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

For LiNbO 3 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 Cr 3+ substituting for Nb. The 53 Cr hyperfine and quadrupole constants are A/sub ///=50.8+or-0.2 MHz, A perpendicular 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 Cr 3+ centres in LiNbO 3 , indicating that those centres are not on the Nb site.