Search

In iron-doped rutile (TiO2) charge compensation is necessary since most of the iron substitutes as Fe3+ for Ti4+. The well known EPR spectrum of iron-doped rutile is due to Fe3+ substitutional ions in a perfect lattice. However, EPR measurements at 9.2 GHz revealed several additional EPR spectra which are explained as due to substitutional Fe3+ ions disturbed by nearest-neighbour oxygen vacancies, protons and Ti4+ interstitials. The number of nearest-neighbour oxygen vacancies and protons was determined from the EPR measurements. In pure rutile the number of oxygen vacancies was determined from measurements of the absorption line at 6.6*103 cm-1 which is associated with polarons. Since the number of EPR centres associated with oxygen vacancies is nearly the same as the number of oxygen vacancies it is concluded that the former are mainly located near to iron ions.

Channeling measurements (2MeV He+) of Au doped CdTe annealed at 800–900°C indicate Au concentrations between 1018 and 1020/cm3 with a substitutional Au solubility that increases with both increasing temperature and decreasing PCd. The partial pressure dependence is consistent with the model of doubly ionized Frenkel defects on the Cd lattice and ionized AuCd. Optical absorption from ∼4μ to the band edge is seen to increase with both increasing anneal temperature and decreasing PCd. Hall measurements show substantial charge compensation in all the annealed samples.

Electron spin resonance has been studied in V1−xCrxO2 crystals in the monoclinic insulating phase M1(x 0.1%) and its spectrum can be interpreted by assuming charge compensation by a nearest neighbour V5+.

ESR measurements of Cr3+ ions in SrTiO3 at orthorhombic lattice sites in the cubic phase of the crystal are described. The orthorhombic distortion is caused by an oxygen vacancy in the neighbourhood of the Cr3+ ion. A model of the displacement of the neighbouring oxygen ions is proposed. The values of the constants of the spin-Hamiltonian are given. ESR-Messungen an Cr3+-Ionen in SrTiO3 auf orthorhombischen Gitterplatzen in der kubischen Phase des Kristalls werden beschrieben. Die orthorhombische Verzerrung wird durch eine Sauerstofflucke in der Umgebung des Cr3+-Ions verursacht. Ein Modell fur die Verschiebung der benachbarten Sauerstoffionen wird vorgeschlagen. Die gemessenen Konstanten des Spin-Hamilton-Operators werden angegeben.

Brown, green, yellow, and red CaF2:U crystals were investigated by means of optical spectra and chemical analyses in order to determine the cause of the different colorations. Whereas earlier work claims the green coloration is due to U2+, we have shown it is due to U4+. Whereas earlier work claims the yellow coloration is due to U4+, we have shown it is due to U6+. The brown coloration appears to be due to U4+ with a different charge compensation that the green coloration.

An experimental investigation on CaS phosphors revealed 31 different activators each producing its own emission characteristics. Most activators require a co-activator but the choice of the best co-activator is not always governed by the rules of charge compensation, the latter principle appearing to be violated in many cases. Emission spectra, optical absorption spectra, and decay modes after excitation by short electron beam pulses are presented.

The ESR spectrum of iron doped V2O5 single crystals shows two different line groups. Analysis of the angular dependence and intensity measurements prove that, contrary to Cr3+ ions, Fe3+ ions occupy lattice sites and tetrahedral sites as well. This is in agreement with published Mossbauer results. Moreover, the influence of the Fe3+ concentration upon the signal intensity of the vanadium 3d1 electron was investigated. Im ESR-Spektrum eisendotierter V2 O5 -Einkristalle treten zwei verschiedene Signalgruppen auf. Die Analyse ihrer Winkelabhangigkeit sowie Intensitatsmessungen ergeben, das im Gegensatz zu Cr3+-Ionen die Feat -Ionen sowohl auf Gitterplatzen als auch auf Tetraeder-Zwischengitterplatzen eingebaut werden. Dies ist in ubereinstimmung mit bekannten Mosbauer-Ergebnissen. Weiterhin wird ein Einflus der Konzentration der Fe3+-Ionen auf die Intensitat des ESR-Signals der Vanadium-3d1-Elektronen untersucht.

The fluorescence of a number of new Ce3+‐activated phosphors is described and discussed. Only host lattices with a sublattice consisting of trivalent lanthanide ions are used to avoid charge compensation of the Ce3+ ion. Usually the Ce3+ emission is in the near‐ultraviolet region. Y3Al5O12–Ce and SrY2O4–Ce, however, show emission in the visible region with a maximum in the green. Conditions for visible Ce3+ emission are indicated, viz., large crystal‐field splittings (Y3Al5O12–Ce) or a large Stokes shift (SrY2O4–Ce). In a number of cases we were able to observe all crystal‐field components of the excited 5d level of Ce3+. The cubic crystal‐field splitting of the 5d level varies strongly with host lattice from 7000 to 14 000 cm−1. The position of the center of the 5d levels in oxides is about 30% lower than in the free ion. For some phosphors we observed more than one emission band at room temperature. This is due to fluorescence from higher excited levels. Efficient energy transfer from Ce3+ to Cr3+ was observed in Y3Al5O12.

Nach dem Czochralski-Verfahren wurden CaWO4- und CaMoO4- Einkristalle mit Nd3+-Dotierung gezuchtet; zur Ladungskompensation dienten Na+ - und Nb5+ - Ionen. Absorptions- und Fluoreszenzmessungen zeigten, das fur die Nd-Ionen der gewunschte Einbauzustand erreicht wurde. Ein wesentlicher Teil der Arbeit ist den Lasereigenschaften gewidmet. Aus dem zeitlichen Emissionsverhalten, der optischen Gute und der Materialfestigkeit folgt, das sich die Kristalle im Impulsbetrieb vorteilhaft bei niedriger Pumpenenergie einsetzen lassen. Die vom Pumplicht herruhrende Verfarbung des aktive Mediums wird diskutiert. CaWO4 and CaMoO4 single crystals with Nd3+-doping are grown by the Czochralski-method, the charge compensation is reached with Na+ and Nb5+ ions. Measurements of absorption and fluorescence show that the desired state of incorporation for the Nd ions has been arrived. An essential part of the work is engaged in the laser properties. From the time-variable emission characteristics. the optical quality and shock resistance of the material it can be concluded that in pulse operation the crystals may be applied at low pumping energy to advantage. The pump light induced coloration of the active medium is discussed.

The EPR spectrum of single crystal, Ni doped; Stannic Oxide, SnO 2 , has been re-examined at 22·7 GHz. The signal which appeared after Ni doping appears to be due to a new Fe 3+ center. Since the grown samples contained approximately 30 ppm Fe and a strong Fe 3+ substitutional resonance was observed, a signal due to approximately 10 per cent of the Fe can easily be detected. A third Fe signal not previously characterized was also noted. Because of a strong analogy with recent work on the similar compound TiO 2 , the centers are identified as Fe 3+ ions on substitutional sites associated with a nearby defect. The charge compensation problem of a 3+ ion in the host is the reason for expecting the associated defect.

A crystal field calculation for the low symmetry Ca2+ site in Scheelite (CaWO4) has been performed using a point charge model based on the crystallographic site parameters. The cases of 3d9Cu2+ and 4f13Yb3+ are treated in detail. The results of the calculation are compared with the absorption and fluorescence spectra of Yb-doped CaWO4. These experimental results do not agree with the predictions, probably because of the serious change in site geometry when trivalent Yb replaces divalent Ca and charge compensation is necessary.

Using single-crystal barium titanate with liquid electrodes, the pyroelectric effect has been used in a technique to extend the measurements of ferroelectric switching times to low fields. In the field range studied (0·2 ts > 10-4 sec) two significant transitions have been found in the switching behaviour at 0·54 kv cm-1 and 0·3 kv cm-1, appearing experimentally as discrete changes in the activation field. They have been shown to be due respectively to a modification in the nucleation mechanism of reversed domains and to the onset of charge compensation behind the moving domain walls.

The existence of a separate cubic phase RF3:3(MeF2), which provides a cubic symmetry site with local charge compensation for a tripositive rare earth ion in a fluorite lattice, is examined in order to explain the increase in cubic sites with increasing rare earth impurity concentration. An expression for the minimum concentration at which such a phase would be stable is presented. For the case of SrF2:Ge3+ or SrF2: (Gd3+, Ce3+) a calculation estimates that such a phase could form at 0.36% total rare earth impurity concentration.

The fluorescence of a number of Bi3+ ‐activated phosphors is reported. Only host lattices containing a sublattice of large, trivalent cations are used, so that charge compensation of the activator is superfluous. The position of the broad emission band of these phosphors depends strongly on the host lattice and is found in the spectral region between 35 000 and 15 000 cm−1. The position of the absorption and excitation bands of the Bi3+ ion depends also on the host lattice but in a different way. The absorption and emission of those Bi3+‐ activated host lattices that absorb considerably in the ultraviolet region even without the activator are discussed. These materials probably do not contain simple Bi3+ centers.

X‐ray diffraction topographs show at least two types of defects in natural quartz, planar defects which are parallel to the natural quartz faces and needle‐like defects. The planar defects color when exposed to γ irradiation, indicating these are sheets of substitutional aluminum, with an interstitial alkali ion nearby for charge compensation. The linear defects are similar to macroscopic needles of TiO2 sometimes found in quartz and have previously been associated with dislocations by Lang. Both types of defects show diffraction contrast when observed from different Bragg planes. There does not seem to be a simple relation between either type of defect density and acoustic loss at 300°K in natural quartz.

Angular-dependence experiments of relaxation times ${T}_{1}$ for the ${\mathrm{Cr}}^{3+}$ ion have already been reported in a ruby sample doped with silicon. They showed minima in ${T}_{1}$ which could not be interpreted in terms of harmonic cross relaxation. The presence of ${\mathrm{Fe}}^{2+}$ ions in the specimen may explain these minima. Ruby samples doped with both iron and silicon have been made to increase the ${\mathrm{Fe}}^{2+}$ concentration by charge compensation with ${\mathrm{Si}}^{4+}$ ions. The minima in relaxation time for ${\mathrm{Cr}}^{3+}$ are enhanced in these crystals and they occur at all the crossing points of the ${\mathrm{Cr}}^{3+}$ and ${\mathrm{Fe}}^{2+}$ lines. The variation of ${T}_{1}$ vs angle for ${\mathrm{Cr}}^{3+}$ is studied and the temperature dependence of ${T}_{1}$ is investigated from 4.2 to 1.2\ifmmode^\circ\else\textdegree\fi{}K. Further work is in progress to see if our results are in agreement with the sign of the zero-field splitting parameter $D$ found by Lewiner et al. or with the one obtained by Ganapol'skii. Theoretical work by Stevens and Walsh and the acoustical-paramagnetic-resonance experiments by Lewiner et al. and Ganapol'skii on ${\mathrm{Fe}}^{2+}$ in corundum are inconsistent.

The thermoluminescence spectra and glow curves of MeF2: Y, MeF2: Tm (Me:Ca, Sr, Ba), and CaF2: Sm single crystals are measured over the temperature region from 89 to 300 °K and compared with earlier results obtained above room temperature. It is established that temperature has a considerable effect on the spectral intensity distribution of the thermoluminescence emission and effects are observed which arise from both the activator concentration and a charge compensation by NaF. A brief discussion is given of the results. Die Thermolumineszenzspektren und Glowkurven von MeF2: Y-, MeF2: Tm(Me: Ca, Sr, Ba)- und CaF2: Sm-Einkristallen werden im Temperaturbereich von 89 bis 300 °K gemessen und mit fruheren, bei Zimmertemperatur erhaltenen Ergebnissen verglichen. Es wird ein bedeutender Einflus der Temperatur auf die spektrale Intensitatsverteilung der Thermolumineszenz festgestellt; dabei werden Effekte beobachtet, die sowohl von der Aktivatorkonzentration als auch von der Ladungskompensation durch NaF verursacht werden. Die Ergebnisse werden kurz diskutiert.

Nonaxial paramagnetic resonance spectra in Ce‐doped CaWO4, with and without sodium compensation, have been observed and the g parameters measured. It is suggested that the compensation‐site g ellipsoids can be largely explained as a perturbation of the axial‐site g ellipsoid caused by the odd fields of the compensating charges. According to this model the compensation‐site g parameters can be predicted by making measurements of the linear g shifts in laboratory applied fields for the axial sites. The model is illustrated by some simple comparisons between experimental g ellipsoids, and g ellipsoids predicted in this way. Electric‐field shifts have also been measured for the compensation‐site spectra. Similarities between the compensation‐site shifts and the shifts measured for axial sites afford some evidence in support of the primary assumption that the strong odd fields arising from the compensating charges can be treated as axial site perturbations. The compensation‐site shifts can also be used to make partial corrections for quadratic and other higher‐order odd‐field effects which were ignored in the sample description of the model. Predictions made for the g ellipsoids due to charge compensation at the nearest‐neighbor Ca site agree reasonably well with the strongest nonaxial spectra observed in the uncompensated (vacancy compensated) and in the Na‐compensated samples. This shows that the local strains, and the even fields due to the compensating charges are of only secondary importance in this system. The local odd fields were estimated by using the bulk dielectric constants of CaWO4. The success of this procedure in predicting g values for the strongest nonaxial spectra in the two samples suggests that compensating charges at a nearest‐neighbor site produce changes in the dielectric similar to those produced by macroscopic electric fields. The g parameters and electric‐field shifts for a second, less intense nonaxial spectrum in the vacancy‐compensated sample were also studied. The results were not so easy to interpret in this case. Miscellaneous observations were also made on some weaker lines in the two samples.

The absorption spectrum of 0.01%—0.05% ytterbium‐doped calcium tungstate is reported, observed at liquid‐helium temperature. Some of the samples contained sodium for charge compensation. The effect of Na charge compensation for Yb was found to be similar to previous results observed for Na‐compensated Ce in the same host. The spectrum was found to contain extensive complex structure that may be associated with the known lattice modes. The crystal‐field parameters have been calculated to fit the main lines of the spectrum, and the g values that are known. The calculation was made both with and without mixture of states of unequal J. Measurements of the Zeeman effect allow unambiguous identification of the symmetry of the lowest 2F5/2 level. In terms of the free‐ion JM states this level consists of a combination of M=±52 and ±32 functions. The g values for this state are g‖ = 1.2±0.1 and g⊥ = 1.5±0.1 observed at 31 kOe.

Tetrahedrally-coordinated trivalent iron has been found to be a common impurity in flux-grown crystals of zinc oxide. The room temperature paramagnetic resonance spectrum of isolated ions may be described by a conventional axial spin Hamiltonian with parameters: $g=2.0060\ifmmode\pm\else\textpm\fi{}0.0005$, $D=\ensuremath{-}(594\ifmmode\pm\else\textpm\fi{}1)\ifmmode\times\else\texttimes\fi{}{10}^{\ensuremath{-}4}$ ${\mathrm{cm}}^{\ensuremath{-}1}$, $F=(4\ifmmode\pm\else\textpm\fi{}5)\ifmmode\times\else\texttimes\fi{}{10}^{\ensuremath{-}4}$ ${\mathrm{cm}}^{\ensuremath{-}1}$, $a=(39\ifmmode\pm\else\textpm\fi{}5)\ifmmode\times\else\texttimes\fi{}{10}^{\ensuremath{-}4}$ ${\mathrm{cm}}^{\ensuremath{-}1}$. Lines due to iron ions with nearby charge compensation (${\mathrm{Li}}^{+}$ ions) have also been observed. The magnitude of the cubic field parameter ($a$) is discussed. The hyperfine coupling constant of ${\mathrm{Fe}}^{57}$ in an enriched sample is $|A|=(9.02\ifmmode\pm\else\textpm\fi{}0.2)\ifmmode\times\else\texttimes\fi{}{10}^{\ensuremath{-}4}$ ${\mathrm{cm}}^{\ensuremath{-}1}$ which is of interest in connection with Robert's nuclear resonance measurements of sublattice magnetizations in yttrium-iron garnet. It appears likely that both sublattices are aligned within 1% at very low temperatures.

Substituted CdCr2S4 spinels containing Ni, Co, V, and Ti were prepared for magnetic study. Substitution of In3+ for Cd2+ was used for charge compensation when divalent transition‐metal ions were substituted for Cr3+. In the spinels Cd0.8In0.2[Cr1.8Ni0.2]S4, Cd0.8In0.2[Cr1.8Co0.2]S4 and Cd0.8In0.2[Co0.2Cr1.8]Se4 the Ni2+ and Co2+ were both found (by magnetic measurements) to interact negatively (antiferromagnetically) with the Cr3+ ion. The V3+ and Ti3+ ions in CdV0.2Cr1.8S4 and CdTi0.2Cr1.8S4 appear to have no magnetic moment. The measured magnetic moments of these spinels are in excellent agreement with theoretical values based only on the moment of Cr3+. In the compound Cd0.8In0.2[Cr1.8V0.2]S4 the measurements indicated that the V2+ ion is not stable with respect to the Cr2+ ion. The resulting ionic distribution would be Cd0.8In0.2[V0.23+Cr0.22+Cr 1.63+]S4 instead of Cd0.8In0.2[V0.22+Cr1.83+] S4. Two additional compositions containing 0.1 and 0.3 mole of vanadium exhibited magnetic moments which are con...

New EPR centres for Ce 3+ , Nd 3+ and Sm 3+ in CaF 2 with tetragonal symmetry are reported where charge compensation is due to interstitial H - or D - ions. The strength of these centres has been correlated with the i.r. local mode absorption of the paired hydrogen.

The paramagnetic resonance spectrum of ${\mathrm{Yb}}^{3+}$ and ${\mathrm{Er}}^{3+}$ in single crystals of Ce${\mathrm{O}}_{2}$ has been measured at 10 Gc/sec and 4\ifmmode^\circ\else\textdegree\fi{}K. In sites of cubic symmetry, the ground states in both cases are found to be isotropic ${\ensuremath{\Gamma}}_{7}$ doublets with $g=3.424\ifmmode\pm\else\textpm\fi{}0.001$ for ${\mathrm{Yb}}^{3+}$ and $g=6.747\ifmmode\pm\else\textpm\fi{}0.006$ for ${\mathrm{Er}}^{3+}$. Hyperfine structures for the odd isotopes were resolved with $A({\mathrm{Yb}}^{171})=(877.1\ifmmode\pm\else\textpm\fi{}1.0)\ifmmode\times\else\texttimes\fi{}{10}^{\ensuremath{-}4}$ ${\mathrm{cm}}^{\ensuremath{-}1}$, $A({\mathrm{Yb}}^{173})=(242.0\ifmmode\pm\else\textpm\fi{}0.3)\ifmmode\times\else\texttimes\fi{}{10}^{\ensuremath{-}4}$ ${\mathrm{cm}}^{\ensuremath{-}1}$, and $A({\mathrm{Er}}^{167})=(232.1\ifmmode\pm\else\textpm\fi{}0.3)\ifmmode\times\else\texttimes\fi{}{10}^{\ensuremath{-}4}$ ${\mathrm{cm}}^{\ensuremath{-}1}$. Nearby charge compensation produces sites of axial symmetry. For ${\mathrm{Yb}}^{3+}$, one set of axes is along the four 111g crystal directions with ${g}_{\ensuremath{\parallel}}=4.733\ifmmode\pm\else\textpm\fi{}0.004$ and ${g}_{\ensuremath{\perp}}=2.744\ifmmode\pm\else\textpm\fi{}0.002$. For ${\mathrm{Er}}^{3+}$ two different axial spectra were measured, also with trigonal symmetry about the 111g directions. For one set ${g}_{\ensuremath{\parallel}}=10.25\ifmmode\pm\else\textpm\fi{}0.05$ and ${g}_{\ensuremath{\perp}}=4.847\ifmmode\pm\else\textpm\fi{}0.005$, and for the other set ${g}_{\ensuremath{\parallel}}=4.539\ifmmode\pm\else\textpm\fi{}0.005$ and ${g}_{\ensuremath{\perp}}=7.399\ifmmode\pm\else\textpm\fi{}0.007$. In most crystals the linewidths were 20 Oe; however, in some crystals in which no cubic sites were found, the axial linewidths were greater than 50 Oe. Comparisons of the axial $g$-tensor traces with the cubic $g$ tensor and the magnitude and sign of $\ensuremath{\Delta}g={g}_{\ensuremath{\parallel}}\ensuremath{-}{g}_{\ensuremath{\perp}}$ are the basis for a discussion of the possible nature of the charge compensation producing the axial symmetry.

1. Study of the IR spectra of unannealed corundum crystals grown in a hydrogen-oxygen flame established that all such crystals have absorption bands corresponding to OH-group valence vibrations and hence do not differ in this respect from other crystals grown under analogous conditions. 2. The experimental data obtained in this investigation indicate that there is a relationship between the absorption bands corresponding to OH groups and the content of impurities requiring charge compensation in the crystals.

Materials in the system Cu0.5+xIn0.5-xCr2S4 have have been prepared with 0.1≥ ×≥-0.1. At x=0, the free holes causing CuCr2S4 to be a metallic ferromagnet with a Curie temperature of 420 K are compensated and the material becomes an antiferromagnetic sem iconductor. By conductivity, susceptibility, and magnetization measurements the magnetic exchange interaction in these materials was found to be conductivity controlled.

In nearly ideal crystals there are many types of imperfection. One type of imperfection that often exists is a cation of different valence state substituted in the regular crystalline array. The question arises: How does this affect the surroundings and the crystalline order? It is well known that in certain cases the symmetry of the crystal system is preserved, since the charge compensation may be located far from the substituted ion. In other cases the charge compensation may be located in the adjacent cells. In either case it is to be expected that the surrounding shells will be affected and that local distortions of the lattice will occur. It is the purpose of this paper to indicate some experimental results which shed light on this problem.

Electron magnetic resonance spectra of Mo5+ in tetragonal GeO2 has parameters: g(001) = 1.857, g(110) = 1.910, g(110) = 1.951, A(001) = 2.4×10−3 cm−1, A(110) = 1.8×10−3 cm−1, A(110) = 5.9×10−3 cm−1 and occupies Ge sites. These values give λ = 0.08 and /N = 3.10 a.u. Excess oxygen is assumed to furnish charge compensation.

ENDOR measurements of the 19F nuclei in CaF2 containing Ce3+ and Yb3+ in tetragonal sites show unambiguously that charge compensation is achieved by an interstitial - ion displaced by 12a0 in the 〈100〉 direction from the rare-earth ion.

The paramagnetic resonance spectra of single crystals of CaWO 4 :Yb have been examined to determine the extent to which crystals charge compensated with sodium have ytterbium ions in sites with lower than tetragonal symmetry. The spectra of crystals prepared with niobium and with no impurity ion added for charge compensation were also examined. To varying extents all crystals showed the presence of Yb 3+ ions in sites with several types of local symmetry. In a sample grown from a melt containing a ratio of sodium to ytterbium of eight to one, approximately 71 per cent of the Yb 3+ ions occupy sites with tetragonal symmetry. It is concluded that much of the unexplained structure observed in the optical spectra of this crystal may be due to Yb 3+ in sites with lower than tetragonal symmetry.

SODIUM tungstate is used to provide charge compensation in neodymium-doped single crystals of calcium tungstate (scheelite) which are widely used as lasers1. These crystals are generally grown by the Czochralski technique from melts which can contain up to 10 wt. per cent sodium. It is therefore desirable to remove impurities from the sodium tungstate which could lead to the formation of light-scattering centres in laser crystals incorporating this material2. In this communication, a zone-refining method of purifying the readily available reagent grade of sodium tungstate is described.

Polycrystalline rare‐earth orthoferrites (LnFeO3) in which some Fe3+ has been replaced by M2+ (M2+ = Ni, Mn, Cu and Co) have been prepared. Charge compensation was effected by the substitution of F− for O= to give the general formula LnFe1−xM+2xO3−xFx. X‐ray techniques and magnetic measurements of Curie points were used to verify the absence of second phases. Materials of the type LnFe0.8Ni0.2O2.8F0.2 (Ln = Y, La–Yb) exhibited room‐temperature magnetic moments which were of the order of four times larger than those of the unsubstituted orthoferrites, implying marked increases in canting angle. Curie temperatures decreased about 20°C. Where Ln = Sm the limit for Ni2+ – F− substitution was x ≈ 0.2. For Ln = Ho the substitution limit was x ≈ 0.3. In both cases increasing Ni2+–F− substitution resulted in increasing magnetic moment. When the substituted orthoferrites contained Cu2+ and F− no large changes in magnetic moment or Tc were observed. For Mn2+–F− substitution the Curie temperature decreased about 30°...