Helmut Bechtel

Optimised co-activated willemite phosphors for application in plasma display panels

AbstractProperties, relevant for PDP application, of Mn2 ‘ -activated Zn2SiO4 phosphors non-co-activatedand co-activatedwith Ba2 ‘ ,Cd2 ‘ ,Fe2 ‘ ,Fe3 ‘ ,Al3 ‘ /Li ‘ or Gd3 ‘ /Li ‘ were investigated. For Zn(1.95)Mn0.05SiO4, co-activation withBa2 ‘ and Gd3 ‘ reduces the q10{value at 170 nm excitation from 17 to 10 ms with e

Lumiramic: a new phosphor technology for high performance solid state light sources

ciencies still 86% relative tonon-co-activatedZn2SiO4 :Mn2 ‘ .Theq10{ valueincreasesforco-activationwithFe2 ‘ orhighconcentrationofCd2 ‘ .Decay properties were also studied as a function of excitation wavelength. ( 2000 Elsevier Science B.V. All rightsreserved. Keywords: Zinc silicate; Plasma display panels; Mn2 ‘ luminescence; Co-activators 1. IntroductionPhosphors for PDPs need to emit at least 90% oftheir luminescence within the refresh rate of the displayafter excitation by the emission of a Xe/Ne gas dis-charge at 170 nm. The commercial PDP phosphorZn2SiO4:Mn2 ‘ (P1) has a 10% value q10{of 15 mswhichis too long for TV application. In the past, severalattempts were made to improve on the P1 reference. Itwas shown [1,2] that the q10{value can be reduced byincreasingthe Mn2

Blue emitting BaMgAl10O17:Eu with a blue body color

A new phosphor technology for phosphor converted light-emitting diodes (pcLEDs) is presented. A polycrystalline ceramic plate (LumiramicTM) of Ce (III) doped yttrium gadolinium aluminum garnet (Y,GdAG:Ce) is combined with a blue LED to produce white light in the range of 5000 K correlated color temperature. Scattering and light extraction means of the Lumiramic ceramic color converter plates enable production of reliable and efficient white pcLEDs. Measurement of the optical properties of the Lumiramic plates before the final LED assembly allows pick and place packaging with exact targeting of the desired white color point of the LED. Combination with a red phosphor powder layer, coated onto the Lumiramic plate, results in high quality white pcLEDs with any color temperature required for the general lighting market.

Phosphor screens for flat cathode ray tubes

Abstract The optical properties of Co 2+ -doped BaMgAl 10 O 17 (BAM) and BaMgAl 10 O 17 :Eu (BAM:Eu) are elucidated with emphasis on reflection, (V)UV excitation and luminescence spectra. Doping of BAM with Co 2+ yields a powder with a blue body color equal to that of CoAl 2 O 4 . Co 2+ is incorporated into the spinel blocks of BAM, which are spaced by Ba–O layers hosting the activator Eu 2+ . By means of reflection spectra it is shown that the local environment of Co 2+ is equal to that in CoAl 2 O 4 , which is responsible for the identical body color. The intrinsic pigmentation of BAM:Eu by Co 2+ yields a phosphor with an improved color point due to the self-absorption of the low-energy tail of the 4f–5d emission band of Eu 2+ . Moreover, the presence of Co 2+ in the host lattice of BAM results in resonant afterglow behavior. Only under photoexcitation at the band gap of BAM:Eu afterglow is observed.

THE DEGRADATION BEHAVIOR OF LAOBR:TB UNDER CATHODE-RAY EXCITATION

Abstract In the Zeus display panel, as in other flat-panel cathode ray tubes, the anode voltage is limited to a few kV. The effects of the anode voltage on phosphor screen performance are discussed which include energy conversion loss processes at the phosphor surface and variation of the number of luminescent centres available. Phosphor efficiency saturation has been measured in the range of 1 to 10 kV, using a pulse-width-modulation scheme. The luminance performance at different excitation conditions is predicted and confirmed experimentally. Coulomb degradation of phosphor screens is shown to increase with decreasing anode voltage. Novel ultra-thin and dense anti-degradation coatings have been developed for zinc sulphide phosphors which effectively prevent fast degradation due to chemical surface reactions. In this way a satisfactory solution has been found to obtain in the Zeus display a luminance level about equal to the best conventional tubes.

Phosphors for plasma‐display panels: Demands and achieved performance

Investigations on the degradation behavior of LaOBr:Tb phosphors under cathode‐ray excitation are presented. The microscopic nature of defects created under prolonged electron bombardment has been identified using extended optical analyses on aged LaOBr:Tb phosphor screens and supported by ion desorption experiments performed in an ultrahigh vacuum system. The degradation behavior of LaOBr:Tb can be improved considerably by codoping this phosphor with chloride or iodide.

Materials design and properties of nitride phosphors for LEDs

Almost two-thirds of the discharge cells in plasma-display panels (PDPs) are covered with phosphors. Beyond the efficient conversion of vacuum UV photons into visible light, the phosphor layer serves as a reflective mirror transporting light in the desired viewing direction. The quantum efficiency of state-of-the-art PDP phosphors is, at its upper limit, 80-95%. Todays improved blue-emitting BaMgAl 10 O 17 :Eu (BAM) phosphor still deteriorates during panel processing and operation, resulting in a loss of efficiency and color purity. A reduction in the phosphor particle size below 2 μm is suited to ease panel manufacturing and to improve light output.

Phosphor degradation under electron excitation with varying anode voltage

We have studied structure-property relations of Eu(II) doped nitridosilicates M2Si5N8 and MSi7N10 (M = Sr, Ba). For both systems that are described as being efficient LED phosphors, we show that a detailed examination of the local activator environment in combination with net positive charge calculations for Eu with the EHTB-MO method allows a qualitative prediction of the luminescence properties of nitridosilicate LED phosphors. The non-linear shift of the amber to red emission of solid solutions Ba2-xSrxSi5N8:Eu is explained by a non-statistical distribution of Eu over the available lattice sites. The Stokes shift differences between the two available Eu sites are significantly larger for Ba2Si5N8:Eu than for Sr2Si5N8:Eu. In contradiction to literature data, BaSi7N10:Eu shows emission in the cyan spectral region and a large Stokes shift, in accordance with the host lattice geometry and the electronic structure calculations that were carried out. SiAlON formation as an additional design tool to tune nitridosilicate phosphor emission properties is demonstrated for Sr2Si5-xAlxOxN8-x:Eu. (Al,O) incorporation leads to anisotropic changes of lattice constants and a red shift and broadening of the Eu emission.

Fully Phosphor-Converted LEDs with Lumiramic™ Phosphor Technology

A model for the variation of phosphor Coulomb degradation with anode voltage is presented, using the volume energy density as scaling parameter. With reference to the bulk phosphor degradation at 30 kV Coulomb degradation down to 2 kV has been calculated. A result of this model is that the degradation at a given charge dose increases with decreasing anode voltage. Considering the high charge doses accumulated in low-voltage displays operated at CRT brightness, only phosphors which are stable at 30 kV are expected to be applicable at low voltages. The predicted phosphor degradation at 4 kV is experimentally confirmed for oxide, silicate, and oxy-sulfide phosphors. For zinc sulfides the degradation measured at 4 kV is much faster than predicted, pointing to considerable contributions of surface-related effects.

Layered oxonitrido silicate (SiON) phosphors for high power LEDs

Fully phosphor-converted LEDs (FpcLeds) with saturated emission have been realized in the green and amber spectral region. With the Lumiramic™ phosphor technology it is possible to achieve high package efficiency with minimum transmission of blue light from the primary LED source. This is done by keeping the scattering properties of the phosphor layer low while the phosphor thickness is chosen to fully convert all blue LED emission. It is shown that this can be done not only for optically isotropic Lumiramic materials like garnets, but also for oxonitridosilicate materials like the green emitting Europium doped SrSi2O2N2, crystallizing in a triclinic lattice with three optical axes. The scattering power of the Lumiramic can be decreased to acceptable levels by increasing the size of the crystallites in the densely sintered ceramics. Light propagation is found to be described well with Mie scattering of mono-sized SrSi2O2N2 spheres with refraction index differing by 0.07 to the refractive index of a SrSi2O2N2 matrix material. Using this technology, the green-yellow gap of visible light emitting LEDs can be bridged and color tunable lamps with the efficiency and flux of todays white phosphor-converted LEDs become feasible.