“Giant” quantum dots encapsulated inside a freeform lens

A freeform lens containing giant red and green quantum dots (QDs) was designed to be used for a direct-illumination-type LED backlight wide-color-gamut display. Encapsulating the QDs with the freeform lens enabled us to not only expand the illumination area, where the uniform lighting area was about 2 cm in radius on the plane 1.5 cm above the LED, but to also avoid QDs coming into direct contact with the LED chip, which reduced the QDs' surrounding temperature from 94°C to 61°C. Moreover, this encapsulation and the thick shell of the QDs significantly improved the device's lifetime up to more than 100 h due to the reduced temperature. A color gamut of ∼130% of the National Television Systems Committee standard was obtained with the freeform lens.