Composite Luminescent Materials and Light-Harvesting Systems

A.光化学。 ** 光伏能源系统的进步需要比今天的硅电池更好地利用太阳光谱。 硅太阳能电池板本身就优化了红色和近红外波长的有效收集，但由于称为热化的能量损失机制，在可见光谱的其他部分效率较低。 此外，更长波长的红外辐射根本不会被收集。我们更好地收集可见光的方法是使用基于荧光的太阳能电池系统。 基于荧光的太阳能电池使用磷光体或量子点来吸收光，然后以选定的波长重新辐射光。 在吸收和再辐射过程中，光的方向是随机的，它可以在收集板中被波导并被引导到板的边缘，在那里小型高效太阳能电池可以实现高转换效率。 为了使收集器板中的光的再吸收最小化，磷光体或量子点的分布和密度可以被优化或空间图案化。 我们正在研究使用空间图案化的磷光体，以允许集中的阳光到达磷光体，同时保持有效的波导系统，以允许荧光到达集电板的边缘。 ** 为了收集长波红外辐射，我们正在开发GaSb（锑化镓）薄膜太阳能电池。 GaSb吸收具有低至0.7电子伏（eV）的能量的光子，这允许有效地收集0.7- 1.1eV光子。 我们正在从允许化学计量（成分）变化的体靶溅射GaSb，从而实现薄膜半导体性能的优化。** B。 发光 ** 粉末材料的电致发光是一种有吸引力的方法来生产柔性光片。 这里，粉末可以夹在两个电极（其中一个是透明的）之间，并且在施加AC电压时，从粉末观察到发光。 传统的电致发光粉末由硫化物制成，但我们正在开发氧化物粉末，如硅酸锌粉末。 这些材料的活化需要引入第二导电相。 ** 虽然发光二极管已经在快速增长的固态照明市场中证明了自己可以取代白炽灯和荧光灯，但它们本质上是点光源，因此不适合需要薄而灵活的光片的应用。 这项工作的目标是提高柔性光片的亮度和稳定性，用于照明，标牌和显示器。 电致发光的一个具体用途是发光带，可以在黑暗环境中标记紧急出口或家具或设备的边缘。 未来更大的市场是可卷式电视机。

A. Photovoltaics. **Advances in photovoltaic energy systems require better use of the solar spectrum than today's silicon cells achieve. Silicon solar panels are inherently optimized for efficient harvesting of red and near-infrared wavelengths but are less efficient over other parts of the visible spectrum due to an energy loss mechanism called thermalization. In addition, longer wave infrared radiation is not harvested at all.**Our approach to better harvest visible light uses fluorescence-based solar cell systems. Fluorescence based solar cells use phosphors or quantum dots to absorb light and then re-radiate the light at selected wavelengths. During the absorption and re-radiation process, the light is randomized in direction and it can be wave-guided in a collection plate and directed to the edges of the plate where small, high efficiency solar cells can achieve high conversion efficiency. To minimize re-absorption of light in the collector plate the distribution and density of phosphors or quantum dots may be optimized or spatially patterned. We are investigating the use of spatially patterned phosphors to allow concentrated sunlight to reach phosphors while maintaining an efficient waveguiding system to allow the fluorescence to reach the edges of the collector plate. **For the harvesting of long wave infrared radiation we are developing GaSb (gallium antimonide) thin film solar cells. GaSb absorbs photons having energies from as low as 0.7 electron volts (eV) which allows the efficient harvesting of 0.7-1.1 eV photons. We are sputtering GaSb from bulk targets that allow the stoichiometry (composition) to be varied thereby enabling the optimization of thin film semiconductor properties.**B. Luminescence. **Electroluminescence in powder materials is an attractive approach to producing flexible sheets of light. Here a powder may be sandwiched between two electrodes (one of which is transparent) and upon the application of an AC voltage, luminescence is observed from the powder. Traditional electroluminescent powders are made from sulphides, however we are developing oxide powders such as zinc silicate powder. Activation of these materials requires the incorporation of a second conductive phase. **Whereas light emitting diodes have proven themselves in the rapidly growing solid state lighting market to replace incandescent and fluorescent lamps, they are inherently point sources and therefore do not lend themselves to applications where thin, flexible sheets of light are needed. The goal of this work is to improve the brightness and stability of flexible light sheets for applications in lighting, signage and displays. One specific use of electroluminescence is for glowing tapes that can mark emergency exits or edges of furniture or equipment in a dark environment. A larger future market is for roll-up televisions.