Color-converting bilayered composite plate of quantum-dot-polymer for high-color rendering white light-emitting diode.

Highly bright CuInS2 quantum dots (QDs), whose emission is easily tuned in orange and greenish-yellow colors through manipulating the ZnS shelling procedure, are integrated with polymethyl methacrylate (PMMA) to obtain a free-standing composite plate of QD-polymer. The composite plate embedded with orange or greenish-yellow QDs is combined in a remote type with a blue light-emitting diode (LED). No color rendering index (CRI) value results when orange QDs are applied, whereas use of greenish-yellow QDs leads to a limited CRI of 72. A higher-color rendering QD-LED is demonstrated through a spectral extension by devising a unique bilayer-structured QD plate, where two types of QD are separately incorporated into each PMMA matrix, with a buffer layer of polymer blend inserted between them. The bilayered QD plate LED exhibits an improved CRI of 81, a high luminous efficacy of 71.2 lm/W at an input current of 20 mA, and exceptional high-stability luminescent characteristics against the variation of applied current.

Preparation of a photo-degradation- resistant quantum dot-polymer composite plate for use in the fabrication of a high-stability white-light-emitting diode.

We report on the synthesis of highly fluorescent double-ZnS-shell-capped, yellow-emitting Cu-In-S quantum dots (QDs) with a surprisingly high quantum yield of 92%, the preparation of a free-standing QD-polymethylmethacrylate composite plate, and the application of the QD plate in the fabrication of QD-based white-light-emitting diodes (WLEDs). A free-standing QD plate with QDs embedded uniformly inside a polymeric matrix is used to fabricate a remote-type, resin-free WLED. The QD plate-based WLED displays a high luminous efficiency; however, it suffers from a significantly unstable device performance due to QD degradation upon prolonged photo-excitation. An exceptional operational stability of the QD plate-based WLED is realized by generating hybrid double layers of an organic adhesion layer and a gas barrier layer of sol-gel-derived silica, rendering the QD plate impermeable to oxygen. Our success in achieving a color converter robust against photo-degradation and applying it in the fabrication of a reliable QD-based LED is greatly encouraging as regards the development of next-generation QD-based LED lighting sources.

Solvothermal preparation of yellow-emitting CuInS2/ZnS quantum dots and their application to white light-emitting diodes.

Based on the development of highly fluorescent colloidal quantum dots (QDs), their successful applications for the fabrication of lighting sources such as light-emitting diodes (LEDs) and lasing devices have been demonstrated. Here, CuInS2/ZnS core/shell QDs are facilely prepared by a two-step solvothermal route. Depending on the amount of a shell precursor of Zn stearate, fluorescent properties such as emission color and quantum yield (QY) of CuInS2/ZnS QDs are tunable and optimized. Yellow-emitting CuInS2/ZnS QD with a peak wavelength of 562 nm, QY of 81%, and emission bandwidth of 114 nm is chosen as an efficient blue-to-yellow downconverter for the fabrication of QD-based white LED (WLED). Various electroluminescent properties including luminous efficacy and color rendering index of QD-WLED are measured as a function of forward current up to 100 mA and described in details.

Facile consecutive solvothermal growth of highly fluorescent InP/ZnS core/shell quantum dots using a safer phosphorus source.

The work presents a facile, stepwise synthetic approach for the production of highly fluorescent InP/ZnS core/shell quantum dots (QDs) by using a safer phosphorus (P) precursor. First, InP quantum dots (QDs) were solvothermally prepared at 180 °C for 24 h by using a P source of P(N(CH(3))(2))(3). The as-grown InP QDs were consecutively placed in another solvothermal condition for ZnS shell overcoating. In contrast to the almost non-fluorescent InP QDs, due to their highly defective surface states, the ZnS-coated InP QDs were highly fluorescent as a result of effective surface passivation. After the shell growth, the resulting InP/ZnS core/shell QDs were subjected to a size-sorting processing, by which red- to green-emitting QDs with quantum yields (QYs) of 24-60% were produced. Solvothermal shell growth parameters such as the reaction time and Zn/In solution concentration ratio were varied and optimized toward the highest QYs of core/shell QDs.

Highly efficient, color-pure, color-stable blue quantum dot light-emitting devices.

For colloidal quantum dot light-emitting diodes (QD-LEDs), blue emissive device has always been inferior to green and red counterparts with respect to device efficiency, primarily because blue QDs possess inherently unfavorable energy levels relative to green and red ones, rendering hole injection to blue QDs from neighboring hole transport layer (HTL) inefficient. Herein, unprecedented synthesis of blue CdZnS/ZnS core/shell QDs that exhibit an exceptional photoluminescence (PL) quantum yield of 98%, extraordinarily large size of 11.5 nm with a shell thickness of 2.6 nm, and high stability against a repeated purification process is reported. All-solution-processed, multilayered blue QD-LEDs, consisting of an HTL of poly(9-vinlycarbazole), emissive layer of CdZnS/ZnS QDs, and electron transport layer of ZnO nanoparticles, are fabricated. Our best device displays not only a maximum luminance of 2624 cd/m(2), luminous efficiency of 2.2 cd/A, and external quantum efficiency of 7.1%, but also no red-shift and broadening in electroluminescence (EL) spectra with increasing voltage as well as a spectral match between PL and EL.

Noninjection, one-pot synthesis of Cu-deficient CuInS2/ZnS core/shell quantum dots and their fluorescent properties.

Non-toxic, environment-benign colloidal CuInS(2) (CIS) quantum dots (QDs) were synthesized through a facile noninjection, one-pot approach by reacting Cu and In precursors with dodecanethiol dissolved in 1-octadecence at 220 °C. The Cu:In precursor molar ratio was varied from 1:1 to 1:4 to intentionally generate Cu-deficient CIS QDs. Depending on the stoichiometry of the QDs, their emission peak wavelengths were tuned in red-deep red region. More Cu-deficient CIS QDs (Cu:In=1:4) were found to be more efficient than ones with Cu:In=1:1. After successive ZnS shell was overgrown on the surface of core QDs with Cu:In=1:4, the resulting core/shell QDs exhibited a highly efficient yellow emission with a quantum yield of ~50%. A substantially blue-shifted emission from the core/shell QDs versus core ones was described by suggesting an alternative recombination pathway that may be induced by the ZnS shell coating.