Electron paramagnetic resonance (EPR), photoluminescence, and infrared optical absorption have been used to investigate a ZnO crystal before and after a thermal anneal for 1 h in air at 900 °C. The sample was an undoped high quality crystal grown by the chemical vapor transport method. In addition to shallow donor impurities, the crystal contained trace amounts of copper ions. Prior to the thermal anneal, these ions were all in the Cu+ (3d10) state and the observed luminescence at 5 K, produced by 364 nm light, consisted of a broad structureless band peaking at 500 nm. After the high-temperature anneal, the Cu2+ (3d9) EPR spectrum was observed and the luminescence had changed significantly. The emission then peaked near 510 nm and showed structure identical to that reported by Dingle [Phys. Rev. Lett. 23, 579 (1969)]. Our data reaffirm that the structured green emission in ZnO is associated with Cu2+ ions. We suggest that the unstructured green emission (observed before the high-temperature anneal) is donor–acceptor pair recombination involving the Cu+ acceptors.

Unorthodox luminogenic polymers without aromatic luminogens have attracted great interest in recent years; however, the low fluorescence efficiency is still a big drawback. In this paper, we synthesized a fluorescent hyperbranched polysiloxane with both carbonyl and vinyl groups (P1). Surprisingly, it exhibited nontraditional intrinsic luminescence with the highest quantum yield up to 43.9% among the reported silica-containing hyperbranched fluorescent polymers to date. Reference oligomers P2 and P3, theoretical calculations, and transmission electron microscopy were employed to explore the fluorescence mechanism. The high fluorescence quantum yield is ascribed to the synergism of vinyl and carbonyl groups as well as the Si−O grouppromoted through-space conjugation. Thus, the supramolecular hyperbranched polysiloxane was assembled by conjugation to increase the oscillator strength and decrease the band gap. Moreover, the solvent effect and pH dependency properties of P1 and its application as an Fe 3+ probe were also studied.

Hyperbranched polysiloxane (HBPSi) is attracting increasing attention due to its intrinsic fluorescence and good biocompatibility. However, it is very challenging to explore its biological applications because of the low fluorescence intensity and quantum yield. Herein, we introduced rigid β-cyclodextrin to the end of flexible polysiloxane chain to synthesize a novel fluorescent polymer (HBPSi-CD) and explore its biological applications. Results showed that the fluorescence intensity and quantum yield of HBPSi-CD, compared with HBPSi, were significantly enhanced. Theoretical calculations and transmission electron microscopy demonstrated that the synergy effect of intra/intermolecular hydrogen bonds and hydrophobic effect promoted the formation of large supramolecular self-assemblies and space electron delocalization systems, leading to intense fluorescence. Notably, the biocompatible HBPSi-CD not only lighted up mouse fibroblast cells, but also possessed high ibuprofen loading capacity (160 mg g–1) and superior pH-responsive drug release performance. This work promoted the development of biological applications of HBPSi.

Fluorescent hyperbranched polysiloxane (HBPSi) has attracted increasing attention due to its good biocompatibility. However, its emission mechanism remains an open question. Unfortunately, the excitation spectra of HBPSi are rarely systematically investigated and show a narrow excitation band, which hinders the emission mechanism study. Herein, we synthesized a series of novel HBPSi containing L-glutamic acid (HBPSi-GA). Surprisingly, these polymers have four excitation peaks and two emission peaks, which are caused by the energy transfer from free functional groups to heterogeneous electron delocalizations in different clusters. Meanwhile, the fluorescence and biocompatibility of HBPSi-GA are significantly improved with increasing L-glutamic acid. Furthermore, HBPSi-GA exhibits dual stimuli-responsive fluorescence to temperature and Fe 3+ as well as potential application in cell imaging. This research possesses important guidance to develop multiexcitation unconventional fluorescent polymers.

A novel kind of water‐soluble fluorescent hyperbranched poly(amino ester) (PAE) is prepared through a one‐pot polycondensation reaction of citric acid (CA) and N‐methyldiethanolamine (NMDEA). The PAE exhibits enhanced and red‐shift fluorescence with increasing solution concentration, showing distinct aggregation‐induced emission character. Interestingly, the resulting PAE exhibits tunable photoluminescence from blue, cyan, and green to red irradiated by altering the excitation wavelengths. Such unique emission of non‐conjugated PAE is attributed to the clustering of ester and tertiary amine groups derived from PAE self‐assembly aggregates. Moreover, the fluorescence of PAE is very sensitive to Fe3+ ions. The facile preparation and unique optical features make PAE potentially useful in numerous applications such as multicolor cellular imaging, Fe3+ ions probe, and light‐emitting diodes.

An intense infrared absorption band has been observed in a hydrothermally grown ZnO crystal. At 12K, the band peaks near 3577.3cm−1 and has a half width of 0.40cm−1, and at 300K, the band peaks at 3547cm−1 and has a half width of 41.3cm−1. This absorption band is highly polarized, with its maximum intensity occurring when the electric field of the measuring light is parallel to the c axis of the crystal. Photoinduced electron-paramagnetic-resonance experiments show that the crystal contains lithium acceptors (i.e., lithium ions occupying zinc sites). Lithium and OH− ions are present in the crystal because lithium carbonate, sodium hydroxide, and potassium hydroxide are used as solvents during the hydrothermal growth. In the as-grown crystal, some of the lithium acceptors will have an OH− ion located at an adjacent axial oxygen site (to serve as a passivator), and we assign the 3577.3-cm−1 band observed at 12K to these neutral complexes. Our results illustrate the role of hydrogen as a charge compensator for singly ionized acceptors in ZnO.

We present a theoretical investigation of high-order harmonic generation in spatially inhomogeneous two-color laser fields by solving three dimensional time dependent Schrödinger equation. The cutoff in the harmonic spectra can be significantly extended by means of our proposed method (i.e., from helium interacting with the plasmon-enhanced two-color laser fields), and an ultrabroad supercontinuum up to 1.5 keV is generated by selecting proper carrier-envelope phase of the controlling field. Moreover, classical trajectory extraction, time-dependent ionization and recombination rates, and time-frequency analyses are used to explain the generation of this ultrabroadband supercontinuum. As a result, an isolated 8.8 attosecond pulse can be generated directly by the superposition of the supercontinuum harmonics.

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