摘要:

Investigation of the optical and photolytic properties of large silver‐halide crystals has shown that both cuprous and cupric ions can be incorporated in the AgCl lattice in true solid solution up to concentrations of the order of 1018ions/cm3, and quantitatively measured by their characteristic optical absorption as well as by their role in the photolysis of such crystals. At elevated temperatures, the valence state of the copper is determined by the external chlorine pressure. The dependence, at equilibrium, of the cupric‐ion concentration on the external chlorine pressure has been determined from measurements of the optical absorption of the cupric ion. This experimentally determined dependence has been compared to that expected from a consideration of the equilibrium number of filled copper levels and the known dependence of free‐hole concentration on halogen pressure. Apart from the absorption bands associated with the copper, another absorption band, whose intensity is proportional to the free‐hole concentration, has been observed in both pure and copper‐containing crystals.

ISSN:0021-8979    

DOI:10.1063/1.1777119

出版商:AIP    

年代:1962

数据来源: AIP

摘要:

The polarized optical spectra of several transition metal ion impurities in crystals with the wurtzite structure; Cs2ZnX4(where X−=Cl−or Br−); and Al2O3have been measured at temperatures ranging from that of liquid helium to room temperature. In all these cases the transition metal ion substitutes for a cation of pure compound. The gross features of the spectra are explained by crystal field theory for the impurity ions in a potential field arising from the nearest‐neighbor ligands in their undistorted configuration. The finer details of the spectra and the polarization effects which are observed are used to infer the actual site symmetry of the impurity ion. The trigonal field splitting compared to the calculated value indicates that certain ions in Al2O3are displaced from the aluminum site along the threefold axis. The breadth of certain bands, and in some cases the lattice vibration progressions which are observed, have been interpreted as being due to a reduction in the symmetry of the electronically exicted ion and its ligand environment from that of the ground‐state configuration. In the case of Mn3+in corundum there is very good evidence for a highly distorted site, presumably due to the Jahn‐Teller effect.

ISSN:0021-8979    

DOI:10.1063/1.1777120

出版商:AIP    

年代:1962

数据来源: AIP

摘要:

Some paramagnetic resonance experiments on pairs of exchange coupled paramagnetic ions in magnetically dilute crystals are described. The exchange parameters found in this way are compared with susceptibility data for the corresponding concentrated salts. For some iridium salts the exchange energy is discussed in terms of a simple model which uses a Morse potential energy curve. The results emphasize the importance in these salts of superexchange through two intermediate nonmagnetic ions and suggest that similar interactions may be important in other antiferromagnetics.

ISSN:0021-8979    

DOI:10.1063/1.1777121

出版商:AIP    

年代:1962

数据来源: AIP

摘要:

ESR of Nd3+and U3+in CaF2(Bleaney, Llewellyn, and Jones, 1956) provided the first confirmation of the hypothesis of Zintl and Udga˚rd (1939) that charge compensation for a trivalent lanthanum ion is provided by an interstitial fluorine ion. In some cases this is in the nearest interstitial site, as shown by observation of magnetic dipole interaction between it and Ce3+(Baker, Hayes, and O'Brien, 1960). In other cases the charge compensating defect is absent or so far away that cubic symmetry is preserved at the lanthanum site. The effects of x‐ray and ultraviolet irradiation at room and lower temperatures are being studied. Initial results show that Tm3+ions can be converted readily to Tm2+, whose ESR spectrum has been measured (Hayes and Twidell, 1961). This has cubic symmetry, indicating that the Tm3+ion is either accompanied by no defect or by a defect mobile at low temperatures. The spectra of Tm2+and Yb3+are compared. The work of Sierro (1961) on the hydrolysis of CaF2is discussed.

ISSN:0021-8979    

DOI:10.1063/1.1777122

出版商:AIP    

年代:1962

数据来源: AIP

摘要:

The optical absorption or emission by an electron localized at a point imperfection in a crystal is broadened by lattice vibrations. In a fundamental discussion the normal modes of vibration of the whole crystal must be considered. The effect of a mode depends on the displacements it produces in ions near the imperfection. The presence of the imperfection will modify the modes, and, in particular, change the displacements of ions near the imperfection even when the modes do not become localized at the imperfection. In the case of theFcenter the temperature dependence of the breadth of theFband suggests that this effect must enhance the broadening produced by low‐frequency modes (which will certainly not be localized). That this is to be expected from the dynamical theory of normal modes will be shown by discussing: (1) the vibrations of a one‐dimensional chain of particles with two adjacent weakened links, (2) the spherical vibrations of an elastic continuum with a spherical cavity, (3) the vibrations with cubic symmetry round theFcenter in NaCl if only the first eleven shells of ions round the center are allowed to vibrate. Results obtained with this last model will be compared with experimental results for the breadth of theFband in NaCl as a function of temperature.

ISSN:0021-8979    

DOI:10.1063/1.1777123

出版商:AIP    

年代:1962

数据来源: AIP

摘要:

The infrared spectra of polyatomic ions in dilute solid solution reflect interactions of the vibrational modes with the lattice environment. The spectra are usually characterized by very narrow bandwidths, and by frequency shifts and changes in absorption intensities which depend upon the host lattice. We have examined the spectra of a number of ions in solid solution in alkali halides. From this data, conclusions have been drawn relative to the symmetries of the ions and the lattice sites which they occupy. The ultimate goal is the use of complex ions as ``probes'' to yield information on crystal lattices. Certain of the ions produced in fused alkali halides are characteristic of chemical equilibria at high temperatures, and have not previously been studied. We have identified several impurities found in the spectra of single crystals from commercial sources. The infrared absorption offers the possibility of determining the types and concentrations of trace impurities in single crystals.

ISSN:0021-8979    

DOI:10.1063/1.1777124

出版商:AIP    

年代:1962

数据来源: AIP

摘要:

There is much evidence that point defects are trapped by dislocation lines. We wished to obtain direct evidence by means of ESR study. Since the structure of the ESR spectrum of manganese ion is quite sensitive to the crystalline field, it is expected to serve as a detector of the local imperfection of the host crystal in which it is dissolved.

ISSN:0021-8979    

DOI:10.1063/1.1777125

出版商:AIP    

年代:1962

数据来源: AIP

摘要:

The results of electron spin resonance experiments on a series of transition metal ions in single crystals of corundum are reviewed and interpreted in terms of crystal field theory emphasizing three topics: (1) The strength of the cubic crystal field, (2) the axial field as an indicator of position of the impurity ion, and (3) Jahn‐Teller effects in the ground state. The 4dand 5dions which were examined, i.e., Ru3+, Rh3+, and Ir3+are found to be strong crystal field cases. In addition, the increased charge of Ni3+(3d7) is shown to be sufficient to drive it to a strong crystal field case (t26e) withS= ½ compared to Co2+(3d7) which ist25e3withS=32. The parametervwhich measures the trigonal field potential, was found to be +850 cm−1in Ru3+in good agreement with other ions such as Co2+and V3+whose cubic field ground states are also orbitally degenerate. In contrast, the determination ofvfrom ESR data on ions with singlet ground states such as Cu3+and Ni2+is regarded as less reliable. The Jahn‐Teller effect was observed for Pt+(or Pt3+), Ni3+, and Cu2+.

ISSN:0021-8979    

DOI:10.1063/1.1777126

出版商:AIP    

年代:1962

数据来源: AIP

摘要:

A brief review will be given of the methods of studying the polarization of luminescence and of the theory of the effect in relation to determining the electronic structure of centers. Reference will be made to the work on the alkali halides and diamond.Detailed experimental results will be presented and discussed of the fluorescence of the 5032 A center in diamond which is formed by heat treatment after irradiation. In these experiments the polarization has been studied as a function of the energy of both the exciting and of the emitted light. Depolarization occurs if the system is excited above the lowest level in the excited electronic state, or decays to a level above the lowest level in the ground electronic state.A comparison of the results will be given with those expected from centers having various electronic axes.

ISSN:0021-8979    

DOI:10.1063/1.1777127

出版商:AIP    

年代:1962

数据来源: AIP

摘要:

Direct ultramicroscopic studies and measurements of the optical scattering spectrum of ``pure'' and doped alkali halide crystals are described showing the existence of elementary scattering centers and of assemblies of such centers. The elementary scatterers are established to be impurity precipitates of dimensions not exceeding a few hundred angstroms. The assemblies lead to characteristic ultra‐microscopically visible diffraction images representing decorations of branch points of a semi‐organized network of dislocations which reflect the state of strain and deformation in the subgrains of the mosaic structure of the single crystals. With increasing temperature the number of elementary scatterers decreases as impurities enter the host lattice into true solid solution, and the size of the assemblies diminishes.Electron spin resonance experiments on doped alkali halides are discussed which provide direct information on the process of dissolution and reprecipitation of impurity ions. Results on strong exchange effects in the electron spin resonance of the systems MnCl2&sngbnd;NaCl and MnCl2&sngbnd;KCl are presented which are explained in terms of the substructure of very small impurity precipitates deduced from the optical investigations.

ISSN:0021-8979    

DOI:10.1063/1.1777128

出版商:AIP    

年代:1962

数据来源: AIP