| white light emitting diodes (WLEDs) are regarded as the forth lighting source and have promising applications due to their high efficiency, small volume, long lifetime, and environment protection. Generally, there are two main ways to gain WLTDs:one is using a blue LED combinated with a yellow or green or red phosphor. The other one is combination of a near-UV(NUV) or UV LED with red, green, and blue phosphor to achieve white light. Both methods have their own Advantages and disadvantages,the former one can achieve high luminous efficiency, but the color rendering index (CRI) of WLEDs is relatively lower. Generally speaking, the latter one can show higher CRI and stability, but the luminous efficiency is need to further improve. In order to gain high efficiency and quality white light, looking for tricolor phosphors that suitable for near-UV excitation is necessary. At present, Alkaline earth sulfides and oxides activated by Rare Earth Ions have received increasing interest for their advantages of high luminous efficiency, low synthesis conditions, low cost and high chemical stability. These phosphor can absorb near ultraviolet or visible light, which are very suitable for near-UV LED or blue LED chips. What’s more, Alkaline earth sulfides and oxides activated by rare earth ions has been widely studied because of it’s simple preparation methods and cheap raw materials. The main purpose of this work is to achieve high efficient electron trapping materials and phosphor for white LEDs which are suitable for blue or near-UV excitation, we study on the electron tapping and photoluminescence properties of rare erth ions droped SrS and CaO, the main results obtained are listed as follow: (1) SrS:Eu2+,Sm3+,Er3+electron trapping materials were prepared by hydrothermal method. The effect of temperature on crystal phase formation, Er content on optical storage and luminescence properties, Photostimulated luminescence decay mechanism are studied. It is revealed that the Er induced luminescent enhancement and the optical storage properties improved. The maximum luminescence intensity and optical storage are obtained at x=0.003, which is as high as1.9times and3.5times of the Er free phosphor respectively. The introduction of Er didn’t change the crystal structure and Photostimulated luminescence decay curve properties of the sample.(2) Eu2+activated CaO were prepared by high temperature solid state reaction. We first realize the intense blue emission of Eu2+among CaO. CaO:Eu2+emit a broadband with a maximum at460nm, the excitation spectrum covers the whole UV and near-UV area. The Er3+and NH4C1content on optical properties and crystal phase formation are studied, It is revealed that the optimization concentration are0.5mol%and6mol%, respectively. Upon near-UV excitation, we compared CaO:Eu2+with the current commercial blue powder BAM. At the same time, we also investigate its temperature characteristics, When temperature reaches200℃, the emission intensity can maintain86.56%of which under normal temperature. The present results suggest that CaO: Eu2+could be a promising blue emitting phosphor for excitation by near-UV light emitting diodes.(3) Ce3+and Li+codoped CaO were prepared by high temperature solid state reaction. The Er3+content and the difrrent kinds of charge compensatio on optical properties are studied, It is revealed that the optimization concentration are both0.7mol%, respectively, we compared CaO:Ce3+, Li+with YAG:Ce3+, and their temperature characteristics are studied. Combining the present phosphor with a blue LED chip, a white LED with an excellent color rendering index of86and lower color temperature of54524K is obtained. It conformed that CaO:Ce3+, Li+is a promising phosphor for enriching red component of white LEDs. |
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