Hybrid remote phosphors for white LEDs : combining quantum dots and rare earth doped phosphors

Current white LEDs (wLEDs) are composed of a blue pumping LED and color convertors U+2013 phosphors U+2013 which are typically rare earth doped inorganic materials. As backlight in displays these wLEDs often have the disadvantage that a substantial fraction of the emitted light needs to be filtered out. In general lighting, efficiency losses are often generated by an emission extending into the infrared region, while also color rendering can be suboptimal. Recently, the use of quantum dots (QDs) as color convertor materials in wLEDs has gained attention as a solution to these problems. Here, we discuss our recent research results obtained to improve both performance and cost-efficiency of wLEDs for display and lighting applications. The focus lies on developing color convertor materials and implementing these in a remote phosphor configuration, thereby improving efficiency, (color) homogeneity and stability compared to conventional designs where the phosphor material is deposited directly on the LED chip. We explore the use of hybrid phosphor layers, consisting of a combination of rare earth doped phosphors with CdSe or InP-based QDs. We provide an overview of synthesis strategies to obtain the required QDs and configurations to implement them in a remote phosphor layer. Characterization of optical and scattering properties of these layers using e.g. emission decay measurements to asses self-absorption is discussed. Finally, we show relevant characteristics of a benchmark wLED device.

Publication year:2015