Yurong Ying

Electroluminescent colloidal inks for flexographic roll-to-roll printing

The academic and commercial interest in organic light-emitting devices is motivated in part by the potential of building devices utilizing simple and inexpensive fabrication routes, for example, commercial printing techniques. The focus on synthetically challenging small molecules and π-conjugated polymers for these devices is countered by the alternative of developing emissive materials that utilize an electroluminescent dye embedded in a hole and electron transporting host. In this effort, we exploit readily obtainable materials and simple fabrication routes to produce light-emitting colloidal particles, which in turn allows us to invoke the concept of a “particle device”. Specifically, we present colloidally based organic light emitting devices that can be designed to produce a range of colors by mixing together various ratios of red-, green-, and blue-emitting particles. These aqueous-based colloids are adaptable to form printing inks and may be utilized in fabricating devices through high-throughput commercial printing technologies.

Pressure tuning the optical transmission properties of photonic band gap composites

A pressure cell was configured to allow the dynamic tuning of the transmission characteristics of a mechanochromic colloidally based photonic crystal. The rejection wavelength exhibited a 212nm shift from 645to433nm with an applied pressure of 20kPa. At pressures greater than 5kPa, the rejection wavelength shifted ∼−8nm for every incremental 1kPa rise in pressure.

Crystalline colloidal arrays : applications in organic lasers

The prospect of an inexpensive organic laser which can dynamically alter its lasing wavelength is desirable for a number of display and communication technologies. In this effort, real-time tuning of the lasing wavelength is accomplished through the use of colloidal crystals to provide the required reflectivity in an external resonator cavity design in which a gain medium is sandwiched between a dielectric stack and colloidal crystal. Optical pumping of the gain medium lead to a lasing peak that corresponded to the stop band of the photonic crystal. By varying the compressive strain placed on the colloidal crystal, the lasing could be tuned across the photoluminescent spectrum of the gain material. Repeated straining of the assembly did not appear to alter its proclivity to lase when photo-excited or introduce hysteresis in the lasing wavelength strain relationship. The fast response of the crystal to compressive strain could lead to pulsed organic lasers operating at kHz modulation frequencies.