Photoluminescence and photostimulated luminescence of BaFBr:Eu2+,Eu3+

In the photoluminescence (PL) of BaFBr:Eu2+,Eu3+, the emissions of Ea(2+), carrier electron-hole (e-h) recombination, and Eu3+ are observed, while in the photostimulated luminescence (PSL) only the emission of Eu2+ is exhibited. This disappearance of e-h recombination in PSL is considered to be caused by carrier migration during photo-stimulation. (C) 1997 American Institute of Physics.

New observation on the luminescence of CdS clusters in zeolite-Y

The excitation spectrum of CdS dusters in zeolite-Y is consistent with their absorption spectrum, both showing two absorption bands that are assigned to the Is-is and Is-lp transitions, respectively. A new emission at 400 nn is considered to be the recombination of the bounded excitons. The emission firstly increases then decreases with increasing cluster size or loading. The emission by excitation into the Is-is band is stronger and sharper than that by excitation into the Is-lp band. This phenomenon is attributed to the size inhomogeneity and the strong electron-phonon interaction of the dusters. Copyright (C) 1996 Elsevier Science Ltd

Photostimulated luminescence of BaFBr:Eu2+ phosphors

After x-irradiation for 10 s, luminescence from BaFBr:Eu2+ phosphors by photostimulation of longer wavelength than F absorption bands was observed and assigned to the surface states or intrinsic defects of the powders. It is found that the luminescence by photostimulation into F bands can be reduced via electron migration from F centers into the surface states or intrinsic defects, thus reducing the x-ray storage or image stability. Surface passivation can lower these defects and improve the phosphors or imaging plate quality. (C) 1996 American Institute of Physics.

Electro-luminescence and photo-luminescence from strained SiGe/Si quantum well

Photo-luminescence and electro-luminescence from step-graded index SiGe/Si quantum well grown by molecular beam epitaxy is reported. The SiGe/Si step-graded index quantum well structure is beneficial to the enhancing of electro-luminescence. The optical and electrical properties of this structure are discussed.

PROCESS OF PHOTOLUMINESCENCE AND PHOTOSTIMULATED LUMINESCENCE IN BAFBR-EU PHOSPHORS

The photoluminescence (PL) and photostimulated luminescence (PSL) of BaFBr: Eu phosphors are reported. In the photoluminescence of BaFBr:Eu, the emission of Eu2+, e-h recombination and Eu3+ have been observed, while in the photostimulated luminescence only the emission of Eu2+ was observed. This phenomenon may be explained well by the suggestion of a two-hand model for the host emission in which the host emission energy may transfer to Eu2+ difference of excitation in those two processes results in different transfer rates which makes the PL and PSL emission different.

LUMINESCENCE-CENTERS IN POROUS SILICON

Photoluminescence studies on porous silicon show that there are luminescence centers present in the surface states. By taking photoluminescence spectra of porous silicon with respect to temperature, a distinct peak can be observed in the temperature range 100-150 K. Both linear and nonlinear relationships were observed between excitation laser power and the photoluminescence intensity within this temperature range. In addition, there was a tendency for the photoluminescence peak to red shift at low temperature as well as at low excitation power. This is interpreted as indicating that the lower energy transition becomes dominant at low temperature and excitation power. The presence of these luminescence centers can be explained in terms of porous silicon as a mixture of silicon clusters and wires in which quantum confinement along with surface passivation would cause a mixing of Gamma and X band structure between the surface states and the bulk. This mixing would allow the formation of luminescence centers.

Luminescence spectroscopy of ion implanted AlN bulk single crystal

High concentrations of Si and Zn were implanted into (0001) AlN bulk crystal grown by the self-seeded physical vapor transport (PVT) method. Cathode luminescence (CL) and photoluminescence (PL) spectroscopy were used to investigate the defects and properties of the implanted AlN. PL spectra of the implanted AlN are dominated by a broad near-band luminescence peak between 200 and 254 nm. After high temperature annealing, implantation induced lattice damages are recovered and the PL intensity increases significantly, suggesting that the implanted impurity Si and Zn occupy lattice site of Al. CL results imply that a 457 nm peak is Al vacancy related. Resistance of the AlN samples is still very high after annealing, indicating a low electrical activation efficiency of the impurity in AlN single crystal.

An Improvement on 2× 2 Silicon-on-Insulator Mach-Zehnder Thermo-Optical Switch

An improved 2 ×2 silicon-on-insulator Mach-Zehnder thermo-optical switch is designed and fabricated, which is based on strongly guided multimode interference couplers and single- mode phase-shifting arms. The multimode interference couplers and input/output waveguides are deeply etched to improve coupler performances and coupler-waveguide coupling efficiencies. However, shallow etching is used in the phase-shifting arms to guarantee single-mode property. The strongly guided coupler presents an attractive uniformity about 0. 03 dB and a low propagation loss of -0.6 dB. The 2× 2 switch shows an insertion loss as low as -6.8 dB, where the fiber-waveguide coupling loss of -4.3 dB is included, and the response-time is measured as short as 6.8 μs, which are much better than our previous results.

An Improved Driving Circuit for Thermo-Optical Switch to Improve the Reliability of Thermo-Optical Switch Matrix

The influence of the heaters on the reliability of the thermo-optic (TO) switch matrix is analyzed and an improved driving circuit based on the analyzed results is designed and fabricated. The circuit can improve the reliability of the switch matrix device from 78.87% to 97.04% for a 4×4 optical switch device with a simplified tree structure. The simulation and experimental results show the circuit can provide suitable driving current for TO switch matrix.

Design and Fabrication of Thermo-Optic 4×4 Switching Matrix in Silicon-on-Insulator

A rearrangeable nonblocking thermo-optic 4×4 switching matrix,which consists of five 2×2 multimode interference-based Mach-Zehnder interferometer(MMI-MZI) switch elements，is designed and fabricated.The minimum and maximum excess loss for the matrix are 6.6 and 10.4dB,respectively.The crosstalk in the matrix is measured to be between －12 and －19.8dB.The switching speed of the matrix is less than 30μs.The power consumption for the single switch element is about 330mW.

SOI thermo-optic modulator with fast response

Silicon-on-insulator (SOI) technology offers tremendous potential for integration of optoelectronic functionson a silicon wafer. In this letter, a 1 * 1 multimode interference (MMI) Mach-Zender interferometer(MZI) thermo-optic modulator fabricated by wet-etching method is demonstrated. The modulator has anextinction ratio of -11.0 dB, extra loss of -4.9 dB and power consumption of 420 mW. The response timeis less than 30μs.

1.55μm Fabry-Perot Thermo-Optical Tunable Filter with amorphous-Si as Cavity

A 1.55μm Fabry-Perot (F-P) thermo-optical tunable filter is fabricated. The cavity is made of amorphous silicon (a-Si) layer grown by electron-beam evaporation technique. Due to the excellent thermo-optical property of a-Si, the refractive index of the F-P cavity will be changed by heating; the transmittance resonant peak will therefore shift substantially. The measured tuning range is 12nm, FWHM (full-width-at-half-maximum) of the transmission peak is 9nm, and heating efficiency is 0.1K/mW. The large FWHM is mainly due to the non-ideal coating deposition and mirror undulation. Possible improvements to increase the efficiency of heating are suggested.

Crystal-Field Symmetry of Luminescence Center in Er-Implanted Silicon

于2010-11-23批量导入

Yellow luminescence mechanism and persistent photoconductivity in n-GaN single crystal films grown on alpha-Al2O3(0001) substrates by LP-MOCVD

Unintentionally doped and Si-doped single crystal n-GaN films have been grown on alpha-Al2O3 (0001) substrates by LP-MOCVD. Room temperature photoluminescence measurement showed that besides the bandedges, the spectrum of an undoped sample was a broad deep-level emission band peaking from 2.19 to 2.30eV, whereas the spectrum for a Si-doped sample was composed of a dominant peak of 2.19eV and a shoulder of 2.32eV. At different temperatures, photoconductance buildup and its decay were also observed for both samples.. The likely origins of persistent photoconductivity and yellow luminescence, which might be associated with deep defects inclusive of either Ga vacancy(V-Ga)/Ga vacancy complex induced by impurities or N antisite (N-Ga), will be proposed.