Catalytic role of adsorbates in the photoluminescence emission of Si nanocrystals

Abstract

Silicon nanocrystals were synthesized and deposited on different substrates. In order to clarify the photoluminescence ͑PL͒ 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.

Giant photoluminescence emission in crystalline faceted Si grains

“…The broad PL spectrum covers the wide range from the red wavelength up to the visible border. A further investigation of the lifetime as a function of the frequency, could add information on the relative percentages between radiative and non-radiative processes distinguishing direct and indirect processes, and allowing the determination of specific quantum yield of emitted PL32.…”

“…Moreover Hydrogen degases quickly at relatively low temperature (400°C), and therefore cannot influence the PL emission at least at the highest temperatures33. In contrast, a substoichiometric oxide layer formed when the fg-Si is exposed to air after deposition can enhance the effect because of two reasons: the first is related to a possible action as antireflection coating of the incoming radiation, the second could be due to a phonon trapping by the surface oxide32.…”

Laser induced heating of Si nanocrystals

“…It is widely accepted that the optical properties of silicon nanocrystals are strongly dependent on both quantum confinement effects and structural and chemical surface characteristics [6][7][8][9] which have a dominant role in a nanoscale regime. As a consequence of the low dimensionality, the fundamental physical properties may be quite different from those of a bulk crystal.…”

Strong infrared photoluminescence in highly porous layers of large faceted Si crystalline nanoparticles

“…In particular, quantum confinement increases the band gap energy 1 and induces also some other attractive electronic and optical properties. This research has opened important new perspectives for applications of Si nanocrystals 2 for, e.g., visible optoelectronics 3 4 5 6 , photovoltaics 7 8 9 10 11 and in medicine 12 . In spite of the impressive progress, size definition represents a major challenge and low-temperature production of Si nanocrystals with truly narrow size distribution remains elusive.…”