Abstract: A luminescent screen provided with a luminescent material having the hexagonal crystal structure, which material is an aluminate, a gallate or an aluminate gallate. The crystal structure of the luminescent material corresponds to that of at least one of the compounds .beta.-aluminium, .beta."-alumina and the hexagonal ferrites. The luminescent material is activated by at least one of the elements manganese, europium, lead, thallium, cerium, indium, terbium, dysprosium and bismuth and is a ternary compound whose composition can be represented in the ternary phase diagram ABC in which A represents at least one of the oxides 1/4Na.sub.2 O, 1/2K.sub.2 O, 1/2Rb.sub.2 O, 1/2Cs.sub.2 O, CaO, SrO, BaO, 1/2La.sub.2 O.sub.3, 1/2Ce.sub.2 O.sub.3, 1/2Tb.sub.2 O.sub.3, 1/2Dy.sub.2 O.sub.3, 1/2Bi.sub.2 O.sub.3, EuO, PbO, 1/2Tl.sub.2 O and 1/2In.sub.2 O, in which B represents at least one of the oxides Al.sub.2 O.sub.3 and Ga.sub.2 O.sub.3 in which up to 25 mol. % of the oxides denoted by B may be replaced by Sc.sub.2 O.