A new type of remote red quantum-dot (QD) component was designed and fabricated to improve the color-rendering properties of conventional white LED (light-emitting diode) lightings. Based on an optical simulation, the rectangular cavity-type QD cap was designed with an opening window on the top surface. Red QD caps were fabricated using a typical injection molding technique and CdSe/ZnS QDs with a core/shell structure whose average size was ~6 nm. Red QD caps were applied to conventional 6-inch, 15-W white LED downlighting consisting of 72 LEDs arrayed concentrically. The red QD caps placed over white LEDs enhanced the red components in the long-wavelength range resulting in the increase of the color rendering index (CRI) from 82.9 to 94.5. The correlated color temperature was tuned easily in a wide range by adopting various configurations consisting of different QD caps. The spatial and angular homogeneities were secured on the emitting area because QD caps placed over the white LEDs did not exhibit any substantial optical path length difference. The present study demonstrates that adopting QD caps in conventional LED lightings provides a flexible and efficient method to realize a high color-rendering property and to adjust correlated color temperature appropriately for a specific application.
The luminance and color properties of backlight units with quantum-dot (QD) films were investigated through experimentation and optical simulation. Red and green QD films were arranged in four different configurations above and below the light guide plate (LGP). The on-axis luminance of the backlight units with QD films was much larger when diffuse reflectors were used instead of specular reflectors, irrespective of the QD configuration. This result is attributed to the higher color conversion efficiency and the outcoupling efficiency caused by the spreading of the light reflected from the diffuse reflectors. The 'red QD film-LGP-green QD film' combination exhibited the highest luminance performance among the four configurations, which can be explained in terms of the reduced radiation load on the two QD films, besides the nearly zero absorption of the red light emitted from the red QD film by the green QD film. The simulation results reproduced all these main results, which indicates that optical simulation can be a useful tool for the optimization of the optical structure of backlight units with QD films in advance of experiment and fabrication.
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