GB1313395A - Visual display apparatus - Google Patents

Abstract

1313395 Luminescent materials and uses thereof WESTERN ELECTRIC CO Inc 16 April 1970 [16 April 1969] 18164/70 Heading C4S [Also in Division H4] Apparatus for producing a visual display (e.g. TV display) includes phosphorescent material 19 capable of line emission at at least two visible wavelengths, the emission at each wavelength being in each case in response to energization by and consisting of conversion of electromagnetic radiation by absorption at one wavelength only within the infra-red spectrum, means for emitting e.m. radiation within the infra-red spectrum, and means for effecting scanning of the radiation from the front or back. The radiation may be amplitude of frequency (e.g. parametrically) modulated, while defection may be digital or continuous or digital in one direction and continuous in the other, e.g. via defector 14 on pivot 15, and the two wavelengths may result from different multiphoton processes associated with a single activator ion, e.g. Er<SP>3+</SP>. The material may be a mechanical admixture of at least two compounds each containing at least one different activator ion, the material being able to selectively absorb and emit according to the frequency of the infra-red radiation, which may be coherent or non-coherent. Optional diodes 5, 6 may emit energy, either or both at an amplitude and/or frequency different from diode 2. Fig. 2 (not shown) includes one or more lasers (26, 27, 28), solid, liquid, or gaseous, second harmonic generator (29), one or more parametric oscillators (31) electrically tuned to a fixed or varying output frequency, one or more amplitude modulators (35), e.g. electro-optic modulators. Generator (29) may be phasematohable non-linear Ba 2 Na 5 NbO 15 . Oscillator (31) may also be Ba 2 Na 5 NbO 15 , modulator (35) of lithium tantalate, deflector (39) one or more rotating prisms, or electric deflector system wherein Á depends on electrical bias, e.g. potassium tantalate with potassium niobate (KTN). Preferred for colour or apparent black and white display use Yb and Er trivalent cations as sensitizer and activator respectively, and single ion Er<SP>3+</SP>, single ion Tm<SP>3+</SP>, or the pair Er<SP>3+</SP> and Ho<SP>3+</SP> are instanced, a preferred matrix being of more complex stoichiometry than MOCl (M any cation) in which the chlorine to oxygen ratio is >1. Fig. 3 (not shown) illustrates energy levels for Yb<SP>3+</SP>, Er<SP>3+</SP>, Ho<SP>3+</SP> and Tm<SP>3+</SP> systems, including split energy levels as inset for example. A combination of oxychloride with broad absorption peaking at 0À94 Á and a Si doped GaAs diode, peaking at 0À93 Á is instanced, small splitting only occurring in lanthanum fluoride and other less an isotropic hosts with absorption peaking at 0À98 Á for Yb<SP>3+</SP>. Green emission A may be 0À55 Á, red emission B 0À66 Á and the host Y 3 OCl 7 , the next strongest C emission being at 0À41 Á for Er<SP>3+</SP>. Ho<SP>3+</SP> and Tm<SP>3+</SP> emissions are instanced. Inset Fig. 3 (not shown) illustrates absorption spectra for Yb<SP>3+</SP> sensitizer in an oxychloride host and in a tungstate host. By amplitude modulation at "a" or "b", the Er-Ho emission may be varied from green to red, while pumping at an order of magnitude higher at 10,350 cm.<SP>-1</SP> effects emission from Tm in the Yb sensitizer-tungstate host system. Phosphors may be powder or polycrystalline, oxychlorides prepared by dissolving rare earth and yttrium oxides in HCl, evaporating, dehydrating (100‹ C.) under vacuum and treating with Cl 2 at 900‹ C., producing one or more oxychlorides, and/or trichloride. The latter may act as flux. Variations are discussed for YbOCl, YbOCl 7 oxybromides and oxyiodides production and dehydration should be sufficiently slow to avoid excessive chlorine loss. Lead fluorochloride and fluorobromide may be prepared by melting PbF 2 and PbCl 2 or PbBr 2 together and products melted with oxyhalide phosphors to adjust properties. Sodium Yb tungstates containing Tm can be grown from a Na 2 W 2 O 7 flux by slow cooling from 1275‹ C. and yttrium ortho-aluminates containing Yb and Ho grown from lead oxide based fluxes by pulling from melt. Phosphor matrices may be rare earth oxychlorides, oxybromides, oxyiodides, corresponding Bi compounds (e.g. those containing BiOCl), the oxychalkogenides (e.g. containing ThOs), fluorohalides (e.g. containing PbFCl or PbFBr), rare earth fluorides, ortho-aluminates, gallium garnets, tungstates, molybdates, phosphates and vanadates. Na 0À5 Yb 0À5 WO 4 , Na 0À5 Yb 0À5 MoO 4 and divalent ion containing fluorides are preferred for the broad band Yb<SP>3+</SP> absorption group. Minimum cation content is 5% or preferably 10% to a maximum of 100%, 80% being preferred. 20 to 50% Yb may be in (YbErY) 3 OCl 7 , to produce mixed R-G output, 50 to 80% producing red. Er range is <SP>1</SP>/ 16 to 20%, preferably “ to 2%, and Ho in amount <SP>1</SP>/ 50 to 5% as adjunct to Er with Yb or with Yb alone. Other concentrations are given and Tm may be <SP>1</SP>/ 16 to 5%. The required cation content may be met by inert "cations" such as Y, Pb<SP>2+</SP>, Gd<SP>3+</SP> and Lu<SP>3+</SP>, and purity should be to 99À9%, desirably 99À999%. One of a mix of two or more phosphors may be preferentially excited by diode arrays with diodes of different frequencies emitting in response to programmed signals or a single beam tuned parametrically by electrical stress or temperature change. Emissions of a mix of (Yb 0À3 Er 0À01 Ho 0À002 Y 0À6898 ) 3 OCl 7 and Na 0À5 Yb 0À49 Tm 0À01 WO 4 are given. The screen 19 may be patterned.