| 1. |
- Dong, N., et al.
(författare)
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Spectroscopic analysis of LiKGdF5 : Er3+, Sm3+ single crystal
- 2006
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Ingår i: Journal of Alloys and Compounds. - : Elsevier BV. - 0925-8388 .- 1873-4669. ; 424:1-2, s. 334-337
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Tidskriftsartikel (refereegranskat)abstract
- Low temperature photoluminescence spectra were measured under the selective excitation to the energy levels of Gd3+,Er3+ and Sm3+, respectively. Corresponding transitions were assigned with the help of fluorescence decay measurements. By assuming that the rare earth ion is in C-2v symmetry instead of the actual C-2, crystal field calculations were carried out based on the deduced experimental energy level data of Er3+ and Sm3+. The theoretical result is in good agreement with the experimental data.
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| 2. |
- Edvardsson, Sverker, et al.
(författare)
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The connection between the dynamic intensity model and the vibronic intensity model for f-f transitions
- 2006
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Ingår i: Journal of physics. B: Atomic, molecular and optical physics. - : IOP Publishing. - 0953-4075 .- 1361-6455. ; 39:9, s. 2127-2143
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Tidskriftsartikel (refereegranskat)abstract
- In this paper we discuss intensity mechanisms of interest for rare-earth ions in optical materials. More specifically, we investigate the character of two models-first, a semi-classical dynamic intensity model, and second, a more traditional quantum mechanical vibronic intensity model. We focus on the case of f-f transitions and show that the predicted oscillator strengths then are the same under very reasonable approximations. We emphasize that this connection between the models cannot be made in the case of f-d transitions. The dynamic intensity model has an interesting classical interpretation. We show that it is very convenient to apply this approach together with classical dynamical techniques such as molecular dynamics simulation or the classical Monte Carlo method. The classical approach simplifies both the interpretation and calculation of vibronic oscillator strengths in complex systems. The concept of an effective temperature works as a bridge between the two models; so realistic predictions can be obtained even at low temperatures.
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| 3. |
- Ning, Lixin, et al.
(författare)
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Dynamic intensity model calculation of vibronic oscillator strengths for Cs2NaNdCl6 : A molecular dynamics study
- 2006
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Ingår i: Journal of Physical Chemistry B. - : American Chemical Society (ACS). - 1520-6106 .- 1520-5207. ; 110:43, s. 21424-21429
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Tidskriftsartikel (refereegranskat)abstract
- We present here a dynamic intensity model calculation of vibronic oscillator strengths for the Cs2NaNdCl6 compound by applying the method of molecular-dynamics simulation (MDS). The force field parameters used for the MDS reproduce the structure and several vibrational frequencies of Cs2NaNdCl6 very well. Both the static-coupling (SC) and dynamic-coupling (DC) mechanisms are taken into account for the intensity parameter calculations, in which the effective point charges and isotropic polarizabilities are optimized with respect to experimental energy levels. A comparison of intensity parameters and vibronic oscillator strengths between the two individual mechanisms indicates that the DC mechanism is operative. The calculated vibronic oscillator strengths for the combined SC and DC mechanism agree quite well with the available experimental values.
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| 4. |
- Ning, Lixin, et al.
(författare)
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Theoretical study ofI-4(13/2) -> I-4(15/2) luminescence quenching by OH for LaF3 : Er3+ nanoparticles in solution
- 2007
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Ingår i: Journal of Physics. - : IOP Publishing. - 0953-8984 .- 1361-648X. ; 19:1
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Tidskriftsartikel (refereegranskat)abstract
- The processes of I-4(13/2)-> I-4(15/2) luminescence quenching by OH vibrations are investigated for LaF3:Er3+ nanoparticles dissolved in solution. The energy transfer (ET) rates, involving the I-4(13/2)-> I-4(15/2) transition of Er3+ and the first overtone absorption of OH, are estimated. In order to calculate the relevant OH transition matrix elements, a model for the OH vibration in solution is developed with the use of a Morse potential. Various multipole-multipole ET mechanisms are considered and their dependences on the distance between Er3+ and OH are studied. Based on these ET mechanisms, the ET rates from an Er3+ in the nanoparticle to all the OH in solution are estimated and compared with respect to changes in location of the ion, size of the nanoparticle and OH concentration in solution. The effective I-4(13/2)-> I-4(15/2) luminescence decay times that are contributed by all the Er3+ in the nanoparticle are then calculated with different Er3+ concentrations. The calculations satisfactorily account for experimental observations.
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| 5. |
- Ning, Lixin X, et al.
(författare)
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High-spin and low-spin f-d transitions of Tb3+ in elpasolite hosts
- 2005
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Ingår i: Physical Review B. Condensed Matter and Materials Physics. - 1098-0121 .- 1550-235X. ; 72:8
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Tidskriftsartikel (refereegranskat)abstract
- The electronic absorption spectra of Cs2NaTbCl6 and Cs2NaYCl6:Tb3+ have been recorded between 34000-43000 cm(-1) at temperatures down to 10 K. Well-resolved spin-forbidden and spin-allowed transitions are observed, comprising three and one electronic transitions, respectively, between the crystal field levels of 4f(8) and 4f(7)d (t(2g)) states. For transitions from the electronic ground state, symmetry selection rules restrict the upper crystal field levels to be Gamma(4u) (T-1u) symmetry. Three vibrational progression modes appear in the electronic transitions and these are assigned to breathing modes with the first, second, and third nearest neighbors of Tb3+. The experimental results are rationalized both from the use of a simple model and from the extended f-shell programs of Reid. The excitation process 4f(8)-> 4f(7)5d (t(2g)) involves a small (5.5 pm) bond length change which is considered to be a contraction rather than an expansion.
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| 6. |
- Wang, Yanan, et al.
(författare)
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The radio detection and accretion properties of the peculiar nuclear transient AT 2019avd
- 2023
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Ingår i: Monthly Notices of the Royal Astronomical Society. - : Oxford University Press (OUP). - 0035-8711 .- 1365-2966. ; 520:2, s. 2417-2435
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Tidskriftsartikel (refereegranskat)abstract
- AT 2019avd is a nuclear transient detected from infrared to soft X-rays, though its nature is yet unclear. The source has shown two consecutive flaring episodes in the optical and the infrared bands, and its second flare was covered by X-ray monitoring programs. During this flare, the UVOT/Swift photometries revealed two plateaus: one observed after the peak and the other one appeared similar to 240 d later. Meanwhile, our NICER and XRT/Swift campaigns show two declines in the X-ray emission, one during the first optical plateau and one 70-90 d after the optical/UV decline. The evidence suggests that the optical/UV could not have been primarily originated from X-ray reprocessing. Furthermore, we detected a timelag of similar to 16-34 d between the optical and UV emission, which indicates the optical likely comes from UV reprocessing by a gas at a distance of 0.01-0.03 pc. We also report the first VLA and VLBA detection of this source at different frequencies and different stages of the second flare. The information obtained in the radio band - namely a steep and a late-time inverted radio spectrum, a high brightness temperature and a radio-loud state at late times - together with the multiwavelength properties of AT 2019avd suggests the launching and evolution of outflows such as disc winds or jets. In conclusion, we propose that after the ignition of black hole activity in the first flare, a super-Eddington flaring accretion disc formed and settled to a sub-Eddington state by the end of the second flare, associated with a compact radio outflow.
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