Peak Wavelength Of Emission Spectrum Research Articles

Direct formation and phase stability of luminescent γ-Ga2O3 spinel nanocrystals via hydrothermal method

Nanocrystals of γ-gallium oxide (γ-Ga2O3) were directly synthesized as a single phase of spinel-type structure from the aqueous precursor solution of Ga(NO3)3 or Ga2(SO4)3 under weakly basic conditions in the presence of citric acid by mild hydrothermal method. The crystallite size of γ-Ga2O3 spinel that was hydrothermally formed at 180–240 °C for 5 h was in the dimension range from 5 to 9 nm. The optical band gap of the as-prepared γ-Ga2O3 was 4.88 eV. The γ-Ga2O3 nanocrystals synthesized at 180 °C showed a broad-band visible violet–blue light emission with a peak wavelength at 410 nm, centered at around 425 nm under excitation at 325 nm. The emission intensity of γ-Ga2O3 synthesized at 210 and 240 °C was lower than that of 180 °C. The spinel-type structure of γ-Ga2O3 was maintained up to 600 °C. The γ-Ga2O3 phase fully transformed into β-Ga2O3 after heating at 800 °C. The luminescence intensity of gallium oxide decreased, and the peak wavelength of emission spectrum shifted into lower wavelengths via heat treatment at 600 and 800 °C for 1 h in air.

Metamorphic growth of 1.55 μm InGaAs/InGaAsP multiple quantum wells laser structures on GaAs substrates

We fabricate a GaAs-based InGaAs/InGaAsP multiple quantum wells (MQWs) laser at 1.55 μm. Using two-step growth method and thermal cyclic annealing, a thin low-temperature InP layer and a thick InP buffer layer are grown on GaAs substrates by low-pressure metal organic chemical vapor deposition technology. Then, high-quality MQWs laser structures are grown on the InP buffer layer. Under quasi-continuous wave (QCW) condition, a threshold current of 476 mA and slope efficiency of 0.15 mW/mA are achieved for a broad area device with 50 μm wide strip and 500 μm long cavity at room-temperature. The peak wavelength of emission spectrum is 1549.5 nm at 700 mA. The device is operating for more than 2000 h at room-temperature and 600 mA.

Laser Measurement of Polycyclic Aromatic Hydrocarbons (PAHs) in a Flame (2nd Report, Presumption of PAHs by Laser-Induced Fluorescence Spectrum)

Laser induced fluorescence (LIF) method was applied to the measurement of PAHs (Polycyclic Aromatic Hydrocarbons) in a propane diffusion flame. Various PAHs were excited by a KrF excimer laser and a dye-laser pumped by the XeF excimer laser. By measuring the enission spectra of various PAHs vapors, it was found that the peak wavelength in the emission spectrom of LIF shifted to the longer wavelength side with an increase of PAHs carbon numbers. The carbon numbers of PAHs in a diffusion flame was presumed from the data of peak wavelength of emission spectrum. It was confirmed that the carbon numbers of PAHs in the diffusion flame increased as approaching to the flame surface. The maximum carbon number was about 26 at the layer close to the flame surface.