Sol−Gel Synthesis and Spectroscopic Properties of Thick Nanocrystalline CdSe Films

Abstract

Two novel metal alkoxide-derived routes were developed for the synthesis of nanocrystalline CdSe layers with quantum dot sizes between 1 and 4 nm. The first route, where cadmium ethoxy−acetate is reacted with bis(trimethylsilyl)selenium in the presence of aminopropyltriethoxysilane (AMEO), yields highly concentrated alcoholic 0.5 M sols for direct coatings. The second route allows to grow CdSe clusters by infiltrating the selenium precursor into Cd-enriched organosilicate gel layers. The resulting optically transparent films with thicknesses near 10 μm (obtained in a single-step coating) were characterized by steady-state optical absorption and photoluminescence spectroscopy, high-resolution electron microscopy (HRTEM), X-ray diffraction (XRD), resonance Raman, and time-resolved photoluminescence spectroscopy. The experimental data reveal the presence of nanocrystals exhibiting a tetrahedral shape. The quantum dot films are strongly fluorescing, with a quantum yield near 10%. The decay characteristics of the photoluminescence signal after pulsed excitation is discussed taking into account the splitting of the quantum dot ground state as well as the influence of surface states. Furthermore, a size-dependent shift of the Raman band, attributed to the longitudinal optical phonon of the consolidated CdSe clusters, could be observed. This shift is accompanied by a broadening of the corresponding Raman line width. Both effects, the size-dependent shift as well as the broadening of the Raman line width, indicate that phonon confinement is present for the clusters under consideration.

Luminescence and Amplified Stimulated Emission in CdSe–ZnS‐Nanocrystal‐Doped TiO2 and ZrO2 Waveguides

“…[15] Such sol-gel matrices have also been found to be excellent hosts for organic chromophores, [16,17] erbium cations, [18,19] and indeed quantum dots (QDs). [20][21][22] Truly optically 'photoluminescence (PL)-active' waveguides have been however ridden with obstacles. The main obstacle is the high annealing temperature needed to achieve densified materials.…”

Size-dependent spectroscopic, optical, and electrical properties of PbSe nanoparticles

“…PbSe microcrystallites have been used to induce the second-harmonic generation of the IR in the range of (5-15 µm) [21]. There are several methods for the preparation of selenides including solid state reaction [22], electrochemical methods [23,24], microwave assisted preparation [25,26], chemical path deposition [27][28][29][30], high temperature pyrolysis of single source precursors [31,32], vacuum deposition [33], H 2 Se methods [34][35][36], and photochemical methods [37]. The PbSe NPs with a spherical 8 nm and rectangular 25 nm shapes are obtained with different capping agents [38].…”

Wet synthesis of nearly monodisperse CdSe nanoparticles at room temperature

“…A variety of methods can be used for the formation of selenides, such as solid-state reaction [1], solid-state metathesis [2], self-propagating high-temperature synthesis [3], and the electrochemical method [4][5][6]. Organometallic precursors have also been used to obtain selenides [7][8][9]. In contrast to these techniques [1][2][3][4][5][6][7][8][9], the solution reaction growth technique appears to be the cheapest and most convenient approach to prepare the selenides because it does not involve special instrumentation and the growth rate of selenides crystals can be easily controlled.…”

“…Organometallic precursors have also been used to obtain selenides [7][8][9]. In contrast to these techniques [1][2][3][4][5][6][7][8][9], the solution reaction growth technique appears to be the cheapest and most convenient approach to prepare the selenides because it does not involve special instrumentation and the growth rate of selenides crystals can be easily controlled.…”