Commercialization of the Phosphor Film "PS Series"
- Achieves Dynamic Range Expansion, Wider Color Gamut, and Thinner Liquid Crystal Display with Direct LED Backlighting -
Dexerials Corporation (Head Office: Shinagawa-ku, Tokyo, Representative Director and President: Yoshihisa Shinya, hereinafter called our company) has launched the Phosphor Film “PS Series” that contributes to an expansion of dynamic range, wider color gamut, and thinner liquid crystal displays with direct LED backlighting. This product has been selected for use in high-definition liquid crystal displays, and shipping have begun.
Currently, increasingly high-resolution displays, such as 4K and 8K, are being developed, and there is also a demand for higher image quality with higher brightness, higher contrast, and wider color gamut.
For this reason, the use of direct LED backlighting that is capable of improving the brightness and contrast (dynamic range) of displays while simultaneously efficiently extracting light and controlling lightness and darkness in order to expand the color gamut is becoming popular. However, when white LEDs are used, there is a possibility of individual differences in light emission.
Our newly launched Phosphor film “PS Series” has been developed by shaping green and red phosphors into a film. Incorporating this product into a display enables the use of blue LEDs with less variation in light emission as the light source in place of white LEDs, and also enables production of higher quality displays than those using a direct LED backlight using white LEDs.
In addition, since the use of this product makes the light source monochromatic blue, the light distribution of the LED is easier to control compared with using white LEDs as the light source, making it possible to shorten the distance between the light source and the diffuser, contributing to a thinner overall display.
■Example of use of phosphor film (cross-section of a liquid crystal display using a direct LED backlight)
This product uses sulfide green phosphor originally developed by our company. This sulfide green phosphor realizes vivid luminescence with a sharp PL* spectrum by utilizing inorganic material synthesis technology, which is one of our elemental technologies, thereby contributing to a wide color gamut for liquid crystal displays.
■Emission spectrum of a sulfide green phosphor (PL spectrum)
- * PL：Photoluminescence
In addition, in order to control unevenness in light emission of phosphor film, the particle diameter of phosphors needs to be reduced, but on the other hand, there is a trade-off in that the moisture resistance decreases due to the increase in surface area and reliability decreases unless a barrier film is used. Our company has improved the moisture resistance by applying a special treatment to the particle surface while simultaneously reducing the particle diameter to reduce unevenness, thereby making it possible to shape phosphors into a film without using a barrier film.
In addition, efficiency of light extraction has been improved by installing a dichroic filter under the phosphor film that transmits only blue light and reflects green light and red light. A part of the blue light emitted from the blue LEDs is converted into green light or red light by the phosphor and is synthesized into white light, but a portion of the white light is reflected in the direction of the light source LEDs. The dichroic filter reflects red light and green light among the reflected light back to the transmission direction, thereby preventing loss of light inside the backlight and enabling highly efficient light extraction and accurate light control.
We have obtained patents in Japan, the United States, China, and South Korea for the structure of the light source, which uses a combination of dichroic filter and phosphor film, contributing to higher brightness & higher contrast in liquid crystal displays.
■Image showing the effect of a dichroic filter (Cross-section of direct LED display)
|Phosphor film “PS Series”||Conventional white LED|
|LED used for backlight||Blue LED||White LED with YAG yellow phosphors|
NTSC area ratio