Nobukata Nagasawa

Generation of Excitonic Molecules by Giant Two-Photon Absorption in CuCl and Their Bose Condensation

Through the studies of excitation spectra of emissions in CuCl crystals by a frequency tunable dye laser, excitonic molecules have been found to be generated directly by the giant two-photon absorption at the photon energy of 3.187 eV, as suggested by Hanamura. Two-photon excitation of crystals at 1.6 K enhanced very narrow emission bands at 3.1647 eV and at 3.1709 eV. These photon energies coincide with those of the high energy edges of the M L and M T bands due to the radiative annihilation of excitonic molecules having K =0. From these facts the Bose condensation of excitonic molecules at K ∼0 has been suggested.

Energy Level Scheme of Excitonic Molecule and Exciton in CuBr

Giant two-photon absorption for the direct generation of excitonic molecue is measured. Three absorption peaks are found at 2.9540, 2.9561 and 2.9576 eV, which are responsible for the two-photon transitions to the \(\varGamma_{1}(J{=}0)\), Γ 5 ( J =2) and \(\varGamma_{3}(J{=}2)\) states, respectively, of the excitonic molecule.

Light mixing induced by the giant two-photon absorption of excitonic molecules in CuCl

Abstract Three-wave mixing of light has been observed in connection with a giant two-photon absorption generating excitonic molecules. The efficiency of mixing of light for energies 2Ω 1 - Ω 2 and 2Ω 2 - Ω 1 is enhanced remarkably when Ω 1 and/or Ω 2 is varied across the giant two-photon absorption band-region. Moreover, the mixed lights with energies 3Ω 1 - 2Ω 2 and 4Ω 1 - 3Ω 2 have also been detected.

Generation of excitonic molecules by giant two-photon absorption in CuCl and CuBr and their Bose condensation

Abstract Theoretical expectation that excitonic molecules are generated directly by the two-photon absorption, has been confirmed experimentally in CuCl and CuBr crystals. The luminescence of the radiative decay of the excitonic molecule thus created directly is found to show a very sharp emission band which is attributable to the Bose condensation at K ≈ 0. In connection with the sharp emission, the two-photon resonance Raman scattering is studied.

Two-photon generation of excitonic molecules in CuCl and CuBr

Radiative recombination of excitonic molecules in CuCl and CuBr is reviewed. The emission consists of ML and MT bands in CuCl and of ML, MT and Mf bands in CuBr. These bands correspond to the recoil of an exciton into the longitudinal, transverse and triplet states, respectively When excitonic molecules are generated indirectly by the excitation of crystals into the band-to-band region, the line shape of the bands is explained by considering that excitonic molecules are in Maxwell-Boltzmann distribution. Excitonic molecules are found to be generated directly by the giant two-photon absorption. In this case, extremely sharp emission lines appear at the high energy edges of each M band, which are attributed to the Bose condensation of excitonic molecules. The two-photon resonance Raman scattering is discussed in connection with the emission from the Bose condensed state.

Radiative Annihilations of Excitons in Solid Rare Gases

Emission spectra of Ar-Xe solid solutions have studied. At small xenon concentration, a band called M , is observed in addition to an intrinsic luminescence of the pure argon crystal. With increasing the doped xenon concentration, another doublet bands, called D 1 and D 2 , are found to appear. Excitation spectra for these emissions reveal that the M and D s bands are attributed to the xenon monomer and dimer in argon lattice, respectively. With further increase of the xenon doping, the D 1 band-peak approaches that of the intrinsic luminescence of the pure xenon crystal. From this fact the intrinsic luminescence of the pure xenon crystal has been considered to arise from a relaxed exciton of a diatomic molecular type.

Photo-stimulated luminescence of solid Kr

Abstract The emission spectra of solid Kr films at 10 K are investigated by irradiation with ultraviolet light in vacuum. Two emissions appear at 5.5 and 8.0 eV. Through the measurements of the excitation spectra, it is found that the high-energy band is emitted by excitation into the intrinsic exciton bands and can be regarded as an intrinsic emission, while the low-energy emission is associated with an impurity.

Optical Absorption Spectra of Ar-Xe Solid Solutions: The Cluster Band Due to Xe Impurities

The optical absorption spectra of Ar this films containing Xe with less than 0.042 molar fraction are studied by using synchrotron orbital radiation from a 1.3 GeV electron synchrotron at INS-Tokyo as a light source. Measurements are made at 10 K in the energy range from 8.5 eV to 11.5 eV. The intensity variation of a band, which appears at about 9.03 eV in a sample containing 0.007 molar fraction of Xe, is investigated as the function of Xe concentration. The analysis reveals that the band is originated from the dimer of Xe atoms in solid Ar.