Abstract
Color converting films of colloidal quantum dots (CQDs) encapsulated with flexible glass are integrated with microsize GaN LEDs (μLEDs) in order to form optical sources for high-speed visible light communications (VLC). VLC is an emerging technology that uses white and/or colored light from LEDs to combine illumination and display functions with the transmission of data. The flexible glass/CQD format addresses the issue of limited modulation speed of typical phosphor-converted LEDs while enhancing the photostability of the color converters and facilitating their integration with the μLEDs. These structures are less than 70 μm in total thickness and are directly placed in contact with the polished sapphire substrate of 450-nm-emitting μLEDs. Blue-to-green, blue-to-orange, and blue-to-red conversion with respective forward optical power conversion efficiencies of 13%, 12%, and 5.5% are reported. In turn, free-space optical communications up to 1.4 Gb/s VLC is demonstrated. Results show that CQD-converted LEDs pave the way for practical digital lighting/displays with multi-Gb/s capability.
Highlights
Colloidal quantum dots (CQDs) have emerged as an attractive luminescent nanomaterial for lighting and displays, in part because of their solution processability, narrow emission linewidth and broad absorption spectra
The forward power conversion efficiency values are lower than the photoluminescence quantum yield (PLQY) because of the quantum defect and because light emitted in other directions, included light waveguided in the CQD film and the flexible glass, is not detected by the system
We have demonstrated high-speed visible light communications (VLC) using μLEDs color converted by CQDs
Summary
Colloidal quantum dots (CQDs) have emerged as an attractive luminescent nanomaterial for lighting and displays, in part because of their solution processability, narrow emission linewidth and broad absorption spectra. Photodegradation starts in the samples once oxygen has permeated the epoxy sealing the edges of the flexible glass and reached the CQD films This takes between ten to more than 250 hours in our converters and during that time color conversion is stable. The forward conversion efficiency (the ratio of the power of the converted light, as measured in the forward direction by the experimental system, by the power of the bare μLED, see Section 4.3) for each wavelength of color converter is consistent with the PLQY. The forward power conversion efficiency values are lower than the PLQY because of the quantum defect and because light emitted in other directions, included light waveguided in the CQD film and the flexible glass, is not detected by the system. These PL lifetime values (between 13 ns and 35 ns) are at least two orders of magnitude shorter than for conventional phosphors
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