William A. Gambling

Enhanced brightness and efficiency in organic electroluminescent devices using SiO2 buffer layers

Organic electroluminescent devices using SiO2 as a hole-injecting buffer have been fabricated. With the presence of the buffer, the luminance of the device reaches 1820 cd/m2 at the current density of 20 mA/cm2, which corresponds to an efficiency of 9.1 cd/A. The enhancements in brightness and efficiency are attributed to an improved balance of hole and electron injections due to blocking of the injected holes by the buffer layer and a more homogeneous adhesion of the hole transporting layer to the anode.

Electron drift mobility and electroluminescent efficiency of tris(8-hydroxyquinolinolato) aluminum

The electron drift mobility in films of tris(8-hydroxyquinolinolato) aluminum (Alq) deposited at different rates (0.2, 0.4, and 0.7 nm/s) on silicon has been determined by the time-of-flight technique. It has been found that the drift mobility of electrons in Alq increased by about two orders of magnitude as the deposition rate decreased from 0.7 to 0.2 nm/s. Further, the electron drift mobility in all Alq samples increased linearly with the square root of the applied electric field. Electroluminescent devices with a structure of indium tin oxide/α-naphthylphenylbiphenyl amine (NPB, 90 nm)/Alq (90 nm)/Mg:Ag were fabricated at different Alq deposition rates. The device efficiency was found to increase with increasing electron mobility in Alq. As the electron is the minority carrier in the present device, an increase in electron mobility in Alq would thus lead to an increase in device efficiency.

Improved Time-of-Flight Technique for Measuring Carrier Mobility in Thin Films of Organic Electroluminescent Materials

Using an improved time-of-flight (TOF) technique, the drift mobilities of electrons and holes in organic films prepared on silicon or indium-tin-oxide (ITO)-coated glass substrates have been determined. For the samples on silicon, the silicon was also used as a carrier-generating layer. This substantially increased the number of charge carriers generated and thus resulted in a higher intensity electrical signal. Consequently, the thickness of the organic layers can be reduced to less than 1/10 of the typical values (several microns) required in the conventional TOF measurement. The typical thickness of the organic layer in the present work is 400 nm. For organic materials with a high optical absorption coefficient, samples for the TOF measurement can be prepared by directly depositing these materials onto ITO glass substrates with a thickness of about 1000 nm. For both types of substrate, the thickness of the organic layer is much closer to the typical value used in organic electroluminescent devices. The signal, and thus the accuracy, in the present measurement were much improved over those of the conventional TOF measurement. The logarithm of the drift mobility changed linearly with the square root of the applied electric field.

Efficient blue light generation from a diode laser pumped Nd:YAG laser

We report on the efficient intracavity doubling of a 946 nm Nd:YAG laser with an LBO crystal at room temperature. A CW single-ended output power of 103 mW at 473 nm is obtained at a pump power of 2.58 W with an optical conversion efficiency of 4.0%. The overall efficiency is 7.2% if blue light output from both directions is taken into account. To our knowledge, this is the highest efficiency to date for a diode laser pumped compact Nd:YAG blue laser with a simple flat-concave resonator using a bulk nonlinear crystal for intracavity doubling.

Carrier transport and high-efficiency electroluminescence properties of copolymer thin films

A novel copolymer with moieties capable of charge transport and electroluminescence was synthesized. The drift mobilities of electron and hole in the spin-coated films of the copolymer on silicon substrate have been determined by the time-of-flight technique. The shape of the photo-current curves obtained for the transport of both electron and hole is typical for dispersive transport in organic polymers. Under an electrical field strength of 5:0 £ 10 5 V/cm, the drift mobility of electron and hole is 4:78 £ 10 26 and 3:46 £ 10 26 cm 2 /V s, respectively. A high-efficiency electroluminescent device with the bi-layer structure of ITO/copolymer/2-(4-biphenylyl)-5-(4-tert-butylphenl)-1,3,4,oxadiazole (PBD) /LiF/Al was fabricated. The device emitted a bright blue-green light peaking at wavelength of 496 nm, originating from copolymer with a maximum current efficiency of 10 cd/A and a maximum luminescence efficiency of 2.9 lm/W at the DC drive voltage of 12 V. q 2000 Elsevier Science S.A. All rights reserved.

A CONTINUOUS-WAVE TUNABLE SOLID-STATE BLUE LASER BASED ON INTRACAVITY SUM-FREQUENCY MIXING AND PUMP-WAVELENGTH TUNING

We report on continuous-wave tunable blue-light generation from a Nd:Y3Al15O12 laser by intracavity sum-frequency mixing of its fundamental laser line at 946 nm with the pump light from a tunable Ti:sapphire laser by use of cadmium–mercury–thiocyanate nonlinear crystal. The tunable range of the blue light was 434.4–437.5 nm, and the maximum output power at 436 nm was measured to be 310 μW.

Spectroscopic and laser properties of Nd: Gd0.8La0.2VO4 crystal

Abstract The polarised absorption and fluorescence spectra of Nd:Gd0.8La0.2VO4 crystal are measured and compared to those of Nd:GdVO4. CW laser properties of diode-pumped Nd:Gd0.8La0.2VO4 crystal operating at fundamental wavelengths of 1.06 and 1.34 μm , as well as when intracavity frequency-doubled to 532 and 670 nm , have been studied. The maximum output powers at 1.06 μm , 1.34 μm , 532 nm and 670 nm are 1.18 W , 671 mW , 206 mW and 42 mW respectively, at a diode-launched pump power of 2.9 W . The threshold pump powers are 80, 267, 7 and 15 mW respectively.

Fast accurate wavelength switching of an erbium-doped fiber laser with a Fabry–Perot semiconductor filter and fiber Bragg gratings

We propose a simple passive method for achieving fast accurate wavelength switching in an erbium-doped fiber laser. The method relies on a laser cavity formed with a Fabry–Perot semiconductor filter (FPSF) and narrow-band fiber Bragg gratings (FBGs), where the FBGs set the wavelength references and the FPSF can be tuned by changing its injection current to select a particular wavelength from those set by the FBGs. Because of the nonlinearity in the FPSF, optical negative feedback can be built up in the laser to suppress relaxation oscillations caused by wavelength switching. With this method, a wavelength switching time of less than 25 μs has been achieved experimentally.

Fabrication of UV-sensitive waveguides for integrated photonics applications

Germanium-doped silica glasses have been fabricated and the UV induced refractive index change have been studied. An order of 10-3 refractive index change has been obtained. With the use of silver ion exchange before UV exposure, much greater refractive index change has been observed. The silver ion exchanged germanium-doped glass has a 10-2 refractive index change when it is exposed to 248 nm excimer laser. This procedure allows the fabrication of integrated optical components in a convenient way.

Influence of Minority Carrier Mobility on Organic Electroluminescent Device Characteristics

The drift mobility of electron in thin films of tris(8-hydroxyquinolinolato) aluminum (Alq) deposited at different rates (0.2 nm/s, 0.4 nm/s and 0.7 nm/s) on silicon has been determined by the time-of-flight (TOF) technique. It has been found that the drift mobility of electron in Alq increased for about two orders of magnitude as the deposition rate decreased from 0.7 to 0.2 nm/s. Further, the electron drift mobility in all Alq samples increased linearly with the square root of the applied electric field. Electroluminescent devices with a structure of ITO / NPB(90 nm) / Alq(90 nm) / Mg:Ag were fabricated at different Alq deposition rates. The device efficiency was found to increase with increasing electron mobility in Alq. As electron is the minority carrier of the present device, an increase in electron mobility in Alq would thus lead to an increase in device efficiency.