Hybrid remote quantum dot/powder phosphor designs for display backlights

• Published in: Light, science & applications science & applications, 2017-06, Vol.6 (6), p.e16271-e16271
• Main Authors: Abe, Sofie, Joos, Jonas J, Martin, Lisa IDJ, Hens, Zeger, Smet, Philippe F
• Format: Article
• Language: English
• Subjects: 639/624/1020/1089; 639/624/399/1017; Applied and Technical Physics; Atomic; Cadmium; Classical and Continuum Physics; Color; Design engineering; Lasers; Light emitting diodes; Molecular; Optical and Plasma Physics; Optical Devices; Optics; Original; original-article; Photonics; Physics; Physics and Astronomy; Powder; Quantum dots; Reabsorption
• ISSN: 2047-7538; 2095-5545; 2047-7538
• DOI: 10.1038/lsa.2016.271

Quantum dots are ideally suited for color conversion in light emitting diodes owing to their spectral tunability, high conversion efficiency and narrow emission bands. These properties are particularly important for display backlights; the highly saturated colors generated by quantum dots justify their higher production cost. Here, we demonstrate the benefits of a hybrid remote phosphor approach that combines a green-emitting europium-doped phosphor with red-emitting CdSe/CdS core/shell quantum dots. Different stacking geometries, including mixed and separate layers of both materials, are studied at the macroscopic and microscopic levels to identify the configuration that achieves maximum device efficiency while minimizing material usage. The influence of reabsorption, optical outcoupling and refractive index-matching between the layers is evaluated in detail with respect to device efficiency and cost. From the findings of this study, general guidelines are derived to optimize both the cost and efficiency of CdSe/CdS and other (potentially cadmium-free) quantum dot systems. When reabsorption of the green and/or red emission is significant compared to the absorption strength for the blue emission of the pumping light emitting diode, the hybrid remote phosphor approach becomes beneficial. Quantum dots: hybrid colour converter for LEDs Combining a green-emitting powder phosphor with red-emitting quantum dots gives a high-performance color converter for white LEDs. This hybrid approach, studied by scientists from Ghent University in Belgium, is promising for improving the performance and cost effectiveness of LED-based display backlights. Sofie Abe and co-workers studied the combination of red-emitting CdSe–CdS core–shell quantum dots with green-emitting europium-doped strontium thiogallate (SrGa 2 S 4 :Eu 2+ ) microcrystals. They found that when this hybrid phosphor is applied to a blue LED, it can yield a white-light source that has a high quantum efficiency and luminous efficiency. The researchers provide general guidelines for optimizing both the cost and efficiency of CdSe–CdS and other quantum dot systems. In particular, the team found that the most economical design is a layered stack of the two materials.