Jonathan R. Tischler

Highly efficient resonant coupling of optical excitations in hybrid organic/inorganic semiconductor nanostructures

The integration of organic and inorganic semiconductors on the nanoscale offers the possibility of developing new photonic devices that combine the best features of these two distinct classes of material. Such devices could, for example, benefit from the large oscillator strengths found in organic materials and the nonlinear optical properties of inorganic species. Here we describe a novel hybrid organic/inorganic nanocomposite in which alternating monolayers of J-aggregates of cyanine dye and crystalline semiconductor quantum dots are grown by a layer-by-layer self-assembly technique. We demonstrate near-field photon-mediated coupling of vastly dissimilar optical excitations in the two materials that can reach efficiencies of up to 98% at room temperature. By varying the size of the quantum dots and thus tuning their optical resonance for absorption and emission, we also show how the ability of J-aggregates to harvest light can be harnessed to increase the effective absorption cross section of the quantum dots by up to a factor of ten. Combining organic and inorganic semiconductors in this way could lead to novel nanoscale designs for light-emitting, photovoltaic and sensor applications.

Critically coupled resonators in vertical geometry using a planar mirror and a 5 nm thick absorbing film

A (5.1+/-0.5) nm thick film of high oscillator strength J-aggregated dye critically couples to a single dielectric mirror, absorbing more than 97% of incident lambda = 591 nm wavelength light, corresponding to an effective absorption coefficient of (6.9+/-0.7) x 10(6) cm(-1) for (film thickness)/lambda < 1%.

Synthesis of J-Aggregating Dibenz[a,j]anthracene-Based Macrocycles

Several fluorescent macrocycles based on 1,3-butadiyne-bridged dibenz[a,j]anthracene subunits have been synthesized via a multistep route. The synthetic strategy involved the initial construction of a functionalized dibenz[a,j]anthracene building block, subsequent installation of free alkyne groups on one side of the polycyclic aromatic framework, and a final cyclization based on a modified Glaser coupling under high-dilution conditions. Photophysical studies on three conjugated macrocycles revealed the formation of J-aggregates in thin films, as well as in concentrated solid solutions (polyisobutylene matrix), with peak absorption and emission wavelength in the range of lambda = 460-480 nm. The characteristic red-shifting of the J-aggregate features as compared to the monomer spectra, enhancement in absorption intensities, narrowed linewidths, and minimal Stokes shift values, were all observed. We demonstrate that improvements in spectral features can be brought about by annealing the films under a solvent-saturated atmosphere, where for the best films the luminescence quantum efficiency as high as 92% was measured. This class of macrocycles represents a new category of J-aggregates that due to their high peak oscillator strength and high luminescence efficiency have the potential to be utilized in a variety of optoelectronic devices.

Using Integrated Optical Feedback to Counter Pixel Aging and Stabilize Light Output of Organic LED Display Technology

We define a metric of useful operating lifetime of an organic light-emitting device (OLED) display and relate it to the commonly measured half-life of constituent OLED pixels. We enumerate sources of OLED operational instability and propose an optical feedback solution in a novel integrated configuration to counter pixel aging and maintain stable light output across all of the pixels of an OLED display. Such optical feedback can correct pixel imperfections in both active matrix and passive matrix OLED displays. As an example, we analyze lifetime data previously published by Kwong et al., in 2002, and demonstrate that our optical feedback technique could maintain 100 cd/m2 display light output within a 2% brightness accuracy for more than 25 000 hours of continuous use for this specific OLED system. From this example we draw conclusions generally applicable to extending stable operating lifetime of other OLED structures.

Exciton-polaritons at room temperature in dielectric microcavities exhibiting rabi-splitting Ω R ≫ 100 meV

Exciton-Polariton states are observed at room temperature in planar sputter-coated dielectric microcavities containing 5 nm thick film of J-aggregated dye as excitonic layer exhibiting Rabi-splitting Ω_R ≫ 100meV and empty cavity Q factor ≫> 700.

Ultrafast exciton response of high optical density J-aggregates from ultrathin films of cyanine dyes

Ultrathin films of cyanine dye J-aggregates show extraordinary exciton cross sections. Exciton dynamics are studied by ultrafast pump-probe and transient photoluminescence spectroscopy. An exciton delocalization length of N=18 monomers was measured at room temperature.

Critically coupling a 5.1 nm thick J-aggregate layer to a single dielectric mirror, resulting in an effective peak absorption constant of 6.9 x 10 6 cm −1

A 5.1 nm thick film of high oscillator strength J-aggregated dye, which gives rise to strong optical coupling, critically couples to a single dielectric mirror, absorbing 97% of incident light (effective absorption coefficient of 6.9 times 106 cm-1).