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The quantum dot (QD)–phosphor hybrid structure is promising for efficient white light-emitting diodes (LEDs). In this article, separation packaging structures (SPSs) having green-QD and red-phosphor configurations for backlight displays are studied. The LEDs with green-QD-down and red-phosphor-down SPSs were achieved to have the same color coordinate (0.282, 0.257) which is a typical cool white color widely used in commercial backlighting. And the optical efficiency, device cost, and thermal performances of the LEDs are comprehensively analyzed. Results indicate that the green-QD-down SPS exhibits higher backscattered loss while less conversion loss. Therefore, the green-QD-down SPS has the same optical efficiency as another structure, owing to the balance between the backscattered loss and conversion loss. The concentration differences in these two structures were discussed combining with the device cost. Moreover, the green-QD-down SPS exhibits a better heat dissipation of QDs by reducing the heat path from QDs to the lead frame, as well as less thermal power generation in conversion layers. Consequently, the maximum (39.8 °C) and minimum (31.9 °C) temperatures of its inner QD layer are 7.7% and 20.3% lower than those of the red-phosphor-down SPS at an injection current of 100 mA. [ABSTRACT FROM AUTHOR]

Quantum dots (QDs) have broad application prospects in displays such as full-color light-emitting diodes (LEDs) and micro-LEDs. However, an ultrahigh concentration of QDs is required to eliminate the pumping light for achieving high color purity, leading to significant reduction in the photoluminescence (PL) intensity of the QDs and the generation of much more heat. In this article, the PL intensity, thermal performance, and color purity of QD-LEDs were comprehensively improved by introducing a pumping-light absorber (PLA). Results indicate that the PLA packaging structure achieves a color purity that is similar to that of a conventional structure with ultrahigh QD concentration; the radiant power of blue light was reduced by 81.6% and this leads to a large shift in the color coordinates from (0.18, 0.26) to (0.20, 0.57). Moreover, the PLA packaging structure results in higher electroluminescence (EL) intensity and lower operating temperatures than the conventional structure. This is because of the higher color-conversion efficiency and partial transfer of thermal energy to the PLA layer. In particular, the EL intensity of the QD-LEDs increased by 25.1% and the steady-state temperature was reduced to 58.9 °C, which is 19.75% lower than that of a conventional structure (73.4 °C). In addition, the PLA packaging structure works equally well with ultraviolet (UV) pumping sources to achieve a higher color purity (enhancing the color gamut by 50.1% when using a 405-nm source). [ABSTRACT FROM AUTHOR]

Quantum dots (QDs) show a great potential for light-emitting diodes (LEDs) packaging, which still face great challenges compared with the matured phosphor downconversion materials. These are probably caused by the unique scattering and absorption properties of QDs, which are extremely different to the traditional phosphor due to their several nanometers size, while their effect on QDs-converted LEDs (QCLEDs) is barely studied. In this paper, we have experimentally and theoretically investigated the effect of scattering and absorption of CdSe/ZnS QDs on the optical performance for QCLEDs by comparing with the traditional yttrium aluminum garnet phosphor. Results indicate that the strong absorption (reabsorption) of QDs causes low radiant efficacy and stability for QCLEDs; their weak scattering also leads to a low color uniformity. It demonstrates that their unique scattering and absorption properties are key factors leading to low optical performance of QCLEDs compared with the traditional phosphor-converted LEDs. For purpose of gaining the white LED with high efficiency and stability, it is highly suggested to use a low QD concentration to reduce the reabsorption loss and the total internal reflection loss. We believe that this paper can provide a better understanding of improving the optical performance for QCLEDs from the prospective of scattering and absorption. In the future, it is important to use low QD concentration to gain high-performance white LEDs with high downconversion efficiency by optimizing packaging structures. [ABSTRACT FROM AUTHOR]

Although the optical simulations have been widely adopted to study phosphor-converted light-emitting diodes (pcLEDs), to the best of our knowledge, there is no study that investigates the pcLED model considering the effect of phosphor particles with irregular shapes. In order to explore this topic, we employ the finite-difference time-domain method to characterize the phosphor-converted element (PCE) model. Furthermore, the PCE-based pcLED with YAG:Ce and nitride phosphors is investigated by the ray-tracing method. The results show that the rod-shaped nitride phosphor can scatter incident light to larger angles compared with the spherical YAG:Ce phosphor of the same size. In turn, their different scattering and absorption characterizations cause that the mixing concentration of the phosphors has a significant effect on the correlative color temperature and light output power of the pcLED. [ABSTRACT FROM PUBLISHER]