Dynamic white lighting to aid sleep and vision for persons living with dementia using off-the-shelf LED strips.

Alzheimer disease and related dementias affect 15-20% of elderly people, and 60-70% of these suffer from sleep disturbances. Studies suggest that lighting can improve sleep. The key challenge is how to deliver light effectively. We have designed a lighting system that adjusts spectrum and irradiance on a 24-hour timetable to provide spatially uniform, shadow-free white light with CRI>85 and up to 1000 Lux for day vision and amber light for night vision. To aid sleep, melanopic illuminance varies over 3 orders of magnitude to enable strong suppression of melatonin in the morning/early afternoon, moderate suppression in the evening, and no suppression at night.

MEH-PPV photophysics: insights from the influence of a nearby 2D quencher.

The effect of 2D quenching on single chain photophysics was investigated by spin coating 13 nm thick films of polystyrene lightly doped with MEH-PPV onto CVD grown graphene and observing the changes in several photoluminescent (PL) observables. With 99% of the PL quenched, we found a 60% drop in the PL lifetime, along with a significant blue-shift of the PL emission due to the preferential quenching of emission at longer wavelengths. During photo-bleaching, the blue spectral shift observed for isolated polymers was eliminated in the presence of the quencher up until 70% of the polymer was photo-bleached. Results were interpreted using a static disorder induced conjugation length distribution model. The quencher, by opening up a new non-radiative decay channel, ensures that excitons do not have sufficient time to migrate to nearby lower energy chromophores. The reduction of energy transfer into the lowest-energy chromophores thus reduces their rate of photo-bleaching. Finally, the difference between the quenched and non-quenched spectra allows the rate of energy transfer along the polymer backbone to be estimated at ∼2 ns-1.

On the potential of solid state LED strips utilizing an organic color converter for non-line of sight visible light communication.

LED strip lighting can provide high quality uniform shadow-free diffuse lighting at low cost as numerous emission sources are controlled by a single transformer. Organic LEDs offer the additional advantages of UV free emission and, for visible light communication, picosecond fluorescent lifetimes allowing the whole visible spectrum to be used without filters. Using parameters determined experimentally for solid-state LED strip lighting and fluorescent lifetimes typical of organic phosphors as the input for a Monte Carlo based ray-tracing simulation, we evaluate the potential bandwidths obtainable for indoor communication. Our work suggests that raw data transfer rates of 4 to 10 Mbps are obtainable in a standard 5m by 5m by 3m room compatible with Internet of Things (IoT) applications.

Local oxidation and reduction of graphene.

Micrometer sized oxidation patterns were created in chemical vapor deposition grown graphene through scanning probe lithography (SPL) and then subsequently reduced by irradiation using a focused x-ray beam. Throughout the process, the films were characterized by lateral force microscopy, micro-Raman and micro-x-ray photoelectron spectroscopy. Firstly, the density of grain boundaries was found to be crucial in determining the maximum possible oxygen coverage with SPL. Secondly, the dominant factor in SPL oxidation was found to be the bias voltage. At low voltages, only structural defects are formed on grain boundaries. Above a distinct threshold voltage, oxygen coverage increased rapidly, with the duration of applied voltage affecting the final oxygen coverage. Finally, we found that, independent of initial conditions, types of defects or the amount of SPL oxidation, the same set of coupled rate equations describes the reduction dynamics with the limiting reduction step being C-C â†’ C=C.

Controlling photoluminescent emission from polymer membranes through the creation of local deformation zones.

Understanding and optimizing light propagation and extraction in light-emitting systems, such as fluorescent chemical sensors, is important for the production of more efficient sensors. We apply Monte Carlo ray tracing to model the effects of one-dimensional perturbations of film thickness on the luminescent emission (spatial, directional, spectral) of a freestanding transparent polymer film embedded with luminescent chromophores. Such modification not only enhances light extraction but also allows its location and direction to be controlled. Optimization of the deformation geometry allows for a 3.6-fold increase in intensity for a far-field detector.