Evolution of excitonic states in two-phase systems with quantum dots of II–VI semiconductors near the percolation threshold

Exciton photoluminescence and energy in a percolation cluster of ZnSe quantum dots as a fractal object

“…In such sub threshold conditions, almost all QDs retain their indi viduality (black circles) and the quantum confined BONDAR, BRODYN exciton state. The size dispersion of QDs means that the radii of some of the QDs exceed the critical radius (R c ≈ 30 Å in the case under consideration) and, there fore, there is no exciton quantum confinement effect in these QDs [13]. As already shown in [13][14][15], the quantum confinement effect disappears through the trapping of one or both charge carriers of the exciton into the external polarization well (dielectric trap).…”

“…In [13][14][15], from analysis of the results, we established the formation of a percolation transition of excitons in the array of QDs and sug gested a mechanism for such a transition in a two phase system with an interphase permittivity mis match. However, in [13][14][15], we did not discuss the manifestation of structural elements of the percolation cluster in the PL spectra of the samples. That is why investigation of this issue is the principal goal of the study presented here.…”

“…Let us briefly recall the main results obtained pre viously in [13][14][15]. Figure 1a shows the absorption spectrum of the matrix (dashed curve) and the PL bands of the samples under study.…”

“…The sol-gel method of ZnSe QD production and the optical spectra of the samples were described by us previously [13][14][15]. In [13][14][15], from analysis of the results, we established the formation of a percolation transition of excitons in the array of QDs and sug gested a mechanism for such a transition in a two phase system with an interphase permittivity mis match.…”

“…As the ZnSe content is increased further, the position of the bands in the PL spectrum ceases changing (curves 4, 5), but the intensities of these bands continue to increase. In [13][14][15], it was noted that the drastic change in the shape and position of the PL spectrum (curves [3][4][5] was caused by the percolation transition of excitons in the matrix. This transition makes it possible to observe PL signals relevant to lh excitons (the short wave length band of curves 3-5).…”