Electron spin resonance and electron-nuclear double-resonance investigation of a new Cr³⁺defect on an Nb site in LiNbO₃:Mg:Cr

Abstract

For LiNbO3 crystals heavily doped with Mg and codoped with Cr a single isotropic ESR line with g=1.971+or-0.002 and a minimal linewidth of 1.8+or-0.2 mT has been observed. With ENDOR it could be shown unambiguously that the new defect is Cr3+ substituting for Nb. The 53Cr hyperfine and quadrupole constants are A/sub ///=50.8+or-0.2 MHz, Aperpendicular to =51.0+or-0.2 MHz and P=0.10+or-0.05 MHz. The crystal field at the chromium site is smaller by more than an order of magnitude than for previously reported Cr3+ centres in LiNbO3, indicating that those centres are not on the Nb site.