Fluorescence of Niobium-Activated Antimonates and an Empirical Criterion for the Occurrence of Luminescence

The fluorescence of Nb5+-activated antimonates is reported. A relation has been found between the position of the maximum of the excitation (and absorption) band of the niobate octahedra and the quenching temperature of their fluorescence. This result can be explained using a simple configuration-coordinate diagram. The displacement of the equilibrium distance of the excited state relative to the ground state can be estimated from the set of radii derived by Waber and Cromer for the principal maxima in the radial wavefunctions of the elements. It is shown that the estimated displacement of the excited state should be 0.3 Å or less to have efficient fluorescence from this state.