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A study of copper impurity centres in NH 4 Cl by dielectric loss and electrical-conductivity measurements is reported in this paper. A theory is given for the dielectric loss due to the reorientations of impurity-vacancy dipoles in a CsCl-type lattice by means of jumps of constituent point defects. Expressions are worked out for tan δ associated with various complexes with substitutional and interstitial divalent impurities by considering the atomic kinetics of reorientations. NH 4 Cl: Cu crystals grown from ammoniacal and acidic solutions give one set of loss peaks each and crystals grown from neutral solutions give two sets of loss peaks. These peaks are attributed to two types of interstitial copper centres. In crystals grown from neutral solutions suppression of the electrical conductivity with respect to pure crystals is observed. The results are interpreted in terms of anion vacancy motion in the intrinsic region and cation vacancy motion in the extrinsic region and a minimum limit of 2.06 eV is suggested for the Schottky defect-formation energy.

In order to make quantitative predictions of the output powers and energies from a laser it is necessary to know the value of the stimulated emission cross section. Conversely by measuring the output power or energy it is possible to calculate the cross section. Cross sections for the 4F(3/2) to 4I(11/2) of Nd doped materials (Nd:glass, Nd:YAG), Nd:SeOCl2 although a literature search by the authors failed to reveal any published figures for Nd:CaWO4. This paper reports a measurement of the 4F(3/2) to 4I(11/2) cross section in Nd:CaWO4 using a method which Edwards first applied to Nd glass materials. The crystal investigated was a Na-compensated crystal grown by AEI (Nd concentration nominally 1 at,%) cut in the form of a cylindrical rod 50mm long, 6mm across, with the c-axis parallel to the cylinder axis. The cross section measured is that of the sigma-polarised emission at 1.065µm since the sigma spectrum and axial spectrum are identical.

In this paper an account is given of the preparation of lead bromide single crystals undoped and doped with monovalent and trivalent cations and with oxygen. The conductivity of these crystals has been measured in the temperature region 50–300°C. The thermal disorder appeared to be of the same Schottky type as in lead chloride. From the slopes of the conductivity curves the activation heat for the anion vacancy migration has been calculated to be 0.29 ± 0.04 eV and the heat required for the formation of one set of vacancies 1.4 ± 0.1 eV. Irradiation of pure lead bromide with ultraviolet light gives a characteristic damaging as is made visible by electron and optical microscopy. The increase of the optical density varies as the square root of the irradiation time.

The energy states and optical spectra of heavily doped mixed crystals are investigated. Studies are made for the following binary systems: (1) naphthalene-h8 and -d8, (2) naphthalene-h8 and -ad1, and (3) naphthalene-h8 and -bd1 , corresponding to strong, medium, and weak perturbations, respectively. In addition to ordinary absorption spectra at 4°K, band-to-band transitions at both 4 and 77°K are also analyzed with emphasis on their relations to cooperative excitation and over-all density-of-states functions for mixed crystals. It is found that the theoretical calculations presented in a previous paper agree generally with experiments except for cluster states observed in system (1) at lower guest concentrations. These features are discussed semiquantitatively. As to the intermolecular interaction parameters, it is found that experimental results compare favorably with calculations based on experimental density-of-states functions but not with those based on octopole interactions or charge-transfer interactions. Previous experimental results of Sheka and the theoretical model of Broude and Rashba are also compared with present investigations.