J. J. Rubin

Some characteristics of niobates having “filled” tetragonal tungsten bronze-like structures

Abstract Alkali metal and mixed alkali metal-alkaline earth niobates having “filled” tetragonal tungsten bronze-like structures are of particular interest for electro-optic and nonlinear optic applications. The characteristics of a number of the more useful materials and particularly Ba 2 NaNb 5 O 15 , Sr 2 NaNb 5 O 15 , and K 3 Li 2 Nb 5 O 15 are considered in some detail here.

CONTINUOUS OPTICAL PARAMETRIC OSCILLATION IN Ba2NaNb5O15

A tunable, optical parametric oscillator using a continuous pump is reported. The threshold was measured to be 45 mW of multimode power at .532 μ. The efficiency was found to be 1% with 300 mW of pump power.

The growth of single crystal niobates for electro-optic and non-linear applications

Abstract Single crystals of ferroelectric niobates that (1) have the tetragonal tungsten bronze or a related structure, (2) have useful electro-optic and non-linear properties, and (3) are stable to focused argon laser radiation (0.488 μm) at least to the 0.3 W level can be grown by the Czochralski technique.

Magnetic properties of a number of divalent transition metal tungstates, molybdates and titanates

Magnetization data taken between room temperature and 1.4°K are reported for MIIMVIO4 compounds (wherein MII = Mn, Co, Ni and Cu and MVI = W and Mo) for Li2M(MoO4)3 (where M = Co, Ni, and Cu) and for CoTiO3. The dependence of Neel temperature upon the electronegativity of the cation present is discussed.

SOME CHARACTERISTICS OF Ba, Sr, Na NIOBATES.

Abstract Curie temperature (T C ) and spontaneous polarization (P S ), dielectric constant (e), and voltage for half-wave retardation (V π ) of 0.6328μ radiation, all at room temperature, are given for single crystals of a Ba, Sr, Na niobate series which have tetragonal tungsten bronze-like structures. P s is a relatively constant 0.38 ± 0.02 C/m 2 for most of the series while T c varies between 560°C and 200°C. V π declines approximately linearly with increasing Sr-content and the product eV π tends to remain constant for poled crystals. Resistivity data are also given.

Mechanisms of Energy Transfer Involving Trivalent Tb and Nd in Sodium Rare‐Earth Tungstates

Self‐quenching of Nd emission from Nd4F3/2 in the Na0.5(Y, Nd)0.5WO4 tungstates (scheelite structure) and transfer from Nd4F3/2 to Tb or Eu involves dipole—dipole interactions. Self‐quenching of Nd is largely by thermally activated interactions at 295°K. However, processes requiring the simultaneous transfer of ∼600 cm−1 to the phonon spectrum are indicated for reduced temperatures. Radiative transfer between Nd ions and excitation migration between exchange coupled Tb ions to Nd sinks are observed also. Transfer from Tb to Nd from either Tb5D3 or Tb5D4 is by dipole—quadrupole interactions. Corrections for self‐quenching, internal conversion, and excessive drain time to the excited level of interest are discussed.

Mechanisms of Energy Transfer Involving Trivalent Er and Tb or Tm in Sodium Rare‐Earth Tungstates

Emission is observed from six manifolds of Er in the tungstates at 77°K. Their signatures and intrinsic lifetimes in microseconds are: Er2H9/2, <5; Er4S3/2, 25; Er4F9/2, ∼5; Er4I9/2, ∼13; Er4I11/2, 120; and Er4I13/2, ∼4500. A seventh manifold (Er2H11/2) emits when thermally populated from Er4S3/2 at 295°K. The principal transitions from all of these manifolds are to the ground manifold (Er4I15/2); as a result, radiation reabsorption is strong for each manifold and random migration of excitation between Er4I13/2 manifolds is possible at low Er concentrations. Further, due to the small spacings between the various manifolds of Er, relaxation by internal conversion processes is prevalent. Taking these factors and self‐quenching interactions of Tb5D3 and Er into account, the nonradiative transfer of energy from Tb5D3 or Tb5D4 to Er, from Er2H11/2, Er4S3/2, Er4I9/2, Er4I11/2, or Er4I13/2 to Tb, and the equivalent self‐quenching interactions of Er are all indicated to be by dipole—dipole in character.

Growth of sapphire and ruby by the Czochralski technique

Abstract An r.f. furnace and control equipment that are suitable for growing single crystals of refractory oxides, such as Al2O3, by the Czochralski technique is described and examples of sapphire and ruby boules grown using this equipment are shown. Thoria is employed throughout the furnace. Thoria has a lower heat capacity and a higher resistivity at the working temperature than any other refractory oxide. This enables iridium susceptor crucibles to be used at temperatures close to their melting point.

Mechanisms of Energy Transfer Involving Trivalent Tb and Pr

The mechanism of energy transfer between Eu and Nd and the migration of excitation between Eu ions in the Na0.5(Y, Eu, Nd)0.5Wo4 tungstates and (Y, Eu, Nd)2O3 sesquioxides are examined. Transfer from Eu to Nd appears to be predominately by dipole—dipole interactions. At high Eu concentrations energy may migrate between exchange coupled Eu ions, however, the migration requires thermal activation.

Graphical Correlation of the Néel Temperatures of Chlorides, Bromides, and Iodides of Divalent 3d Transition Metal Ions

Indirect exchange in isostructural compounds of divalent Mn, Fe, Co, and Ni increases with the electron affinities of the cations and the polarizabilities of the anions. Spin‐orbital coupling can increase TN (for Fe) in a strong trigonal field, and decrease TN in a cubic field. Exchange interactions in the chlorides, bromides, and iodides take place via double layers of anions. As a result, a higher threshold cation electron affinity is required to effect spin alignment than for single anion intermediaries. A graphical comparison of the TN values of the chlorides, bromides, and iodides as a function of the ionization potentials of the cations demonstrates the consistency of these data with those of cubic oxides and fluorides and with simple principles.