ELECTROLUMINESCENCE OF RARE EARTHS-DOPED SEMICONDUCTING ZINC-OXIDE ELECTRODES - KINETICS ASPECTS OF THE ENERGY-TRANSFER BETWEEN SM3+ AND EU3+

The electroluminescence emission of triply charged rare earth ions (Sm3+ and Eu3+) inserted in a semiconducting zinc oxide matrix has been observed in RE3+ doped ZnO electrodes in contact with aqueous electrolytes. Under cathodic polarization, the sole luminescence found is that of ZnO. On the contrary, with an anodic polarization (ca. +9.8 V/SCE) only the characteristic emission of the two rare earth ions Sm3+ and Eu3+ is observed. The energy transfer between Sm3+ (donor) and Eu3+ (acceptor) has been investigated with electrodes containing both rare earth ions. For low donor concentrations ( < 0.6 at.%), the excitation is found to be transferred directly to the acceptor without significant migration of the energy between the donor ions. The energy transfer experimental results are consistent with a dipole-dipole interaction mechanism in which the energy transfer coupling constant of the Sm3+ (4G5/2 --> H-6(5/2)) to the EU3+ (5D0 --> F-7(2)) system is of the order of C = 4.0 x 10(-42) cm6 s-1.