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Showing papers by "Solid State Physics Laboratory published in 1969"


Journal ArticleDOI
TL;DR: In this article, it was shown that a magnetically sensitive coupling of singlet states to a double-triplet-exciton state at 2.40 eV is an important channel for radiationless decay in crystalline tetracene above 160.
Abstract: The fluorescence efficiency of tetracene single crystals may be enhanced by as much as 38% in a magnetic field $Hg2000$ G. The enhancement is anisotropic with respect to the orientation of $H$ in the $\mathrm{ab}$ plane. It is shown that a magnetically sensitive coupling of singlet states to a double-triplet-exciton state (${T}_{1}{T}_{1}$) at \ensuremath{\sim}2.40 eV is an important channel for radiationless decay in crystalline tetracene above 160\ifmmode^\circ\else\textdegree\fi{}K.

257 citations


Journal ArticleDOI
16 Aug 1969-Nature
TL;DR: New NMR results for a mineral hydroxyapatite have been obtained which provide a detailed model of the locations of the impurity-fluoride ions in hydroxyAPatite, their influence on neighbouring hydroxyl ions, and a mechanism by which small amounts of fluorine can strongly inhibit diffusion.
Abstract: NEW NMR results for a mineral hydroxyapatite have been obtained which, in combination with recent precision X-ray crystallographic studies, provide a detailed model of the locations of the impurity-fluoride ions in hydroxyapatite, their influence on neighbouring hydroxyl ions, and a mechanism by which small amounts of fluorine can strongly inhibit diffusion.

76 citations


Journal ArticleDOI
TL;DR: A theoretical evaluation of the maximum attainable solar conversion efficiencies of p-n and n-p heterodiodes is presented in this paper, where the Anderson diffusion model is used and carrier concentrations of the two semiconductors are so chosen that photo-carriers generated do not have to surmount any junction barrier.
Abstract: A theoretical evaluation of the maximum attainable solar conversion efficiencies of p-n and n-p heterodiodes is presented. The calculations are made for some of the theoretically efficient and feasible heterojunctions of IV and III-V group semiconductors. In these calculations, the Anderson diffusion model is used and carrier concentrations of the two semiconductors are so chosen that photo-carriers generated do not have to surmount any junction barrier. The calculated efficiencies are compared with the reported experimental values and with the conventional Si photovoltaic cell.

21 citations



Journal ArticleDOI
TL;DR: The frequency dependence of the transverse optical mode in the long-wavelength limit on the density of conduction electrons is calculated in this paper, which is a consequence of the dielectric properties of the free electron gas which gives a change of the effective ion-ion interaction.
Abstract: The frequency dependence of the transverse optical mode in the long-wavelength limit on the density of conduction electrons is calculated. This dependence is a consequence of the dielectric properties of the free electron gas which gives a change of the effective ion-ion interaction. By putting the limiting frequency equal to zero one finds an equation for the ferroelectric Curie temperature.

15 citations


Journal ArticleDOI
TL;DR: In this article, the modified Jain and Krishnan method was used to measure the thermal conductivity of zirconium in the temperature range 1100-1500 K and the electrical resistivity and total emissivity of ZrO.
Abstract: Using the modified Jain and Krishnan method, the thermal conductivity of zirconium has been measured in the temperature range 1100-1500 K. The thermal conductivity of zirconium is found to increase with temperature. Also, the electrical resistivity of zirconium and the total emissivity of ZrO have been measured in the temperature range 1050-1500 K and are reported in this paper.

14 citations


Journal ArticleDOI
TL;DR: In this article, single crystals were doped with FeCl 3 by slow diffusion and after X-ray irradiation the samples exhibit complex ESR spectra produced by more paramagnetic centers.

9 citations


Journal ArticleDOI
TL;DR: In this paper, a method for preparing pure FexS containing no more than traces of oxygen is described, and a Methode zur Herstellung von FExS unter Vermeidung von Sauerstoff-Verunreinigungen wird beschrieben.
Abstract: A method for preparing pure FexS containing no more than traces of oxygen is described. Eine Methode zur Herstellung von FexS unter Vermeidung von Sauerstoff-Verunreinigungen wird beschrieben.

9 citations


Journal ArticleDOI
TL;DR: The phase trans tion in single crystals of CsCl mixed with CsBr, RbCl, and KCl was investigated by means of ionic conductivity measurements and differential thermal analysis.
Abstract: The phase trans tion in single crystals of CsCl mixed with CsBr, RbCl, and KCl was investigated by means of ionic conductivity measurements and differential thermal analysis. Adding RbCl or KCl to CsCl reduces both the transition temperature, Ttr, and the enthalpy of transformation, ΔHtr. In the system CsClCsBr Ttr shifts to higher values relative to that of pure CsCl, whereas ΔHtr decreases considerably. A thermodynamical consideration of the phase transition temperatures in the CsClCsBr system shows that pure CsBr should exhibit a transition from the B2 to the B1 structure at 880 °C with an enthalpy variation of (300 ± 100) cal/mol. From the DTA experiments one should expect an enthalpy of (100 ± 50) cal/mol for the transformation of pure CsBr. Die Strukturumwandlung in CsClEinkristallen, gemischt mit CsBr, RbCl und KCl, wurde mittels Ionenleitfahigkeitsmessungen und differentieller thermischer Analyse untersucht. Der Zusatz von RbCl oder KCl zu CsCl erniedrigt die Umwandlungstemperatur Ttr, sowie die Umwandlungsenthalpie ΔHtr; bei den CsClCsBr-Mischkristallen dagegen nimmt Ttr mit steigender CsBr-Konzentration zu, wahrend ΔHtr abnimmt. Eine thermodynamische Betrachtung der Umwandlungstemperaturen des CsClCsBr-Systems zeigt, das in reinem CsBr bei 880 °C ein Ubergang von der B2-in die Bl-Struktur stattfinden sollte, mit einer Umwandlungsenthalpie von (300 ± 100) cal/mol. Aus den DTA-Messungen wurde man auf eine Enthalpie (100 ± 50) cal/mol fur reines CsBr schliesen.

8 citations


Journal ArticleDOI
TL;DR: In this paper, the effects of covalency on the isomer shift and quadrupole interaction in some divalent iron compounds were discussed, and the quadrupoles were analyzed.

7 citations


Journal ArticleDOI
TL;DR: Oscillatory magnetoresistance has been observed in p-type lead telluride at liquid nitrogen temperatures as discussed by the authors, assuming that this is due to scattering of carrier by optical phonons, the effective mass of holes has been calculated.

Journal ArticleDOI
TL;DR: In this paper, two types of paramagnetic centres have been detected: one with axial symmetry and the other with orthorhombic symmetry, which proves that the responsible electron for the observed absorption is not in an s state.
Abstract: The defects formed by introduction of Ca2+ ions in NaCl and NaBr single crystals and after UV irradiation at room temperature have been observed by the electron spin resonance method. Two types of paramagnetic centres have been detected: one with axial symmetry and the other with orthorhombic symmetry. The highly anisotropic g-factor of these centres proves that the responsible electron for the observed absorption is not in an s state. The formed centres decay at approximate 400 °K. Mit der ESR-Methode wird die Fehlordnung beobachtet, die nach Einfuhrung von Ca2+-Ionen in NaCl und NaBr und Bestrahlung mit ultraviolettem Licht bei Zimmertemperatur entsteht. Es werden zwei Arten von Zentren identifiziert: eines mit axialer und eines mit orthorhombischer Symmetrie. Die Anisotropie des g-Faktors beider Zentren zeigt, das das verantwortliche Elektron der beobachteten Absorption sich nicht in einem s-Zustand befindet. Bei ungefahr 400 °K verschwinden die gebildeten Zentren.


Journal ArticleDOI
01 Jan 1969-Nature
TL;DR: In this paper, the authors investigated the effect of the intensity of an X-ray beam on the rate of generation of the late stage anion vacancies in very pure KCl crystals using thermoluminescence technique.
Abstract: SEVERAL authors1–3 have studied how the intensity of an X-ray beam, E, affects the parameter “a” which defines the rate of generation of the late stage anion vacancies. Mitchell et al.1 have shown that a ∝ E2. Abramson and Caspari2, however, have suggested that for large values of E, a should vary linearly with E and for low intensities a should vary as E2. According to Pooley3, the power x of E in the relation a ∝ Ex should be unity for large values of E and should increase to a limiting value of 1.5 on decreasing E. We have made investigations with very pure KCl crystals using the thermoluminescence technique4 to find the variation of x in the relation a ∝ Ex for low and high X-ray intensities.

Journal ArticleDOI
TL;DR: In this article, the design and fabrication of a three-stage thermoelectric cooler are discussed and the performance characteristics of this cooler for various heat loads are presented and the experimental results are compared with the theoretically predicted values.
Abstract: Design and fabrication of a three-stage thermoelectric cooler are discussed. The performance characteristics of this cooler for various heat loads are presented and the experimental results are compared with the theoretically predicted values. The possible uses of this particular unit are also discussed in this paper.


Journal ArticleDOI
TL;DR: In this paper, the amplitude modulation is produced by superimposing the audio signal on the exciting d.c. voltage of the discharge tube and the resulting intensity modulated laser beam (λ = 0·6328 μ) is focused on a PMT/solar cell to detect the audio signals.
Abstract: Preliminary experiments, demonstrating the feasibility of laser communication, using a He-Ne gas laser of cavity length of about 45 cm. with confocal reflector arrangement and of output power of the order of a milliwatt, have been reported. The amplitude modulation is produced by superimposing the audio signal on the exciting d.c. voltage of the discharge tube and the resulting intensity modulated laser beam (λ = 0·6328 μ) is focused on a PMT/solar cell to detect the audio signal. Without using any sophisticated collimating or receiving optics, communication up to a distance of about 100 ft. has been demonstrated and can easily be extended further.

Journal ArticleDOI
TL;DR: In this paper, the results obtained on computing temperature variation of energy gap in tellurium from Hall and conductivity data are analyzed and compared with those obtained in the previous work.


Journal ArticleDOI
TL;DR: In this paper, various evaporated sintered contacts have been tried on low resistivity n-type GaAs for use in bulk GaAs devices, including In-Au, In-Ni, Au-Sn and Au-Ge-Ni.
Abstract: Various evaporated sintered contacts have been tried on low resistivity n-type GaAs, for use in bulk GaAs devices. Some of the materials tried are In-Au, In-Ni, Au-Sn, Au-Ge-Ni and contact resistances of less than 1 × 10−4 ohm-cm.2 on 0·005 ohm-cm. base resistivity GaAs have been achieved in certain cases. Details of the contact behaviour are discussed in the paper.