Investigation of photo-chromic properties of remote phosphor film and white light emitting diode mixed with TiO2 particles

Abstract

Based on the hot pressing method, the remote phosphor films are prepared by adding TiO2 particles into YAG:Ce and silicon binder, and then they are packaged into white light emitting diode (WLED) device with chip on board (COB) blue light source. The photo-chromic properties and mechanism are studied and calculated. Based on Mie theory and Henyey-Greenstein function, forward scattering is the main light scattering form of YAG:Ce phosphor powder, while the forward scattering intensity is close to the back scattering intensity of TiO2 particles. The emission spectral intensity and relative luminance of remote phosphor film change with increasing the concentration of TiO2 particles, and the optimum concentration is 0.966 g/cm3. Forward transmission intensity and back reflection intensity are calculated and analyzed, when the concentration of TiO2 is low, the forward transmission intensity of blue light is stronger than that of yellow light and the main transmission form is forward transmission, while the forward and backward intensity of yellow light are similar because of isotropy. With increasing the concentration of TiO2, the forward intensity of blue light gradually decreases, and the transmission intensity is lower than that of yellow light. The forward and backward intensity of yellow light reach their maxima when the TiO2 concentration is 0.966 g/cm3. The main reason for this phenomenon is that the increasing of the utilization ratio between blue light and transmission of yellow light is affected by the strong scattering ability of TiO2. Finally the WLEDs are packaged by remote phosphor films and COB blue light source, the luminous flux of WLED reaches 415.28 lm (at 300 mA and 9.3 V) at a concentration of 0.966 g/cm3, which is increased by 8.15% compared with the concentration in the case of no TiO2 mixing. Besides, the correlated color temperature changes from cool white 6900 K to warm white 3832 K gradually. Consequently, the adding of TiO2 particles can not only improve the emission intensity of remote phosphor film and the luminous flux of WLED, but also regulate the correlated color temperature.