EFFECTS OF CHROMOPHORE DISSOCIATION ON THE OPTICAL-PROPERTIES OF RARE-EARTH-DOPED POLYMERS

The observed dissociation of tetrakis rare-earth chromophores in rare- earth-doped organic polymers is reported, and a time-resolved spectros copic technique is presented to determine quantitatively the fractiona l concentrations of different chromophore species in various solvents. Based on this technique, the equilibrium constants of tetrakis rare-e arth chromophores in rare-earth-doped polymers are determined. Thus, t he equilibrium constants for tetrakis rare-earth compounds of benzoylt rifluoroacetonate (BTF), for example, Sm(BTF)(4)P and Eu(BTF)(4)P in m ethyl methacrylate monomer, are K = 4.7 +/- 0.5 x 10(-4) M and K = 1.2 +/- 0.5 x 10(-4) M, respectively. In contrast, the tetrakis rare-eart h compounds of hexafluoroacetylacetonate (HFA), for example, Sm(HFA)(4 )Net(4) and Eu(HFA)(4)Net(4), are quite stable and show no evidence of dissociation. We further characterize the dissociation of several chr omophore systems and discuss the influence such dissociation has on ov erall optical performance. The results enable determination of optimal doping concentrations as well as preferred rare-earth chromophore pre paration and doped polymer fabrication procedures. (C) 1998 Optical So ciety of America.