Stimulated blue emission in reconstituted films of ultrasmall silicon nanoparticles

We dispersed electrochemical etched Si into a colloid of ultrabright blue l uminescent nanoparticles (1 nm in diameter) and reconstituted it into films or microcrystallites. When the film is excited by a near-infrared two-phot on process at 780 nm, the emission exhibits a sharp threshold near 10(6) W/ cm(2), rising by many orders of magnitude, beyond which a low power depende nce sets in. Under some conditions, spontaneous recrystallization forms cry stals of smooth shape from which we observe collimated beam emission, point ing to very large gain coefficients. The results are discussed in terms of population inversion, produced by quantum tunneling or/and thermal activati on, and stimulated emission in the quantum confinement-engineered Si-Si pha se found only on ultrasmall Si nanoparticles. The Si-Si phase model provide s gain coefficients as large as 10(3)-10(5) cm(-1). (C) 2001 American Insti tute of Physics.