The Pi Cloud Chamber offers a unique opportunity to study aerosol-cloud microphysics interactions in a steady-state, turbulent environment. In this work, an atmospheric large-eddy simulation (LES) model with spectral bin microphysics is scaled down to simulate these interactions, allowing comparison with experimental results. A simple scalar flux budget model is developed and used to explore the effect of sidewalls on the bulk mixing temperature, water vapor mixing ratio, and supersaturation. The scaled simulation and the simple scalar flux budget model produce comparable bulk mixing scalar values. The LES dynamics results are compared with particle image velocimetry measurements of turbulent kinetic energy, energy dissipation rates, and large-scale oscillation frequencies from the cloud chamber. These simulated results match quantitatively to experimental results. Finally, with the bin microphysics included the LES is able to simulate steady-state cloud conditions and broadening of the cloud droplet size distributions with decreasing droplet number concentration, as observed in the experiments. The results further suggest that collision-coalescence does not contribute significantly to this broadening. This opens a path for further detailed intercomparison of laboratory and simulation results for model validation and exploration of specific physical processes.

The luminescence of the Eu3+ ion in some Zr4+ compounds is reported in order to study the influence of the effectively negative charge of the Eu3+ ion on the quantum efficiency for charge-transfer excitation.This effectively negative charge of the Eu3+ ion does not in principle enhance radiationless relaxation rates in the excited charge-transfer state, but the presence of vacancies in the structure may lower the efficiency considerably. For the Eu3+ luminescence in Zr02 and ZrPzO, the quantum efficiencies amount to about 30% and 60%, respectively. In these compounds the presence of vacancies may account for these values. In LizZr03:Eu3+ with a relatively low Li+ concentration it seems as though the partial incorporation of the Eu3+ ions on a Li+ site accounts for the low efficiency (about 10% at room temperature). The incorporation of the Mg2+ ion as a charge compensator in the LizZro3 lattice increases the quantum efficiency up to at least 60%.

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Several possibilities to design a cheap red lamp phosphor are reviewed. It appears to be possible to increase the amount of energy transfer from the niobate group in CaNb2O6 to Eu3+ on calcium sites by suitable substitutions. However, part of the niobate excitation energy still does not reach the Eu3+ ion. Only the method of using appropriate associates in a lattice is able to satisfy the requirements of highly efficient Eu3+ emission in a cheap host lattice.

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