EVIDENCE FOR ADDUCT FORMATION AT THE SEMICONDUCTOR-SOLUTION INTERFACE - PHOTOLUMINESCENT PROPERTIES OF CADMIUM SELENIDE IN THE PRESENCE OF LANTHANIDE BETA-DIKETONATE COMPLEXES

Photoluminescence (PL) measurements of etched, single-crystal n-CdSe demonstrate that the semiconductor surface engages in adduct formation with a family of lanthanide β-diketonate complexes, Ln(fod)3 (Ln = lanthanide; fod = 6,6,7,7,8,8,8-heptafluoro-2,2-dimethyl-3,5-octanedionato anion), in isooctane solution. Exposure of CdSe to Ln(fod)3 complexes reversibly decreases the red band edge PL of the semiconductor relative to an isooctane ambient. The PL changes were fit to the Langmuir adsorption isotherm model to yield adduct formation constants that increase monotonically across the lanthanide series: values range from ∼102 M-1 for the early lanthanides to ∼103 M-1 for the late lanthanides, paralleling the cross-period trend in lanthanide acidity. The changes in PL are in accord with a dead-layer model, permitting the determination of the expansion in depletion width in the semiconductor resulting from adduct formation; expansions in depletion width, typically hundreds of angstroms, do not follow the trend in adduct formation constants but appear to correlate with contact shifts calculated for use of the lanthanide complexes as NMR shift reagents. © 1990 American Chemical Society.