Using a Layer‐by‐Layer Assembly Technique to Fabricate Multicolored‐Light‐Emitting Films of CdSe@CdS and CdTe Quantum Dots

Abstract

The fabrication of hybrid structures of quantum dots (QDs) having sizes in the range from 2 to 6 nm is currently of interest because of their unique optical and electronic properties. [1,2] Although applications of such films have yet to be realized, QD films show promise for the development of, for example, novel multiplexed biological sensors, [3] photonic and optoelectronic devices, [4] electronic memory devices, [5] and multicolored-light-emitting diodes [6] (LEDs). Owing to their ease of preparation, high quantum yields (QYs), and tunable emissions in the visible range, CdSe and CdTe QDs are undoubtedly among the most promising materials used for the fabrication of fluorescent thin films. The techniques that are currently used for the construction of thin films-such as phase separation, [7] Langmuir-Schäfer deposition, [8] Langmuir-Blodgett transfer, [9] and layer-bylayer (LBL) assembly [10][11][12] -should also be useful for the fabrication of QD films. Of these approaches, LBL assembly using polyelectrolytes is one of the most efficient methods for fabricating thin films, mainly because of its low cost and simplicity, its independence of substrate size and topology, and the good mechanical and chemical stabilities of the resulting films. [10][11][12] For example, LEDs that emit a single color in the wavelength range 500-700 nm have been fabricated through LBL assembly of charged CdSe QDs with their oppositely charged polymers. [13,14] When used in conjunction with photolithography or electron-beam patterning, the LBL assembly technique can provide precise control over the deposition of QDs; these approaches have been applied to the fabrication of certain patterned QD films. [15,16] Alternatively, microcontact printing has been used to fabricate three-dimensional surface structures containing highly fluorescent CdSe-ZnS coreshell QDs.[17] Fluorescent micropatterns consisting of a bilayer of 3.4 nm cationic polyallylamine and 7.8 nm anionic CdSeZnS core-shell QDs treated with mercaptoacetic acid, which are green and red, respectively, have been fabricated using a LBL assembly technique.[18] Multicolor QD patterns have been obtained through photoactivation of thin solid films of low-quantum-efficiency citrate-stabilized CdSe/CdS core/shell (CdSe@CdS) QDs with poly(diallyldimethylammonium chloride) (PDDA) by applying a LBL assembly technique.[19] The applications of QD thin films can be further optimized through the fabrication of graded semiconductor films of QDs. Graded films have been prepared through LBL assembly using PDDA and thioglycolic acid-stabilized CdTe QDs of four different sizes, which exhibit green, yellow, orange, and red luminescence, respectively. [20] In this communication, we report the fabrication of thin films of QDs on indium tin oxide (ITO) glass; these QD films exhibit high fluorescence intensities in the visible range. The fluorescence spectra and quantum yields are tunable by altering the coating sequences and by employing different-size QDs, that is, mainly through control of the de...

ZnMgO quantum dots grown by low-pressure metal organic chemical vapor deposition

“…1 Consequently, considerable research efforts have been devoted to the QD system, including single-electron devices, 2,3 core/shell structure, 4,5 QD light emitting, 6,7 and biological applications. 8,9 ZnO is presently receiving worldwide attention because of its advantages for blue/UV light emitters and detectors.…”

Protein-Conjugated Quantum Dots for Detecting Trypsin and Trypsin Inhibitor Through Fluorescence Resonance Energy Transfer

“…The presence of signals for the (111), (220), and (311) facets in the XRD and EDX spectra (not shown) confirm that the asprepared nanoparticles were cubic zinc blended CdTe QDs [29][30][31][32]. The QY of the CdTe QDs was 10%, as determined through comparison with that of rhodamine 6G.…”

“…Because BSA-CdTe QDs are stable and highly fluorescent, 2-step preparation process for forming core-shell QDs is not required. We also note that our preparation method is simple and more biologically friendly than other methods [16,32]. Because the maximum excitation wavelength for RITC appears at 550 nm, the fluorescence of BSA-RITC is quite weak when excited at 350 nm.…”

“…The fluorescence QY of CdTe QDs is very sensitive to the environment, including the pH, ionic strength, and matrix species [29][30][31][32]. The changes in fluorescence of CdTe QDs are due mainly to variations in their surface properties.…”

Tunable Phosphorescent Emission through Energy Transfer within Multilayer Thin Films Based on a Carbazole‐Based Host and Ir(III)‐Complex Guest System

“…[1] Because of the ability to control the film thickness on a nanometer scale, as well as to incorporate various functional materials within the multilayers, LbL deposition methods are well suited for the control of energy transfer efficiency within multilayers, [2][3][4][5][6][7][8][9][10][11][12][13] which has been known to be extremely sensitive to the distance between donor and acceptor chromophores. [14] Several research groups have already employed various donor and acceptor chromophores such as water-soluble dyes, [2] dye-labeled polyelectrolytes, [3,4] quantum dots, [5][6][7][8] and conjugated polymers [9,10] A new method to tune both phosphorescence emission intensity and spectroscopic colors based on the alternatively structured host/guest multilayer thin films prepared by the spinassisted LbL deposition is presented. Their emission characteristics are demonstrated with pairs of positively charged Ir-PEI complexes as guests and negatively charged CBZ-PAA as hosts.…”