Experimental and theoretical study of α–Eu2(MoO4)3 under compression

The compression process in the α-phase of europium trimolybdate was revised employing several experimental techniques. X-ray diffraction (using synchrotron and laboratory radiation sources), Raman scattering and photoluminescence experiments were performed up to a maximum pressure of 21 GPa. In addition, the crystal structure and Raman mode frequencies have been studied by means of first-principles density functional based methods. Results suggest that the compression process of α-Eu2(MoO4)3 can be described by three stages. Below 8 GPa, the α-phase suffers an isotropic contraction of the crystal structure. Between 8 and 12 GPa, the compound undergoes an anisotropic compression due to distortion and rotation of the MoO4 tetrahedra. At pressures above 12 GPa, the amorphization process starts without any previous occurrence of a crystalline-crystalline phase transition in the whole range of pressure. This behavior clearly differs from the process of compression and amorphization in trimolybdates with β′-phase and tritungstates with α-phase.We thank Diamond Light Source for access to beamline I15 (EE1746) that contributed to the results presented here. Part of the diffraction measurements were performed at the 'Servicio Integrado de Difraccion de Rayos X (SIDIX)' of University of La Laguna. This work has been supported by Ministerio de Economia y Competitividad of Spain (MINECO) for the research projects through the National Program of Materials (MAT2010-21270-C04-01/02/03/04, MAT2013-46649-C41/2/3/4-P and MAT2013-43319-P), the Consolider-Ingenio 2010 MALTA (CSD2007-00045), the project of Generalitat Valenciana (GVA-ACOMP/2014/243) and by the European Union FEDER funds. C Guzman-Afonso wishes to thank ACIISI and FSE for a fellowship. J A Sans thanks the FPI and 'Juan de la Cierva' programs for fellowships.Guzmán-Afonso, C.; León-Luis, S.; Sans-Tresserras, JÁ.; González -Silgo, C.; Rodríguez-Hernández, P.; Radescu, S.;  muñoz, A.... (2015). Experimental and theoretical study of α–Eu2(MoO4)3 under compression. Journal of Physics: Condensed Matter. 27(46):465401-1-465401-11. https://doi.org/10.1088/0953-8984/27/46/465401S465401-1465401-11274

Pressure-induced luminescence quenching in KY(WO 4 ) 2 :Pr 3+

International audienceThe quenching of the red Pr3+ (1D2 → 3H4) luminescence in a single crystal of KY(WO4)2 doped with Pr3+ is investigated at room temperature under high hydrostatic pressure. The quenching is ascribed to a pressure-induced downshift of the Pr3+ → W6+ metal-to-metal charge transfer (or impurity trapped exciton) state. The concomitant decrease of the 1D2 → 3H4 emission lifetime is reproduced using a phenomenological model. The fitting allows the determination of the pressure-induced shrinkage of the Pr3+(Y3+)-W6+ distance in the crystal. The value is consistent with the quantity previously determined in CaWO4 by means of X-ray diffraction

High pressure evolution of YVO4:Pr3+ luminescence

Photoluminescence and time-resolved photoluminescence spectra of YVO4 doped with Pr3+ obtained at high hydrostatic pressure up to 76 kbar applied in a diamond anvil cell are presented. At pressures lower than 60 kbar the steady state emission spectra consist of sharp lines related to the D-1(2) -> H-3(4) transition in Pr3+. At pressures above 68 kbar the Pr3+ emission intensity decreases and the corresponding bands are replaced by a broad band peaking at 19 500 cm(-1) attributed to perturbed VO3-4 host luminescence. The quenching of the D-1(2) -> H-3(4) emission has been attributed to nonradiative transition to the charge transfer exciton trapped at Pr3+ ion. The recovering of the VO3-4 host luminescence at high pressure has been attributed to energy transfer from a Pr3+ trapped exciton (PTE) to the host YVO4. The kinetics of such a process is analyzed using the model of PTE considered as a Pr4+ + electron bound by the Coulomb potential at the delocalized Rydberg states

Luminescence of CaWO4:Pr3+ and CaWO4:Tb3+ at ambient and high hydrostatic pressures

Photoluminescence spectra of CaWO4 doped with Pr3+ and Tb3 obtained at high hydrostatic pressures up to 315 kbar applied in a diamond anvil cell (DAC) are presented. The intensities of the luminescence from the 3P0 state of PO+ and from the D-5(3) state of Pr3+ decreased with increasing pressure. At pressures greater than 50 kbar, the D-1(2) H-3(1) transitions in Pr+ and the D-5(4) E-7(1) transitions in Tb3 dominated the spectra. At pressures greater than 100 kbar, only emissions from the lower excited states were observed. At pressures greater than 150 kbar, luminescence from the D-1(2) and D-5(4) states also decreased with increasing pressure, and at a pressure of 315 kbar for CaWO4:Pr3+ and 190 kbar for CaWO4:Pr3+, the emissions related to the PO+ and TIP+ were quenched. These effects were related to the influence of impurity trapped excitons (ITEs) on the efficiency of the f f emission in the PO+ and Tb3+ ions. Analysis of the emission spectra collected at different pressures allowed the energies of the ground states of the Pr3+ and Tb3+ ions with respect to the band edges of the CaWO4 host to be estimated

Luminescence of Ca(NbO3)2:Pr3+: Pr3+ and self-trapped exciton emission

Photoluminescence and time resolved photoluminescence spectra of Ca(NbO3)(2) doped with Pr3+, excited under 37,000 cm(-1) (270 nm), obtained at high hydrostatic pressure up to 20 kbar applied in a sapphire anvil cells, are presented. At ambient conditions, the emission spectrum obtained in the time interval 0-1 is is dominated by spin allowed transitions from the P-3(0) state. The luminescence related to transitions from D-1(2), characterized by a decay time equal to 33 mu s, is observed when one excites directly the Pr3+ ion with 30,770 cm(-1) (325 nm) wavelength. The introduction of Pr3+ impurities in Ca(NbO3)(2) does not quench the self-trapped exciton (STE) luminescence. This luminescence, peaking at 20,000 cm(-1) (500 nm), having a decay time of 61 +/- 1 mu s, still occurs when the crystal is excited with a wavelength of 37,000 cm(-1) (270 nm) or shorter. Under such excitation a fraction of the STE luminescence is reabsorbed by Pr3+ ions; in this case the emission lifetime of the D-1(2) -> H-3(4) transition of Pr3+ is 64 +/- 3 mu s. This effect is stable also at high pressure. (C) 2010 Elsevier Ltd. All rights reserved

Pressure effects on the luminescence properties of CaWO4:Pr3+

Steady state and time resolved emission measurements of CaWO4 doped with Pr3+ have been carried out as a function of hydrostatic pressure in the 1-315 kbar range. The increase of pressure induces several effects: a progressive red shift of the spectral features and a decrement of the decay times of both P-3(o) and D-1(2) emitting levels, the decrease of the intensity of the P-3(o) emission, that is completely quenched at around 100 kbar, and the increase of the 1D2 emission intensity in the 1-120 kbar range followed by a fast decrease at higher pressures. In addition, a variation in the structure of the emission manifolds has been observed in the 80-100 kbar range as a consequence of the tetragonal to monoclinic phase transition of the host lattice induced by pressure. These effects have been accounted for by means of a model that takes into account the role played by a praseodymium trapped exciton in the excited state dynamics of the investigated material

High pressure luminescence spectra of CaMoO4:Pr3+

Steady state and time resolved luminescence measurements of CaMoO4 doped with Pr3+ as a function of hydrostatic pressure in the 1-175 kbar range are presented. It has been observed that with increasing pressure the spectral features shift towards lower energies, the decay times of both P-3(0) and D-1(2) emitting levels become shorter and the intensity of the P-3(0) emission decreases to complete quenching at about 110 kbar, whereas that of the D-1(2) emission increases in the 0-100 kbar range and then rapidly decreases when the pressure exceeds 127 kbar. A variation of the structure of the spectral manifolds indicates that a pressure induced phase transition of the host lattice occurs in the 80-100 kbar range. The quenching of the luminescence and the shortening of the decay times have been accounted for by means of a model that takes into account the role played by a praseodymium trapped exciton in the excited state dynamics of the investigated material

Energy levels in CaWO4:Tb3+ at high pressure

International audienceThe luminescence properties of Tb3+ in CaWO4 crystals are investigated under a hydrostatic pressure of up to 200 kbar, i.e. across scheelite-to-fergusonite phase transition. It is shown that the typical blue (5D3) and green (5D4) emissions in this material are progressively quenched at room temperature as pressure is increased. This quenching is caused by a downshift of the charge transfer (or impurity trapped exciton) state that is formed between Tb3+ and nearby W6+ cations in conjunction with a pressure-induced increase of the lattice relaxation experienced by this excited state. An empirical model is introduced to calculate the evolution of the (Tb3+–W6+) charge transfer energy with pressure. Combined with the pressure dependence of the energy bandgap in CaWO4, the model allows locating the 4f levels of Tb3+ relative to the fundamental host lattice for any pressure in the range 0–200 kbar

Luminescence and Luminescence Kinetics of Gd3Ga5O12Gd_{3}Ga_{5}O_{12} Polycrystals Doped with Cr3+Cr^{3+} and Pr3+Pr^{3+}

In this paper spectroscopic investigations of $Gd_3Ga_5O_{12}$ (GGG) polycrystals, containing $Cr^{3+}$ and intentionally doped with $Pr^{3+}$ of concentrations 0.5, 1 and 1.5 mol% are presented. We have measured the steady state luminescence and luminescence excitation spectra, as well as the time resolved spectra and luminescence kinetics. The main goal was to investigate the excitation energy transfer from lattice to impurity and between impurities. We found that relative intensity of $Cr^{3+}$ and GGG lattice luminescence decreased when material was doped with $Pr^{3+}$. On the other hand, time resolved spectroscopy and luminescence decay measurements showed that the $Cr^{3+}$ and GGG lattice luminescence decays were independent of $Pr^{3+}$ content. The lifetime of $Pr^{3+}$ luminescence related to $\text{}^{1}D_{2} \rightarrow \text{}^{3}H_{4}$ and $\text{}^{3}P_{0} \rightarrow \text{}^{3}H_{4}$ transitions decreased with concentration of $Pr^{3+}$, which was attributed to the concentration luminescence quenching. No energy transfer between GGG lattice defects and $Cr^{3+}$, and $Pr^{3+}$ ions was observed. We proposed the model of radiative recombination of electron and hole, which took place through three independent pathways: by GGG host emission that peaked at 12750 $cm^{-1}$, by $Cr^{3+}$ luminescence that peaked at 15400 $cm^{-1}$, and by $Pr^{3+}$ luminescence