GB1161339A - Luminescent Materials - Google Patents

Abstract

1,161,339. Luminescent materials. LOCKHEED AIRCRAFT CORP. 9 Dec., 1966 [13 Dec., .1965; 22 Aug., 1966], No. 55374/66. Heading C4S. A phosphor has the empirical formula (La 1-x Ax) 2 O 2 S, where A is -trivalent Eu alone or trivalent Eu and Sm, x is 0À01 to 0À09 (preferably 0À05 to 0À07) and is a minimum of 0À03 when the maximum 0À01 amount of Sm is present. Y and/or Gd may replace up to 10 atom per cent of the La and incidental traces of Pr, Nd, Ce, Mn or Pb may be present. Under 2537A and 3660A radiation and cathode rays, maximum red colour is obtained at higher Eu concentrations (6À5 atm per cent), maximum total brightness at lower Eu concentrations (0À1 to 1 and 2 atom per cent) and maximum red component intensity (at 6200A) at intermediate concentrations (3 atom per cent), with an increase in red colour with temperature within the 30‹ to 202‹ C. range, the maximum red colour component being at 100‹ C. The phosphor may be used in colour TV, low and high pressure mercury lamps and fluorescent lamps (or advertizing, display and agricultural purposes) with Eu concentration 1 to 4, preferably 1 to 3 atom per cent, mixed with CaHPO 4 : Mn for instance and thermographic applications in medicine and for relative and absolute temperature measurements is also mentioned, utilizing potassium silicate as binder to improve thermal contacts. In preparation, rare earth oxides may be prefired at 1000‹ C., dissolved in HCl, the pH adjusted to from 2 to 5, the precipitate added to oxalic acid, dried, calcined at 1250‹ to 1300‹ C. and heated and 900‹ to 1100‹ C. in a hydrogen-sulphur dioxide atmosphere, then heated at 500‹ C. in-air or argon; for 4 to 10 micron particles precipitation proceeds at 50‹ C. followed by heating at 150‹ C. for 8 hours. Alternatively, La 2 O 3 and Eu 2 O 3 are separately prefired at 1000‹ C.,. dissolved in water and nitric acid, precipitated with excess .NH 4 OH, dried, ground, heated with NH 4 SO 4 , heated at 825‹ C. in A and H 2 -A, then heated with sulphur in an evacuated enclosure. Prior art phosphors instanced include YV0 4 : Eu with Gd<SP>3+</SP>, Lu<SP>3+</SP> and La<SP>3+</SP> substitutions, lanthanum oxysulfides and oxychlorides with Eu-Pb and Eu-Sm activator combinations respectively.