Catalytic role of adsorbates in the photoluminescence emission of Si nanocrystals

Silicon nanocrystals were synthesized and deposited on different substrates. In order to clarify the photoluminescence (PL) emission of these agglomerates, we studied the luminescence spectra of several samples as a function of the exposure to air, oxygen, nitrogen, and rare gases. Measurements at different pressures reveal a strong enhancement of the PL at atmospheric pressure, when the sample is in air. In contrast no significant PL is observed for clean Si quantum dot in rare-gas atmosphere and in air at low pressure. Different behavior is detected in oxygen and in nitrogen as a function of the pressure. These data point out a catalytic role of the surface adsorption adding significant information for clarifying the PL mechanism. A comparison of our results, including the decay-time spectra with data and models of literature, demonstrates the important role of the phonon interaction in the relaxation and decay processes.