Department of Chemistry, The Pennsylvania State University , University Park, Pennsylvania 16802, United States.
The Dow Chemical Company, Midland, Michigan 48674, United States.
ACS Appl Mater Interfaces. 2017 Apr 12;9(14):12547-12555. doi: 10.1021/acsami.6b15323. Epub 2017 Mar 29.
Phosphor-converted light emitting diodes (pcLEDs) produce white light through the use of phosphors that convert blue light emitted from the LED chip into green and red wavelengths. Understanding the mechanisms of degradation of the emission spectra and quantum yields of the phosphors used in pcLEDs is of critical importance to fully realize the potential of solid-state lighting as an energy efficient technology. Toward this end, time-resolved photoluminescence spectroscopy was used to identify the mechanistic origins of enhanced stability and luminescence efficiency that can be obtained from a series of carbidonitride red phosphors with varying degrees of substitutional carbon. The increasing substitution of carbon and oxygen in nitrogen positions of the carbidonitride phosphor (SrSiNCO:Eu) systematically changed the dimensions of the crystalline lattice. These structural changes caused a red shift and broadening of the emission spectra of the phosphors due to faster energy transfer from higher to lower energy emission sites. Surprisingly, in spite of broadening of the emission spectra, the quantum yield was maintained or increased with carbon substitution. Aging phosphors with lowered carbon content under conditions that accurately reflected thermal and optical stresses found in functioning pcLED packages led to spectral changes that were dependent on substitutional carbon content. Importantly, phosphors that contained optimal amounts of carbon and oxygen possessed luminescence spectra and quantum yields that did not undergo changes associated with aging and therefore provided a more stable color point for superior control of the emission properties of pcLED packages. These findings provide insights to guide continued development of phosphors for efficient and stable solid-state lighting materials and devices.
磷光转换发光二极管（pcLED）通过使用荧光粉将 LED 芯片发出的蓝光转换为绿光和红光波长来产生白光。了解荧光粉发射光谱和量子产率降解的机制对于充分实现固态照明作为节能技术的潜力至关重要。为此，采用时间分辨光致发光光谱法来确定一系列碳化氮红色荧光粉的增强稳定性和发光效率的机制起源，这些荧光粉具有不同程度的取代碳。碳和氧在碳化氮荧光粉（SrSiNCO:Eu）的氮位的取代程度的增加系统地改变了晶格的尺寸。这些结构变化导致由于较高能量发射位点向较低能量发射位点的能量转移加快，荧光粉的发射光谱发生红移和展宽。令人惊讶的是，尽管发射光谱变宽，但量子产率保持或随碳取代而增加。在准确反映在功能 pcLED 封装中发现的热和光学应力的条件下，使含碳量降低的荧光粉老化，导致光谱变化取决于取代碳含量。重要的是，含有适量碳和氧的荧光粉具有不发生与老化相关的变化的发光光谱和量子产率，因此为更稳定的颜色点提供了更好的 pcLED 封装发射特性控制。这些发现为高效和稳定的固态照明材料和器件的荧光粉的进一步开发提供了思路。
