Highly Luminescent, Size- and Shape-Tunable Copper Indium Selenide Based Colloidal Nanocrystals

Abstract

We report a simple, high-yield colloidal synthesis of copper indium selenide nanocrystals (CISe NCs) based on a silylamide-promoted approach. The silylamide anions increase the nucleation rate, which results in small-sized NCs exhibiting high luminescence and constant NC stoichiometry and crystal structure regardless of the NC size and shape. In particular, by systematically varying synthesis time and temperature, we show that the size of the CISe NCs can be precisely controlled to be between 2.7 and 7.9 nm with size distributions down to 9–10%. By introducing a specific concentration of silylamide-anions in the reaction mixture, the shape of CISe NCs can be preselected to be either spherical or tetrahedral. Optical properties of these CISe NCs span from the visible to near-infrared region with peak luminescence wavelengths of 700 to 1200 nm. The luminescence efficiency improves from 10 to 15% to record values of 50–60% by overcoating as-prepared CISe NCs with ZnSe or ZnS shells, highlighting their potential for applications such as biolabeling and solid state lighting.

Energy band structure ofCuInS2and optical spectra ofCuInS2nanocrystals

“…The PL line measured in large-size CuInS 2 NCs is below the bulk absorption edge 16,18 and hence this line is likely associated with deep defects created by the Cu vacancies.…”

“…In addition, the absorption energy gap and photoluminescence in these materials are tunable over a wide range of the spectrum, from the near-infrared through the visible to the ultraviolet. [15][16][17][18] These flexible optical properties, combined with non-toxicity, indicate the great potential of CuInS 2…”

Independent Composition and Size Control for Highly Luminescent Indium-Rich Silver Indium Selenide Nanocrystals

“…[1][2] After ten years of research, I-III-VI NCs now boast photoluminescence (PL) efficiencies of 86% for Cu-In-S, 3 68% for Ag-In-S, 4 60% for Cu-In-Se, [5][6] and 40% for AgIn-Se systems. 7 These high luminescent efficiencies along with long-term photostability, size and composition tunable electronic structure, reduced self-absorption, and lower toxicity put I-III-VI colloids well on their way to potential use in display, lighting, bio-medical applications.…”

“…15 Cu 3 In 5 E 9 (E = S, Se), one of the ODC compositions of the Cu-In-S and Cu-In-Se systems, exhibits peak luminescent efficiencies prior to ZnE shell coating. 6,14 For Ag-In-S materials, indium-rich AgIn 5 S 8 ODC NCs also possess superior PL QYs with respect to AgInS 2 composition. 16 4 Synthetically, Ag-In-Se (AISe) colloids are the least developed of highly luminescent, indiumcontaining I-III-VI NCs 10 because of two main problems in their synthesis: (i) Ag (I) compounds easily reduce to metallic Ag (0) , which eliminates many silver sources, and (ii) Ag + is a soft acid while In 3+ is a hard acid, which leads to imbalanced Ag and In reactivity during the nucleation as explained by the hard and soft acids and bases theory.…”

Incorporation of luminescent semiconductor nanoparticles into liquid crystal matrix

“…One can substitute the values for CuInS 2 , which are following: the energy gap for bulk material E g ¼1.53 eV [15], reduced effective electron-hole pair mass m ¼0.142m 0 , when taking effective electron and hole masses equal 0.16m 0 and 1.3m 0 [16] (m 0 is electron rest mass) and dielectric constant ε¼10.2 [17]. Resulting function is non-monotonical as opposed to empirical dependence found for CuInS 2 [13] and similar material-CuInSe nanoparticles [18] and the obtained value is about 0.8 nm, what is 1.6 nm as diameter of a sphere. Some empirical results shown, that the prediction is not exact and second term in Eq.…”