Highly Efficient and Stable Luminescence from Microbeans Integrated with Cd‐Free Quantum Dots for White‐Light‐Emitting Diodes

Abstract

922 wileyonlinelibrary.com www.particle-journal.com www.MaterialsViews.com COMMUNICATION achieved was 71.2 lm W −1 at an input current of 20 mA by employing a CIS QDs-based composite plate as the light convertor that was integrated with a blue LED chip. [ 26 ] The luminous effi ciencies of QD-WLEDs, however, are still obviously inferior to conventional phosphors-converted (pc) WLEDs, even if high-quality CIS QDs with 92% QY are employed. [ 9 ] The low effi ciency of QDs-based WLEDs can probably be attributed to two main factors. Firstly, micromolecules, such as penetrative oxygen or moisture, could corrode the surface ions and ligands of the QDs, resulting in defect trap states that cannot be ignored. [27][28][29] Secondly, the QDs tend to aggregate themselves because of incompatibility issues between the surface ligands and the ambient matrix. [30][31][32] Jang et al. [ 9 ] have developed a barrier layer formed of poly(vinylpyrrolidone) (PVP) and silica on the composite surface of the QDs to prevent photodegradation by oxygen molecules. The as-prepared remote-type WLEDs exhibited a luminous effi ciency of about 60 lm W −1 accompanied by good white-light quality at an input current of 20 mA. This assembled WLED proved to be effi cient, however, as the incompatibility between the surface organic ligands of the QDs and the polymer matrix remains, a gradually decaying light-converting effi ciency is inevitable due to aggregation of the QDs, especially after silicone high-temperature curing. Another strategy to improve the stability of QDs is the deposition of a compatible organic or inorganic layer on the quantum dots, by means of, for instance, surface modifi cation by amidocyanogen [ 5 ] or chemical growth of a silica layer. [ 2,24 ] QDs with compatible layers under ambient conditions showed an outstanding stability in the composite. However, the declining quantum effi ciency resulting from surface ligands phase transition at the initial stage remains a considerable challenge as they make the devices more vulnerable.In this communication, we use a low-cost paraffi n liquid to replace conventional octadecene (ODE) as the exclusive non-coordinating solvent for the synthesis of high-quality CIS QDs with core-shell structure. Mesoporous silica particles were combined with the QDs to obtain luminescent microbeans (LMBs) by a non-chemical method. These mesoporous structures do not only work as the barrier structure in the matrix to reduce the contact surface between the QDs and penetrative micro molecules, but also function as the lattice to avoid aggregation of the QDs. In order to reduce the thermal effect of the QDs from the InGaN chip, a composite plate with LMBs and poly(methyl methacrylate) (PMMA) was remotely packaged on a surface-mounted device (SMD) type LED to obtain a white-light device. The WLED demonstrated high stability, as well as a high luminous effi ciency. Quantum dots (QDs) have attracted widespread attention for use in white-light-emitting diodes (WLEDs) and QDs-based displays because of their high ...

52.2: Invited Paper: Application of Quantum‐dot Patterned Film with Scattering Nanoparticles for the High Efficiency Displays

“…We used the WSQs to improve the down-converting efficiency of QDs in the film. Basically, the WSQs have synthesized without any surface modification of QDs by hybridization process [9]- [10].…”

Heavy Metal Free Nanocrystals with Near Infrared Emission Applying in Luminescent Solar Concentrator

“…However, it still faced the problem of heavy metal employment, such as Pb and Cd, mainly according to the instruction of Restriction of Hazardous Substances Directive (RoSH) by the European Union in 2003. To avoid large utilization of heavy metals in BIPV, our group had fabricated CuInS 2 /ZnS (CIS) NCs with high QY, and introduced them in LSCs materials with PV cells with emission light in yellow . Meinardi et al have recently developed the heavy metal free CuInSe 1− x S x /ZnS (CISeS) NCs and silicon QDs in LSC materials with NIR emission with a high efficiency, which indicated these NCs based LSC materials were colorless in the daylight and had low reabsorption as well .…”

“…In this work, to address the three key factors in applying NCs‐LSCs, such as “heavy metal free,” “low reabsorption,” and “NIR emission,” we have introduced another heavy metal free AgInS 2 /ZnS (AIS/ZnS) NCs with a core‐shell structure and an NIR emission to the LSC technique for the first time. The NCs have been successfully synthesized in mild reaction conditions . The prepared NCs have also demonstrated a variable emission from the visible range to the NIR range with a high quality.…”

Photobleaching-resistant ternary quantum dots embedded in a polymer-coated silica matrix

“…[1][2][3] These advantages include emission wavelength tunability, excellent solubility in various solvents and matrices, good stability against photobleaching compared to most organic dyes, broad excitation bands and high quantum yields, matching those of conventional phosphors. [7][8][9] However, due to increasing restrictions on the use of heavy metals in consumer goods, 10 Cd-based semiconductors cannot serve as sustainable LED converter materials, especially since to date no LED recycling methods are available. [7][8][9] However, due to increasing restrictions on the use of heavy metals in consumer goods, 10 Cd-based semiconductors cannot serve as sustainable LED converter materials, especially since to date no LED recycling methods are available.…”