An Optically Detected Electron-Paramagnetic-Resonance Study of the Luminescent Triplet State of Fresnoite, Ba(2)TiSi(2)O(8)

The luminescent center of the fresnoite crystal has been studied by electron paramagnetic resonance with optical detection at temperatures between 0.5 and 10 K. The results prove that the strong blue-green luminescence originates from a spin triplet state that is centered on the Ti ion. The C(4) symmetry of the Ti site is lost on excitation through a static Jahn-Teller effect, and eight sets of equivalent, strongly inhomogeneously broadened optically detected EPR signals appear. The signals are described by a spin hamiltonian with S = 1, vertical bar D vertical bar approximate to 70 GHz, vertical bar E vertical bar = 3.02 GHz, g(zz) = 1.93, and g(xx) = g(yy) g(e) = 2.0023. The lifetimes of the three sublevels are t(x) = 3.4, t(y) = 30, t(z) = 23 ms; the dominant radiative decayis from tau(x) and polarized perpendicular to the c axis.