Wide Luminescence Band Research Articles

Optical properties of CaGd4Si3O13 (CGS)crystals with Er3+ used as 1.5 µm laser material

The Stark structure of the 4I13/2 and 4I15/2 multiplets of the Er3+ ion in CaGd4Si3O13 (CGS) was determined. The transition cross-sectionshave been obtained from the absorption and the luminescence spectra.The emission cross-section for π-polarization in the 1529.5 nmluminescence band is equal to 2.1×10-20 cm2. Again curve has been plotted for π-polarization, and positiveamplification occurs at 1550 nm. A wide luminescence band makes itpossible to obtain tunable generation in the range 1540-1590 nm.The spectral parameters of the crystals Er, Ce:CGS indicate amplescope for developing an effective 1.5 µm laser withsemiconductor pumping.

PREPARATION AND SPECTRAL CHARACTERIZATION STUDIES OF FERROELECTRIC ULTRAFINE PARTICLES/STEARIC ACID LB FILM

Ferroelectric ultrafine particles were fabricated with LB film technique. The experimental results showed: The ferroelectric ultrafine particles were stable with a higher coverage ratio, and had a dielectric confinement effect in the LB films. The LB film showed photoluminescence at room temperature. The fluorescence spectrum consisted of wide luminescence bands. The emission spectrum had up-conversion.

On the physical nature of the wide band at 2.8 eV in the visible luminescence spectrum of high- Tc superconductors

Photoluminescence spectra of different Bi- and Y-based oxide high- T c superconductors are measured under laser excitation ( E exc = 4.03 eV). A wide luminescence band with a maximum near 2.8 eV is investigated and its temperature evolution (20-300K) is followed. Comparison of the spectra of various materials and their temperature evolution permits us to draw conclusions about local luminescence centers in the bulk. The experimental data are used to propose a model of a charge-transfer excimer complex involving the F-center and the negative molecular oxygen ion. In spite of the low quantum yield, the luminescence of such centers can be observed due to absence of the radiation electron-hole recombination. Analysis of experimental data suggests the existence of a strong radiationless relaxation over discrete levels inside the optical pseudo-gap which competes with the radiation recombination.

Saturation of the fullerite photodarkening at high laser energy fluences

The simple theory of the fullerite photodarkening dependence on the laser energy fluence is presented. The theory is based on the realistic electron band structure of fullerites. It is shown that this theory is sufficient for the qualitative description of the nonlinear optical properties of fullerites in the energy region around ħω=2 eV. The physical effects that appear at high excitation levels are disccused. The multi-step ionization and wide-band luminescence are predicted.

Optical emission of YBa2Cu3O7–δ and copper samples irradiated by slow electrons under laser-induced evaporation

A comparative analysis of emission spectra of laser-induced plasma and cathodoluminescence of YBa2Cu3O7–δ and copper samples is carried out. The identification of plasma luminescence reveals the presence of Y, Y+, Ba, Ba+, and Cu emission lines and continual emission of molecular and cluster fragments Cu–O with a peak at 2.7 eV. The bands of intrinsic electron–photon radiation emitted by copper irradiated by slow electrons are detected at 2.0 and 4.5 eV. It is shown that the main contribution to the wide-band luminescence of Y–Ba–Cu–O at 2.7 and 3.7 eV is made by radiative transitions at the defect centers on oxygen vacancies of the type F and F+. The narrow-band radiation at 3.36 and 2.95 eV, which is sensitive to the superconducting transition, is found to belong to charge-sensitive centers of oxygen chemisorption appearing at the surface due to free charge carriers.

Visual Spectral Sensitivities of Bioluminescent Deep-sea Crustaceans

The spectral sensitivities of eight species of deep-sea decapod shrimps (Family Oplophoridae) were determined from shipboard measurements of electroretinograms of dark-captured specimens. Notostomus gibbosus and N. elegans are maximally sensitive at 490 nm, and chromatic adaptation experiments indicate that a single visual pigment is present. Peak sensitivities of Acanthephyra smithi and A. curtirostris are at 510 nm, a longer wavelength than expected for such deep-sea dwellers. The four photophore-bearing species, Systellaspis debilis, Janicella spinacauda, Oplophorus spinosus, and O. gracilirostris have sensitivity maxima at 400 and 500 nm, and chromatic adaptation experiments indicate the presence of two visual pigments. This unusual short wavelength sensitivity may provide the basis for congener recognition based on the spectral bandwidth of luminescence.

Structural luminescence spectra of biogenous porphyrins under selective laser excitation and dependence of this effect on excitation wavelength

Selective laser excitation removes an inhomogeneous width in wideband luminescence spectra of solid solutions of biogenous porphyrins resulting in spectra consisting of narrow zero-phonon lines and phonon sidebands. The effect depends strongly on excitation frequency and disappears gradually upon increasing this frequency within the inhomogeneously broadened pure electronic transition band.