I. Introduction
Semiconductor lighting is a new type of lighting technology based on high-power, high-brightness light-emitting diodes ( LEDs ). Compared with traditional illumination sources, white light-emitting diodes (WLEDs) have the characteristics of low power consumption, high luminous efficiency, high reliability, safety and environmental protection, and long life. In the context of today's increasingly serious environmental pollution, climate warming and increasing energy, semiconductor lighting technology has been recognized as one of the most promising high-tech fields in the 21st century.
In the field of semiconductor lighting, high color rendering (Ra>90) while achieving high light efficiency, and obtaining natural and comfortable lighting effects like natural light is the goal that the LED industry has been pursuing, and whether LED lighting products can be widely accepted by consumers. One of the key factors for the successful promotion of LED energy-saving projects. At present, the existing GaN-based blue LED combined with YAG:Ce3+ yellow phosphor can obtain higher light efficiency, but due to the lack of red light band, the color rendering index is difficult to reach a high level. Increasing the red phosphor can increase the index, but at the same time, it will greatly reduce the light efficiency of the white LED, and the red phosphor is unstable under moisture, which is easy to cause color temperature drift. How to achieve high-efficiency, high-light color quality LED lighting, while achieving high lumen efficiency and color rendering index, has become one of the urgent problems of next-generation lighting.
Quantum dots are semiconductor nanocrystalline materials with quantum confinement effects in three dimensions of space, also known as "artificial atoms." The quantum dot material has a particle size generally between 1-10 nm. When the size of the semiconductor crystal is smaller or close to the exciton Boer radius, the continuous band structure in the material becomes a discrete energy level structure due to the quantum confinement effect. Thereby, the advantages of narrow luminescence spectrum, high color purity and wide color gamut are brought about, and the stability of the quantum dots can be improved by wrapping the thick shell material.
Second, research and conclusion
The project adopts organic chemical synthesis method, and uses the fast injection growth method assisted by n-trioctylphosphine (TOP) to improve the traditional preparation process and realize the synthesis of CdSe/CdS thick-shell core-shell quantum dot composites. The lattice structure, morphology and luminescence properties of the synthesized core, core-shell quantum dots and their composites were tested by XRD, TEM, SEM, UV-vis, PL and red light compensation. The synthesized CdSe has a diameter of about 5 nm and a half-width of 27 nm. It has a cubic wurtzite lattice structure. See Figure 1 for details. The CdSe/CdS core-shell quantum dots are about 11 nm in diameter and have a half-width of 33 nm. They have the characteristics of CdS lattice structure. The synthesized CdSe/CdS quantum dot fluorescent microspheres have a diameter of about 45-75 μm and a half-width of 30 nm. The appearance is rhomboid regular morphology and the particle dispersion is good, as shown in Fig. 2. The material was combined with YAG:Ce3+ yellow phosphor to obtain a white light-emitting diode with high luminous efficiency (148.29 lm/W) and high color rendering index (Ra=90.1, R9=97.0). The compensation effect of the CdSe/CdS core-shell quantum dot composite in the deep red band of white light-emitting diodes. It is of great significance for the industrialization to realize the batch preparation of core-shell quantum dot composites and the scale production of WLED.
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