| Compared with traditional lighting technology,white light-emitting diodes(LEDs)have exhibited unique advantages,such as low energy consumption,high efficiency,no pollution and long life,and they are replacing incandescent lamps and fluorescent lamps.At present,there are mainly two kinds of white LED used for lighting:one is based on white light emission by coating YAG:Ce3+yellow phosphor on blue LED chip.However,it is not suitable for high-quality indoor lighting due to its high color temperature and low color index(Ra<80).Another effective method to obtain white light illumination is based on tri-color phosphors excited by near-ultraviolet(n-UV)LED chips.As the excitation light source in this method has higher energy,more different kinds of efficient phosphors can be selected and white LEDs with high color rendering index and various color temperatures can be theoretically designed.Therefore,more researches are focused on how to develop novel high performance(high color rendering index,low color temperature,high thermal stability)phosphors excited by n-UV LED chips.Among them,silicate-based phosphors doped with rare earth ions have been attracted much attention because of the use of environmentally friendly raw materials,good chemical stability and strong absorption capacity in the n-UV region.In this dissertation,Li+/La3+co-doped Li0.066La0.06Ba0.84Si2O5:4%Eu2+(LLBSO:Eu2+)high-efficient green-emitting powders excited by n-UV light were prepared by a solid sintering method in hydrogen atmosphere,and their optical properties and the thermal stability of their luminescent performance were systematically studied.Moreover,a series of white LED devices were fabricated by using the above phosphors in combination with the corresponding encapsulation technology.The color rendering index,color temperature and CIE coordinates of the related device were calculated and analyzed.The main results were given as follows:A series of Ba0.96Si2O5:4%Eu2+(BSO:Eu2+)powders doped with Li+and La3+ions were prepared at different synthesis temperatures and synthesis time by high temperature solid phase method.It was found that it was difficult to obtain single-phases BSO:Eu2+powders without the addition of Li+and La3+ions,i.e.there existed impurity phase in the above powders prepared at 1250? for 4h.The addition of Li+and La3+will benefit the synthesis of single-phased LLBSO:Eu2+phosphors and can effectively reduce the sintering temperature and shorten the synthesis time.The related tests showed that,for Li+/La3+co-doped BSO:Eu2+phosphors,the particle agglomeration was not obvious and the average particle size was mainly in the range of 1.1?2.7 ?m and larger than that of the un-doped phosphor,which met the requirement of the phosphors coated on n-UV LED chips.These phosphors can be effectively excited by a n-UV LED light(365 nm)to produce a strong broadband green emission at 502 nm,whose luminescent intensity is 168%as strong as that of the un-doped phosphor.In addition,the luminescent intensity of LLBSO:Eu2+phosphors at 150? remains about 98%of that at room temperature,showing their good thermal stability.It was found that the CIE coordinates of LLBSO:Eu2+green-emitting phosphors(0.217,0.410)were in the green region.The unique position of their color coordinates enables the phosphor powder to be mixed with red CaSiAlN3:Eu2+phosphors to achieve the warm white light emission with color rendering index(Ra)greater than 85 in the application of white LED devices.The above LED device not only reduced the harm of blue light to human eyes but also decreased the synthesis cost.Our results showed that single-phased Li+/La3+co-doped BSO:Eu2+green-emitting phosphors are an excellent candidate for fabricating n-UV excited white LEDs. |
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