Seng Lee Ng

Luminescence of Eu3+ and Tb3+ doped Zn2SiO4 nanometer powder phosphors

Abstract We report, for the first time to the best of our knowledge, the luminescent properties of Tb 3+ and Eu 3+ doped Zn 2 SiO 4 phosphors prepared by a sol–gel process. The phosphors have shown prominent luminescence in green and red, respectively, due to the electronic transitions of 5 D 0 → 7 F 2 (Eu 3+ ) and 5 D 4 → 7 F 5 (Tb 3+ ). Structural characterization of these luminescent materials was carried out with XRD and TEM. Luminescence spectra were analyzed by measuring the excitation, photoluminescence spectra and lifetimes of the emission transitions of Eu 3+ ( 5 D 0 → 7 F J , J =1–5) and Tb 3+ ( 5 D 4 → 7 F J , J =1–6). Our experimental results have shown that these phosphors have comparable luminescence properties as those currently used in TVs and CRTs.

Photoluminescence of ZnS:Mn embedded in three-dimensional photonic crystals of submicron polymer spheres

ZnS:Mn has been in-filled in photonic crystals of submicron polymer spheres. The effect of the photonic band gap on the photoluminescence (PL) properties of ZnS:Mn has been investigated. Because of the overlap of the transmission dip of the photonic crystal and the photoluminescence band of ZnS:Mn, both suppression and enhancement in the PL of the phosphor have been observed. A strong dependence of the fluorescence lifetime on the emission wavelength in the range of the stop band has been found. This strong dependence is believed to arise from the very low photon density of state within the stop band of the ZnS:Mn in-filled photonic crystal as result of a high dielectric contrast between ZnS:Mn and the polystyrene spheres.

Three-dimensional photonic band gap structure of a polymer-metal composite

A three-dimensional photonic band gap structure based on self-assembled crystals of polystyrene microspheres was fabricated by filling the pores with metallic silver. An almost complete stop band at 580–600 nm is observed in the optical transmission spectra. In comparison with pure polystyrene colloid crystals, the absorption band of Bragg diffraction in the composite was much more intense and broader, due to an enlargement of the contrast between the spheres and the background. A shift to shorter wavelengths in the band occurred because of a decrease in the average refractive index.

Green color luminescence in Tb3+: (La,Ln)PO4 (Ln=Gd or Y) photonic materials

Abstract We report the results of the time-resolved emission spectra and the decay curves, concerning the important green emission transition at 544 nm ( 5 D 4 → 7 F 5 ). Five other transitions at 489 nm ( 5 D 4 → 7 F 6 ), 585 nm ( 5 D 4 → 7 F 4 ), 620 nm ( 5 D 4 → 7 F 3 ), 674 nm ( 5 D 4 → 7 F 2 ) and 648 nm ( 5 D 4 → 7 F 1 ) of Tb 3+ : (La,Y)PO 4 and (La,Gd)PO 4 were measured to understand the influences of the wavelengths of excitation, in emitting green color from these two novel phosphor materials. It was observed that the spectral features possess sharp and bright emission for potential applications on the monitors of the television and some other related electronic systems, in observing the images in green color.

Generation of Multiple Energy Bandgaps Using a Gray Mask Process and Quantum Well Intermixing

We report a technique for generation of multiple energy bandgaps using a combination of one-step gray mask lithography and low-energy arsenic ion implantation induced disordering. Using this technique, we have successfully integrated 12-section with variable energy bandgaps on a single InGaAs/InGaAsP laser heterostructure. When compared to conventional processes, this novel technique is simple, promising and cost effective.

Green up-conversion emission in Er3+:BaTiO3 sol-gel powders.

Bright green emissions at 549 and 526 nm have been observed from sol-gel derived Er3+:BaTiO3 powders upon excitations at two near infrared (NIR) wavelengths of 973 and 816 nm. The decay characteristics were measured and studied. It was found that the predominant emission at 549 nm has very different lifetimes upon excitation at 973 and 816 nm, which was explained by the mechanisms of excited state absorption (ESA) of individual Er3+ ion and cooperative energy transfer (CET) between two near Er3+ ions for the up-conversion emission. Analysis also showed that 973-nm excitation is more effective for the green up-conversion emission.

Monolithic intracavity laser-modulator device fabrication using postgrowth processing of 1.55 μm heterostructures

In this letter, we present the attractive characteristics of a fabrication method based on quantum-well intermixing induced by low energy ion implantation for the realization of photonic integrated circuits on GaInAsP–InP heterostructures. Intracavity electro-absorption modulators monolithically integrated with laser devices were fabricated, using this postgrowth technique. The modulator section of the integrated devices was blueshifted by 75 nm while keeping the laser section unshifted and preserving very low values of the lasing threshold current density. Modulation depths in excess of 10 dB/V at 1.55 μm were obtained on these integrated devices which incorporate both a modulator and a laser.

Multiple-wavelength operation of electroabsorption intensity modulator array fabricated using the one-step quantum well intermixing process

Multiple-wavelength selective channel electroabsorption intensity modulators have been fabricated on a single InGaAs/InGaAsP chip using a one-step quantum well intermixing process. This technique was demonstrated for tailoring the intensity modulator operating wavelength by incorporating low-energy (360 keV) phosphorus ions implantation induced disordering process with gray-mask lithography technology. A modulation depth of −15 dB has been measured from these devices with a voltage swing of −4.5 V.

Characterization of rapid thermal oxidation of AlAs on GaAs/AlGaAs structure

We report on the oxidation of the AlAs epitaxial layer on a GaAs/AlGaAs double-quantum-well laser structure using a one-step rapid thermal process. Oxidation of the AlAs layer was carried out under oxygen-rich conditions in the temperature range 600–800 °C using a rapid thermal processor. Energy dispersive x-ray and Raman spectroscopy measurements were performed on the oxidized samples to study the composition of the AlAs layer after processing. It was found that oxidation of the AlAs layer was due to the strong preferential oxidation of aluminium compared to arsenic. From the atomic force microscopy measurements, the film was found to be of good uniformity. Copyright

Impact of quantum well intermixing on polarization anisotropy of InGaAs/InGaAsP quantum well modulators

This article reports on the impact of the induced strain on the polarization anisotropy of a parallel set of electroabsorption intensity modulators on a single InGaAs/InGaAsP wafer chip. The strain build up due to the interdiffusion of atomic species across the quantum well region has been demonstrated experimentally using the gray mask-based quantum well intermixing process followed by an annealing step. A voltage swing of 5 V and an intensity modulation depth of more than −15 dB has been measured from these modulators. An interdiffusion process modeling has been developed to investigate the consequence of different interdiffusion ratios between the group III and the group V sublattices on the polarization behavior of these modulators, owing to the strain build up and the refractive index profiles for both transverse electric and transverse magnetic modes. The numerical modeling agrees with the experimental results, which indicates that the degree of intermixing on the group V sublattices is more signifi...