Fast modelling of the optical characteristics of electroluminescent pixel structures

An analytic model of the optical behaviour of laterally light emitting thin film structures is developed. It is employed to calculate the outcoupled light of a pixel used in light emitting dot matrix displays such as laterally emitting thin film electroluminescent displays (LETFEL) with micromirrors. Consequently, one can identify the optimum pixel geometry. Here, the optical behaviour of the circular, square and hexagonal pixel geometry is modelled. The presented closed form solutions are based on a ray optics approximation whereby the absorption of the light within the light generating medium (phosphor material) and the transmission behaviour of the phosphor-air interface is taken into account, as well as the micromirror width. These solutions, however, neglect back reflected light. The effect of this neglect is investigated for square pixels by taking into account the first reflection. The model is applied to a typical LETFEL display with ZnS material doped with Mn. An optimal pixel diameter of 35 μm is estimated for that particular type of display