Colin D. Flint

Vibronic spectra and lattice dynamics of Cs2MnF6 and A12MIVF6:MnF2−6

The 2Eg→4A2g luminescence spectra of Cs2MnF6 and A12MIVF6:MnF2−6(A1=K, Rb,MIV=Si; A1=Cs,MIV=Si,Ge) are reported, In each case the spectrum can be analyzed into (a) the magnetic dipole allowed pure electronic orgin, (b) a set of one phonon sidebands characteristic of the lattice, (c) several bands involving two lattice phonons, (d) three strong vibronic origins corresponding to the odd vibrational modes of the anion, (e) progressions in up to three quanta of the three even anion modes based on the strong vibronic origins, and (f) bands involving combinations of one internal mode and one or two lattice phonons. Apart from small differences in the vibrational frequencies, the only difference between the spectra of the pure and the diluted compounds is the observation of the transverse–longitudinal (TO–LO) splitting of the ν3 and ν4 internal modes and an additional small splitting of the ν4 TO mode in the pure compound. The spectra are compared with the predictions of a simple lattice dynamical model for Cs2M...

Vibronic transitions in the luminescence spectrum of Cs2NaEuCl6

The luminescence spectrum of Cs2NaEuCl6 has been measured at temperatures down to 5 K. Twenty-one electronic transitions between the 5 D 0, 5 D 1 and 5 D 2 excited states and ten of the crystal field states derived from the 7 FJ have been analysed. Overlapping transitions involving different excited states are distinguished by time resolved spectroscopy. Vibronic origins involving vibrational modes of about 80, 102, 240 and 250 cm-1 are prominent and are attributed to the v 6, v 4, v 3(TO) and v 3(LO) modes of the EuCl6 3- complex ion. This contrasts with a previous assignment.

Luminescence and electrical conductivity of CsSnBr3, and related phases

Abstract The black cubic compound CsSnBr3 shows intense red luminsecene under blue light or electron beam excitation. A second emisssion band occurs in the near IR. This compound shows semiconductor behaviour with a band gap of 0.34 eV up to 303 K when a minor phase transition occurs. As bromide is replaced by chloride the emission band and the absorption edge move to higher energy and the electrical conductivity decreases by a factor of 105. These results are discussed in terms of a possible band structure.

F.t.i.r. and Raman spectra of triphenylphosphine, triphenylarsine, triphenylstibine, and dibenzylsulphide

Abstract The f.t.i.r. and Raman spectra of triphenylphosphine, triphenylarsine, triphenylstibine, and dibenzylsulphide in the solid state at ca 80 K have been recorded over the ranges 3500-40 cm−1 (infra-red, 1 cm−1 resolution) and 1650-30 cm−1 (Raman, 2 cm−1 resolution). The data, particularly those in the low wavenumber region, are more extensive, more complete, and of higher quality than those obtained in previous studies. Detailed band assignments are given.

High resolution infrared and visible luminescence spectra of ReCl6 2- and ReBr6 2- in cubic crystals

The high resolution infrared luminescence spectra of ReCl6 2- in K2PtCl6 and of ReBr6 2- in Cs2ZrBr6 have been measured between 10 000 cm-1 and 3000 cm-1 at liquid helium temperatures. Comparison with the luminescence spectra in the visible region has enabled nine luminescence transitions to be observed in the bromide and five in the chloride. These correspond to every transition between states separated by more than six quanta of the ν3 vibrational mode of the ion. Most of the transitions show extensive vibrational structure but the relative intensities of the magnetic dipole origins and the three vibronic origins vary greatly from transition to transition. The mechanisms of the various radiative and non-radiative processes are discussed.

A shell model for cross relaxation in elpasolite crystals: application to the 3P0 and 1G4 states of Cs2NaY1−xPrxCl6

Abstract A model for cross relaxation in high symmetry systems is developed. The positions of all acceptor ions and all multipole-multipole interactions may be included. The geometric factors are explicitly considered. A feature of the model is that it enables decay rates and the form of decay curves to be predicted a priori if the exponential decay curves of very dilute and stoichiometric materials are experimentally accessible. The model is applied to the title system and excellent agreement with experiment is achieved.

Vibronic intensities in the electronic spectra of transition metal ions

The relative vibronic intensities of the vibronic origins due to the three odd parity vibrational modes have been calculated for the 2 Eg ↔2 A 2g transition of the octahedral MnF6 2- ion, using a crystal field model. Two methods for treating the sum over the intermediate odd parity states are considered, the closure approximation and the single 4 T 2u d 2 p state method. It is shown that in the latter limit the relative vibronic intensities depend only on the vibrational force field whereas using closure there is also some dependence on the radial functions employed. Calculations using six different force fields and several radial functions are presented several of which reproduce the experimental relative intensity for both methods, although there is a strong dependence of the calculated intensity on the force field.

Vibronic spectra of U 4 + in octahedral crystal fields IV. Absorption spectra and crystal field calculations

The absorption spectra of UCl2- 6 diluted into the cubic lattices Cs2ZrCl6 and Cs2SnCl6, and of UBr2- 6 diluted into Cs2ZrBr6 have been measured at liquid helium temperatures. The derived energy levels, together with earlier luminescence measurements have been used to evaluate the crystal-field, spinorbit coupling, inter-electron repulsion and Trees correction parameters and the corresponding eigenvalues. Several of the states are derived from an almost equal admixture of two or more Russell-Saunders terms. Some magnetic properties are also computed and discussed.

Second-order Jahn—Teller effect in the 2Eg state of d3 ions

Abstract Comparison of the vibronic structure of the 2 Eg 2 → 4 A 2g transition in Cs 2 MnF 6 and K 2 NaGaF 6 :Cr 3+ indicates that a second-order Jahn—Teller effect is operative in the 2 E g state of these compounds.

Site-selective spectroscopy of the uranyl ion in borosilicate glass

Abstract The spectra of the uranyl ion in borosilicate glasses were investigated at room temperature and at 15 K using conventional and site-selective laser spectroscopy. Time-resolved spectra were taken at 15 K. Site-selective spectroscopy reveals a structured emission band which exhibits characteristic vibronic bands. No energy transfer was observed between the various subsets of uranyl sites which correspond to definite excitation wavelengths.