Electron nuclear double resonance of stable Rh centers in solution-grown NaCl single crystals

Abstract

Unlike the photographically important silver halides, large NaCl single crystals can be grown from solution. In such NaCl crystals, with doping comparable to practical AgCl and AgBr microcrystals, three stable Rh centers were detected and studied by electron paramagnetic resonance (EPR) and electron nuclear double resonance (ENDOR). The primary center was identified as a nonlocally compensated [RhCl6]4− complex, at variance with earlier reported EPR work. By lack of sufficient EPR and/or ENDOR evidence, the identity of the two other Rh related centers with orthorhombic and isotropic symmetry respectively, remains rather speculative.

Optical transitions ofRh2+in NaCl crystals studied by electron spin resonance and magnetic circular dichroism

“…3 The properties of the other two Rh 2ϩ centers O͑I͒ and O͑II͒ are quite similar. The Rh 2ϩ RTAX ESR spectra, for Hʈ͗100͘ and ͗110͘, are presented in Fig.…”

“…This center is identified as being not locally charge compensated. 3 In subsequent ESR and optical experiments the foregoing procedure was shortened to a simple warm-up to room temperature after x irradiation at 77 K and an exposure to ambient light. Sometimes this procedure was repeated once or twice in an attempt to enhance the RTAX Rh 2ϩ concentration.…”

“…At that time, the presence of two symmetrically placed cation vacancies along ͗001͘ was proposed in order to explain the charge compensation and axial symmetry of the ESR spectrum. In a recent paper 3 the center was reexamined, both with ESR and electron nuclear double resonance ͑ENDOR͒ and was established to be uncompensated. This Rh 2ϩ center, which possesses D 4h symmetry, will be referred to as the RTAX center and is the subject of this paper.…”

“…Rh 2ϩ centers with quantitatively quite similar g and hyperfine matrices, implying the same 4d z 2 ground state, were observed in Bridgman-grown 4 AgCl and NaCl single crystals 5 and in solution-grown AgCl microcrystals 1 and NaCl single crystals. 3,6,7 The optical absorption spectrum of the Rh 3ϩ (4d 6 ) complex in solution is known to consist of two vibronically allowed dϪd transitions near 19 300 cm Ϫ1 and 24 330 cm Ϫ1 and they were associated with A 1g (t 2g 6 )→ 1 T 1g , 1 T 2g (t g 5 e g 1 ) transitions. 8 In a recent paper 9 the analogous transitions were found at 18 700 cm Ϫ1 and 23 750 cm Ϫ1 in solution-grown Rh 3ϩ doped NaCl single crystals.…”

Theoretical study of the electron paramagnetic resonance parameters and local structure for the tetragonal Ir2+ centre in NaCl

“…Generally, these properties are closely related to the local structures and electronic states of the dopants in this material, which can be conveniently investigated by means of electron paramagnetic resonance (EPR). In general, EPR studies of transition-metal ions in NaCl are largely confined to the first (3d n ) and second (4d n ) groups [5][6][7], while those on the third group (5d n ) transition-metal ions in this material are relatively fewer. For example, EPR and electron nuclear double resonance (ENDOR) studies were carried out on iridiumdoped solution and melt-grown NaCl single crystals after X-ray irradiation at 77 K [8,9], and the EPR parameters (the anisotropic g factors, the hyperfine structure constants and the superhyperfine parameters) were measured for the tetragonal Ir 2+ centre [8,9].…”