The distance dependence of the fluorescence efficiency from Langmuir Blodgett (LB) dye layers deposited on top of silicon substrates was studied for different silicon crystal orientations (< 100 > and < 111 >). The distance to the silicon surface was varied with stearic acid LB layers (SA). Spectroscopic Ellipsometry (SE) provided accurate measurements of the thickness of the separation steps and the refractive index of the dye layer. It was found that the fluorescence efficiency of the overlying LB dye layers was quenched significantly by the presence of the semiconductor at close distances to the surface. No significant difference in the fluorescence quenching for the LB dye between the two crystal orientations was observed. The results obtained are compared with previous work from fluorescence time and intensity measurements. The importance of interference effects is stressed at high semi conductor-dye distances but the fluorescence quenching observed at small distances is due to efficient energy transfer to the semiconductor. (c) 2007 Elsevier B.V. All rights reserved.