Due to the advent of high-brightness blue LEDs, white LEDs can be easily obtained using a combination of phosphors and blue LEDs. At present, white LED has become the main backlight light source of portable information products, and it may even become a general household light source in the future. In addition, high-power near-ultraviolet LEDs have appeared in recent years. The same phosphors can be turned into white LEDs. The characteristics of LEDs are small size, low power consumption, and long life. If they have the characteristics of color design freedom, stability, and easy handling, etc. When the phosphor is combined, it can become a new lighting source.
Generally, when combining LED and phosphor, the typical method is to place the phosphor near the LED. The main reason is that the phosphor can efficiently convert the light generated by the LED to a wavelength, and the phosphor is placed in a region with a high light emission density. , Is the easiest method for wavelength conversion. In addition, the phosphor packaging method determines the luminous efficiency and hue of the white LED. Therefore, the packaging technology of the LED and the phosphor will be discussed in depth from the perspective of white light.
White LED package of blue LED + YAG phosphor
It is a commercially available white LED. Specifically, it disperses YAG: Ce phosphor that can produce yellow light in a transparent epoxy resin, and then uses the blue LED in the bowl to excite the light and convert it into White light. The white light emission mechanism of this method is to use LEDs to generate blue light. Part of the blue light will excite the YAG phosphor to become yellow light. The remaining blue light will be mixed externally with blue light and yellow light to become white light. The feature of this method is that the structure is simple, and only the phosphor coating process needs to be added to the production process of the LED, so the production cost can be greatly suppressed, and the other feature is that the chromaticity adjustment is very simple.
As long as the color coordinate is within the straight line formed by the two color coordinates of the LED and the YAG phosphor, the color tone can be adjusted arbitrarily. It can be seen that when the concentration of the YAG phosphor is low, the ratio of blue penetration light is large, and the overall Blue tone white light; relatively, if the YAG phosphor concentration is higher, the ratio of yellow converted light is more, and the whole is yellow tone white light.
As mentioned above, using some blue LEDs as complementary colors does not require high-density (percentage of resin) phosphor coating, so it can effectively reduce the amount of phosphor used. Generally speaking, although the percentage of phosphor to resin will change with the conversion efficiency of YAG phosphor and the shape of bowls and cups, white light can be obtained with a low mixing ratio of about 10 to 20 wt%. In addition, due to the light intensity emitted by the blue LED, the distribution on the central axis is not the same as the surrounding. Even if the density of the YAG phosphor around the LED chip is completely the same, it will still cause problems such as uneven light on the axis and the surrounding, which is also necessary in the future. One of the problems overcome.
Lead Frame Type and Chip Type both set blue LEDs in bowls and cups, and then coat with resin mixed with a certain amount of YAG phosphor. Because LEDs have the characteristics of small size, power saving, and long life, they have been widely used in backlighting light sources of portable information products such as mobile phones and PDAs, as well as trail guide lights and other fields.
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