Quantum phospors

摘要

In luminescent-tube lighting (TL), mercury is used to excite (λ_(max) = 254 nm) three phosphors, resulting in white light. The use of mercury however gives environmental problems and causes an unitesired delay in lamp startup, IT mercury is replaced by xenon, which is already gaseous at room temperature and harmless to the environment, both problems are solved. Xenon however emits at higher energy (λ_(max) = 172 nm) and the phosphors used in mercury-based tube lighting show a less efficient absorption to this vacuum ultra violet (VUV) radiation. Therefore, much effort is put in developing new phosphors. The Pr~(3+) (4f~2) ion shows strong absorption in the VUV range, which can be assigned to the 4f~2→4f~15d~1 transition. Another interesting effect is that in some hosts the Pr~(3+) ion can, after excitation into the 4f~15d~1 bands, show a two-step relaxation to the ground state. This process is called photon cascade emission (PCH) or quantum culling and could result in a quantum efficiency larger than 100%. The emitted photons are typically in the violet and green spectral region. This contribution describes the principles of Pr1' quantum cutting and presents methods to select host materials in which Pr~(3+) shows quantum cutting. Furthermore, several Pr~(3+)-doped hosts are presented, which show the PCE process both under VUV and host excitation.