Low-energy-electron-exciting fluorescent display device

Claim 1

A low-energy-electron-exciting fluorescent display device comprising an anode coated with SnO 2 :Eu powder phosphor, a cathode as a thermoelectronic emission source confronting said anode, a mesh grid located between said anode and cathode, and a glass tube for sealing said components in vacuum, wherein Eu content in said phosphor is such that the quantity of Eu based on the amount of Sn present is 5×10 -2 to 10 atomic % and the phosphor is prepared by the steps comprising: (a) admixing a material comprising at least one member selected from the group consisting of metallic tin, stannous halides, stannic halides and stannous sulfate; with an additive which includes europium in such amount that the quantity of europium based on the amount of tin present is 5×10 -2 to 10 atomic %; (b) simultaneously heating and stirring the mixture of step (a) with nitric acid until it becomes dry through evaporation, thereby forming a mixed powder of metastannic acid and europium; and then (c) subjecting the powder to heat treatment at a temperature in the range of from 1300° to below the melting temperature of stannic oxide, causing the metastannic acid to be thermally decomposed to stannic oxide and the europium to be diffused into said stannic oxide, whereby the phosphor exhibits a luminescence intensity more than 25 f.L when excited by 1.5 mA/cm 2 of electrons with an anode voltage of 10 V.