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Quantum dots (QDs) are promising materials for various optoelectronic applications. However, the efficiency of QD white light-emitting diodes (QD-white-LEDs) is not at the desired level, particularly when the QD concentration in the silicone matrix is high and the corresponding mechanism has not been fully elucidated. In this study, we experimentally and theoretically investigated the aggregation-induced scattering (AIS) effect of QDs in silicone and unraveled the origin of low efficiency for QD-white-LED devices. Three-dimensional finite-difference time domain and ray tracing simulations were carried out to establish the AIS model for QDs. Results indicate that the AIS effect is stronger for higher QD concentrations and leads to a larger effective aggregate size (EAS), which was confirmed by comparing with the experimental results of QD-silicone films. Furthermore, we found that the AIS effect causes a significant reduction in the radiant efficiencies of QD-white-LEDs when the EAS exceeds 50 particles, which is validated by fabricated devices. According to the spectral energy analysis, the low efficiency of QD-white-LEDs can be attributed to a strong AIS effect at high QD concentrations, causing severe backscattering and reabsorption loss. This study is also important for nondestructive testing the degree of aggregation demonstrated by QDs in a silicone matrix and for precisely modeling QD-white-LEDs. [ABSTRACT FROM AUTHOR]

A liquid matrix is beneficial for improving the luminescence performance of quantum dots (QDs), although it is difficult to be packaged with light-emitting diode (LED) chips. In this study, liquid-QDs with chlorobenzene solution and melamine-modified urea-formaldehyde (MUF) were used as the core and shell structures, respectively, successfully yielding liquid-QD/MUF microcapsules for white LED packaging. The concentration of the liquid-QDs in the microcapsules was optimized, demonstrating an increase of 15.9% in the luminous efficiency, as compared to the traditional solid-QDs at a specific QD energy proportion. The efficiency roll-off can be attributed to the increased reabsorption and back-scattering loss at higher liquid-QDs and microcapsules concentrations. It was also confirmed that the liquid-QD/MUF microcapsules have an excellent thermal stability below 200 °C, owing to the protection of the MUF shells. Finally, white LEDs compounding the red liquid-QD/MUF microcapsules and YAG phosphor particles were fabricated, achieving a high luminous efficiency of 149.2 lm/W at 20 mA, correlated color temperature of 3301 K, and color rendering index of 88.8. This study will open new research avenues for liquid-QD packaging in white LEDs. [ABSTRACT FROM AUTHOR]

The scattering effect plays an important role in improving the optical performance of the quantum dot (QD) white light-emitting diodes (LEDs). A majority of the previous studies have focused on the planar packaging structure only with respect to total internal reflection (TIR). In this study, SiO2 nanoparticles are incorporated into QD-silicone encapsulation of LEDs with semi-spherical lens packaging (SSLP) to exploit their scattering effect. The results show that the radiant efficacy (31.35%@100 mA) and luminous efficacy (87.56 lm/W@100 mA) of QD white LEDs can be optimized using SiO2 nanoparticle concentration (0.1 wt%) and that they increase by 5.04% and 11.08%, respectively, as compared to the conventional structure. A comprehensive ray-tracing simulation validates that the nanoparticles in the SSLP structure lead to severe loss of chip light. On the contrary, the fluorescence light increases due to the enhancement of conversion by QDs. The transmission electron microscopy images and the finite-difference time-domain simulation have been introduced to investigate the surface adsorption of SiO2 nanoparticle. This study indicates that SiO2 incorporation is an effective method to improve the efficiency of QD white LEDs, and provides a better understanding on the scattering effect based on TIR, color conversion, and surface adsorption. [ABSTRACT FROM AUTHOR]

Vertical-cavity surface-emitting laser (VCSEL) devices operate using a variety of viewing angles to satisfy the demands of different applications. One simple and universal approach to accomplish this is by using scattering elements in the packaging process for VCSEL chips. However, inevitable backward scattering loss is introduced, which suppresses the radiant efficacy of VCSEL devices. Therefore, we have proposed an enhanced specular reflection (ESR) structure with an opening circle window (OCW) to recycle the backward scattered light. The ray-tracing method is used to optimize the diameter of the OCW, as well as the thickness of the ESR structure. Furthermore, the light extraction mechanism is discussed. According to theoretical results, VCSEL devices with optimized ESR structures are fabricated and compared with traditional VCSEL devices. The experiment results demonstrate that ESR structures can significantly enhance the radiant efficacy of VCSEL devices using scattering elements. This shows great potential for applications involving illumination and 3-D imaging. [ABSTRACT FROM AUTHOR]

ZnO nanoparticles were incorporated into quantum dot (QD)-silicone encapsulation materials of the light-emitting diodes (LEDs) to exploit their strong scattering effect, which were proved by the ZnO-only film experiment. The novel packaging scheme led to a decrease in the radiation flux because of the conversion-energy loss of QDs and backscattering of ZnO nanoparticles. Under the similar color coordinate, the luminous flux of the ZnO-incorporated QD-LED showed a 3.37% increase compared to the conventional structure. This was attributed to the scattering effect, which enhanced the utilization of blue light and the conversion of yellow light. And the angular-dependent correlated color temperature (CCT) deviation was reduced from 862 to 712 K in the range of −70° to 70°. Moreover, the CCT monotonically decreased, and the chromaticity coordinate steadily shifted to the yellow region as the amount of ZnO nanoparticles increased. Therefore, ZnO nanoparticles can be a favorable optical performance enhancer for the future generation of QD-converted LEDs. [ABSTRACT FROM PUBLISHER]