A LANTHANIDE LANTHOLOGY (.pdf) - Davidson Physics

THULIUMThulium, the rarest of the "abundant earths", is a typical heavy lanthanide with chemistrysimilar to Yttrium. Its most specific property is, upon appropriate excitation, an emission in theblue. The luminescence of Tm, for example, under X-ray excitation is in the near u.v (≈375 nm)and blue (≈465 nm), closely matching the sensitivityof normal photographic film. As Tm:LaOBr, it isused in sensitive Xray phosphors to reduce X-rayTmexposure.[ljAnother luminescence application is asTm-doped CaSO 4 , in dosimeters for radiationmeasurement. Incorporated in personal badgedetectors, it makes possible the precise measurementof low radiation doses in the ≈O.lmR to ≈50Rrange[2].Ln halides emit, at high temperatures, manyspectral lines and are added to metal halide dischargelamps. The aim of the emission is to reproduceclosely - within the visible but not outside thatregion - a black body spectrum. Thulium-sodiumiodidemixtures, at milligrams per lamp, provide highluminous efficiencies and good color rendition[3]probably through transient formation of a ternaryiodide.ElementAtomic Number 69Atomic Weight 168.93Electron configuration [Xe]4f 13 6s 2Valencies 3Ionic radius for8-coordination99 pmMagnetic moment 7.56 µBmetalCrystal StructurehcpMelting Point 1545°CBoiling Point 1950°CDensity 9.32 g/cm 3Metallic Radius175 pmA flat panel CRT display based onelectroluminescence depends critically ondeveloping a bright blue emitter. Although thulium, as the TmF 3 :ZnS phosphor, has the rightwavelength[4] it does not yet have the luminance / brightness required.[1] J.G.Rabatin, U.S.Patent 3,677,743, 1971 : Rare Earth X-Ray Phosphors for Medical Radiography,J.G.Rabatin, in "Industrial Applications of Rare Earth Elements", ed. K.A.Gschneidner, ACS Symp. 164, publ.Am.Chem.Soc., 1981, p. 135: New X-Ray Phosphors, LH.Brixner, Mat.Chem.Phys., 1987, 16, 253[2] The Use of Metal Filters to Flatten the Energy Response of CaSO 4 : Tm TL Dosemeters, and to ProvideSpectral Information, KStammers et al., Rad.Prot.Dos., 1991, 36(l), 23[3] Spectral Properties of Metal Halide Alamps with Rare Earth Iodide or Sc-Iodide and Sodium Iodide,P.Tielemans et al., Lighting Res.Tech., 1985, 1985, 17, 79 : Measurement of Enhanced Thulium Abundance inMetal Halide Discharge Lamps, M.J.Shea et al., in "High Temperature Lamp Chemistry", Vol 93-16, publ.Electrochem.Soc., 1993[4] Preparation and Photoluminescence of Thulium-Activated Zinc Sulfide Films, B.T.Collins et al.,J.Electrochem.Soc., 1991, 138(11), 351547