Explore the vast range of titles available.

The dispute about whether the 1s core-hole is localized on one atom or delocalized over both in a homonuclear diatomic molecule has continued for decades, which has been extensively studied by the photoelectron and electron–ion coincidence spectroscopies. For N2, if the 1s core-hole is delocalized, the K-shell excitation into the 1πg orbital should split into two components, i.e., the dipole-allowed transition from the ungerade 1σu state and the dipole-forbidden transition from the gerade 1σg state. However, only the dipole-allowed transition has been observed up to now. Here, we report the inner-shell electron energy loss spectra of N2 at different scattering angles with an incident electron energy of 1500 eV and an energy resolution of 65 meV. The vibrational structures of both the dipole-allowed (1sσu)−1(1πg)1 and dipole-forbidden (1sσg)−1(1πg)1 states of N2 have been identified at different momentum transfers. The splitting between the (1σg)−1(1πg)1 and (1σu)−1(1πg)1 states with the reverse symmetry is determined to be 67 ± 7 meV. Moreover, the momentum transfer dependence behavior of the transition intensity ratio agrees with the theoretical predictions, as increasing to a maximum and then decreasing. The experimental observations clearly show that the inner most electrons can be described by 1σg and 1σu, which indicates that the inner-shell 1s core-hole of N2 is delocalized over two N atoms based on the excitation process.

Molecular vibrations are often factors that deactivate luminescence. However, if there are molecular motion elements that enhance luminescence, it may be possible to utilize molecular movement as a design guideline to enhance luminescence. Here, the authors report a large contribution of symmetry‐breaking molecular motion that enhances red persistent room‐temperature phosphorescence (RTP) in donor‐π‐donor conjugated chromophores. The deuterated form of the donor‐π‐donor chromophore exhibits efficient red persistent RTP with a yield of 21% and a lifetime of 1.6 s. A dynamic calculation of the phosphorescence rate constant (kp) indicates that the symmetry‐breaking movement has a crucial role in selectively facilitating kp without increasing nonradiative transition from the lowest triplet excited state. Molecules exhibiting efficient red persistent RTP enable long‐wavelength excitation, indicating the suitability of observing afterglow readout in a bright indoor environment with a white‐light‐emitting diode flashlight, greatly expanding the range of anti‐counterfeiting applications that use afterglow. Organic donor‐π‐donor chromophores exhibit a selective enhancement of radiation rate without increasing nonradiative transition from the lowest triplet excited state by symmetry‐breaking molecular motion. This results in a bright red persistent room‐temperature phosphorescence (RTP) yielding 21% and a lifetime of 1.6 s. This enables ubiquitous afterglow readout and expands the range soft anti‐counterfeiting applications.

The design of efficient aggregation‐induced emission materials requires an improved understanding of photophysical processes in aggregated materials. Herein, the photophysical behavior of an Au(I) complex (R6) that exhibits intense room‐temperature phosphorescence (RTP) in crystals is described. In addition, the photophysical processes related to RTP are discussed based on the structure of the molecular aggregates and the primary structure of the molecule. An extremely efficient S0–Tn direct transition is found to occur in the R6 crystal. Furthermore, intermolecular Au–Au interactions and the internal/external heavy‐atom effects of Au atoms are demonstrated to enhance the electronic transitions involving intersystem crossing, namely, direct S0–Tn excitation, radiative T1–S0 transition (phosphorescence), and S1–Tn intersystem crossing. Because of the dense molecular packing, both Au–Au interactions and heavy‐atom effects play important roles in the crystals. As a result, R6 shows more efficient RTP in crystals than in solution. These insights into the mechanism of highly efficient RTP in Au(I)‐complex crystals are expected to advance the development of new luminogens for a variety of sensing and imaging applications. The photophysical behavior of an Au(I) complex that exhibits intense room‐temperature phosphorescence (RTP) in crystals is described. Intermolecular Au–Au interactions are demonstrated to enhance S0–Tn direct excitation, and RTP. The insights into the mechanism of highly efficient RTP in Au(I)‐complex crystals could advance the development of new luminogens for various applications.

Energies, weighted oscillator strengths (gf), line strengths (S) and radiative rates (A) for allowed and forbidden transitions are presented for 2s2p62S1/2 − 2s22p52P1/2, 2P3/2 and 2s22p52P1/2 − 2s22p52P3/2 transitions in fluorine-like Ca XII (Z = 20), Ti XIV (Z = 22), Cr XVI (Z = 24), Fe XVIII (Z = 26) and Ni XX (Z = 28) ions. Moreover, the allowed electric dipole (E1) and the forbidden electric quadrupole (E2), octupole (E3), magnetic dipole (M1) and quadrupole (M2) transition rates for some transitions are obtained. The 2s22p5–2s 2p6-type transitions of F-like ions are prominent in high-temperature plasmas and are useful for diagnostics. The present results are obtained from configuration interaction atomic structure calculations using the code SUPERSTRUCTURE (SS) which includes relativistic effects in Breit–Pauli approximation. The comparison of the present energies with the available observed energies displayed very good agreement (< 1%). The presented excitation energy results have been compared with other detailed relativistic approaches such as Dirac–Fock, coupled cluster and configuration interaction for a few ionic states.

Experimentally, under laboratory conditions in the nitrogen acoustic plasma in the region of the forbidden lines at 654.81 and 658.36 nm, a spectral emission line of high intensity was obtained (up to 17 stronger than the neighboring lines of the first positive system of nitrogen). The results were obtained both in pure low-pressure nitrogen acoustic plasma (several hundreds of Pa) and various mixtures containing nitrogen, including the CO 2 : N 2 : He = 1 : 1 : 8 mixture. The results obtained are explained by the acoustic plasma state of the discharge and an analog of Rahman scattering, which remove some of the quantum mechanical prohibitions. The possible influence of the Coriolis force is also considered.

Lighting accounts for one-fifth of global electricity consumption 1 . Single materials with efficient and stable white-light emission are ideal for lighting applications, but photon emission covering the entire visible spectrum is difficult to achieve using a single material. Metal halide perovskites have outstanding emission properties 2 , 3 ; however, the best-performing materials of this type contain lead and have unsatisfactory stability. Here we report a lead-free double perovskite that exhibits efficient and stable white-light emission via self-trapped excitons that originate from the Jahn–Teller distortion of the AgCl 6 octahedron in the excited state. By alloying sodium cations into Cs 2 AgInCl 6 , we break the dark transition (the inversion-symmetry-induced parity-forbidden transition) by manipulating the parity of the wavefunction of the self-trapped exciton and reduce the electronic dimensionality of the semiconductor 4 . This leads to an increase in photoluminescence efficiency by three orders of magnitude compared to pure Cs 2 AgInCl 6 . The optimally alloyed Cs 2 (Ag 0.60 Na 0.40 )InCl 6 with 0.04 per cent bismuth doping emits warm-white light with 86 ± 5 per cent quantum efficiency and works for over 1,000 hours. We anticipate that these results will stimulate research on single-emitter-based white-light-emitting phosphors and diodes for next-generation lighting and display technologies. After alloying with metal cations, a lead-free halide double perovskite shows stable performance and remarkably efficient white-light emission, with possible applications in lighting and display technologies.

Rare-earth-doped upconversion nanoparticles are attracting considerable attention because of their stable, coherent, narrowband and multi-colour luminescence, which features less dephasing effects, crosstalk, photo-blinking and photo-bleaching compared with quantum dots and organic dyes. However, due to the 4f–4f forbidden transitions of rare-earth ions, upconversion nanoparticles exhibit long luminescence decay times, ranging from microseconds to milliseconds, restricting their application in time-dependent nanophotonic devices. Here we fabricate a tilted plasmonic nanocavity to shorten the luminescence decay time of a rare-earth-doped nanoparticle to sub-50 ns while maintaining high quantum efficiency enhancement, tunable polarization-dependent and far-field directional emissions and selective polychromatic chirality. We expect this new type of ultrafast, directional and polarized luminescence of a rare-earth-doped nanoparticle to vigorously promote the development of coherent single-photon sources, quantum communications and nanolasers.A tilted plasmonic nanocavity enables shortening of the luminescence decay time of a rare-earth-doped nanoparticle to sub-50 ns. High quantum efficiency enhancement, chiral polarization and directional far-field emission are maintained.

Localized surface plasmon polaritons can confine the optical field to a single-nanometer-scale area, strongly enhancing the interaction between photons and molecules. Theoretically, the ultimate enhancement might be achieved by reducing the “photon size” to the molecular extinction cross-section. In addition, desired control of electronic transitions in molecules can be realized if the “photon shape” can be manipulated on a single-nanometer scale. By matching the photon shape with that of the molecular electron wavefunction, optically forbidden transitions can be induced efficiently and selectively, enabling various unconventional photoreactions. Here, we demonstrate the possibility of forming single-nanometer-scale, highly intense fields of optical vortices using designed plasmonic nanostructures. The orbital and spin angular momenta provided by a Laguerre–Gaussian beam are selectively transferred to the localized plasmons of a metal multimer structure and then confined into a nanogap. This plasmonic nano-vortex field is expected to fit the molecular electron orbital shape and spin with the corresponding angular momenta.

The generation, control and transfer of triplet excitons in molecular and hybrid systems is of great interest owing to their long lifetime and diffusion length in both solid-state and solution phase systems, and to their applications in light emission 1 , optoelectronics 2 , 3 , photon frequency conversion 4 , 5 and photocatalysis 6 , 7 . Molecular triplet excitons (bound electron–hole pairs) are ‘dark states’ because of the forbidden nature of the direct optical transition between the spin-zero ground state and the spin-one triplet levels 8 . Hence, triplet dynamics are conventionally controlled through heavy-metal-based spin–orbit coupling 9 – 11 or tuning of the singlet–triplet energy splitting 12 , 13 via molecular design. Both these methods place constraints on the range of properties that can be modified and the molecular structures that can be used. Here we demonstrate that it is possible to control triplet dynamics by coupling organic molecules to lanthanide-doped inorganic insulating nanoparticles. This allows the classically forbidden transitions from the ground-state singlet to excited-state triplets to gain oscillator strength, enabling triplets to be directly generated on molecules via photon absorption. Photogenerated singlet excitons can be converted to triplet excitons on sub-10-picosecond timescales with unity efficiency by intersystem crossing. Triplet exciton states of the molecules can undergo energy transfer to the lanthanide ions with unity efficiency, which allows us to achieve luminescent harvesting of the dark triplet excitons. Furthermore, we demonstrate that the triplet excitons generated in the lanthanide nanoparticle–molecule hybrid systems by near-infrared photoexcitation can undergo efficient upconversion via a lanthanide–triplet excitation fusion process: this process enables endothermic upconversion and allows efficient upconversion from near-infrared to visible frequencies in the solid state. These results provide a new way to control triplet excitons, which is essential for many fields of optoelectronic and biomedical research. Optically dark (non-emitting) triplet excitons on organic molecules may be rendered bright by coupling the molecules to lanthanide-doped nanoparticles, providing a way to control such excitons in optoelectronic systems.

Design-specific control over the transitions between excited electronic states with different spin multiplicities is of the utmost importance in molecular and materials chemistry 1 – 3 . Previous studies have indicated that the combination of spin–orbit and vibronic effects, collectively termed the spin–vibronic effect, can accelerate quantum-mechanically forbidden transitions at non-adiabatic crossings 4 , 5 . However, it has been difficult to identify precise experimental manifestations of the spin–vibronic mechanism. Here we present coherence spectroscopy experiments that reveal the interplay between the spin, electronic and vibrational degrees of freedom that drive efficient singlet–triplet conversion in four structurally related dinuclear Pt(II) metal–metal-to-ligand charge-transfer (MMLCT) complexes. Photoexcitation activates the formation of a Pt–Pt bond, launching a stretching vibrational wavepacket. The molecular-structure-dependent decoherence and recoherence dynamics of this wavepacket resolve the spin–vibronic mechanism. We find that vectorial motion along the Pt–Pt stretching coordinates tunes the singlet and intermediate-state energy gap irreversibly towards the conical intersection and subsequently drives formation of the lowest stable triplet state in a ratcheting fashion. This work demonstrates the viability of using vibronic coherences as probes 6 – 9 to clarify the interplay among spin, electronic and nuclear dynamics in spin-conversion processes, and this could inspire new modular designs to tailor the properties of excited states. Many aspects of materials chemistry rely on singlet–triplet spin conversion, but spin–vibronic effects are shown to accelerate the process when vibronic coupling causes the quantum-mechanical mixing of spin states.