Upconversion in a divalent rare earth ion: optical absorption and luminescence spectroscopy of Tm2+ doped SrCl2 (original) (raw)
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Absorption, excitation and emission spectra of SrCl2:Eu2+
Chemical Physics Letters, 2006
The 10 K ultraviolet emission spectrum and low-energy ultraviolet absorption spectra are reported for dilute SrCl 2 :Eu 2+ . Only one luminescent state is observed under various synchrotron radiation excitation wavelengths. The broad room temperature 4f 6 5d ! 4f 7 emission spectrum, peaking at 410 nm, sharpens considerably at 10 K and vibrational progressions in the totally symmetric Sr-Cl stretching mode of 210 cm À1 upon the zero phonon line and vibronic structure are predominant. The low-energy 4f 7 ! 4f 6 5d absorption spectrum comprises similar vibronic structure but many transitions overlap. The emission, absorption and excitation spectra are well simulated by calculation.
Red luminescence and persistent luminescence of Sr3Al2O5Cl2:Eu2+,Dy3+
Journal of Luminescence, 2013
a b s t r a c t Dy 3 þ phosphors have been investigated. Both materials show d-f emission of Eu 2 þ in the orange/red spectral region around 615 nm at room temperature. The temperature dependent emission spectra and decay curves of Eu 2 þ ions doped into Sr 3 Al 2 O 5 Cl 2 are reported and discussed. Sr 3 Al 2 O 5 Cl 2 :Eu 2 þ shows considerable thermal quenching of its luminescence. It is also observed that the position of the emission band strongly depends on the temperature and shifts toward higher energy with increasing temperature, from 645 nm at 77 K to 594 nm at 500 K. Both, Sr 3 Al 2 O 5 Cl 2 :Eu 2 þ and Sr 3 Al 2 O 5 Cl 2 :Eu 2 þ ,Dy 3 þ show persistent luminescence. The persistent luminescence of Sr 3 Al 2 O 5 Cl 2 :Eu 2 þ is rather weak and lasts only for solely a few seconds, while the same material co-doped with Dy 3 þ shows longer and stronger afterglow.
Energy transfer and upconversions in cubicCs2NaYCl6:Er3+andCs2NaErCl6
Physical Review B, 1997
Upconversion by two-ion energy transfer, two-photon absorption ͑TPA͒, and stepwise absorption processes has been reported for Er 3ϩ in cubic Cs 2 NaYCl 6 crystal. Blue emission from the 2 G 9/2 and green emission from the 4 S 3/2 state have been observed under the pulsed excitation of 4 F 9/2 in the red. Using a rate equation analysis of the time behavior of the upconverted signal, energy pathways have been determined. On the basis of the time evolution and the concentration dependence of the blue emission a two-ion energy-transfer process has been proposed. TPA in the 2 H 9/2 state (EϾ36 000 cm Ϫ1) is also observed. However, a resonant one-photon absorption in the 4 S 3/2 state at low temperatures greatly complicates and modifies the TPA spectrum. Fluorescence and excitation spectra associated with 2 H 9/2 and 4 I 9/2 states, and fluorescence lifetimes of various f n states involved in upconversion processes are also reported. ͓S0163-1829͑97͒07232-9͔
201 Electronic spectra and crystal field analysis of Yb2+ in SrCl2
The 10 K emission spectrum and absorption spectrum between 27 000 and 30 000 cm −1 have been recorded and assigned for SrCl 2 :Yb 2+ ͑0.05 and 1 at. %͒, where the divalent ion is situated at a site of O h symmetry with eightfold coordination to chloride ions. In emission, two broad bands are observed at room temperature and these are assigned to orbitally forbidden and allowed transitions from 4f 13 5d to the 4f 14 ground state 1 S 0 . Nearly all of the transitions, except for some of the highest energy absorption bands, are spin forbidden in the sense that the transition final states are dominated by spin triplet components, while the initial state is a pure spin singlet. The spectral intensities in the absorption spectrum have been fitted satisfactorily, following the crystal field calculation for 4f 13 5d in which four parameters were freely varied. There is no need to cite the presence of Yb 2+ ions at several sites in order to explain the observed absorption bands, as has been done previously, but we invoke the coparticipation of the ͑low-lying͒ 4f 13 6s configuration. The rationale for the parameter values is explained in detail as are the effects of parameter variations. The calculated radiative lifetime for the orbitally allowed emission transition is in agreement with that measured at low temperature ͑ϳ1 s͒ and the nonradiative rate from the luminescent level has been modeled as a function of temperature.
Spectroscopic properties of SrZnCl4:M2+ and BaZnCl4:M2+ (M=Eu, Sm, Tm)
Journal of Alloys and Compounds, 2000
21 21 21 The emission spectra of the divalent rare-earth ions Eu , Sm and Tm , doped into the new compounds SrZnCl and BaZnCl , are 4 4 21 21 n 21 n reported. Eu and Tm show broad 4f 5d → 4f emission. Due to the smaller crystal-field splitting, the emission bands for 21 21 21 5 6 BaZnCl :M are shifted to higher energies when compared to SrZnCl :M. For SrZnCl :Sm at 298 K broad 4f 5d → 4f emission 4 4 4 5 7 2 1 is observed, while at 20 K additional lines due to the D → F transition appear. BaZnCl :Sm shows only line spectra at low 0 J 4 temperature. At 298 K a weak d → f transition is observed. The results are discussed and compared with the corresponding measurements of SrCl and BaCl doped with the divalent rare-earth ions.
Chemical Physics, 1992
Crystals of CsMgCl,. CsMgBr3 and CsCdBr, doped with Er'+ exhibit an mtense up-conversIon luminescence in the UV region when the 4S,,2 (E) state of Er '+ is pumped by pulsed excitation between 546 and 550 nm. The primary up-conversion process IS associated with doubly excited Er3+-vacancy-E?+ centers. The most intense emissions arlse from the 4Gs,z(T) state at 36 200 cm-' and the "G, I,z(L) state at 26 000 cm-'. The time resolved emlsslons which exhibit rise and fall kinetics provide reasonably precise lifetimes for the relaxation of the doubly excited centers. The relaxation lifetimes range from roughly 3 to about 25 KS dependmg on temperature and host lattice. These lifetimes are more than an order of magnitude shorter than the lifetimes of the pumped 4S3,2(E) state which fall between 160 and 600 ps. It appears that energy transfer between ions (presumably up-converslon) 1s the dominant relaxation process for simultaneously excited pairs. There is evidence of weak up-conversion luminescence from other doubly excited Er'+ centers and from encounters between pairs of 4S,,2 (E) excited states migrating through the lattice (exciton transport).
Spectral properties and quantum efficiency of optical emission in rare earth doped crystals
Journal of Physics: Conference Series, 2006
We have studied the spectral properties of Pr 3+-doped CaAl 4 O 7 and SrAl 4 O 7 crystals at 77 and 290 K. Emissions from the 4f5d band are detected using two-photon stepwise excitation. We demonstrated a new method to conveniently measure the quantum efficiency of deep UV emission using the two-step excitation and the difference of the integrated spectral intensities. The quantum efficiencies of the emission from the lowest 4f5d state in the two systems have been estimated and are less than 10% at room temperature. The effect of excited state absorption of the lowest 4f5d on the measurement of the quantum efficiency is analyzed. The actual efficiency may be higher when the effect is taken into account, especially under the condition of strong excitation.
Journal of Materials Science, 2008
Samples of SrAl 2 O 4 and SrAl 2 O 4 :Cr 3+ were prepared by mixing the powder materials SrCO 3 , Al 2 O 3 , and Cr 2 O 3. The crystal structures of the undoped and doped samples were analyzed by X-ray diffraction (XRD) measurements. The diffraction patterns reveal a dominant phase, characteristic of the monoclinic SrAl 2 O 4 compound and another unknown secondary phase, in small amount, for doped samples. The data were fitted using the Rietveld method for structural refinements and lattice parameter constants (a, b, c, and b) were determined. Luminescence of Cr 3+ ions in this host is investigated for the first time by excitation and emission spectroscopy at room temperature. Emission spectra present a larger band and a smaller structure associated to the 4 T 2 (4 F) ! 4 A 2 (4 F) and 2 E (2 G) ! 4 A 2 (4 F) electronic transitions, respectively. The obtained results are analyzed by crystal-field theory and the crystal-field parameter, Dq, and Racah parameters, B and C, are determined from the excitation measurements.
Yb[sup 2+]-doped SrCl[sub 2]: Electronic structure of impurity states and impurity-trapped excitons
The Journal of Chemical Physics, 2010
First principles electronic structure calculations of the excited states of Yb 2+ -doped SrCl 2 crystals up to 65000 cm −1 reveal the existence of unexpected excited states with double-well potential energy surfaces and dual electronic structure lying above and very close in energy to the 4f 13 5d manifold, with which they interact strongly through spin-orbit coupling. The double-well energy curves result from avoided crossings between Yb-trapped exciton states (more stable at short Yb-Cl distances) and 4f 13 6s impurity states (more stable at long Yb-Cl distances); the former are found to be pre-ionization states in which the impurity holds the excited electron in close lying empty interstitials located outside the YbCl 8 moiety. Spin-orbit coupling between the double-well states and lower lying 4f 13 5d impurity states spreads the dual electronic structure character to lower energies and, hence, the instability of the divalent oxidation state is also spread. To some extent, the dual electronic structure (impurity-trapped exciton -impurity state) of some excited states expresses and gives support to hypotheses of interaction between Yb 2+ and Yb 3+ pairs proposed to understand the complex spectroscopy of the material and conciliates these hypotheses with interpretations in terms of the existence of only one type of Yb 2+ defect. The results presented confirm the presence of impurity states of the 4f 13 6s configuration among the 4f 13 5d manifolds, as proposed in the literature, but their energies are very different from those assumed.