Cluster Emitters Research Articles

Spring Lock: Constructing Cluster Emitters with Colorful TADF from Non‐Conjugated Polymaleimide Helical Chains

AbstractNon‐conjugated luminescent polymers have received much attention due to their excellent flexibility, processability, and biocompatibility. However, the single emission color and low solid‐state luminescence efficiency restrict their further development. Herein, by introducing carboxyl‐terminated alkyl chains on the rigid and helical polymaleimide backbone, a series of non‐conjugated luminescent polymers are designed and synthesized. Due to the “spring lock” formed by the synergism of scalable helical main chains and flexible alkyl side chains, these polymers exhibit effective cluster luminescence with thermally activated delayed fluorescence (TADF) property, thereby significantly improving the solid‐state luminescence efficiency with the quantum yield up to 59.6%. The TADF emission wavelengths of the polymer powders can be tuned from 498 to 639 nm through changing reaction solvents, because the conformation of helical chains forming clusters is sensitive to solvent polarity. Interestingly, metal ions can induce the polymers to construct self‐repairing cluster luminescence gels, which show excellent potential applications in ammonia detection and information encryption. This work not only provides an effective design strategy for the colorful cluster luminescence with high‐efficiency TADF, but also further reveals the cluster luminescence mechanism and enlightens the promising applications of cluster luminescent gels.

Electroluminescent Clusters

AbstractOptoelectronic cluster materials emerge rapidly in recent years especially for light‐emitting devices, owing to their 100 % exciton harvesting and unique organic–inorganic hybrid structures with tunable excited‐state characteristics for thermally activated delayed fluorescence and/or phosphorescence and inheritable photo‐ and thermo‐stability. However, for efficient electroluminescence, excited‐state compositions of cluster emitters should be tuned through ligand engineering to enhance ligand‐centered radiative components and reduce cluster‐centered quenching states. Nonetheless, the balance of optoelectronic properties requires delicate and controllable ligand functionalization. On the other hand, in addition to balancing carrier fluxes, it showed that device engineering, especially host matrixes and interfacial optimization, can not only alleviate triplet quenching, but also modify processing and passivate defects. As consequence, the record external quantum efficiencies of cluster light‐emitting diodes already reached ≈30 %. Herein, we overview recent progress of electroluminescent cluster materials and discuss their structure–property relationships, which would inspire the continuous efforts making cluster light‐emitting diodes competent as the new generation of displays and lighting sources.

Electroluminescent Clusters.

Optoelectronic cluster materials emerge rapidly in recent years especially for light-emitting devices, owing to their 100 % exciton harvesting and unique organic-inorganic hybrid structures with tunable excited-state characteristics for thermally activated delayed fluorescence and/or phosphorescence and inheritable photo- and thermo-stability. However, for efficient electroluminescence, excited-state compositions of cluster emitters should be tuned through ligand engineering to enhance ligand-centered radiative components and reduce cluster-centered quenching states. Nonetheless, the balance of optoelectronic properties requires delicate and controllable ligand functionalization. On the other hand, in addition to balancing carrier fluxes, it showed that device engineering, especially host matrixes and interfacial optimization, can not only alleviate triplet quenching, but also modify processing and passivate defects. As consequence, the record external quantum efficiencies of cluster light-emitting diodes already reached ≈30 %. Herein, we overview recent progress of electroluminescent cluster materials and discuss their structure-property relationships, which would inspire the continuous efforts making cluster light-emitting diodes competent as the new generation of displays and lighting sources.

Cluster Light‐Emitting Diodes Containing Copper Iodine Cube with 100 % Exciton Utilization Using Host‐Cluster Synergy

AbstractClusters combine the advantages of organic molecules and inorganic nanomaterials, which are promising alternatives for optoelectronic applications. Nonetheless, recently emerged cluster light‐emitting diodes require further excited state optimization of cluster emitters, especially to reduce population of the cluster‐centered triplet quenching state (3CC). Here we report that redox‐active ligands enhance reverse intersystem crossing (RISC) of Cu4I4 cluster for triplet‐to‐singlet conversion, and thermally activated delayed fluorescence (TADF) host can provide an external RISC channel. It indicates that the complementarity between TADF host and cluster in RISC transitions gives rise to 100 % triplet conversion efficiency and complete singlet exciton convergence, rendering 100‐fold increased singlet radiation rate constant and tenfold decreased triplet non‐radiation rate constant. We achieve a photoluminescence quantum yield of 99 % and a record external quantum efficiency of 29.4 %.

Cluster Light-Emitting Diodes Containing Copper Iodine Cube with 100% Exciton Utilization Using Host-Cluster Synergy.

Clusters combine the advantages of organic molecules and inorganic nanomaterials, which are promising alternatives for optoelectronic applications. Nonetheless, recently emerged cluster light-emitting diodes require further excited state optimization of cluster emitters, especially to reduce population of the cluster-centered triplet quenching state (3CC). Here we report that redox-active ligands enhance reverse intersystem crossing (RISC) of Cu4I4 cluster for triplet-to-singlet conversion, and thermally activated delayed fluorescence (TADF) host can provide an external RISC channel. It indicates that the complementarity between TADF host and cluster in RISC transitions gives rise to 100% triplet conversion efficiency and complete singlet exciton convergence, rendering 100-fold increased singlet radiation rate constant and tenfold decreased triplet non-radiation rate constant. We achieve a photoluminescence quantum yield of 99% and a record external quantum efficiency of 29.4%.

Cluster radioactivity around shell closures: correlation of half-lives with the energy levels of daughter nuclei

The emission of Be, C, O, and Ne clusters from seven parent nuclei with neutron numbers around the neutron magicities N = 82 and 126 are considered. The universal decay law (UDL) formula, as well as the double-folding model derived from the Michigan three-range Yukawa–Paris NN interaction with zero- and finite-range exchange components, are utilized to compute the half-life time for 23 cluster decay processes. The calculations utilizing the UDL formula show satisfactory agreement with the experimental data. The reliable UDL formula is used to calculate log T c for more than 1500 cluster emitters and its variation with the neutron number, N d, of the daughter nuclei is presented. The behavior of log T c with neutron number variation is studied and correlated to the energy levels of the daughter nuclei. For a neutron number N d larger than the neutron magic number, log T c increases almost linearly with increasing N d, leaving the daughter nuclei in most cases with the same nuclear spin value. This linear behavior of log T c results from equal nuclear spin values of the daughter nuclei. At the magic neutron number, the nuclear spin changes strongly and as a result log T c increases as N d decreases. Log T c reaches to a maximum value when all the neutrons in the cluster are emitted from levels below the neutron gap. Leaving the daughter nuclei in the same spin produces almost linear variation of log T c. For protons in various clusters emitted from the same level or the same group of levels, log T c has almost the same value and the same behavior of variation with N d. Also, the values of log T c for specific types of cluster depend on the N to Z ratio for different isotopes of this cluster. From the available nuclear spin values, the neutron energy levels around the magic numbers are presented.

Overcoming Efficiency Limitation of Cluster Light-Emitting Diodes with Asymmetrically Functionalized Biphosphine Cu4I4 Cubes.

Electroluminescent (EL) nanoclusters holding promise for new-generation cluster light-emitting devices (CLEDs) rapidly emerge. However, slow radiation and serious quenching of cluster emitters largely limit the device performance. Herein, we report two monofunctionalized biphosphine chelated Cu4I4 clusters [DMACDBFDP]2Cu4I4 and [DPACDBFDP]2Cu4I4. The asymmetric modification and electron-donating effect of acridine groups lead to the iodine-to-ligand charge transfer predominant excited states of the clusters, which feature thermally activated delayed fluorescence with markedly improved singlet radiative rate constants and reduced triplet nonradiative rate constants. As consequence, compared to the nonfunctionalized parent cluster, [DPACDBFDP]2Cu4I4 achieves 16-fold increased photoluminescence (81%) and 20-fold increased EL (19.5%) quantum efficiencies. Such new-record efficiencies make CLEDs achieve the state-of-the-art performance of all kinds of EL technologies.

An improved semi-empirical relationship for cluster radioactivity * *Supported by the National Natural Science Foundation of China (U1832120, 11675265), the Natural Science Foundation for Outstanding Young Scholars of Hebei Province of China (A2020210012, A2018210146), the Continuous Basic Scientific Research Project (WDJC-2019-13) and the Leading Innovation Project (LC 192209000701)

An improved semi-empirical relationship for cluster radioactivity half-lives is proposed by introducing an accurate charge radius formula and an analytic expression of the preformation probability. Moreover, the cluster radioactivity half-lives for the daughter nuclei around 208Pb or its neighbors and the 12C radioactivity half-life of 114Ba are calculated within the improved semi-empirical relationship. It is shown that the accuracy of the new relationship is improved significantly compared to its predecessor. In addition, the cluster radioactivity half-lives that are experimentally unavailable for the trans-lead and trans-tin nuclei are predicted by the new semi-empirical formula. These predictions might be useful for searching for the new cluster emitters of the two islands in future experiments.

Alpha and heavy cluster radioactivity of superheavy nuclei 100 ⩽ Z ⩽ 120

Using Cubic plus Yukawa plus Exponential (CYE) model, half lives of alpha decay and heavy cluster radioactivity of Superheavy nuclei have been systematically investigated for even-even, even-odd, odd-even and odd-odd nuclei with 100 ⩽ Z ⩽ 120. We have done our calculations by considering the Coulomb, centrifugal and Yukawa plus exponential potentials as an interacting barrier for separated fragments and the cubic potential for the overlapping region.The predicted half life time values by including deformation effects on parent and parent cluster have been compared with theAnalytical Super Asymmetric Fission (ASAF) model of D.N.Poenaru et.al. In this work, we have compared the half life time values of alpha and heavy cluster radioactivity of Super heavy nuclei leading to 208Pb. This study suggests that heavy-cluster radioactivity may be comparable to or even dominant over a decay for some of the isotopes with Z ⩾ 118. Furthermore, branching ratio calculations have been performed to find out the probable cluster emitters. The predictions for cluster emitters are in agreement with CPPM model by Santhosh et. al.,and Wentzel-Kramers-Brillouin (WKB) method by A.Soylu et. al. We hope that this study will help in future measurements on α-decay and cluster radioactivity half-lives of SHN.

Cluster decay half-lives and preformation probabilities

An improved semi-analytic approach to the barrier penetration probability is developed in the frame work of the Wentzel-Kramers-Brillouin (WKB) approximation. It is used to calculate decay half-lives and preformation probabilities for a set of 304 cluster emitters in the range 87 ≤ Z ≤ 96 and a set of 390 α-emitters in the range 52 ≤ Z ≤ 120. For cluster decay, the validity of our approach is tested against Coulomb and proximity potential model (CPPM) by comparing decay half-lives and barrier penetration probabilities. Our results are found to be in a good agreement with CPPM calculations and with the available experimental data. In case of α-decay, our calculations are tested against the experimental data and also a very good agreement is achieved. In both cases, results are also compared with calculations of some other well known universal decay laws that are used in many recent studies. Our approach shows a better agreement with experimental data than most of the other models. Our study is extended to calculate the assault frequency and preformation probability of the cluster inside the parent nucleus. A strong correlation is obtained for all these parameters with each other. Neutron shell closures are found to be more important in the cluster decay process than proton shell closure. It is also noted that the odd–even staggering behavior dominates the decay processes involving the emission of clusters with odd neutron number.

The predictions on the heavier cluster decays of superheavy nuclei

We have calculated the half-lives of the $ \alpha$ and heavy-cluster decays of superheavy nuclei in the framework of the Wentzel-Kramers-Brillouin (WKB) method. Good agreement with the present experimental data with the WKB method and Universal Decay Law (UDL) has been obtained for the $ \alpha$ -decay half-lives of superheavy nuclei having proton numbers with $ 107 \le Z \le 118$ . We have utilized the cluster preformation factor form proposed by Santhosh and Nithya [#!san!#] with new parameters sets produced by fitting of the results with the UDL formula in order to obtain the cluster decay half-lives. Reasonable results have been obtained by using the cluster preformation factor together with the WKB formalism for the cluster decays. Furthermore, ratio calculations have been performed to find out the candidates of possible cluster emitters. The predictions for cluster emitters are in agreement with estimates with the CPPM model by Santhosh and Nithya [#!san!#] and new additional estimates with the WKB and UDL are made. The present results and predictions would be important for both the theoretical and experimental studies in this field.

Optical properties and charge distribution in rod-shape DNA-silver cluster emitters.

While the atomic structure of DNA_Agn clusters remains unknown many efforts have been made to understand the photophysical properties of this type of systems. It is known that partial oxidation of the silver cluster is necessary for generation of fluorescent emitters. In this sense, the rod-shape model proposed by Gwinn and coworkers (D. Schultz, K. Gardner, S. S. R. Oemrawsingh, N. Markeševic, K. Olsson, M. Debord, D. Bouwmeester, and E. Gwinn, Adv. Mater., 2013, 25, 2797-2803), based on the idea that a neutral rod is generated with Ag+ acting as a "glue" in between the neutral rod and the DNA bases, is a good approximation in order to explain experimental results. With the aim to shed light towards the understanding of these systems, we explore the electronic dynamics and charge distribution in zigzag rod-shape DNA_Agn clusters, using the Ag0/Ag+ stoichiometry found experimentally.

The isovector nuclear density and improved description of cluster decay half-lives using isospin-dependent NN interaction

The sensitivity of cluster-decay half-life time to the isospin effect of the nucleon–nucleon (NN) interaction and the neutron-skin thickness is explored in the framework of the Wentzel–Kramers–Brillouin approximation. Within the generalized double-folding model, the cluster-daughter potential is calculated in terms of the isoscalar and isovector parts using the explicit proton and neutron density distributions. Realistic density-dependent Michigan-three-Yukawa (CDM3Y1 and CDM3Y6) NN interactions with the finite-range exchange NN force are considered in the present work. The calculated cluster-decay half-lives including the isospin effect and the differences between neutron and proton density distributions are found to be in somewhat better agreement with the experimental data as compared without these effects. This may indicate the necessity of considering the isospin effect and the neutron–proton differences of the density distributions in cluster-decay, especially for extremely neutron-rich nuclei. Predictions of cluster decay half-lives from possible cluster emitters are presented which may be helpful for future experiments. The present study could be a significant step forward in improving the description of cluster decay half-lives.

Constraints on both the symmetry energy E2(ρ0) and its density slope L2(ρ0) by cluster radioactivity

Within the density-dependent cluster model (DDCM), the decay half-lives of 22 cluster emitters are calculated by using experimental decay energies. Based on our previous study on cluster radioactivity [Phys. Rev. C 90, 064310 (2014)], not only the quadratic symmetry energy ${E}_{2}({\ensuremath{\rho}}_{0})$ and its slope ${L}_{2}({\ensuremath{\rho}}_{0})$ but also the quartic symmetry energy ${E}_{4}({\ensuremath{\rho}}_{0})$ and its slope ${L}_{4}({\ensuremath{\rho}}_{0})$ at the saturation density ${\ensuremath{\rho}}_{0}$ are constrained by considering the neutron skin thicknesses in the daughter nuclei. With the extracted values of ${E}_{2}({\ensuremath{\rho}}_{0})$ and ${L}_{2}({\ensuremath{\rho}}_{0})$, the exponent $\ensuremath{\gamma}$ of the quadratic density-dependent symmetry energy ${E}_{2}(\ensuremath{\rho})={E}_{2}({\ensuremath{\rho}}_{0}){(\ensuremath{\rho}/{\ensuremath{\rho}}_{0})}^{\ensuremath{\gamma}}$ is estimated. Moreover, the symmetry energy coefficient of nuclei ${a}_{\mathrm{sym}}(A)$ and the ratio $\ensuremath{\kappa}$ of the surface symmetry coefficient to the volume symmetry coefficient are extracted as well.

Proton emission half-lives within a Gamow-like model

Proton emission is described using a model which has previously given good results in the description of $\alpha$ and cluster radioactivity. The simple phenomenological formalism, based on the Gamow theory for alpha decay, is now extended by including the centrifugal term. The model contains only one parameter: the effective nuclear radius constant. Its value was once found for alpha and cluster emitters. A good agreement with the experimental half-lives for proton radioactivity is achieved without any additional fitting procedures to the data for proton emission.

Reexamining cluster radioactivity in trans-lead nuclei with consideration of specific density distributions in daughter nuclei and clusters

We further investigate the cluster emission from heavy nuclei beyond the lead region in the framework of the preformed cluster model. The refined cluster-core potential is constructed by the double-folding integral of the density distributions of the daughter nucleus and the emitted cluster, where the radius or the diffuseness parameter in the Fermi density distribution formula is determined according to the available experimental data on the charge radii and the neutron skin thickness. The Schr\odinger equation of the cluster-daughter relative motion is then solved within the outgoing Coulomb wave-function boundary conditions to obtain the decay width. It is found that the present decay width of cluster emitters is clearly enhanced as compared to that in the previous case, which involved the fixed parametrization for the density distributions of daughter nuclei and clusters. Among the whole procedure, the nuclear deformation of clusters is also introduced into the calculations, and the degree of its influence on the final decay half-life is checked to some extent. Moreover, the effect from the bubble density distribution of clusters on the final decay width is carefully discussed by using the central depressed distribution.

Consistent description of the cluster-decay phenomenon in transactinide nuclei

Systematic investigation of the known even-even transactinide cluster emitters has been carried out by considering the cluster as a point particle and using the exact quantum mechanical treatment of the decay process. It is shown that the cluster decay phenomenon can be described reasonably well using a simple Woods-Saxon mean field. Sensitivity of the half-lives on various aspects of the mean field has been investigated in detail.

Simple nuclear mass formula

A simple formula for ground state nuclear masses based on the microscopic-macroscopic approach is proposed. Considering a set of 2353 nuclei with $Z\ensuremath{\ge}8$ and $N\ensuremath{\ge}8$, the formula yields an rms deviation of just 266 keV. A few applications, including the loosely bound proton rich nuclei, superheavy nuclei, and cluster emitters, are presented and discussed, establishing the reliability of the proposed formula. The present investigation has a major advantage: it allows one to reliably parametrize the fluctuating part of the ground state energy. This result is very interesting and important, since the fluctuating part of the energy is related directly to the trace formula, which in turn encodes the interaction itself.

An empirical relation for cluster decay preformation probability

Empirical relations for the preformation probability of cluster decay process in terms of the Q-value, mass asymmetry (η), mass number of the emitted cluster A2 is analyzed based on the discrepancy between the calculated and experimental half-lives of the cluster emitters. For the different empirical expressions considered corresponding to different physical quantities the preformation probability for the complete binary breakup of 226 Ra is calculated and the obtained results are compared with the preformed cluster model calculation (P0( PCM )) and another calculation in which the overlapping penetration probability is treated as the preformation probability (P0(μ)). Our empirical results for the use of Q-value compare well with P0(μ). Results due to the use of Q and its powers along with the combination of mass number A2 of the cluster emitted, and mass asymmetry η, reveal that preformation factor depends strongly on Q-value rather than A2 and η. Calculated half-lives of different cluster decays for the use of empirical P0 values are found to be in good agreement with the experimental values.

Individual and collective properties of fermions in nuclear and atomic cluster systems

Usually in nuclear physics the minimum of the liquid drop model (LDM) energy for synthesis of superheavy nuclei or cluster decay modes occurs at a mass asymmetry which is different from the minimum of shell correction. Three examples are given: potential energy surfaces of 300120; a table showing the magic numbers of target nuclei used to produce superheavies at GSI and RIKEN and a table of magic numbers of daughter for identified cluster emitters. On the other hand, charged metallic clusters are ideal emitters of singly ionized trimers because both LDM and shell correction reach a minimum for the same mass asymmetry corresponding to the emission of a charged particle with two delocalized electrons; for example, the fission of alkali (Cs, K, Na and Li) clusters with 146 atoms and an excess charge z = 6. Calculations of Q2-values for Cs, Na, Au and Cu atomic clusters multiply ionized (z = 2, 4, 6, 8, 10) and spheroidally deformed prove that large dissociation energy is obtained for metallic clusters with high surface tension and low Wigner–Seitz radius (transition metals).