Evidence for electron-tunneling-limited Knudsen diffusion of mercury in phosphor layers and coatings of fluorescent lamps

Recent experimental studies and modelling of the mercury loss (i.e. the mercury consumption) in fluorescent lamps yield diffusion coefficients of mobile mercury in phosphor layers and coatings, which are several orders of magnitude smaller than expected for a gas diffusion in a situation in which the mean free path of the diffusing particles is restricted by the pore radius in those materials (Knudsen diffusion). In the present work it is shown that the transition of mercury ions from the plasma to the Knudsen diffusion regime may be one reason for this observation. Another possibility is that only discharged ions from the plasma form the mercury oxide as which mercury is deposited in the phosphor layer and coating, from the investigation of which the diffusion coefficient of mobile mercury is concluded by fitting the model to the experiment.