Based on the characteristics of LED high light efficiency, low carbon environmental protection and energy saving, most LCD TVs and mobile phones on the market have adopted LED as backlight. At the same time, in order to meet the high color gamut coverage of LED backlight sources, the industry is gradually introducing some new fluorescent materials with narrow half-wave width, such as fluoride phosphors and quantum dot phosphors. In order to better understand the characteristics of these phosphor materials, we will focus on the introduction and description of fluoride phosphors and their applications.
First of all, before we understand and understand fluoride phosphors, we will introduce some basic knowledge of LED light sources in backlight applications.
1, LCD related knowledge introduction
A, LCD meaning
LCD: Abbreviation for Liquid Crystal Display, the full name of liquid crystal display, which includes TFT, UFB, TFD, STN and other types of liquid crystal display.
LCD TV, mobile phone: TV or mobile phone with LCD display as display;
B, LCD construction
Taking a TFT type liquid crystal display as an example, the structure mainly includes a backlight, a light guide plate, an upper and lower polarizing plate, a liquid crystal, a color filter, a thin film transistor, etc. (the structure is shown in FIG. 1), and the main structural functions are as follows:
1. Back Light: The principle of LCD display is to block the light and light by the liquid crystal to control the light and dark. It is necessary to have a light source to see the image on the screen, so the backlight is responsible for providing the most basic for LCD display. Light source.
2. Light Guide Plate: distributes the light evenly across the entire screen;
3. Up/Down Polarizer: The direction of the light sent by the backlight is inconsistent and radial. If such light passes through the twist of the liquid crystal molecules, we still can't see the image we want to see on the screen. At this time, the polarizing plate below assumes the work of normalizing the direction of the light to the liquid crystal layer.
4. Thin Film Transistor (TFT): Controls the twist angle of liquid crystal molecules
5. Liquid crystal: This layer of liquid crystal molecules is twisted under the control of the TFT, and the light with the same direction is controlled to be bright, so that the brightness of the light to the rear pixel unit changes.
6. Color Filter: After the white filter is filtered, we can see that the light corresponding to the color of the filter is transmitted, so in the LCD screen, the function of the color filter is to color. .
LCD backlight high color gamut display principle
C, LCD imaging principle
The principle of LCD imaging is to place the liquid crystal between two sheets of conductive glass. By controlling the driving of the electric field between the upper and lower polarizing plates and the upper and lower electrodes, the electric field effect of the liquid crystal molecules is twisted and nematic to control the transmission of the backlight or Masking, combined with other control and auxiliary function layers to achieve the function of restoring the picture.
D, LCD backlight introduction
Since the liquid crystal must be illuminated by an additional light source, the backlights commonly used in LCDs are CCFL (Cold Cathode Fluorescent Lamp), LED (Light Emitting Diode), HCFL (Hot Cathode Fluorescent Lamp), Surface Light Source VFD (Flat Fluorescent Lamp), EL ( Electroluminescent sheet), OLED (organic electroluminescent sheet) and the like. Among them, CCFL is currently the most commonly used LCD backlight, usually called traditional backlight;
CCFL vs. LED:
CCFL--made of hard glass and trichromatic phosphors. The tube has proper amount of mercury and inert gas. The inner wall of the tube is coated with phosphor and there is one electrode at each end. The disadvantage is that the color is limited. .
LED--a semiconductor solid-state light-emitting device that uses a solid semiconductor chip as a light-emitting material to recombine excess energy in a semiconductor by carrier to cause photon emission, directly emitting red, yellow, blue, green, cyan, and orange. , purple, white light. Because LED LEDs have good color performance, they have completely replaced the light source of traditional cold cathode fluorescent tubes.