RECOMBINATION LUMINESCENCE QUENCHING OF NONSTOICHIOMETRIC CDS CLUSTERS BY ZNTPP

The recombination luminescence of CdS(e-/h+) clusters is quenched effectively by ZnTPP. The quenching process is described by static interactions at low [ZnTPP], leading to a quenching constant <K(Q)>, and by Langmuir isotherms, leading to adsorption-desorption equilibrium constants K. Values of <K(Q)>, ranging from 5 x 10(4) to 2.5 x 10(5) M-1, increase slightly with decreasing cluster size (or increasing Eg value) at constant CdS cluster composition. On the other hand, values of <K(Q)> decrease slightly with increasing Cd2+ nonstoichiometry (i.e., Cd2+ excess) at constant Eg value. Values of K range from 1.5 x 10(5) to 9.5 x 10(5) (i.e., k(ads) >> k(des)), implying a strong binding of ZnTPP on the surface of CdS clusters. Treatment of recombination luminescence quenching by Poisson statistics indicates that an average CdS cluster consists of at least 100-150 CdS units (i.e., 25-30-angstrom diameters). Fluorescence quenching of 1ZnTPP*(S1) by CdS is less efficient, and it is dependent upon the size of the cluster. Values of k(Q)tau-degrees(1ZnTPP*) range from 0 to 2 x 10(3) M-1 for Eg values varying from 3.1 to 2.9 eV.