LUMINESCENCE OF TETRAHEDRALLY COORDINATED CO2+ IN ZIRCONIA

Co2+ enters the lattice of zirconia stabilized with a 46% of yttria in fourfold coordinated cation sites. The absorption spectrum consists m ainly of two triplets, one of which is rather weak at around 5500 cm-1 (corresponding to the 4A2 --> 4T1(4F) transition), while the other is very intense at around 15 175 cm-1 corresponding to the 4A2 --> 4T1 ( 4P) transition. Excitation in the visible region produces two strong b road emission bands at 13330 and 10 420 cm-1 due to the 4T1(4P) --> 4A 2 and 4T1(4p) --> 4T2(4F) transitions respectively. The lifetime of th e emitting level is congruent-to 0.75 mus at 10 K. The structure of th e triplet states is caused by the combined effect of spin-orbit and Ja hn-Teller interactions which, besides the splitting of the cubic level s, produce a strong admixture of some spin doublets With the 4T1(4P) l evel. We have calculated the energy levels using the Eisenstein matric es thus taking into account both Coulomb, crystal field and spin-orbit interactions. The best fit with the experimental measurements is obta ined for the following values of the parameters. 10Dq = 3025 cm-1, B = 720 cm-1, C/B = 4.0 and spin-orbit constant zeta3d = -515 cm-1. The 4 T1 (4P) emission suffers a strong thermal quenching at temperatures ab ove 100 K. The evolution with temperature of the intensity of the phot oluminescence and its decay curves are discussed with reference to the energy level diagram of the ion and the defective character of the sa mple. er of the sample.