1. Field of the Invention
The present invention relates to a fluorescent material, and more particularly, to a fluorescent material used in an active dynamic liquid crystal display device and a method for manufacturing the same.
2. Description of the Prior Art
Generally, in an active dynamic liquid crystal display device, a light emitted from a back light is directed to a liquid crystal layer through a polarizer. The light directed to the liquid crystal layer is transmitted to a fluorescent material or interrupted in accordance with orientations of the liquid crystal molecules. The light transmitted to the fluorescent material excites the material to display an image.
As described above, since the active dynamic liquid crystal display device is designed such that the light emitted from the back light directly excites the fluorescent material, there is a need for a fluorescent material with high luminance.
In general, SrGa.sub.2 S.sub.4 :Eu which is excited by violet light having a wavelength of about 380 to about 420 nm has been used as a green fluorescent material, and BaMgAl.sub.10 O.sub.17 :Eu has been used as a blue fluorescent material.
However, the light emission luminance of these materials are not enough to apply to the active dynamic liquid crystal display device.
Therefore, U.S. Pat. Nos. 4,249,108 and 4,733,126 have proposed a method for improving the luminous efficiency by changing composition of the fluorescent material or adding another material to the fluorescent material, and U.S. Pat. No. 5,350,971 has proposed a method for improving the luminous efficiency by adjusting a diameter of each grains of the fluorescent material.
However, the fluorescent materials proposed by the above patents are not still enough in light emission luminance.
In addition, to increase the luminous efficiency, there has been proposed SrGa.sub.2 S.sub.4 :Eu,Tb and BaMgAl.sub.10 O.sub.17 :Eu,Tb. These materials are not also still enough in luminance.
As is well known, the active dynamic liquid display device requires a fluorescent material which is excited in a dark blue color range. The luminous efficiency of SrGa.sub.2 S.sub.4 :Eu and BaMgAl.sub.10 O.sub.17 :Eu is determined by transmission efficiency of light emission energy to Eu. Tb is used to transmit the light emission energy to Eu.