Intraband spectroscopy and photophysics inGaSenanoparticles

Abstract

The spectroscopic and dynamical characteristics of electron and hole intraband transitions in small ͑2.7 nm͒, mid-sized ͑4.9 nm͒, and large ͑12 nm͒ GaSe nanoparticles have been studied using polarized femtosecond transient absorption spectroscopy. Assignments of the observed absorptions are made in terms of the known band structure and an effective mass model in which the electron and hole states are described by particle-ina-cylinder states. The energies and relative intensities of the optical transitions are calculated. Assignments of the dynamical aspects of the spectra are facilitated by comparison with time-resolved polarized fluorescence results. The results on the large particles indicate that the transient absorption spectrum is dominated by a size-independent, z-polarized hole intraband transition having an absorption maximum at about 600-650 nm. In addition, there is a smaller contribution from a broad x , y-polarized transition. The small particle spectra exhibit the same z-polarized hole transition and a much more intense x , y-polarized transition. The x , y-polarized absorption is assigned to an electron charge transfer transition from the conduction band to particle surface ͑edge͒ states. The intensity of this transition depends on the particle size and the momentum state ͑⌫ or M͒ of the electron. ⌫ to M electron momentum relaxation is responsible for the fast decay of the x , y-polarized electron transition in the small particles. This fast decay is not present in the large particles because the relative energetics of the M to ⌫ states are size dependent and are in reverse order, compared to the small particles. Relative intensities of the x , y-polarized electron transition may be semiquantitatively understood in terms of overlap considerations calculated from a simple two-dimensional, particle in a nonrigid box model.

Synthesis and characterization of colloidal gallium selenide nanowires

“…The spectra look very similar to that of GaSe nanodiscs aggregates [9][10][11]. They contain lower and higher energy absorbance bands, connected with z polarized and xy polarized transitions in GaSe nanodiscs respectively.…”

“…Presented study first to date illustrates the possibility of colloidal GaSe nanowires arrays formation. Such objects looked problematic to be obtained in the case of employing highly reactive metalorganic precursor in alkylphosphonic solutions mainly due to an inability of the growth processes to compete with that of the nucleation [9][10][11]. So the aim of this work was a development of the new 'greener' synthesis of GaSe nanocolloids.…”

Effect of the phosphorous-containing ligands on synthesis and properties of GaSe nanoparticles

“…Earlier investigations, conducted on GaSe syntheses [6][7][8] imply that above-mentioned particles were stabilised and capped either by distilled TOP/TOPO ligands (like II-VI core/shells), being weakly bonded; thus, not allowing prolonged storage of such particles or by strongly bonded intrinsic anhydride. The last one was formed by thermal treatment of technical TOP/TOPO mixtures.…”

“…Thus, numerous precipitation/redissolving cycles are impossible and even careful washing of the precipitate does not allow to get completely rid out of the ligating complexes. Since the spectroscopic properties of TOP/TOPO (i.e., TOPSe/TOPO)-capped GaSe particles were subject of many reports, we omit them and refer the reader to original works [6][7][8]. Figure 3 illustrates UV-Vis absorbance of OPA-capped particles.…”

“…Among the variety of semiconductor nanoparticles, layered III-VI compounds in low-dimensional forms have already reached the level of implementation in microelectronic devices due to their unique anisotropic properties [1,2]. Nevertheless, colloidal III-VI nanostructures investigations are far from the successful II-VI compounds and limited by several reports on the single-source metalorganic precursor [3,4], amine-capped particles syntheses from metal chloride [5] and growth by reaction of metalorganic precursor with trioctyphosphine (TOP) selenium in alkylphosphonic solvent [6][7][8]. The last method appeared to be strictly dependent on the TOP impurities and generally is irreproducible in pure TOP/TOPO solvents.…”