionic impurities of all possible charge states in the deuterium-tritium plasma that could contribute to radiation losses in controlled nuclear devices. The radiative properties of these ions have therefore potential important applications in this field. In this context, a multiplatform approach has been adopted in order to compute the Ta VII radiative rates and estimate their accuracy. The oscillator strengths and transition probabilities have been calculated for the 237 electric dipole (E1) transitions of the Ta VII spectrum as classified by Ryabtev et al. (2014). Three independent atomic structure models have been used; one based on the semi-empirical pseudo-relativistic Hartree–Fock (HFR) method and two based on the fully relativistic ab initio multiconfiguration Dirac–Hartree–Fock (MCDHF) method. • f -values have been computed for 237 E1 transitions in Ta VII. • A -values have been also determined. • These lines fall in the UV spectral range from 191 Å to 355 Å. • A multiplatform approach has been used to assess the accuracy these rates. [ABSTRACT FROM AUTHOR]

The carbon nanodots (CNDs) can absorb short wavelength light and enable excited electrons to achieve light conversion to long wavelength emission by radiative transition, while accompanying the non-radiative transition of excited electrons, in order to block the short wavelength light. The CNDs were prepared from chitosan as the carbon source, and then mixed with polyvinyl alcohol (PVA) to prepare CNDs-based optical blocking films (CND-OBFs) containing different proportions of CNDs. Images were clearly visible through CND-OBFs under both close and long-distance observation, demonstrating good transparency. The CND-OBFs were shown to block both UV light from sunlight and harmful blue light from computers, mobile phones and white light-emitting diodes. The CND-OBFs can thus be used to effectively block short wavelength light. Samples of wood were covered with different CND-OBFs and the wood surfaces were then irradiated with UV light (340 nm, 80 W). The results show that different CND-OBFs block short wavelength light to different extents; CND-OBF containing 15.7 % CNDs can completely block short wavelength light through absorption and conversion, protecting the wood samples from discoloration. This work provides a new research approach in which CNDs are used to protect wood by blocking short wavelength light. The carbon nanodots (CNDs) based optical blocking film (CND-OBF) containing concentration-dependent long wavelength emitting CNDs was developed and used to protect wood from damage caused by short wavelength light. [Display omitted] • Carbon nanodots (CNDs) with concentration-dependent long wavelength emission were synthesized from chitosan. • The blocking level of CNDs based optical blocking films (CND-OBFs) to short-wave light is adjustable. • CND-OBFs can block harmful blue light emitted by WLED, computer and mobile phone screens. • CND-OBFs with more than 15.7 % CNDs content can completely protect wood from damage caused by short wavelength light. [ABSTRACT FROM AUTHOR]

Integrating high charge‐carrier mobility and low‐threshold lasing action in an organic semiconductor is crucial for the realization of an electrically pumped laser, but remains a great challenge. Herein, we present an organic semiconductor, named as 2,7‐di(2‐naphthyl)‐9H‐fluorene (LD‐2), which shows an unexpected high charge‐carrier mobility of 2.7 cm2 V−1 s−1 and low‐threshold lasing characteristic of 9.43 μJ cm−2 and 9.93 μJ cm−2 and high‐quality factor (Q) of 2131 and 1684 at emission peaks of 420 and 443 nm, respectively. Detailed theoretical calculations and photophysical data analysis demonstrate that a large intermolecular transfer integral of 10.36–45.16 meV together with a fast radiative transition rate of 8.0×108 s−1 are responsible for the achievement of the superior integrated optoelectronic properties in the LD‐2 crystal. These optoelectronic performances of LD‐2 are among the highest reported low‐threshold lasing organic semiconductors with efficient charge transport, suggesting its promise for research of electrically pumped organic lasers (EPOLs). [ABSTRACT FROM AUTHOR]

In this study, a series of well-crystallized Yb3+/Er3+/Tm3+-tridoped Y2O3-ZnO ceramic nano-phosphors were prepared using sol–gel synthesis, and the phosphor structures were studied using X-ray diffraction, scanning electron microscopy, and thermogravimetric analysis. The phosphors were well crystallized and exhibited a sharp-edged angular crystal structure and mesoporous structure consisting of 270 nm nano-particles. All phosphors generated blue, green, and red emission bands attributed to Tm: 1G4→3H6, Er: 2H11/2 (4S3/2)→4I15/2, and Er: 4F9/2→4I15/2 radiative transitions, respectively. Increasing in luminescent centers, weakening of lattice symmetry, and releasing of dormant rare earth ions can enhance all emissions. Er3+ can obtain energy from Tm3+ to enhance green and red emission. These colors can be tuned by optimizing the doping concentrations of the Er3+ ion. The color coordinates were adjusted by tuning both the Er3+ concentration and excitation laser pump power to shift the color coordinates and correlated color temperature. The findings of this study will broaden the potential practical applications of phosphors. [ABSTRACT FROM AUTHOR]

We briefly discuss the history of pumping schemes for the common 22-GHz maser transition in o-H2O, and note that radiative mechanisms have been considered in the past, as well as the better known collisional pumping mechanisms associated with shock waves. Substantial IR irradiation is indeed destructive to inversion at 22-GHz under a wide range of physical conditions. We identify a small number of transitions, including 22 GHz, that can be pumped by both collisional and radiative schemes, and, through radiative transfer modelling over a grid of values in kinetic temperature, number density, and dust temperature, identify loci in density-kinetic temperature space where these schemes lead to strong inversions. The radiative pumping scheme generally operates at higher dust temperature, and lower kinetic temperature, than the collisional scheme. We identify a small network of transitions that form a radiative pumping scheme for the 22-GHz maser, involving radiative transitions of wavelength approximately 6  |$\mu$| m. This network is capable of supplying more than 50 per cent of the 22-GHz inversion under typical radiative pumping conditions, and it is consistent with the need for high dust and low kinetic temperatures determined from the modelling. We identify a probable case of radiative pumping in a massive star-forming region from the observation of a positive correlation between the flux densities of 22-GHz H2O masers and 6.7-GHz methanol masers. We discuss possibilities for finding radiatively pumped H2O maser lines in other source types. [ABSTRACT FROM AUTHOR]