Abstract: Suitable starting materials for the manufacture of a heavy metal fluoride glass composition are mixed with solid xenon fluoride as the fluoridizing reagent, after which the mixture is heated to temperatures between 200.degree. and 400.degree. C. in an inert atmosphere for a time which suffices to bring about fluoridation of the starting materials. The intermediate product thus obtained is melted thereby forming a stable glass composition of a high purity and a high transparency. The method can be carried out in a simple manner in a furnace which need not be gastight.

Abstract: Luminescent quartz glass comprising as a glass matrix oxide mainly SiO.sub.2 and furthermore per mole of SiO.sub.2 from 0 to 0.15 mol of at least one of the oxides Al.sub.2 O.sub.3, B.sub.2 O.sub.3, P.sub.2 O.sub.5, ZrO.sub.2, Sc.sub.2 O.sub.3, Y.sub.2 O.sub.3, La.sub.2 O.sub.3, Gd.sub.2 O.sub.3, Lu.sub.2 O.sub.3, the alkali metal oxides and the alkaline earth metal oxides. The glass comprises as an activator oxide at least one of the oxides Tb.sub.2 O.sub.3 and Ce.sub.2 O.sub.3 in a quantity of 0.75 to 15 mol % calculated with respect to the glass matrix oxides. In one embodiment the glass comprises Tb.sub.2 O.sub.3 and also not more than 0.2 mol % of Eu.sub.2 O.sub.3 as an activator oxide. The glasses are preferably obtained by a sol-gel technique and are useful, for example, in luminescent screen of low-pressure mercury vapor discharge lamps.

Abstract: Luminescent alumino-silicate and/or alumino-borate glass comprising lanthanum and/or gadolinium and activated by Tb.sup.3+ and/or Ce.sup.3+ and have a composition comprising 35-85 mol % of SiO.sub.2 and/or B.sub.2 O.sub.3, 1-35 mol % of La.sub.2 O.sub.3 and/or Gd.sub.2 O.sub.3, 5-45 mol % of Al.sub.2 O.sub.3 and 0.5-30 mol % of Tb.sub.2 O.sub.3 and/or Ce.sub.2 O.sub.3. The La.sub.2 O.sub.3 and/or Gd.sub.2 O.sub.3 may be replaced up to not more than 50 mol % by Y.sub.2 O.sub.3, Sc.sub.2 O.sub.3, Lu.sub.2 O.sub.3, ZrO.sub.2, P.sub.2 O.sub.5 and/or alkaline earth metal oxides. The glass can be used in a luminescent screen, for example, of a low-pressure mercury vapour discharge lamp.