We experimentally and theoretically investigated the optical switching characteristics of bacteriorhodopsin (bR) at lambda=633 nm using the pump-probe method. A diode-pumped second harmonic YAG laser (lambda=532 nm which is located around the maximum initial Br state absorption) was used as a pumping beam and a cw He-Ne laser (lambda=633 nm which is around the peaks of K and O states) was used as a probe. Due to the nonlinear intensity induced excited state absorption of the K, L, M, N, and O states in the bR photocycle, the switching characteristics are sensitive to the intensity of the probe and pump beams. Based on this property, we have demonstrated an all-optical device functioning as 11 kinds of variable binary all-optical logic gates.

An approach combining back- and front-side doping of Ce3+ in Si nanocrystals embedded in SiO2 (nc-Si:SiO2) with hydrogen passivation has been developed, which largely enhances the photoluminescence (PL) of Si nanocrystals. The sample of nc-Si:SiO2 was prepared via a phase separation process of SiO thin film at 1100 °C. For the back-side doping, a SiO2 buffer layer was placed between the CeF3 layer and SiO one, thus Ce3+ doping could be accomplished without disrupting the phase separation of SiO. The front-side doping was then followed by evaporating CeF3 onto the front surface of the formed nc-Si:SiO2, followed by diffusion annealing at 500 °C. The double-side doping enhanced the PL intensity of Si nanocrystals by a factor of 7.3. After hydrogenation of the double-side doped sample, a 14.6-fold increase in the PL intensity was finally achieved.

Ce 3 + ions were doped into Si nanocrystals (nc-Si) embedded in SiO2 matrix (nc-Si∕SiO2) by evaporation of CeF3 powder onto the surface of nc-Si∕SiO2 and followed by thermal annealing in nitrogen ambient at different temperatures. Photoluminescence (PL) properties of the doped samples were studied. It has been found that the PL intensity of nc-Si can be remarkably enhanced and the enhancement depends on the doping concentration. Photoluminescence excitation spectra of the doped and undoped nc-Si imply that the enhancement comes from energy transfer from Ce3+ ions to nc-Si when excitation wavelength ranges from 240 to 320 nm.

Photoinduced birefringence in bacteriorhodopsin films was investigated using pump–probe method and its application for photonic switching explored. A diode-pumped second-harmonic YAG laser was used as a pumping beam and a diode laser at λ=660 nm was used as a probing beam. The pump and probe beams overlap at the sample. Without the pumping beam, the probing light cannot transmit the analyzer to the detector. However, due to the photoinduced anisotropy, a portion of the probing light is detected when the pumping beam is present. Since λ=660 nm is far from the absorption peak (∼570 nm) of the ground state, the photoinduced birefringence predominates. Using the intensity-dependent photoinduced birefringence in a bacteriorhodopsin film, we have demonstrated a photonic switch with ∼1000:1 contrast ratio, ∼0.6 s rise time and ∼1.5 s decay time.

The electroluminescence (EL) and photoluminescence of Si nanocrystals (Si-nc) from multilayered samples of Si/SiO are investigated. Si-nc are formed within Si and SiO layers after furnace annealing. It is found that the presence of Si interlayers creates extra carrier paths for EL emission. A comparative study is further performed on a multilayered Si/SiO sample and a single-layered one with Si and SiO homogeneously mixed. Both samples have the same ratio of Si to O and the same contents of Si and O. The multilayered sample is found to have higher EL intensity, less turn-on voltage, lower resistance, and higher current efficiency than the single-layered one. The results indicate that Si interlayers in Si/SiO may act as carrier channels, which promote carrier transport and enhance the EL emission of Si-nc.