Jung-Ho Jo

Remote-type, high-color gamut white light-emitting diode based on InP quantum dot color converters

This work reported on synthesis of highly efficient, color-pure green- and red-emitting non-Cd InP/ZnS core/shell quantum dots (QDs) and their utilization as color converters for the fabrication of display backlighting QD-based white light-emitting diode (LED). Green and red QD emitters were first individually embedded into a transparent polymeric matrix of polyvinylpyrrolidone and the resulting two free-standing QD composite plates were then physically combined into a bilayered form. White QD-LED was fabricated by remotely loading the bilayered QD plate of a red-on-green configuration onto blue LED chip. This remote-type white device generated a spectrally well-resolved, tricolored electroluminescent spectrum, and exhibited luminous efficacies of 8.9−16.7 lm/W, depending on forward currents of 20−100 mA, and a high color gamut of 87%.

White Electroluminescent Lighting Device Based on a Single Quantum Dot Emitter

Using a single emitter of Cu-Ga-S/ZnS quantum dots, all-solution-processed white electroluminescent lighting device that not only exhibits the record quantities of 1007 cd m(-2) in luminance and 1.9% in external quantum efficiency but also possesses satisfactorily high color rendering indices of 83-88 is demonstrated.

A near-ideal color rendering white solid-state lighting device copackaged with two color-separated Cu–X–S (X = Ga, In) quantum dot emitters

I–III–VI chalcogenide quantum dots (QDs) are regarded as the most promising downconverters for the fabrication of high-efficiency, high-color rendering solid-state lighting devices, particularly enabled by their exceptional photoluminescence (PL) quantum yields (QYs) along with substantially Stokes-shifted, broad PL characters. In this work, we first synthesize highly efficient green Cu–Ga–S (CGS) and red Cu–In–S (CIS) QDs, having PL QYs of 85 and 83%, respectively, after elaborate ZnS shelling. Then, these two QD emitters that are well color-separated are simply copackaged in a single blue LED chip for the fabrication of tricolored white QD-light-emitting diodes (QD-LEDs). A series of white QD-LEDs with this novel QD combination are prepared by varying the weight ratio of the two QDs loaded. A QD-LED with an optimal weight ratio between CGS and CIS QDs produces a spectrally well-balanced tricolored white electroluminescence, possessing not only near-ideal color rendering index values of 94–97 but high luminous efficacies of 43.1–68.8 lm W−1, depending on the driving current.

Near-complete photoluminescence retention and improved stability of InP quantum dots after silica embedding for their application to on-chip-packaged light-emitting diodes

Silica is the most commonly used oxide encapsulant for passivating fluorescent quantum dots (QDs) against degradable conditions. Such a silica encapsulation has been conventionally implemented via a Stober or reverse microemulsion process, mostly targeting CdSe-based QDs to date. However, both routes encounter a critical issue of considerable loss in photoluminescence (PL) quantum yield (QY) compared to pristine QDs after silica growth. In this work, we explore the embedment of multishelled InP/ZnSeS/ZnS QDs, whose stability is quite inferior to CdSe counterparts, in a silica matrix by means of a tetramethyl orthosilicate-based, waterless, catalyst-free synthesis. It is revealed that the original QY (80%) of QDs is nearly completely retained in the course of the present silica embedding reaction. The resulting QD–silica composites are then placed in degradable conditions such UV irradiation, high temperature/high humidity, and operation of an on-chip-packaged light-emitting diode (LED) to attest to the efficacy of silica passivation on QD stability. Particularly, the promising results with regard to device efficiency and stability of the on-chip-packaged QD-LED firmly suggest the effectiveness of the present silica embedding strategy in not only maximally retaining QY of QDs but effectively passivating QDs, paving the way for the realization of a highly efficient, robust QD-LED platform.

Towards the fluorescence retention and colloidal stability of InP quantum dots through surface treatment with zirconium propoxide

ABSTRACT Through the synthetic development of sophisticated core/shell heterostructures, the fluorescent properties of quantum dots (QDs) have been steadily improved to a level that can ultimately meet the industrial demands, but their reliability is still insufficient, particularly showing low fluorescence stability against degradable conditions. As one solution to this issue, an additional physical barrier typically with an oxide phase has been introduced to protect the QD surface from the environment. In this work, a strategy for improving the stability of QDs involving the passivation of their surfaces with zirconium propoxide (Zr(PrO)4) is suggested. Multi-shelled green QDs of InP/ZnSeS/ZnS were first synthesized, and then their surfaces were in-situ-treated with Zr(PrO)4. To confirm the presence of Zr(PrO)4-derived species on the QD surfaces, chemical analyses of the Zr(PrO)4-treated QDs were performed through Fourier transform infrared, X-ray photoelectron, and inductively coupled plasma optical emission spectroscopic measurements. A photostability test of two comparative InP/ZnSeS/ZnS QDs – one treated without and one with Zr(PrO)4 – was performed by exposing their dispersions to ultraviolet (UV) irradiation for prolonged periods of time, up to 120 h. It was revealed that Zr(PrO)4 treatment is highly effective in improving fluorescence retention and colloidal stability.