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Excitation-induced infrared optical absorption in silver halides
Vol. 7, No. 11
CONFERENCE ON PHOTOCONDUCTIVITY
3-2.
SPIN DEPENDENT PHOTOCONDUCTIVITY IN ALKALI HALIDES J. Hodby (Claredon Lab Oxford University)
3-3.
EXCITATION-INDUCED INFRARED OPTICAL ABSORPTION IN SILVER HALIDES H. Kanzaki and T. Hattori (Institute for Solid State P h y s i c s , University of Tokyo)
Induced infrared absorption due to excitons generated by band-to-band excitation in silver halides is studied through modulation of fluorescence at visible wavelength by simultaneous irradiation of infrared monochromatic lights. Experiments are carried out below 4.2°K on pure silver halides(AgC1 and AgBr)and silver halides containing isoelectronic impurities (AgCl : I and AgBr : I), so far in the wavelength range 5-25/.z. Induced infrared absorption spectra thus obtained show features characteristic of coupling of optical phonons with the optical transition evidenced by the presence of equally spaced multiphonon structures in the induced spectra. The energies of coupled phonons are nearly equal to those of LO phonons in the corresponding silver halides matrices. Nature of the optical transitions can be understood as those from the ls type bound exciton ground state up to the higher excited states with different parity. The modulation technique adopted here may well have practical application as infrared detectors as well as useful method in studying the nature of higher excited states in nonmetallic solids. 3n4
°
ELECTRONIC PROCESSES IN THALLOUS CHLORIDE K. Kobayashi, Y. Makita, T. Kawai, M. Kanada and S. Kurita (Institute for Solid State Physics, University of Tokyo, Tokyo, Japan)
We investigate the band structure and the polaron transport properties in TICI by the measurements of the spectral dependence of
ix
photoconductivity, the drift mobility of photoelectrons and the Hall and the transient magnetoconductive effects of photocarriers in zonerefined samples above 1.8°K together with the magneto-optical absorption study. It is observed that the crystal is photoconductive by the illumination at the exciton band even below 4°K because of a small exciton binding energy of 10.9 meV determined by the magneto-optical measurements. By analyzing the results of photoconductivity and Hall effect, it is found that the photoconduction is of two-carrier with a longer unit range of holes than that of electrons at low temperatures and vice versa at high temperatures. We observe that the polaron mobility theories are accurate to describe the measured electron drift mobilities only at temperatures well below the Debye temperature of LO phonon. The transient magnetoconductive effect due to hole motion measured at low temperature is almost isotropic and the data are analyzed by using its phenomenological expressions. A spherical energy surface is proposed at the top of the valence band. 3-5.
MECHANISMS OF MULTI-PHOTON PHOTOCONDUCTIVITY M. Weiler, R. Dierig and B. Lax (National Magnet Laboratory, Cambridge, Massachusetts)
3-6.
AC PHOTOCONDUCTIVITY OF THE FA CENTERS (TYPE I AND TYPE II) IN KCI Hiroshi Ohkura (Dept. of P h y s i c s , University of Utah, Salt Lake City, Utah, U.S.A.) and Yutaka Ohta (Dept. of Applied P h y s i c s , Osaka City University, Osaka, Japan)
F.4 centers are /: centers adjacent to substitutional foreign cations. As shown by Liity, 1 F A centers can be classified into two groups ('type I' and 'type II') according to their different luminescence and alignment behavior. Photoconductivity should clearly reflect this difference. AC photoconductivity measurements for the PA (Na) centers in KC1 (an example for the type I centers) show indeed a behavior very similar to
CONFERENCE ON PHOTOCONDUCTIVITY
3-2.
SPIN DEPENDENT PHOTOCONDUCTIVITY IN ALKALI HALIDES J. Hodby (Claredon Lab Oxford University)
3-3.
EXCITATION-INDUCED INFRARED OPTICAL ABSORPTION IN SILVER HALIDES H. Kanzaki and T. Hattori (Institute for Solid State P h y s i c s , University of Tokyo)
Induced infrared absorption due to excitons generated by band-to-band excitation in silver halides is studied through modulation of fluorescence at visible wavelength by simultaneous irradiation of infrared monochromatic lights. Experiments are carried out below 4.2°K on pure silver halides(AgC1 and AgBr)and silver halides containing isoelectronic impurities (AgCl : I and AgBr : I), so far in the wavelength range 5-25/.z. Induced infrared absorption spectra thus obtained show features characteristic of coupling of optical phonons with the optical transition evidenced by the presence of equally spaced multiphonon structures in the induced spectra. The energies of coupled phonons are nearly equal to those of LO phonons in the corresponding silver halides matrices. Nature of the optical transitions can be understood as those from the ls type bound exciton ground state up to the higher excited states with different parity. The modulation technique adopted here may well have practical application as infrared detectors as well as useful method in studying the nature of higher excited states in nonmetallic solids. 3n4
°
ELECTRONIC PROCESSES IN THALLOUS CHLORIDE K. Kobayashi, Y. Makita, T. Kawai, M. Kanada and S. Kurita (Institute for Solid State Physics, University of Tokyo, Tokyo, Japan)
We investigate the band structure and the polaron transport properties in TICI by the measurements of the spectral dependence of
ix
photoconductivity, the drift mobility of photoelectrons and the Hall and the transient magnetoconductive effects of photocarriers in zonerefined samples above 1.8°K together with the magneto-optical absorption study. It is observed that the crystal is photoconductive by the illumination at the exciton band even below 4°K because of a small exciton binding energy of 10.9 meV determined by the magneto-optical measurements. By analyzing the results of photoconductivity and Hall effect, it is found that the photoconduction is of two-carrier with a longer unit range of holes than that of electrons at low temperatures and vice versa at high temperatures. We observe that the polaron mobility theories are accurate to describe the measured electron drift mobilities only at temperatures well below the Debye temperature of LO phonon. The transient magnetoconductive effect due to hole motion measured at low temperature is almost isotropic and the data are analyzed by using its phenomenological expressions. A spherical energy surface is proposed at the top of the valence band. 3-5.
MECHANISMS OF MULTI-PHOTON PHOTOCONDUCTIVITY M. Weiler, R. Dierig and B. Lax (National Magnet Laboratory, Cambridge, Massachusetts)
3-6.
AC PHOTOCONDUCTIVITY OF THE FA CENTERS (TYPE I AND TYPE II) IN KCI Hiroshi Ohkura (Dept. of P h y s i c s , University of Utah, Salt Lake City, Utah, U.S.A.) and Yutaka Ohta (Dept. of Applied P h y s i c s , Osaka City University, Osaka, Japan)
F.4 centers are /: centers adjacent to substitutional foreign cations. As shown by Liity, 1 F A centers can be classified into two groups ('type I' and 'type II') according to their different luminescence and alignment behavior. Photoconductivity should clearly reflect this difference. AC photoconductivity measurements for the PA (Na) centers in KC1 (an example for the type I centers) show indeed a behavior very similar to