Blue and green pigments are phthalocyanine metal complex compounds. The organic red pigments that BASF manufactures consist mainly of carbon, nitrogen, and oxygen, and belong to the class of diketopyrrolopyrroles (DPPs). The underlying molecular structure is what determines which parts of the color spectrum are filtered out. ![]() Researchers control the process mainly by managing the conditions in which pigment crystallization takes place. “A good rule of thumb is: The smaller and more regular the crystals, the lower the scattering and the better the LCD image quality,” de Keyzer said. This contaminates the colors and compromises the contrast. Any interferences resulting in scattering and depolarization of light will allow the light to pass uncontrolled through the filter. ![]() To ensure that subpixels switch on and off the way they are supposed to, it is essential to prevent interferences from the color filter pigments. When an electrical field is applied, however, the crystals prevent some or all of the light from getting through. “The liquid crystals change direction, and in that way alter their optical properties depending on the voltage applied.” They rotate the plane of oscillation of light waves to allow the light to pass through the second polarization filter. “This determines the brightness and color of the subpixels,” said Ger de Keyzer, in charge of applications engineering for color filter materials at BASF. The liquid crystals fine-tune the blend of colors by twisting the plane of oscillation of the light waves. Fine-tuning the portions of the three primary colors in this manner produces millions of hues. If, on the other hand, light penetrates through the red and green subpixel while the blue is deactivated, the colors combine to give a rich yellow. The other two subpixels – for blue and green – are deactivated when this happens. When the color red appears on the screen, the corresponding subpixel lets the red portion of light pass through and absorbs the rest. Screen contrast and color purity remain a challenge, however. The color filter pigments attached to the liquid crystal cells are what give each pixel its color. The images on a liquid crystal display with the standard resolution are made up of about two million picture elements, better known as pixels. ![]() Flat screen TVs started sweeping the world in the 1990s, mainly because of the availability of high-performance color filter materials. Commercialization of the first color monitors took another 20 years. Heilmeier, unveiled the first monochrome LCD monitor to the expert community in 1968. Liquid crystals form the basis for billions of flat-panel displays. After all, with experts forecasting six percent global annual sales growth for flat-panel displays until 2020. LCD technology is also the basis for many other contemporary communication devices, including smartphones, laptops and tablets. And this figure is rising, Germans are estimated to have purchased eight million flat screen television sets in 2015, most of which are LCDs. ![]() Flat screen TVs now provide energy-efficient, low-emission entertainment in three out of four German households, according to the Federal Statistical Office. Cathode ray tube television sets have long had their day.
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