Lanthanide oxide or oxy-sulphide phosphor prodn. - via oxalate pptd. uniformly from over-acidified oxide soln., giving regular crystals, used to provide red phosphors for colour TV tubes

摘要

In the prodn. of a lanthanide phosphor by dissolving the crude oxide in an inorganic acid, converting to a mixed oxalate by adding oxalic acid and producing the phosphor by calcination and opt. further treatment, the crude oxide soln. is over-acidified by adding 0.3-3 times, esp. about the same amt. of (in)organic acid, which is required for dissolving the crude oxide, and then this soln. is treated with the required amt. of oxalic acid, in solid (pref. crystalline) form, as uniformly as possible over a period of 1/2-3, esp. 1-1 1/2 h. The process is used for the prodn. of lanthanide oxide or oxysulphide phosphors, esp. a Y2O3:Eu phosphor, which are used as red phosphors in colour TV tubes. It gives better and as uniform as possible crystal structure, so that the addn. of flux in the calcination stage can be (partly) eliminated. Brilliant light outputs are obtd. at calcination temps. from 1000 degrees C, whereas a calcination temp. of 1600 degrees C is normally necessary without flux. The process gives phosphor crystals with esp. favourable mechanical strength, regular (cubic) structure and very uniform size, whilst the size of the oxalate crystals is up to 200 mu m and the content of water of crystallisation is very low.