Abstract: A gas discharge lamp fitted with a gas discharge vessel filled with a gas filling suitable for a gas discharge which emits VUV radiation, with a phosphor coating containing a down-conversion phosphor and with means for igniting and maintaining a gas discharge, in which the down-conversion phosphor has, in a host lattice, a pair of activators of a first lanthanoid ion and a second lanthanoid ion and a sensitizer selected from the group formed by the thallium(I) ion and lead(II) ion, is environmentally friendly and has a high lamp efficiency (lamp. The invention also relates to a down-conversion phosphor comprising, in a host lattice, a pair of activators of a first lanthanoid ion and a second lanthanoid ion and a sensitizer selected from the group formed by the thallium(I) ion and lead(II) ion, wherein the sensitizer occupies a crystallographic site with a coordination number C.N.?10.