II-VI semiconductors can exhibit strong photoluminescence throughout the visible spectrum and are excellent candidates
for filling the so-called "green gap". We report on the performance of green color-converted LEDs fabricated by bonding
CdMgZnSe multiple quantum well structures to high-efficiency blue-emitting GaInN LEDs. A device efficacy of 181
lm/W at 537 nm (dominant) is measured under room temperature, 350 mA/mm<sup>2</sup> quasi-cw conditions, more than twice as
efficient as typical commercial green LEDs today. The thermal roll-off is shown to be comparable to that of typical
green GaInN LEDs. Finally, the implications of the availability of high-efficiency, narrow-band, green and yellow
emitters in display applications will be discussed.
Two-photon induced photopolymerization allows fabrication of complex three-dimensional structures with sub-micron resolution in a single exposure/development cycle. We analyze the kinetics of two-photon polymerization in multi-functional acrylic photopolymers and SU-8 epoxy resins as a function of two-photon photosensitizer and electron acceptor concentrations. The rate of polymerization is observed to be directly proportional to the concentration of the two-photon photosensitizer, directly proportional to the square of the intensity, and varies more weakly with the concentration of electron acceptor. A transition from high aspect ratio to low aspect ratio structures is observed that depends on both the energy absorbed per unit area and the concentration of the photoinitiator system. In acrylates, quantitative estimates of the photoinitiation rates suggest that the concentration of radicals at threshold is much higher under two-photon exposure conditions than under one-photon exposure conditions. Diffusion of radicals or inhibitors into or out of the illuminated region may have important effects on the overall reaction rate for two-photon induced polymerization.
Maximization of scan speed and throughput while maintaining resolution is critical for commercialization of two-photon microfabrication technology. We report contrast curves for cationic and free radical two-photon polymerization. An unusual relationship between voxel shape and dose is observed where the voxel ranges from highly asymmetric (aspect ratio of 4:1 or greater) at high dose to nearly spherical low dose (aspect ratio 1:1 or lower). Similar behavior is observed for both types of polymerization systems suggesting that the change is aspect ratio is not a function of the specific type of chemistry. It is found that a simple optical model describing the intensity distribution near the focal point can predict the change in aspect ratio.
Conference Committee Involvement (2)
Nonlinear Optical Transmission and Multiphoton Processes in Organics II
5 August 2004 | Denver, Colorado, United States
Nonlinear Optical Transmission and Multiphoton Processes in Organics
3 August 2003 | San Diego, California, United States