New blue and green emitting BAM Phosphors for Fluorescent Lamps and Plasma Displays

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1 New blue and green emitting BAM Phosphors for Fluorescent Lamps and Plasma Displays T. Jüstel*, W. Busselt, P. Huppertz, W. Mayr, J. Meyer, P.J. Schmidt, D.U. Wiechert Philips Research Laboratories, D Aachen, Germany *University of Applied Science Münster, D Steinfurt, Germany

2 Outline Application of BAM phosphors Phases in the BaO-MgO-Al 2 O 3 -(EuO) system Luminescence of Eu 2+ doped BAM-I and BAM-II BAM-I and II doped by transition metal ions BAM-I with a blue body color Summary Prof. Dr. T. Jüstel, March 17 th,

3 Applications of BAM Phosphors Blue and green emitter in exc. at [nm] Hg low pressure lamps 185, 254 Xe 2 * excimer lamps 172 Plasma displays 147, 172 Commercial products BAM-I blue BAM-I blue-green BAM-I green Main concerns thermal and photostability colour point (shift) Prof. Dr. T. Jüstel, March 17 th,

4 Phases in the BaO-MgO-Al 2 O 3 System ß-alumina phases BAM-I = BaMgAl 10 O 17 BAM-II = BaMg 3 Al 14 O 25 extended spinel blocks MgAl 2 O 4 mol-% 1800 C Impurity phases BaO excess BaAl 2 O 4 MgO/Al 2 O 3 excess MgAl 2 O 4 Al 2 O 3 excess Al 2 O BaMgAl 10 O 17 BaMg 3 Al 14 O AlO 1,5 BaAl 2 O 4 2 BaMg 2 Al 16 O 27 = BaMgAl 10 O 17 + BaMg 3 Al 14 O Al 2 O 3 impurity phase (M. Goebbels et al., 1998) Prof. Dr. T. Jüstel, March 17 th,

5 Structure of BAM-I and BAM-II BAM-I BaO + MgAl 10 O 16 BAM-II BaO + Mg 3 Al 14 O 24 Spinel block Conduction layer BaO Spinel block c-axis Conduction layer BaO Spinel block Prof. Dr. T. Jüstel, March 17 th,

6 Phases in the BaO-MgO-Al 2 O 3 -EuO System Impurity phases (presence of Eu) BaO excess BaAl 2 O 4 :Eu 2+ Al 2 O 3 excess EuAl 12 O 19 Eu 2+ EuAlO 3 Eu 3+ MgO MgAl 2 O 4 EuO Synthesis of BAM-I and BAM-II requires strict control of starting composition (EuAlO 3 ) BaO BAM-II BaAl 2 O 4 BAM-I (M. Dauscher, diploma thesis, 2001) BaAl 12 O 19 EuAl 12 O 19 AlO 1,5 Prof. Dr. T. Jüstel, March 17 th,

7 Luminescence of Eu-doped BAM-I (10% Eu 2+ ) Reflection [%] 10 Host lattice Reflection spectra Eu 2+ 4f 7-4f 6 5d 1 Emission and excitation spectra Relative Intensity Host lattice 4f 6 5d 1-4f 7 4f 7-4f 6 5d Optical band gap E g = 7.0 ev (~180 nm) Excitation bands at 170, 250, and 310 nm (4f 7 4f 6 5d 1 ) Emission band at 453 nm x = y = QE 254nm > 90% Prof. Dr. T. Jüstel, March 17 th,

8 Luminescence of Eu-doped BAM-II (10% Eu 2+ ) Relative intensity Reflection and excitation spectra Host lattice Eu 2+ 4f 7-4f 6 5d Sample WM137 Excitation spectrum Reflection spectrum Emission spectra BaMgAl10O17:Eu10% BaMg3Al14O25:Eu10% Excitation bands at 170, 250, and 310 nm (4f 7 4f 6 5d 1 ) Emission band at 450 nm x = y = QE 254nm > 90% Weaker absorption due to lower BaO/MgO-Al 2 O 3 ratio Reflection (%) Prof. Dr. T. Jüstel, March 17 th, Emission intensity [a.u.]

9 BAM-I and II doped by Transition Metal Ions λ UV λ 1 λ 2 Divalent RE ions Ba 2+ sites in the conduction layer Eu 2+, Yb 2+ Divalent TM ions tetrahedral gaps in the spinel blocks Mn 2+, Co 2+ Trivalent TM ions octahedral gaps in the spinel blocks Cr 3+, Ti 3+ Prof. Dr. T. Jüstel, March 17 th,

10 BAM-I doped by Transition Metal Ions Luminescence spectra of BaMgAl 10 O 17 :Cr 3+ Luminescence spectra of BaMgAl 10 O 17 :Mn 2+ Relative intensity Emission spectrum Excitation spectrum Reflection spectrum Reflection (%) Relative intensity Sample WM123 Emission spectrum Excitation spectrum Reflectionspectrum Reflection (%) BAM-I: exc. at λ max at x y transition Cr nm 694 nm d 3-3d 3 Mn nm 515 nm d 5-3d 5 Prof. Dr. T. Jüstel, March 17 th,

11 BAM-I:Eu doped by Mn 2+ Relative intensity BAM-I:0.05Mn BAM-I:0.10Eulow Mn BAM-I:0.10EumediumMn BAM-I:0.10EuhighMn Emission spectra Light output LO = QE*(1-R) Light output BAM-I:0.05Mn BAM-I:0.1EumediumMn BAM-I:0.1EuhighMn Efficient energy transfer from Eu 2+ to Mn 2+ Eu 2+ improves VUV efficiency of Mn 2+ doped BAM-I High Mn 2+ concentration reduces VUV efficiency of BAM-I:Eu,Mn Prof. Dr. T. Jüstel, March 17 th,

12 Energy Pathways in BAM-I:Eu,Mn ET ET Host lattice Eu 2+ (4f 6 5d 1 ) Mn 2+ (3d 5 *) sensitiser for Mn 2+ luminescence 515 nm CB E g = 7.0 ev (< 180 nm) VB 170 nm 4f 6 5d nm 310 nm 4f 7 ( 8 S 7/2 ) ET 450 nm 515 nm 3d 5 Eu 2+ Mn 2+ Mn 2+ (3d 5 ) 3d 5* Prof. Dr. T. Jüstel, March 17 th,

13 BAM-II doped by Mn 2+ Relative intensity Excitation and reflection spectra of BAM-I:Mn and BAM-II:Mn BaMgAl10O17:Mn BaMg3Al14O25:Mn Emission spectra of BAM-I:Mn and BAM-II:Mn BaMgAl10O17:Mn BaMg3Al14O25:Mn Phosphor λ max at [nm] x y LE (lm/w) BAM-I:Mn BAM-II:Mn (data for 160 nm excitation) Reflection spectrum (%) Emission intensity [a.u.] Prof. Dr. T. Jüstel, March 17 th,

14 BAM-II:Eu (10%) doped by Mn 2+ Relative intensity Excitation and reflection spectra Excitation spectrum Reflection spectrum 160 nm Host lattice Reflection (%) Emission spectra of BAM-II:Eu,Mn Emission intensity [a.u.] Eu 2+ Emission spectrum 160 nm exc. Emission spectrum 254 nm exc. Mn 2+ Eu 2+ Mn nm 520 nm 254 nm Eu nm Prof. Dr. T. Jüstel, March 17 th,

15 Colour Points and Decay Times of BAM-I and BAM-II Phosphors Composition Decay time 1/e* Color points BAM-I:10%Eu 1.5 µs BAM-I:10%Eu, Mn BAM-I:10%Eu, Mn BAM-I:Mn 1.5 µs, 5.7 ms 4.8 ms 5.8 ms BAM-II:Mn BAM-I:Mn BAM-II:10%Eu 1.4 µs BAM-II:10%Eu, Mn 5.5 ms *for 160 nm excitation and a monoexponential decay fit BAM-I:Eu,Mn BAM-I:Eu BAM-I:Eu,Co BAM-I:Cr Prof. Dr. T. Jüstel, March 17 th,

16 BAM-I:Eu with a Blue Body Colour The blue pigment CoAl 2 O 4 is isomorphous to MgAl 2 O 4 spinel Standard blue pigment for blue CRT phosphor ZnS:Ag Co 2+ : 3d 7 (high-spin) occupies tetrahedral sites in Co-spinel small crystal field splitting small energy distance between t 2 and e orbitals Co 2+ (0.72 Å) is likely also located on tetrahedral sites in the spinel blocks of BAM-I and BAM-II as Mg 2+ (0.66 Å) Intensity XRD of BAM-I:Eu,Co (Cu k α radiation) BAM blue Reference BAM V two theta [ ] Prof. Dr. T. Jüstel, March 17 th,

17 BAM-I:Eu with a Blue Body Colour Emission intensity [a.u.] Emission spectrum BAM-I:Eu BAM-I:Eu, Co1% BAM-I:Eu, Co4% Reflection [%] Reflection spectrum BAM-I:Eu BAM-I:Eu, Co1% BAM-I:Eu. Co4% ZnS:Ag (no pigment) ZnS:Ag + 2 wt-% CoAl 2 O Co 2+ doping results in absorption band equal to that of CoAl 2 O 4 Body colour intensity increases by enhancing Co 2+ concentration Prof. Dr. T. Jüstel, March 17 th,

18 BAM-I:Eu with a Blue Body Colour BaMgAl 10 O 17 :10%Eu,x%Co Co 2+ conc. x y x = x = x = Colour filter effect! Light output = QE*(1-R) 170 nm Light output BaMgAl10O17:Eu BaMgAl10O17:Eu,Co Efficiency of BAM-I:Eu,Co at 254 nm = BAM-I:Eu at 172 nm = BAM-I:Eu (+ afterglow) at 147 nm < BAM-I:Eu (+ afterglow) Prof. Dr. T. Jüstel, March 17 th,

19 BAM-I:Eu with a Blue Body Colour Normalised Intensity 1 0, Decay after 160 nm excitation Eu 2+ decay BAM:10%Eu,1%Co BAM:10%Eu Time (s) BAM-I:Eu,Co afterglow can be fitted by a bi-expontential decay function Prof. Dr. T. Jüstel, March 17 th,

20 Normalised intensity 1 0,1 1 BAM-I:Eu with a Blue Body Colour Decay curves as function of excitation wavelength Time (s) 121 nm 140 nm 160 nm 170 nm 180 nm 185 nm 190 nm 0,3 0,1 Results of a bi-exponential fit I = a 1 exp(-t/ t 1 ) + a 2 exp(-t/ t 2 ) a 1 (t = 9 s) a 2 (t = 100 s) Most intense afterglow under band edge excitation! Excitation wavelength (nm) Excitation at band edge can result in hole trapping on Co 2+ Co 3+ a 1 (t = 9 s) Band edge 0, a 2 (t = 100 s) Prof. Dr. T. Jüstel, March 17 th,

21 Summary BAM-I and BAM-II are stable phases in the BaO-MgO- Al 2 O 3 system Impurity phases are easily formed by small deviations from ideal stoichiometry BAM-II:Eu is as BAM-I:Eu an efficient blue-emitting phosphor Eu 2+ facilitates ET from the host lattice to Mn 2+ in BAM BAM-II:Mn is more saturated green than BAM-I:Mn Co-doping of BAM:Eu with Co yields a blue-emitting phosphor with a blue body colour (and afterglow) Prof. Dr. T. Jüstel, March 17 th,