Colloidal quantum dot nanocomposites for visible wavelength conversion of modulated optical signals

We report on the steady-state and optical modulation characteristics of a luminescence down-converting colloidal quantum dot/polyimide nanocomposite system suitable for integration with gallium nitride optoelectronics. The approach provides solution-processable and environmentally stable composite materials whose optical conversion and intrinsic modulation properties were evaluated at wavelengths from 535 to 624 nm. A nanocomposite for white-light generation upon excitation and mixing with 450-nm light was also obtained by blending colloidal quantum dots of different sizes in the same matrix. The forward external quantum efficiencies of the resulting nanocomposites were found to depend on the wavelength and can be as high as 33%. Optical modulation bandwidth above 25 MHz, which is an order of magnitude higher than for typical phosphor-based color-converters for GaN LEDs, and wavelength-converted data with an open-eye diagram at 25 Mb/s are demonstrated under external gallium nitride light-emitting diode excitation. These modulation characteristics are correlated with carrier lifetimes. This work provides guideline parameters and creates a possible path to integrated hybrid visible light sources for scientific and communications application