EPR AND ENDOR INVESTIGATION OF SINGLE CRYSTALLINE AND POWDERED NaCl:Rh2+ and AgCl:Rh2+

Abstract Single crystalline NaCl doped with Rh 2+ was investigated with electron paramagnetic resonance (EPR) and electron nuclear double resonance (ENDOR). An orthorhombic Rh 2+ centre was found similar to that observed previously in AgCl, where Rh 2+ substitutes for Na + forming an [RhCl 6 ] 4− complex elongated along a [001] axis with a charge compensating Na + vacancy in a second nearest Na + position in the equatorial plane. In addition, two further axial Rh 2+ centres were found, where the Na + vacancy is not in the nearby equatorial plane. In the powder ENDOR spectra of NaCl:Rh 2+ the interactions with axial second nearest 23 Na and axial 103 Rh nuclei could be resolved. Powder ENDOR spectra of AgCl:Rh 2+ precipitated from aqueous solution showed that the Rh 2+ defect is different from that generated in Rh 2+ -doped AgCl grown from the melt. The limitations and possibilities of powder ENDOR are discussed. © 1997 Elsevier Science Ltd