Riso Kato

A plane-grating monochromator for 2 eV ≤ hv ≤ 150 eV

Abstract Design and performance of a plane-grating monochromator at UVSOR facility are described. Two monochromators of the present design have been constructed and are used for optical and photoelectron spectroscopy of solids.

Phonon Side Bands of UV Absorption in NaNO2

Phonon side bands of u v absorption in NaNO 2 have been studied by the measurement of high resolution spectrum with light polarized along each crystallographic axis at low temperatures. Strong peaks in the side bands are assigned to the phonon branches in the first Brillouin zone by taking account of the selection rules for the optical transitions in which an exciton and a phonon are created simultaneously. The integrated intensities of the E // b and E // c absorptions have been found to increase with temperature obeying the coth ( h ν/2 k T ) law with ν b ≃220 cm -1 and ν c ≃130 cm -1 respectively. The relation between the temperature dependence of the E // b and E // c absorptions and the profiles of their phonon side bands is discussed in terms of the averaged phonon frequency \barν.

Fine Structures in Luminescence Spectra of NaNO2 Crystal in the Ultraviolet Region

Luminescence spectra of NaNO 2 single crystal associated with 1 B 1 → 1 A 1 . transition in NO 2 - have been measured for the E // a , E // b and E // c polarizations. Intensities of the series of sharp vibronic lines are described by a Poisson distribution I n ∝( e - s s n / n !) with s ≃4. These lines are interpreted by a simple configuration coordinate model. It has been found that the profile of the phonon side band of the E // a luminescence is nearly a mirror image of that of the absorption with respect to the zero-phonon line, while the profile of the side band of the E // b luminescence is quite different from that of the absorption. The latter result is interpreted in terms of the exciton-phonon bound state. Two extra series of weak satellite bands have been found and are interpreted as the vibronic lines due to isotopic species N 15 O 2 16- and N 14 O 16 O 18- .

Optical Properties of LiF in the Extreme Ultraviolet

The reflection spectrum of LiF single crystal was measured in the extreme ultraviolet region at room temperature. The Kramers-Kronig relation was applied to derive the optical constants n and κ from the reflectivity. The maximum absorption coefficient and the peak position of the first fundamental band were determined to be 2.2±0.1×10 6 cm -1 and 12.7±0.1 ev respectively. Variations of the real and imaginary parts of the complex dielectric constant in the given region were analysed by the quantum-mechanical analogue of the Lorentz dispersion formulas and the oscillator strength of the first fundamental band was determined to be 0.4±0.05/molecule. The value supports the excitation model of the exciton discussed by Dexter on NaCl. Experiments and discussions are also described on the effect of hydrolysis of LiF.

Phonon Side Bands of the Triplet Absorption in NaNO2

Absorption spectra of NaNO 2 associated with the electronic transition 1 A 1 → 3 B 1 in NO 2 - have been measured for the E // a , b and c polarizations. The E // b and E // c spectra show the series of vibronic lines accompanied with the phonon side bands, while the E // a absorption is too weak to be observed. The selection rules are discussed for the modes of phonons which interact with the triplet exciton to give rise to the phonon side band of each polarization. The assignments are given to the prominent peaks and shoulders in the side bands of the E // b and E // c spectra. Two extra series of weak satellite bands have been found on the low energy tails of the vibronic lines and they are interpreted as the lines due to the isotopic species N 14 O 16 O 18- and N 15 O 2 16- .

Phonon Sidebands of ν00 Line in Absorption and Luminescence Spectra of NaNO2: Spatial Dispersion of ν00 Exciton

Profiles of the phonon sidebands associated with the ν 00 line in the singlet absorption and luminescence spectra of NaNO 2 have been investigated by the measurement of high resolution spectra at 2 K. It is confirmed that energy separations of prominent peaks of the absorption sideband from the ν 00 line are larger than those of the corresponding peaks of the luminescence sideband by 2∼9 cm -1 . From the result the band width of the ν 00 exciton is estimated to be 3∼5 cm -1 . Profiles of vibronic lines in the luminescence spectrum are discussed in connection with the spatial dispersion of the ν 00 exciton.

Isotope Shifts of Zero-Phonon Transition in Highly Purified NaNO2 Crystal

Low temperature optical spectra of highly purified NaNO 2 crystals have been investigated in near u v region. The width of the zero-phonon absorption line at ν 00 due to the electronic transition 1 A 1 → 1 B 1 in NO 2 - is remarkably reduced in the purified crystal and three satellite absorption lines are observed separately from the high energy tail of the strong zero-phonon absorption line. The energy separations of these lines from ν 00 are 4 ±1, 6 ±1 and 7.5 ±1 cm -1 and are identified as the isotope shifts of the zero-phonon transition in NO 17 O - , NO 18 O - and 15 NO 2 - , respectively.

Fine Structure in Luminescence Spectra of NaNO2. III. Vibronic Lines Perturbed by NO-3 Impurity

It has been found that the peculiar lines A, B, C, D and E which appear in the spectrum of the singlet luminescence in NaNO 2 crystal are strongly enhanced when the crystal is doped with NO - 3 impurity. A number of sharp lines on the tail of the zero-phonon line of the singlet absorption in the crystal are also enhanced by NO - 3 impurity. From the excitation spectra for the luminescence lines, it is shown that both luminescence and absorption lines have common origins. They are interpreted as the lines due to the transition 1 A\(_{1}{\rightleftarrows}^{1}\)B 1 in NO - 2 ions which are perturbed by the presence of NO - 3 impurity in the crystal.

Optical Studies on Thallium-activated Alkali-iodide Crystals

Absorption and emission spectra of KI–Tl and NaI–Tl phosphors have been investigated at both room and liquid air temperatures. In order to perform optical measurements on NaI-Tl, special caution was given to prevent the crystal surface from being clouded by moisture. In the absorption spectra of NaI–Tl, new bands due to the presence of thallium were found. Their maximum absorption coefficients seemed to vary with the square of the thallium concentrations. The similar fact has already been found by Yuster and Delbecq in their investigation on KI–Tl. In emission, both KI and NaI crystals containing high concentrations of thallium showed a subsidiary band overlapping the short wavelength tail of the hitherto observed main band. The relations between these absorption and emission bands were investigated and discussions were given in terms of an extended model proposed by Seitz.

Resonant secondary emission in NaNO2: Time-resolved study

Abstract Spectral and transient behaviors of resonant secondary emission in NaNO 2 are studied with exciting light ν i around the zero-phonon absorption line at ν 00 =25975±2 cm −1 . In the region ν i ≲ν 00 , the emission spectrum consists of multiple-order scattering lines due to the bending vibration of NO 2 − . Each line shifts in parallel with the change in ν i . Time response of each emission line can be resolved into short-lived and long-lived components which correspond to Raman scattering and luminescence, respectively. The intensity ratio of the long-lived component to the short-lived one is found to decrease with increase in the detuning frequency Δν indicating the non-motional-narrowing effect in the second order optical process. In the region ν i ≳ν 00 , each emission line splits into Raman-like and luminescence-like components spectrally. The latter has the property of ordinary luminescence, while the former shows the characteristics of hot luminescence.