Abstract

We dispersed electrochemical etched Si into a colloid of ultrabright blue luminescent nanoparticles (1 nm in diameter) and reconstituted it into films or microcrystallites. When the film is excited by a near-infrared two-photon process at 780 nm, the emission exhibits a sharp threshold near 106 W/cm2, rising by many orders of magnitude, beyond which a low power dependence sets in. Under some conditions, spontaneous recrystallization forms crystals of smooth shape from which we observe collimated beam emission, pointing to very large gain coefficients. The results are discussed in terms of population inversion, produced by quantum tunneling or/and thermal activation, and stimulated emission in the quantum confinement-engineered Si–Si phase found only on ultrasmall Si nanoparticles. The Si–Si phase model provides gain coefficients as large as 103–105 cm−1.

Highlights

  • The discovery in 1990 of visible red luminescence by Canham and co-workers[1,2] in electrochemical etched Si surprised the scientific community, since Si is an indirect gap material

  • we demonstrated another surprising effect of the presence of micron-size regions that are rich in ultrasmall structures

  • for which the intensity of the luminescence has a sharp threshold near an average intensity of 106 W

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