Thomas Luxbacher

Competitive cross-relaxation and energy transfer within the shell model: The case of Cs2NaSmxEuyY1 − x − yCl6

Abstract Electronic energy-transfer processes between Sm 3+ ( 4 G 5 2 ) donor ions and Eu 3+ ( 7 F 0 , 7 F 1 ) acceptor ions in the cubic hexachloroelpasolite crystals Cs 2 NaSm x Eu y Y 1 − x − y Cl 6 have been investigated over a wide range of Sm 3+ and Eu 3+ concentrations at temperatures of 80 and 300 K. In these systems the luminescence from the 4 G 5 2 state of Sm 3+ is strongly quenched by both cross-relaxation to nearby Sm 3+ ions and energy transfer to the 5 D 0 state of Eu 3+ . The lifetime of the 5 D 0 state is not affected by the presence of Sm 3+ . The rates of cross-relaxation and energy transfer are determined from luminescence decay curve measurements for the Sm 3+ 4 G 5 2 → 6 H 7 2 emission and the Eu 3+ 5 D 0 → 7 F 2 emission following excitation into the 4 G 5 2 state of Sm 3+ . The luminescence decay curves for the 4 G 5 2 state are analysed in terms of a recently developed discrete shell model for energy transfer assuming electric dipole vibronic-electric dipole vibronic and magnetic dipole-magnetic dipole interaction between Sm 3+ donor ions and Eu 3+ acceptor ions. Exact agreement is achieved for the energy transfer from Sm 3+ donor ions to Eu 3+ acceptors without curve fitting.

Fast cross relaxation in lanthanide hexachloroelpasolites: application of the shell model

Abstract Luminescence decay curves from the 4 G 5 2 state of Sm3+ in the cubic hexachloroelpasolite crystals Cs2 NaSmxY1−xCl6 (x = 0.005 to x = 1) have been measured in the temperature range 10–300 K. Energy transfer from the 4 G 5 2 to the 6FJ states occurs at all concentrations studied. At intermediate concentrations the decay curves are strongly non-exponential and are interpreted using a recently developed shell model. Extensions of the model which may provide a better description of the data are briefly discussed.

Luminescence and electronic absorption spectra of Rb2NaY0.95Tm0.05F6

Abstract The 360 and 458 nm excited luminescence spectra of single crystals of Rb 2 NaY 0.95 Tm 0.05 F 6 have been measured at temperatures down to 15 K. The 1 D 2 → 3 F 4 , and 1 G 4 → 3 F 4 , 3 H 5 transitions each show extensive vibronic structure which has been analysed in detail. In addition, under 458 nm excitation, several transitions from the 1 D 2 state located at 28050 cm −1 are observed following up-conversion. The 3 H 6 → 1 D 2 transition has been located in absorption and its vibronic structure analysed. A further eight electronic states of the TmF 6 3− ion have been located. The crystal field splittings are substantially larger than for the TmCl 6 3− and TmBr 6 3− ions.

Temperature dependence of luminescence decay from the 4G52 state of Sm3+ in Cs2NaSmxY1 − xCl6 and Cs2NaSmxEuyY1 − x − yCl6

Luminescence decay curves for the 4G52 → 6H72 emission of Sm3+ in the cubic hexachloroelpasolite crystals Cs2NaSmxY1 − xCl6 (x = 0.005–1) and Cs2NaSmxEuyY1 − x − yCl6 (x = 0.01–0.95, y = 0.05–0.99) have been measured over the temperature range 10–300 K using pulsed laser excitation into the (6H52)Γ7 → (4G52)Γ8 magnetic-dipole-allowed electronic transition of Sm3+. The luminescence from the 4G52 state is strongly quenched by both cross relaxation to nearby Sm3+ ions and energy transfer to the 5D0 state of Eu3+ acceptors. The temperature dependence of cross relaxation and energy transfer is discussed in terms of the involved mechanisms.

Vibronic intensities in the optical absorption spectra of Pr3+ in Cs2NaPrxY1−xCl6: concentration and temperature dependence

Abstract The 3 H 4 → 3 P 0 transition in the absorption spectra of Pr 3+ in the hexachloroelpasolites Cs 2 NaPr x Y 1− x Cl 6 ( x = 0.1 to x = 1) have been measured from 300 to 10 K. The electronic spectra are dominated by electric-dipole allowed vibronic origins enabled by Herzberg-Teller coupling. The two odd parity vibrations of the [PrCl 6 ] 3− ion ( ν 3 and ν 4 ) appear strongly in the vibronic sidebands and are accompanied by weaker lattice vibrations. The small change in the oscillator strength of the vibronic transitions is readily accounted for by the change in lattice parameter with x . There is no evidence for cooperative effects.

Spectroscopy of hexanitritoelpasolite crystals: the effect of the rare-earth ion on the progressions in the nitrite vibration

The low temperature absorption spectra of the cubic hexanitritoelpasolite crystals Cs2NaLn(NO2)6 (Ln, rare-earth ion) in the blue spectral region are dominated by progressions in the bending mode of the nitrite ion. The vibrational structure on which these progressions are based is strongly dependent on the rare-earth ion which is surrounded by twelve oxygen ions from six nitrite groups. The lanthanide–oxygen distances show a remarkable change with temperature. The f–f transitions of the rare-earth ion are extremely weak in comparison to the corresponding hexachloroelpasolite crystals Cs2NaLnCl6 which have a similar structure except for the high frequency vibrations. We compare the 12 K absorption spectra of Cs2NaY(NO2)6 with hexanitritoelpasolite crystals containing Ln=La, Sm, Gd, and Er. The change in the relative intensities of the origins of the nitrite progression lines is related to the change in the ionic radii of the rare-earth ions, which in turn affects the metal oxygen distance and the O–N–O bond angle.

Theoretical manifestation of the shell model for energy transfer

Abstract Luminescence decay curves for the 4G5/2→6H7/2 emission of Sm3+ in the hexachloroelpasolite crystals Cs2NaSm0.01Gd0.99Cl6 and Cs2NaSm0.01Eu0.1Y0.89Cl6 have been measured over the temperature range 10–300 K using pulsed laser excitation into the magnetic-dipole allowed 6H5/2→4G5/2 electronic transition of Sm3+. The emission is quenched by cross relaxation to nearby Sm3+ ions and energy transfer to the 5D0 state of Eu3+ acceptors and the decay curves are analyzed using a recently developed shell model for energy transfer. The corresponding energy-transfer rate to a single Eu3+ acceptor at a distance R1=7.65 A shows a rapid increase in the temperature range 200–300 K which is explained in terms of the thermal population of the initial Sm3+(4G5/2)Γ7 donor state and the Eu3+(7F1)Γ4 acceptor state. The near-resonant magnetic dipole–magnetic dipole contribution to the total energy-transfer rate between a Sm3+ donor ion and a nearest-neighbour Eu3+ acceptor is calculated. We show the applicability of the shell model for the simultaneous treatment of cross-relaxation and energy-transfer processes to the 4G5/2 decay kinetics of Sm3+ in a cubic lattice.

Energy transfer in high-symmetry crystals

Abstract Luminescence decay curves from the 5D1 state of Eu3+in the cubic hexachloroelpasolite crystals Cs2NaSmxEu0.1Gd0.9−xCl6 have been investigated at 80 K. In this system the emission from the 5D1 state of Eu3+ is strongly quenched by cross relaxation to nearby Eu3+ ions and energy transfer to the 4G5/2 state of Sm3+. The decay curves are analysed in terms of a discrete shell model for competitive cross-relaxation and energy-transfer processes assuming electric dipole vibronic-electric dipole vibronic interactions between Eu3+ donor ions and Sm3+ acceptors. We demonstrate the properties of the shell model and the limitations involved in the modelling of luminescence decay curves.