Observation of two-step excitation of photoluminescence in silicon nanostructures

Efficient visible-range photoluminescence with photon energy higher than the photon energy of the exciting radiation is observed in nanostructures of porous silicon subjected to heat treatment in vacuum. The photoluminescence intensity is found to be virtually identical for cw and femtosecond excitation by Ti:sapphire laser radiation with the same average power. The results can be explained by a two-step cascade photoluminescence excitation process in which optical passivation of defects of the dangling silicon bond type occurs. Pis’ma Zh. éksp. Teor. Fiz. 68, No. 10, 732–736 (25 November 1998)     

Synthesis of 1,2-O-isopropylidene-α-d-glucofuranose 3,6-cyclophosphates

Translated from Izvestiya Akademii Nauk SSSR, Seriya Khimicheskaya, No. 9, pp. 2191–2192, September, 1988.     

Strong selective excitation of Raman-active vibrations and energy transfer between low-lying vibrational states of a CO2 molecule studied by PARS and CARS

We experimentally demonstrate the novel technique of inducing the highly nonequilibrium distribution of molecules over vibrational states by two-frequency coherent Raman excitation. The technique can be used for selective excitation of totally symmetric and other Raman-active molecular transitions. Two counter propagating focused laser beams (second harmonic of Nd: YAG and dye laser) were used to induce population difference changes at the 00⁰0–10⁰0 transition in CO₂ molecules. The excitation and relaxation kinetics of this and neighbours vibrational modes of CO₂ were studied both by CARS and PARS. Vibrational excitation of up to 20% of the total number of irradiated molecules is measured; previously unknown desactivation constant of CO₂ (10⁰0) and CO₂ (02⁰0) states via CO₂ (01¹0) state is estimated to be K = (3±1) × 1 ⁵s^-1torr^-1.     

Saturation spectroscopy of coherent raman scattering in molecular gases

We present the theory of two-photon Raman saturation of a two-level Raman transition studied by an independent CARS process. The main goal here is to probe the saturated homogeneous Raman line shape. It is shown that there appears a saturation dip with a width determined by the relaxation timeT ₁. In the case of Doppler-broadened line the coherent Raman saturation spectroscopy may be used to determine both theT ₁ andT ₂ relaxation times.     

Effect of the atomic composition of the surface on the electron surface states in topological insulators A<Stack><Subscript>2</Subscript><Superscript>V</Superscript></Stack>B<Stack><Subscript>3</Subscript><Superscript>VI</Superscript></Stack>

The results of the theoretical investigation of the surface electronic structure of A₂^VB₃^VI compounds containing topologically protected surface states are reported. The ideal Bi₂Te₃, Bi₂Se₃, and Sb₂Te₃ surfaces and surfaces with an absent external layer of chalcogen atoms, which were observed experimentally as monolayer terraces, have been considered. It has been shown that the discrepancy between the calculated Fermi level and the value measured in the photoemission experiments can be attributed to the presence of the “dangling bond” states on the surface of the terraces formed by semimetal atoms. The fraction of such terraces on the surface has been estimated.     

Effect of Hydroxyl Groups in a Cation Structure on the Properties of Ionic Liquids

Two series of imidazolium ionic liquids with the bis(trifluoromethylsulfonyl)imide anion were synthesized, which differ by the presence of a hydroxyl group at the ω-position of the alkyl substituent in the cation structure (n_C = 2–8). The properties of the liquids were studied by DSC, TGA, and IR and NMR spectroscopy. Their thermal stability was studied, and the melting points, viscosity, and volatility in vacuum were measured. The effect of OH groups in the structure of the ionic liquid on its properties was evaluated.     

Reactions of glycosylamines with diphenylphosphine oxide and ethyl and phenyl phenylphosphinates

A novel procedure has been proposed for the synthesis of chiral α-aminophosphoryl compounds from glycosylamines and PH compounds (diphenylphosphine oxide and ethyl and phenyl phenylphosphonates) under mild conditions. The reaction is accompanied by dehydration of the carbohydrate moiety in unprotected monosaccharides to form furan ring.