Faculty Sponsor's Department:
In order to replace current inefficient methods of producing white light (such as incandescent light bulbs), extensive effort has been expended on the development of phosphor-converted white light-emitting diodes (LEDs). Among the many materials used for this purpose, silicates are good candidates for phosphors, due to their structural variety and chemical/ temperature stability. The end members, glaserite-type Ba3MgSi2O8 and merwinite-type (Sr,Ca)3MgSi2O8 are crystal phases which, when doped with small quantities of Eu2+, exhibit blue fluorescence (436-492nm) under near UV excitation, making them suitable candidates for applications in white LEDs (for example as the blue component in phosphor blends). A wide range of compositions (Bax (Ca,Sr)yMgSi2O8, where x+y=3) was achieved by employing a sol-gel preparation method, which ensures uniform dispersion of europium ions throughout the crystal lattice. An inexpensive domestic microwave oven was used to heat treat the gel, which drastically reduced both time and energy cost, compared to conventional high temperature furnace methods. Carbon was used as a susceptor: acting as both the initial heat source, whilst also reducing the europium to its desired divalent state. Samples were characterized using X-ray diffraction, and various optical techniques (such as absorption and emission spectroscopy). Through substitution of barium with calcium or strontium, it is possible to adjust the emission wavelength of the blue emission, while retaining high absorption strength at 365nm. After optimizing the alkaline earth metal cation (Ba to Ca or Ba to Sr) ratio, a phosphor containing silicone cap will be studied in a commercial device, to determine quantum yield and to test efficiency.