The interaction between negatively charged all-inorganic silicon quantum dots (Si QDs) and bovine serum albumin (BSA) is studied. It is shown that a small difference in the size of Si QDs affects the structure of Si QD–BSA composites significantly. When the diameter of Si QDs is 4 nm, a heterodimer (~20 nm) composed of one Si QD and one BSA molecule is a preferable and stable structure. On the other hand, when the diameter is 7 nm, the size of the composites increases to ~50 nm. The Si QD–BSA composites exhibit stable photoluminescence in the near-infrared range in phosphate-buffered saline.

A process for bioconjugation of an IgG antibody and silicon quantum dots (Si-QDs) having the luminescence in the near-infrared (NIR) range was developed. For the bioconjugation, the surface of water-soluble all-inorganic Si-QDs was functionalized by using silane-coupling agents. In amino-functionalized Si-QDs, successful conjugation was achieved without strongly affecting the luminescence property. Detailed analyses revealed that Si-QDs are bound covalently to both the light and heavy chains of an IgG antibody. It was also confirmed that the binding property of an IgG antibody with antigen nucleoprotein was not ruined by the process. The successful conjugation of an IgG antibody and NIR luminescent Si-QDs paves the way for designing environmentally friendly bio-sensing and -imaging processes.

We demonstrate formation of allylamine (AAm) and acrylic acid (AAc)-functionalized colloidal silicon nanocrystals (Si NCs) exhibiting near-infrared (NIR) luminescence and immobilization of the NCs on substrates via covalent bond. The surface functionalization is confirmed by IR absorption spectroscopy and specific binding property of functionalized NCs. Atomic force microscope observations reveal that AAm- and AAc-functionalized Si NCs are chemically immobilized on self-assembled monolayers via covalent bonds. The functionalized Si NCs exhibit photoluminescence in a NIR region (1.5–1.6 eV), which is not significantly affected by the functionalization.

We analyze phosphorus (P)- and boron (B)-doped silicon nanocrystals (Si NCs) with various compositions of silicon-rich oxide using atom probe tomography. By creating Si iso-concentration surfaces, it is confirmed that there are two types of Si NC networks depending on the amount of excess Si. A proximity histogram shows that P prefers to locate inside the Si NCs, whereas B is more likely to reside outside the Si NCs. We discuss the difference in a preferential location between P and B by a segregation coefficient.

We report the Eu doping induced improvement on the second harmonic generation (SHG) of ZnO nanowires and correlates with the structural modification and corresponding linear absorption. A non-monotonic enhancement in the SHG emission is observed with the increase of Eu concentration. To understand the underlying mechanism, the effective second order non–linear coefficient (deff) is calculated from the theoretical fitting with considering the absorption effect. The highest deff (19.09±0.11 pm/V) is obtained for the 1 at.% Eu doped ZnO nanowires, which is several times larger than the standard SHG material β-BaB2O4 (BBO). Dependence of the deff with the Eu doping, structural modification and absorption magnitude are systematically discussed.

We prepare Nd-Bi codoped zeolites by a method consisting of a simple ion-exchange process and subsequent high-temperature annealing. The emission covers the range of 970∼1450 nm, corresponding to the electronic transitions of Nd3+ ions and Bi-related active centers (BiRAC), respectively. The introduction of Bi distinctly broadens the excitation band of Nd3+ in the visible region, and the lifetime of Nd3+ reaches as long as 354 μs. In the zeolite matrix, Bi ions exist as BiRAC and Bi oxide agglomerates. The former one act as a sensitizer of Nd3+ ions, and the latter one act as a blockage to avoid the quenching effect of coordinated water, which enable Nd3+ ions to show efficient near-infrared (NIR) emission even the zeolites contain large amount of coordinated water. The excellent optical and structural properties make these NIR emitting nanoparticles promising in application as laser materials and biological probes.

We report on efficient electronic energy transfer from excitons confined in silicon (Si) nanocrystals to molecular oxygen (MO). The remarkable photosensitizing properties of Si nanocrystal assemblies result from a broad energy spectrum of photoexcited excitons, a long triplet exciton lifetime and a highly developed surface area. Quenching of photoluminescence (PL) of Si nanocrystals by MO physisorbed on their surface is found to be most efficient when the energy of excitons coincides with the triplet-singlet splitting energy of oxygen molecules. Spectroscopic analysis of the quenched PL spectrum evidences that energy transfer is accompanied by multi-phonon emission. From time-resolved measurements the characteristic time of energy transfer is found to be in the range of microseconds. The dependence of PL quenching efficiency on the surface termination of nanocrystals is consistent with short-range resonant electron exchange mechanism of energy transfer. The energy transfer to oxygen molecules in the gaseous phase at elevated temperatures is demonstrated.

We report on the photosensitizing properties of optically excited Silicon (Si) nanocrystal assemblies that are employed for an efficient generation of singlet oxygen. Spin triplet state excitons confined in Si nanocrystals transfer their energy to molecular oxygen (MO) adsorbed on the nanocrystal surface. This process results in a strong suppression of the photoluminescence (PL) from the Si nanocrystal assembly and in the excitation of MO from the triplet ground state to singlet excited states. The high efficiency of the energy transfer if favored by a broad energy spectrum of photoexcited excitons, a long triplet exciton lifetime and a highly developed surface area of the nanocrystal assembly. Due to the specifics of the coupled system Si nanocrystal – oxygen molecule all relevant physical parameters describing the photosensitization process are accessible experimentally. This includes the role of resonant and phonon-assisted energy transfer, the dynamics of energy transfer, and its mechanism.

Photoluminescence (PL) of SiO2 films co-doped with Si nanocrystals (nc-Si) and Er was studied. The average size of nc-Si was changed in a wide range in order to tune the exciton energy of nc-Si to the energy separations between the discrete electronic states of Er3+. PL from exciton recombination in nc-Si and the intra-4f shell transition of Er3+ were observed simultaneously. At low temperatures, periodic features were observed in the PL spectrum of nc-Si. The period agreed well with the optical phonon energy of Si. The appearance of the phonon structures implies that nc-Si which satisfy the energy conservation rule during the energy transfer process can resonantly excite Er3+. The effects of the quantum confinement of excitons in nc-Si on the energy transfer process are discussed.

Effects of impurity (P and B) doping on the photoluminescence (PL) properties of Si nanocrystals (nc-Si) in SiO2 thin films are studied. It is shown that with increasing P concentration, PL intensity first increases and then decreases. In the P concentration range where PL intensity increases, quenching of the defect-related PL is observed, suggesting that dangling-bond defects are passivated by P doping. On the other hand, in the range where PL intensity decreases, optical absorptiondue to the intravalley transitions of free electrons generated by P doping appears. The generation of free electrons andthe resultant three-body Auger recombination of electron-hole pairs is considered to be responsible for theobserved PL quenching. In the case of B doping, the behavior is much different. With increasing B concentration, PL intensity decreases monotonously. By combining the results obtained for P and B doped samples, theeffects of donor and acceptor impurities on the PL properties of nc-Si are discussed.

The surface of Li-doped ZnSe grown on misoriented GaAs(001) substrates by molecular beam epitaxy is studied by means of reflection high energy electron diffraction. Sharp and curved streaky RHEED patterns are observed for all the layers grown on the misoriented substrate towards [110], irrespective of off-angles. No curved pattern, however, is observed on ZnSe layers grown on misoriented GaAs(001) towards [110] with off-angle larger than 5°. We confirmed that the Li-array is surely formed along [110], and that the length of the Li-array is longer than 32Å to be observable as curved streaks. It is also confirmed that the growth rate of Li-doped ZnSe is proportional to the step density, and that the growth rate on the misoriented substrate towards [110] is higher than that on the misoriented substrate towards [110]. The photoluminescence spectra of Li-doped ZnSe layers grown on misoriented GaAs are reported.