Phosphorescent materials that can be used in white O LEDs have three primary colors of blue, green and red. Although yellow and orange are not one of the three primary colors, they can be matched with dark blue because of yellow, or blue or sky blue for orange, and white light of two colors is mixed.
The judgment of each color or color saturation is distinguished by 1931 CIEx, y color coordinates (see Figure 4-13).
1931CIEx, y color coordinate color division example diagram
In the case of a green light color, a substantially x coordinate value of less than or equal to 0.3 can be regarded as green. The y-coordinate value is an indicator of color purity, such as Ir(ppy)3 and (ppy)2Ir(acac) OLED 1931CIEx, the y color coordinates are (0.27, 0.63) and (0.31, 0. 64) (The phosphorescence spectrum is λmax, 510 and 525 nm, respectively). It can be said that Ir(ppy)3 is a relatively green material, but it is relatively green (py) zIr (a little yellowish green relative to the former). Acac) its color (yellow-green) saturation is higher.
Therefore, for those green phosphorescent materials, the 1931 CIEx, yx coordinate values ​​of 0.33, 0.34, 0.35, or even 0.40 or more than 0.40, are generally referred to as yellow-green phosphorescent materials.
Yellow is the middle color. It is impossible to say a clear range. You can only select ((0.50, 0.50) coordinate value as the saturated yellow 1931CIEx, y coordinate value. The smaller the x coordinate value, the closer to yellow-green; The larger the x coordinate value, the closer it is to orange.
Compared with the condition of the green phosphorescent material, if the 1931 CIEx, the y color coordinate two values ​​are 0. 50 small too much (about less than 0. 45), such materials will be considered as yellow-green phosphorescent materials, will not be listed for discussion. Orange is also a middle color, can not say a clear range, if a lot of red phosphorescent material color is slightly insufficient, the color will fall in the orange place, roughly can be fixed ((0.60, 0.40) The coordinate value is taken as the saturation orange 1931CIEx, y coordinate value.
The orange color is sandwiched between yellow and red. 1931CIEx, the y coordinate is shifted to the left ((the value of x becomes smaller, the value of y becomes larger) becomes yellow, and the rightward deviation (the value of x becomes larger and the value of y becomes smaller) turns red.
How to define yellow and orange or orange and red is different from person to person.
Distinguish whether the color of the phosphorescent material is green, yellow or orange. If the OLED 1931CIEx, y is not marked and cannot be known, then the color of the illuminating wavelength can be roughly judged to predict its possible color. See the example of Figure 4-14. .
Phosphorescence spectrum of Ir coordination complex from green light to orange light distribution
At present, there are 50 kinds of OLED materials that have been reported to emit red phosphorescence. Since the discovery of OLED organic phosphorescent materials in the late 1990s, the development of blue phosphorescent materials has always lagged behind red and green light. Phosphorescent materials have so far rarely achieved color purity like deep red or dark green.
Even in dark blue with high color purity, the effect of making an OLED is often not unsatisfactory, that is, the material (also causing the device) has a short life. In order to produce a white OLED with satisfactory performance, the current choice is mainly a sky blue phosphorescent material, which requires that the red phosphorescent material to be matched is close to the saturated red dark red.
Therefore, the requirements for color purity of red phosphorescent OLED materials have to be raised very high, otherwise the white OLEDs produced cannot be close to positive white.
The earliest appearance in OLEDs as a phosphorescent material is PtOEP, an organic phosphorescent material that emits a deep red color and is nearly saturated red. The wavelength of red light emitted by PtOEP is both long and narrow.
Electroluminescence Spectra of PtOEP Red Phosphorescent OLED and Its 1931 CIEx, y Color Coordinates
The appearance of this material in OLEDs was due to the red material of the OLED (in the late 1990s).
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