Hajime Yamamoto

Phosphor Materials for Cathode-Ray Tubes

Publisher Summary The cathode-ray tube (CRT) was invented by Karl Ferdinand Braun essentially for displaying electrical signals. This chapter discusses the basic luminescent processes.It describes the specific excitation processes occurring under electron bombardment. The chapter also examines the phosphor materials for specific applications along with the methods for the synthesis of phosphors. Furthermore, the chapter discusses screen fabrication techniques and describes phosphor screens with special properties. The processes involved in the aging of phosphors are also presented in the chapter. The chapter describes the methods for enhancing the image contrast of phosphor screens. It is noted that the highly advanced state of development of CRTs used for consumer, military, and industrial applications has largely been made possible by the advances in phosphor materials. However currently, the central issue remains the development of a blue phosphor that can substitute for ZnS:Ag, Al or ZnS:Ag, and Cl materials whose brightness saturation often presents a serious problem under high loading power. In this context, exploratory work on rare-earth phosphors as well as improving ZnS:Ag phosphors is necessary.

MgB2 films with very high critical current densities due to strong grain boundary pinning

MgB2 superconductor has a great potential for applications because of its high Tc and Bc2, exceeding those of any Nb-base superconductors at any temperature. It is now important to understand its flux pinning so as to raise Jc to high values over a wide field range. We show that nanometer-sized columnar-grain structure can produce Jc exceeding 5×106A∕cm2. The angular dependence of Jc indicates that the strongest pinning occurs when the field is aligned parallel to the grain boundaries. Our results confirm earlier deductions that grain boundaries in MgB2 act as effective pinning centers like those in Nb3Sn.

p-Type conduction of ZnSe highly doped with nitrogen by metalorganic molecular beam epitaxy

Abstract Highly conductive p-type ZnSe layers have been grown reproducibly as a consequence of high nitrogen-doping (≈1019cm-3) by using metalorganic molecular beam epitaxy (MOMBE). The dependence of electrical and photoluminescent properties on substrate temperature (Ts) has been investigated. p-Type conductivity of the ZnSe films at room temperature is enhanced with an increase in Ts; e.g. from a high 0.1 MΩcm resistivity at Ts=300°C to a low 0.57 Ωcm resistivity at 450 °C. By contrast, the dependence of the electrical properties for undoped ZnSe on Ts is similar to that of nitrogen-doped ZnSe except for the type of conductivity. The n-type resistivity of undoped ZnSe also decreases with an increase in Ts (e.g. 20 KΩcm at 300°C to 3.5 Ωcm at 400°C). A nitrogen-doped p-type ZnSe/undoped n-type ZnSe junction grown at 350°C on n-GaAs (100) has been succesfully produced. The diffusion potential of the p-n junction can be evaluated to be between 2.45 and 2.55 eV from the C-2-V plot. Observations of electron beam induced current (EBIC) have also shown formation of the p-n junction. At 77 K bluish emission has been observed from the p-n junction with a 5V forward-bias voltage.

Problems and progress in cathode-ray phosphors for high-definition displays

Abstract The state-of-the-art development of phosphors mainly for projection tubes is reviewed with an emphasis on improvement of degradation by electron bombardment. Oxygen depletion observed for InBO 3 :Tb 3+ ,Zn 2 SiO 4 :Mn 2+ , and Zn 3 (PO 4 ) 2 :Mn 2+ indicates a potential to form oxygen vacancies, which can change into color centers by trapping electrons. Formation of traps is possibly associated with oxidation of Eu 2+ by electron bombardment in Sr 3 MgSi 2 O 8 :Eu 2+ . An impurity ion can also affect the degradation; for example, in Y 3 Al 5 O 12 :Tb 3+ and Y 3 (Al, Ga) 5 O 12 :Tb 3+ , doping of 10 1 -10 2 ppm Yb 3+ or Eu 3+ reduces the degradation. When heat stored in a phosphor layer assists the degradation, a thin layer with dense packing is desirable. In this respect, surface coating techniques as well as the size and shape of phosphor particles are important.

Relationship between microstructure and Jc property in MgB2/α-Al2O3 film fabricated by in situ electron beam evaporation

A transmission electron microscopy (TEM) study has been carried out on an MgB2/?-Al2O3 film that exhibits the typical property of critical current density (Jc) under magnetic fields. The MgB2 layer of 300?nm in thickness was grown on a (001)?-Al2O3 substrate using an in situ electron beam evaporation method. Jc of the film takes significantly high values when the applied magnetic field is perpendicular to the film surface. The MgB2 layer consists of fine columnar MgB2 crystals 20?30?nm in size. The columnar MgB2 crystals grow almost perpendicular to the substrate surface and have no crystallographic orientation relationship with the ?-Al2O3 substrate because of an amorphous layer formed first on the substrate. A high density of columnar grain boundaries within the MgB2 layer may be effective for the enhancement of the flux-pinning under the perpendicular magnetic field.

The Eu site symmetry in AEu(MoO4)2 (A = Cs or Rb) generating saturated red luminescence

Abstract The luminescence spectrum of CsEu(MoO 4 ) 2 is characterized by a single line at 614.5 nm, which has an intensity more than 10 times larger than any other visible line. This spectral feature can be ascribed to D 4 site symmetry, which is higher than the exact symmetry, D 2 , derived from the space group. The apparent inconsistency results from the fact that Cs ions are located between layers consisting of (EuO 8 ) and (MoO 4 ) polyhedra with a long nearest-neighbor distance (0.475 nm) from Eu. A similar luminescence spectrum is observed also for RbEu(MoO 4 ) 2 except for line broadening due to random distribution of Rb and Eu ions. The luminescence of these compounds has high colorimetric purity resulting from the high probability of electric dipole transitions including the strong line at 614.5 nm.

The preparation of ZnS:Mn electroluminescent layers by MOCVD using new manganese sources

In the preparation of ZnS:Mn polycrystalline films by MOCVD, CPM [(C5H5)2Mn: di-π-cyclopentadienyl manganese] and BCPM [(CH3C5H4)2Mn: bismethylcyclopentadienyl manganese] are employed as new doping sources, and are compared with previously reported TCM [(CH3C5H4)Mn(CO)3: tricarbonyl methylcyclopentadienyl manganese]. In contrast to TCM, which is only partially decomposed even at 400 ∼ 500°C, CPM and BCPM are completely decomposed around the optimum growth temperature of ZnS, i.e. 280–350°C. When thermally decomposed, TCM produces a by-product containing Mn and carbonyl, which does not contribute to the luminescence, but CPM and BCPM do not. By these advantages, the double-insulator type electroluminescent (EL) devices prepared with CPM or BCPM show higher luminance than those prepared with TCM. A 500 nm thick ZnS:Mn layer by CPM gives the maximum efficiency (ηmax) of 4.8 lm/W and a saturated luminance (Lsat) of 4300 cd/m2 at 1 kHz sine wave excitation. By BCPM, Lsat of 3150 cd/m2 was obtained. Meanwhile, the devices prepared with TCM in this investigation show Lsat to be less than 1000 cd/m2 and a low efficiency of less than 1 lm/W. By the combination with red filters, ZnS:Mn by MOCVD with CPM or BCPM can also provide efficient red EL. When a glass filter (the cut-off wavelength is 590 nm) is used, the EL device prepared with CPM gives Lsat=1420 cd/m2 and ηmax=1.6 lm/W (the color coordinates, x=0.626 and y=0.373) at 1 kHz sine wave excitation.

Luminescence properties of ZnS/GaAs grown by gas source MBE

Abstract High purity cubic ZnS films were grown on GaAs(100) by the gas source MBE method using (CH 3 ) 2 Zn and H 2 S as source materials. Photoluminescence studies of these films by the excitation of an N 2 or an Xe-Cl excimer laser have shown that the intensity of self-activated emission depends on the [S]/[Zn] ratio and the substrate temperature. No SA emission was observed for ZnS films grown at 400 °C or more with an [S]/[Zn] ratio of 2.3. Band edge emission consists of four sharp lines. The one at the highest photon energy, 3.797 eV, can be assigned to the recombination of a free exciton.

Luminance Improvement of Red‐Emitting CaS : Eu Thin film Electroluminescent Cells Prepared by Electron Beam Evaporation

Luminance of red-emitting CaS: Eu thin-film electroluminescent (TFEL) cells is improved by increasing deposition rate through control of the electron beam current. Crystallinity and cathodoluminescence characteristics are investigated. Crystallinity was improved by increasing the deposition rate or the surface temperature of the evaporation sources; both the grain size and the fraction of the grains with the (111) direction normal to the substrate were increased. From the cathodoluminescence study it is suggested that with increase of the deposition rate the distribution of Eu{sup 2} + ions became more uniform, causing an increase in luminance.

Satellite Lines Due to Ion-Pairs in the Luminescence Spectra of Y2O2S:Eu3+

In the luminescence spectra of the 5 D 0 → 7 F 1 transition of Y 2 O 2 S:Eu 3+ , satellite lines separated from the main lines by several cm -1 were observed. Under the excitation by 365 mµ radiation, the intensity of the main line increases linearly with the concentration of Eu 3+ , whereas that of the satellite lines increases as the 1.36 th power of the concentration. When Gd 3+ is codoped in Y 2 O 2 S:Eu 3+ keeping the concentration of Eu 3+ constant, the intensity of the satellite lines relative to the main line increases with the concentration of Gd 3+ . It is concluded that the satellite lines originate from the splitting and shift of the crystalline-field components resulting from a slight lattice distortion around a pair of Eu 3+ ions or that of an Eu 3+ ion and a Gd 3+ ion which occupy two nearest cation sites.