LUMINESCENCE SPECTROSCOPY OF WIDE-GAP SOLIDS Eduard Aleksanyan PostDoc at the Institute of Physics, University of Tartu F I Tartu Ülikool · FÜÜSIKA INSTITUUT INSTITUTE OF PHYSICS · University of Tartu 29.08.2013, Yerevan Education • • • • • • • • 1990 – 1997 Secondary School #20, Yerevan 1997 – 2000 Anania Shirakaci Lycey, Yerevan 2000 – 2004 Yerevan State University, Department of Physics Bachelor of Science 2004 – 2006 Yerevan State University, Department of Physics, Master’s School 2006 – 2009 Yerevan Physics Institute, Department of Solid State Physics, PhD student 2007 – 2008 Institute of Physics, University of Tartu, Department of ionic crystals, Tartu, Estonia, PhD student 2009 – 2011 Yerevan Physics Institute, Department of Solid State Physics, Researcher 2011 - 2014 Institute of Physics, University of Tartu, Department of ionic crystals, Tartu, Estonia, PostDoc OUTLINE Luminescence Spectroscopy Synchrotron Radiation o o o SUPERLUMI BW3 MAX-III Intrinsic (e-h pairs or excitons) and extrinsic (impurity ions and defects) luminescence Scintillators, phosphors, LEDs Conclusion Spectral ranges of electromagnetic radiation Conduction band - Exciton Energy 1. Radio and mirowave radiation: > 1 mm 2. Inrfa-red (IR) radiation: 750 nm < < 1 mm a) Far_IR: 10 m < < 1 mm b) Mid-IR: 2.5 m < < 10 m c) Near-IR: 750 nm < < 2500 nm (2.5 m) 3. Visible light: 400 nm < < 750 nm 4. Ultraviolet (UV): 200 nm < < 400 nm 5. Vacuum ultraviolet (VUV): 10 nm < < 200 nm 6. X-rays: 0.01 nm < < 10 nm 7. Gamma-rays: < 0.01 nm Excited states Eex Eg Impurity ion Ground state + Valence band Regions where most of electronic transitions take place SPECTROSCOPY OF 4fn-1 - 5d CONFIGURATION SPECTROSCOPY OF 4fn-1 - 5d CONFIGURATION CONFIGURATION OF Er3+ ENERGY OF LOWEST 4f n-1 - 5d LEVELS 3+ 90 RE :LiYF4 SA 70 3 -1 Energy (10 cm ) 80 VUV 60 SF 50 LS 40 HS 30 Ce Pr Nd Pm Sm Eu Gd Tb Dy Ho Er Tm Yb Lu 20 1 2 3 4 5 6 7 8 9 10 Number of 4f electrons 11 12 13 14 CONFIGURATIONAL CURVES Crossluminescence and luminescence of selftrapped excitons Luminescence Spectroscopy Types of luminescence Fast luminescence: fluorescence Slow luminescence: phosphorescence Luminescence excited by: 1) light: photoluminescence; 2) electron beam: cathodoluminescence; 3) ionizing radiation: radioluminescence; 4) heating: thermoluminescence; 5) electric current: electroluminescence 6) chemical reaction: chemiluminescence; 7) … Typical shapes of emission and excitation spectra Stokes shift Light sources Continuum light sources - Deuterium lamp (200-600 nm), Rare gas continua Gas He Ne Ar Kr Xe Line sources - Mercury lamps, Rare gas resonance line lamps Lasers – Solid state, gas, other Useful range (nm) 58 - 110 74 - 100 105 - 155 125 - 180 148 - 200 Synchrotron radiation Characteristics of Synchrotron Radiation: • Synchrotron radiation is highly collimated (within angle ~1/ = mec2/E) • High brightness: synchrotron radiation is extremely intense (hundreds of thousands of times higher than conventional X-ray tubes). • Wide energy spectrum: synchrotron radiation is emitted within a wide range of energies, allowing a beam of any energy to be produced. • Synchrotron radiation is highly polarized. • It is emitted in very short pulses, typically less than a nano-second. • It’s spectral characteristics are calculable. Synchrotron radiation – a perfect tool for material science Properties of synchrotron radiation 35 / 2 e 2 c E c I 16 2 R 3 mc 2 7 3 4R mc 2 4R 1 c 3 E 3 3 3 K d 5/3 c / c (nm) ~ 1 / mc2 / E 0.559 R(m) E 3 (GeV ) max 0.42c Undulators Wigglers Characteristics of synchrotron radiation from different magnet structures SUPERLUMI set-up at HASYLAB 2-meter primary monochromator 3 secondary monochromators PMT and position-sensitive detectors • excit. energy 3.7-40 eV • Time-resolved measurements 500 ns • absorption, reflection • em=60-1000 nm • T=5-800 K • UHV BW3 at HASYLAB Spectroscopy using XUV excitation • excitation energy 40-1500 eV • Time-resolved measurements 500 ns • VUV SEYA-monochromator • Fiber optics coupled UV-visible spectrograph • T=5-350 K • UHV MAX-III • excitation energy 5-50 eV • Time-resolved measurements 10 ns • VUV SEYA-monochromator • Fiber optics coupled UVvisible spectrograph • T=5-350 K • UHV SR Setups Doris MAX-III Particle e+ e Energy 4.45 GeV 700MeV Beam current 140 mA 280 mA Circumference 289.2 m 36 m Bunch Length 19.5 mm Beamline stations 36 2 Insertion devices 9 2 Energy range SUP – 3.7-40 eV I3 – 5-50 eV BW3 – 40-1500 eV Resolving power Photon flux on sample I3 – 100 000 1012 ph/s/nm I3 - 1011 - 1013 ph/s/0.1%bw Cathodoluminescence Experimental Setup • Liquid helium cryostat (5 – 400 K temperature range) with LakeShore 331 Temperature Controller. • Double VUV monochromator (4 – 12 eV photon energy range). Johnson-Onaka mounting, 1200 l/mm Al+MgF2 gratings. Hamamatsu solar-blind photomultiplier R6836. • Double UV-VIS prism monochromator (1.5 – 6 eV photon energy range). Hamamatsu photon counting head H6240. • Electron gun: 1 – 30 keV, 10nA - 1µA. • LabView based data acquisition. Photo- and cathodoluminescence Photoluminescence • very sensitive and selective • nature of emission centres and excitation mechanisms • fast and high throughput method • non-destructive diagnostic method Cathodoluminescence • tuneable excitation depth • sensitive for weak phenomena • recharging of defects and traps Scintillation detector Main requirements to scintillators: (i) high density, (ii) low cost, (iii) high radiation resistance (iv) (iv) fast scintillation decay . Principles of PET Ring of Photon Detectors Patient injected with drug having + emitting isotope. Drug localizes in patient. Isotope decays, emitting +. + annihilates with e– from tissue, forming back-toback 511 keV photon pair. 511 keV photon pairs detected via time coincidence. Positron lies on line defined by detector pair (a chord). Produces planar image of a “slice” through patient LED Schematic representation of a single plasma display cell, illustrating the process of light generation. Quantum splitting (quantum cutting) schemes We need phosphor with Q > 100% YAG:Ce phosphor-based white LED: blue LED + yellow phosphor Emission spectrum from YAG:Ce based white LED Dosimeters Mechanism of thermoluminescence Free electrons Conduction band Diffusion E T Trapped electrons and holes L T L Free holes Bond electrons Thermal release T L Light Valence band (1) Irradiation (2) Storage (3) Heating MOBILITAS Postdoctoral Research Grant DEVELOPMENT OF NOVEL SCINTILLATORS BASED ON THIN NANOCRYSTALLINE FILMS SUPERVISOR – Marco Kirm 23.09.2011 – 22.09.2014 Objects of research • Pure and RE doped HfO2 and ZrO2 1. Defects and traps in pure hafnia and zirconia 2. Intrinsic excitations 3. RE (Ce3+, Pr3+, Gd3+, Eu3+ etc.) in hafnia and zirconia. 4. Methods – ALD, PLD, sol-gel chemistry • • • • High-k material – HfO2 - 16-50, ZiO2-18-38, SiO2 – 3.9 High density - HfO2 – 11.78 g/cm3, ZiO2- 6.21 g/cm3 Possible control of crystallographic phases Data from localized volume Why to investigate and how to get thin film scintillators ? X-ray Microimaging application - thin scintillators with high spatial resolution - high effective Z values - high absorption - efficient converters of X-rays - Atomic layer deposition – two or more precursors - ion implantation Investigated Thin Films Ion implanted films. D = 200nm HfO2:Sm; HfO2:Eu; HfO2:Er – RE content = 40-500 ppm ZrO2:Sm; ZrO2:Eu; ZrO2:Er Multi-precursor-based films. D = 25nm ZrO2:Er2O3 – Er content = 3-15% Application Scintillators Microelectronic devices Protective layers Laser media Conferences and Publications • • • • • • • • • • • • • • • • • • Harutunyan, V.V.; Saakyan, A.A.; Aleksanyan, E.M.; Grigoryan, R.P.; Hakobyan, G.R. Creation of Aluminium Nanolayer on a Corundum Monocrystals Surface by High-Energy Electron Irradiation. International Conference “New technologies for development of heterosemiconductors for device applications. 2006, 65. Lixin Ning, Peter A. Tanner, Vachagan V. Harutunyan, Eduard Aleksanyan, Vladimir N. Makhov, Marco Kirm. Luminescence and excitation spectra of YAG:Nd3+ excited by synchrotron radiation. Journal of Luminescence, Volume 127, Issue 2, 2007, 397 - 403. Aleksanyan Eduard, Harutunyan Vachagan, Kink Margarita, Kink Rein, Kirm Marco, Maksimov Yuri, Makhov Vladimir, Ouvarova Tatiana. Upconverted VUV 5d - 4f luminescence of Er3+ doped into LiYF4 and BaY2F8 crystals under ArF-laser excitation. The 15th International Conference on Luminescence and Optical Spectroscopy of Condensed Matter. Lyon, 7-11 July, 2008, 525. Aleksanyan Eduard, Harutunyan Vachagan, Kostanyan Radik, Feldbach Eduard, Kirm Marco, Liblik Peeter, Makhov Vladimir, Vielhauer Sebastian. Luminescence and excitation spectra due to inter- and intraconfigurational transitions of Er3+ in YAG:Er. The 15th International Conference on Luminescence and Optical Spectroscopy of Condensed Matter. Lyon, 7-11 July, 2008, 336. Aleksanyan Eduard, Harutunyan Vachagan, Kostanyan Radik, Feldbach Eduard, Kirm Marco, Liblik Peeter, Makhov Vladimir, Vielhauer Sebastian. 5d – 4f luminescence of Er3+ in YAG:Er3+. International Baltic Sea Region conference “Functional materials and nanotechnologies 2008”, April 1-4, Riga, 2008, 38. V.N. Makhov, A. Lushchik, Ch.B. Lushchik, M. Kirm, E. Vasil’chenko, S. Vielhauer, V.V. Harutunyan, E. Aleksanyan. Luminescence and radiation defects in electron-irradiated Al2O3 and Al2O3:Cr. Nuclear Instruments & Methods in Physics Research B, Volume 266, Issues 12-13, 2008, 2949 - 2952. Алексанян, Э.М. ВУФ люминесценция ионов Er3+ в кристаллах LiYF4 и BaY2F8. Известия НАН Армении. Физика // Journal of Contemporary Physics, 44(2), 2009, 113 118. E. M. Aleksanyan. VUV Luminescence of Er3+ Ions in LiYF4 and BaY2F8 Crystals. Journal of Contemporary Physics (Armenian Academy of Sciences), 2009, Vol. 44, No. 2, pp. 75–79. Eduard Aleksanyan, Vachagan Harutunyan, Radik Kostanyan, Eduard Feldbach, Marco Kirm, Peeter Liblik, Vladimir N. Makhov, Sebastian Vielhauer. 5d–4f luminescence of Er3+ in YAG:Er3+. Optical Materials, Volume 31, Issue 6, 2009, 1038 - 1041. Eduard Aleksanyan, Vachagan Harutunyan, Margarita Kink, Rein Kink, Marco Kirma, Yuri Maksimov, Vladimir N. Makhov, Tatiana V. Ouvarova. Upconverted 5d–4f luminescence from Er3+ and Nd3+ ions doped into fluoride hosts excited by ArF and KrF excimer lasers. Optics Communications, Volue 283, Issue 1, 2010, 49 - 53. E. Aleksanyan, M. Kirm, E. Feldbach, K. Kukli, S. Lange, I. Sildos, A. Tamm. Luminescence Properties of RE3+ Doped Hafnia and Zirconia Thin Films Grown by Atomic Layer Deposition Method. International Conference “Functional materials and nanotechnologies 2012”, April 17-20, Riga, 2012, 50. E. Aleksanyan, M. Kirm, S. Vielhauer, V. Harutyunyan. Investigation of Luminescence Processes in YAG Single Crystals Irradiated by 50 MeV Electron Beam. Lumdetr 2012 8th International Conference on Luminescent Detectors and Transformers of Ionizing Radiation. September 10-14, 2012, Halle (Saale), Germany, P-Tue-56. Eduard Aleksanyan, Marco Kirm, Sebastian Vielhauer, Vachagan Harutyunyan. Investigation of Luminescence Processes in YAG Single Crystals Irradiated by 50 MeV Electron Beam. Radiation Measurements 2013, In Press, Accepted Manuscript, DOI: 10.1016/j.radmeas.2013.01.036. V. Nagirnyi, E. Aleksanyan, G. Corradi, M. Danilkin, E. Feldbach, M. Kerikmäe, A. Kotlov, A. Lust, K. Polgár, A. Ratas, I. Romet, V. Seeman. Recombination luminescence in Li2B4O7 doped with manganese and copper. Radiation Measurements 2013, In Press, Accepted Manuscript, DOI: 10.1016/j.radmeas.2013.02.005. Eduard Aleksanyan, Marco Kirm, Eduard Feldbach, Vitali Nagirnyi, Aarne Maaroos, Hugo Mändar. Luminescence Properties of Hafnia and Zirconia Nanopowders Prepared by Solution Combustion Synthesis. International Conference “Functional materials and nanotechnologies 2013”, April 21-24, Tartu, Estonia, 2013, OR-25. N.V. Vasil’eva, D.A. Spassky, I.V. Randoshkin, E.M. Aleksanyan, S. Vielhauer, V.O. Sokolov, V.G. Plotnichenko, V.N. Kolobanov, A.V. Khakhalin. Optical Spectroscopy of Gd3(AlxGa1-x)5O12:Ce3+ Epitaxial Films. International Conference “Functional materials and nanotechnologies 2013”, April 21-24, Tartu, Estonia, 2013, OR-1. Vachagan Harutunyan, Vladimir Makhov, Eduard Aleksanyan. X-ray Excited Emission of YAG and YAG:Nd3+ Single Crystals. International Conference “Functional materials and nanotechnologies 2013”, April 21-24, Tartu, Estonia, 2013, PO-177. Sebastian Vielhauer, Eduard Aleksanyan, Eduard Feldbach, Marco Kirm, Henri Mägi, Vitali Nagirnyi, Ergo Nõmmiste and Sergey Omelkov. VUV Photoluminescence Spectroscopy Setup MAX III. International Conference “Functional materials and nanotechnologies 2013”, April 21-24, Tartu, Estonia, 2013, PO-187. Thank You For Your Attention ! There is a continuous demand for efficient and durable luminescent materials due to the rapid development of new applications like plasma displays, LED emitters, solid state lasers and various scintillators. These applications are frequently based on wide-gap materials activated with rare earth (RE) ions. Wide band gap enables 4f transitions of RE3+ ions to emit within the optical window of the host material and lets the host act as an efficient absorption medium for the optical excitation in UV range. Even though the absorption may occur in both the host and in the RE emission centre itself it is more preferred to happen indirectly via host if we consider that the concentration of RE ions does not usually exceed ~10 mol% and the f-f transitions have a forbidden nature. Higher RE concentrations would lead to increasing cross-relaxation among ions which quenches the emission considerably. Within the wide-gap materials the major attention has been focused on various metal oxides because these materials are less sensitive to oxygen surface contamination and also the preparation route of the materials is relatively simple. The wide band-gap, high refractive index, good transparency in visible spectral range and low phonon energies make titania, zirconia, and hafnia increasingly popular hosts for doping with RE ions.