E. van der Kolk

Temperature dependent spectroscopic studies of the electron delocalization dynamics of excited Ce ions in the wide band gap insulator, Lu2SiO5

Electron delocalization processes of optically excited states of Ce3+ impurities in Lu2SiO5 were investigated by means of a temperature and spectrally resolved photoconductivity study. By monitoring separately the strength of the photocurrent resulting from excitation into each of the Ce3+ 5d absorption bands, over a broad temperature region, three different delocalization processes, namely direct photoionization, thermal ionization, and tunneling, have been identified. The relative probabilities and temperature dependencies of each of these processes are discussed. The observed exponential temperature increase in the photocurrent, which spans six orders of magnitude, allows for the exact placement of the lowest energy 5d levels of the Ce3+ ions within the band gap. For Lu2SiO5:Ce3+, the lowest 5d state is determined to be 0.45 eV below the conduction band edge.

Location of lanthanide impurity levels in the III-V semiconductor GaN

Knowledge from lanthanide spectroscopy on wide band gap (6–10?eV) inorganic compounds is used to understand and predict optical and electronic properties of the lanthanides in the III-V semiconductor GaN. For the first time the location of the 4fn ground state energy of each divalent and trivalent lanthanide ion relative to the valence and conduction bands in GaN is presented. The authors will demonstrate that the quantum efficiency of luminescence from Pr3+, Eu3+, Tb3+, and Yb3+ depends on the location of the lanthanide levels. Level location also controls electron acceptor and electron donor properties of lanthanide ions.

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

VUV excitation and 1S0 emission of Pr3+ in BaSiF6 and selecting host lattices with 1S0 Pr3+ emission

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

Vacuum ultraviolet excitation and quantum splitting of Pr3+ in LaZrF7 and α-LaZr3F15

Abstract We have studied the luminescence characteristics of Pr3+ in BaSiF6 powder samples co-doped with K+ in the 60– 800 nm range at room and liquid He temperature. After excitation in the 4f5d configuration of Pr3+, emission from the 1 S 0 state is observed but no 4f5d→4f2 emission. The 1 S 0 state is measured in excitation spectra as a weak line about 6200 cm −1 below the maximum of the lowest energy 4f5d crystal field state. Emission from the 3 P 0 and 1 D 2 multiplets is almost completely quenched which is not yet fully understood. Under band-to-band ( 11.7 eV or higher energy) excitation at 12 K , we observe excitonic emission, peaking at 327 nm , which is quenched at room temperature. A reliable prediction can be made whether 1 S 0 emission of Pr3+ can be expected in a host lattice. It is based on the 4fn→4fn−15d excitation energy of other trivalent lanthanides or on the 4f7→4f65d excitation energy of Eu2+ in the same host lattice. It also appears that when 6 P 7/2 line emission of Eu2+ is observed, 1 S 0 emission of Pr3+ can be expected. A list of host lattices is presented for which 1 S 0 emission is expected when doped with Pr3+.

Vacuum ultraviolet excitation of 1S0 and 3P0 emission of Pr3+ in Sr0.7La0.3Al11.7Mg0.3O19 and SrB4O7

Abstract Excitation and emission characteristics of Pr 3+ doped in LaZr 3 F 15 and LaZrF 7 at ≈293 and at ≈10 K are described. Synchrotron radiation facilities were used. Both zirconium fluorides show quantum splitting after excitation in the 4f5d configuration. The 3 P 0 emission has an internal quantum efficiency close to unity while the 1 D 2 emission is completely quenched. In LaZr 3 F 15 :1%Pr 3+ broad emission and excitation bands are observed that are tentatively assigned to oxygen-to-metal charge transfer. In LaZrF 7 band-to-band or higher energy excitation result in the creation of self-trapped excitons (STEs), luminescent at 10 K. At 293 K energy is transferred from STE to the 3 P 0 state of Pr 3+ and not to the 1 S 0 state.

Lanthanide 4f-level location in lanthanide doped and cerium-lanthanide codoped NaLaF4 by photo- and thermoluminescence

The emission and excitation properties of a SrB4O7:1% Pr3+ powder sample and a Sr0.7La0.3Al11.7Mg0.3O19:3.5% Pr3+ single crystal were investigated using x-ray and synchrotron radiation. The 4f5d states of Pr3+ in these host lattices are at a higher energy than the 4f2[1S0] state. In the hexa-aluminate this results in the successive emission of two photons. 1S0→1I6 emission is followed by emission from the 3P0 state. The quantum efficiency of the total 3P0 emission is 25%. In the tetra-borate the 3P0 emission is quenched by multiphonon relaxation to the 1D2 state from which only weak emission is observed. In the hexa-aluminate as in the tetra-borate, host lattice excitation does not result in efficient emission from the 1S0 state. In the hexa-aluminate the excitation energy is transferred from the host lattice preferentially to the lower-energy 3PJ and 1I6 states, resulting in 3P0 emission only.

Luminescence excitation study of the higher energy states of Pr3+ and Mn2+ in SrAlF5, CaAlF5, and NaMgF3

Photo- and thermoluminescence (TL) spectra of NaLaF4:Ln3+ (Ln = Ce,Pr,Nd,Sm,Eu,Gd,Tb,Dy,Ho,Er,Tm) and NaLaF4:Ce3+, Ln3+ (Ln = Nd,Sm,Ho,Er,Tm) are presented and used together with the empirical Dorenbos model in order to establish the 4f energy level positions of all tri- and divalent lanthanide ions doped in NaLaF4. The information will be presented in the form of an energy level diagram. It is shown that in addition to this diagram only two assumptions, viz., the presence of two host related electron traps and the presence of Vk-centers, are necessary for explaining the lanthanide-specific TL glow curves of both Ln mono- and Ce–Ln codoped NaLaF4.

Luminescence quenching by photoionization and electron transport in a LaAlO3:Ce3+ crystal

The possibility to use Mn2+ co-doping to modify the emission properties of Pr3+-based quantum cutting phosphors—i.e., phosphors that emit one UV and one visible photon for each absorbed vacuum UV (VUV) photon—into phosphors that emit two visible photons, was studied experimentally. In this respect a luminescence excitation study, using synchrotron radiation, between 500 and 50 nm of Pr3+ and Mn2+ impurities in SrAlF5, CaAlF5, and NaMgF3 was performed. Excitation of Pr3+ into the 4f5d excited states results in emission of UV photons from the 1S0 state followed by visible photons from the 3P0 state with an internal quantum efficiency exceeding 100%. It was found that a favorable overlap between the 1S0→1I6 Pr3+ emission and the 6A1→4Eg, 4A1g Mn2+ absorption exists that should promote energy transfer from Pr3+ to Mn2+. However no such energy transfer could be observed in SrAlF5. At higher excitation energies (>7 eV) intense structured Mn2+ excitation bands are found that are assigned to 3d5→3d44s transitions...

Systematics in the optical and electronic properties of the binary lanthanide halide, chalcogenide and pnictide compounds: an overview

A combined photoconductivity, absorption, and thermoluminescence study was performed to understand the absence of luminescence from Ce3+ in LaAlO3:Ce3+. It is demonstrated that the absence of luminescence is the result of Ce3+ ionization from the 5d excited states, which are all located in the conduction band. Ce3+ ionization is accompanied by the formation of several broad absorption and photoconductivity bands, which are assigned to electron traps. A time and temperature dependent optical investigation of these traps reveals the conditions under which electrons are transferred from Ce3+ to traps and vice versa, from traps back to Ce4+. The observed difference in energy needed to thermally or optically release electrons from traps is qualitatively explained in terms of the location of the ground and excited states of the electron traps with respect to the conduction band.