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Photonic crystals doped with fluorescent nanoparticles offer a plenty of interesting applications in photonics, laser
physics, and biosensing. Understanding of the mechanisms and effects of modulation of the photoluminescent properties
of photonic crystals by varying the depth of nanoparticle penetration should promote targeted development of
nanocrystal-doped photonic crystals with desired optical and morphological properties. Here, we have investigated the
penetration of semiconductor quantum dots (QDs) into porous silicon photonic crystals and performed experimental
analysis and theoretical modeling of the effects of the depth of nanoparticle penetration on the photoluminescent
properties of this photonic system. For this purpose, we fabricated porous silicon microcavities with an eigenmode width
not exceeding 10 nm at a wavelength of 620 nm. CdSe/CdS/ZnS QDs fluorescing at 617 nm with a quantum yield of
about 70% and a width at half-height of about 40 nm were used in the study. Confocal microscopy and scanning electron
microscopy were used to estimate the depth of penetration of QDs into the porous silicon structure; the
photoluminescence spectra, kinetics, and angular fluorescence distribution were also analyzed. Enhancement of QD
photoluminescence at the microcavity eigenmode wavelength was observed. Theoretical modeling of porous silicon
photonic crystals doped with QDs was performed using the finite-difference time-domain (FDTD) approach. Theoretical
modeling has predicted, and the experiments have confirmed, that even a very limited depth of nanoparticle penetration
into photonic crystals, not exceeding the first Bragg mirror of the microcavity, leads to significant changes in the QD
luminescence spectrum determined by the modulation of the local density of photonic states in the microcavity. At the
same time, complete and uniform filling of a photonic crystal with nanoparticles does not enhance this effect, which is as
strong as in the case of a very limited depth of nanoparticle penetration. Our results will help to choose the best
technology for fabrication of efficient sensor systems based on porous silicon photonic crystals doped with fluorescent
nanoparticles.
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