Резонансное отражение света оптической решеткой экситонов, сформированной 100 квантовыми ямами InGaN

Optical properties of a structure with a periodic system of 100 InGaN quantum wells (QWs) separated by non-tunneling GaN barriers have been investigated at room temperature. The structure periodicity corresponded to the Bragg diffraction condition at the frequency of the QW excitons. Numerical modeling using transfer matrices gave a quantitatively accurate fit of the experimental results. The model included the resonance response of A, B, and C excitons in QWs and an optical absorption tail in the barriers and buffer layer. We have determined the radiative and non-radiative broadening of the excitons in the InGaN QWs.

Establishment of the Qy Absorption Spectrum of Chlorophyll a Extending to Near-Infrared

A weak absorption tail related to the Qy singlet electronic transition of solvated chlorophyll a is discovered using sensitive anti-Stokes fluorescence excitation spectroscopy. The quasi-exponentially decreasing tail was, at ambient temperature, readily observable as far as −2400 cm−1 from the absorption peak and at relative intensity of 10−7. The tail also weakened rapidly upon cooling the sample, implying its basic thermally activated nature. The shape of the spectrum as well as its temperature dependence were qualitatively well reproduced by quantum chemical calculations involving the pigment intramolecular vibrational modes, their overtones, and pairwise combination modes, but no intermolecular/solvent modes. A similar tail was observed earlier in the case of bacteriochlorophyll a, suggesting generality of this phenomenon. Long vibronic red tails are, thus, expected to exist in all pigments of light-harvesting relevance at physiological temperatures.

Defect absorption in selenium films by photothermal deflection spectroscopy

Sub-gap absorption spectra of selenium films are investigated by photothermal deflection spectroscopy. The selenium films are prepared by vacuum evaporation of selenium pellets. Raman spectroscopy reveals that as-deposited films are amorphous, and the films annealed at 100 °C are trigonal crystal. Photothermal deflection spectroscopy is extended to infrared light of 0.31 eV with maintaining high sensitivity, and detects weak absorption at energies below the band gap. Five absorption peaks and tail absorption are observed in selenium films, and the absorption peak energies are 1.32, 1.08, 0.47, 0.41 and 0.34 eV, respectively. These absorption tail and peaks are derived from selenium, and the origin of these absorptions is explained based on the oxygen impurity and the defect structure of the selenium film.

Правила Урбаха в монокристаллах MnGa-=SUB=-2-=/SUB=-Sе-=SUB=-4-=/SUB=- при оптических поглощениях

The Urbach rule in MnGa_2Se_4 single crystals is studied. It is found that the long-wavelength absorption tail obeys the Urbach rule at photon energies in the range 2 . 1–2 . 2 eV. It is shown that a strong electron–phonon interaction exists in MnGa_2Se_4 single crystals.

Compositional Dependence of Optical Absorption in Barium Oxychloride Borate Glasses

The present communication deals with some significant results pertaining to the optical absorption analysis of glasses in the compositional range of xBaCl2·(30–x)·BaO·68B2O3·2V2O5 (x = 0, 5, 7 and 10 mol%) prepared via convenient melt-quench route. The optical absorption data recorded in wavelength range of 200–800 nm is analyzed by means of Davis-Mott model to evaluate optical band gaps corresponding to direct and indirect transitions. The absorption tail is analyzed to obtain Urbach's energy. Behavioral change in optical band gap and Urbach's energy with changing chlorine concentrations is discussed to predict the structural changes governed in the glass matrix.

Fundamental Band Edge Absorption in 3C-SiC: Phonon Absorption Assisted Transitions

An alternative approach based on non-equilibrium free-carrier density measurements was used to characterize the fundamental absorption edge of 3C-SiC at room and 77 K temperatures. At 77 K temperature the extracted absorption edge compared well to the previous literature data revealing characteristic thresholds due to the phonon emission assisted transitions. At room temperature the absorption tail due to the phonon absorption assisted transition was revealed up to the value of 0.01 cm-1 exceeding the previous 5 cm-1 limit induced by unintentional sample doping.