Luminescent Glass Ceramics for White LED Applications

白光LED主要由蓝色发光LED芯片与黄色发光荧光粉结合而成。由于缺乏红色光谱成分，这类led的色彩印象往往会轻微地向冷的蓝色光谱范围偏移。荧光粉的限制是当暴露在LED芯片的高温下会降解。使用发光玻璃和玻璃陶瓷作为荧光粉和封装剂的组合，比传统的聚合物基封装更耐高温。通过选择性地掺杂稀土金属族元素，可以调整发射和随后的颜色印象。由于其高的机械、化学和热稳定性，硼酸盐玻璃被用作基体材料。在该项目的框架内，开发并优化了新型发光玻璃陶瓷的光学性能。对预合成的发光玻璃进行热处理，得到微晶。通过在晶体上的散射和多次反射，这些系统中的光程长度可以显著增加，从而在相同的光激发功率下增加光输出。所研究的玻璃陶瓷由不同稀土金属离子掺杂程度的锂、钠或硼酸钡玻璃组成。稀土被用作光学活化剂。在紫外线或蓝色光谱范围内激发后，它们在可见光谱中显示出强烈的发射。

White LEDs mostly consist of blue emitting LED chips combined with a yellow-emitting phosphor. Due to the lack of red spectral component, the color impression of such LEDs is often shifted slightly to the cold blue spectral range. The limitation of the phosphor is its degradation when exposed to the high temperatures of the LED chips. The use of luminescent glasses and glass ceramics as a combination of phosphor and encapsulant are more resistant to high temperatures than conventional polymer-based encapsulation. Through selective doping with elements from the group of rare-earth metals, the emission and subsequently the color impression can be adjusted. Owing to their high mechanical, chemical and thermal stability, borate glasses are to be used as matrix material.Within the framework of this project, new luminescent glass ceramics are developed and optimized in terms of their optical properties. Crystallites were obtained through the thermal treatment of pre-synthesized luminescent glasses. By scattering and multiple reflections on the crystallites, the optical path length in these systems can be significantly increased, so that the light output at the same optical excitation power increases. The glass ceramics under examination consist of lithium, sodium or barium borate glasses with different levels of doping of different rare-earth metal ions. The rare-earths are used as optical activators. Upon excitation in the ultraviolet or blue spectral range, they show a strong emission in the visible spectrum.