Abstract

The Pr³⁺ ion is an interesting ion with respect to its possible use in next generation fluorescent lamps based on the Xe noble gas discharge, see e.g. [1,2], The Pr³⁺ ion exhibits an efficient absorption into the 4f5d bands of Pr³⁺ below 200 nm matching the emission of Xe. After nonradiative relaxation into the ¹S₀ level a cascade emission occurs within the 4f² manifold. The first step (¹S₀→¹I₆) occurs in the blue spectral range around 400 nm and is followed - after nonradiative relaxation into the ³P₀ level - by the second step (³P₀→³F_j,³H_j) accompanied by visible emission at longer wavelengths. The overall quantum efficiency η of this cascade emission is > 1 in some fluoride materials [2], However, the main fraction of the emitted radiation occurs at approx. 400 nm and is, therefore, not suitable for the application as lamp phosphor, because the responsivity of the human eye is too small at this wavelength. Thus a reasonable color rendering is not possible. Therefore, there is ongoing research for suitable transfer partner ions allowing the conversion of the 400-nm radiation into longer wavelength radiation. From the group of lanthanide rare earth ions, Sm³⁺, Eu³⁺, Dy³⁺ and Er³⁺ seem to be suitable candidates, because they have a resonant transition around 400 nm and they emit mainly in the visible spectral range with high quantum efficiency.

© 2007 IEEE