Spin-Allowed and Spin-Forbidden fd Emission from Er3+ and LiYF4
Division of Condensed Matter and Interfaces, Utrecht University, Utrecht, Utrecht, Netherlands Physical Review B
(Impact Factor: 3.74).
01/1998; 57(4). DOI: 10.1103/PhysRevB.57.R2025
Luminescence measurements in the vacuum ultraviolet of 4f11-->4f10 5d transitions on Er3+ in LiYF4 have shown the presence of a weak fd band. The weakness of the band is explained by the spin-forbidden character of transitions from the ground state to this fd state, which is at lower energy than the spin-allowed fd bands. Upon excitation in the spin-allowed fd bands, both fast spin-allowed fd emission (tau=5 ns) and slow spin-forbidden fd emission (tau>2 mus) are observed. These results can be understood with a configurational coordinate diagram analogous to the Jablonski diagrams that are used to explain the fluorescence and phosphorescence from organic molecules.
Available from: Andrzej J. Wojtowicz
- "Surprisingly, the dominant VUV emissions in these two closely related materials, shown in Figs. 1 and 2, are different. The emission of BaF 2 :Er, peaking at 163.5 nm, is slow, as reported earlier  , and similar to VUV emissions from other Er-activated fluorides . The emission of (Ba,La)F 2 :Er, peaking at 162.5 nm is, unexpectedly, relatively fast (35 ns at room temperature and 45 ns at 10 K). "
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ABSTRACT: The laser induced fluorescence spectrum of Tb3+ ions in LiLuF4 single crystals, pumped by a fluorine pulsed discharge molecular laser at 157.6 nm, was obtained in the vacuum ultraviolet (VUV) and ultraviolet (UV) regions of the spectrum. The 4f75d→4f8 dipole allowed transitions originate from the Stark components and the edge of the levels of the 4f7()5d electronic configuration. The LIF spectra were interpreted on the basis of phonon trapping and phonon reabsorption within the levels of the 4f75d electronic configuration. The absorption spectrum of the crystal samples in the VUV was obtained as well. We observed eight transitions between the ground level 4f8() and the Stark components of the levels of the 4f7()5d electronic configuration and five transitions between the ground level 4f8() and the Stark components of the levels of the 4f7()5d electronic configuration. The edge of the levels of the 4f75d electronic configuration was found to be at 45.2×103±0.2×103 cm−1 and the band gap of the crystal host was 77.6×103±0.3×103 cm−1 wide.
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ABSTRACT: The use of vacuum ultraviolet radiation (VUV; <200 nm) in lanthanide spectroscopy has been triggered by the need for new luminescent materials for VUV excitation. In spite of this 'applied' incentive, the VUV studies have resulted in a wealth of new fundamental knowledge on the luminescence of lanthanides. Here, an overview of our recent results is presented. For the intraconfigurational 4f n transitions many new VUV energy levels for various lanthanides ions have been observed, resulting in an extension of the 30 year old Dieke diagram from 40,000 to 70,000 cm -1. New emitting 4f levels in the VUV are identified as well. For interconfigurational 4f n→ 4f n-15d (fd) transitions the observation of weak spin-forbidden fd bands for the heavy lanthanides is reported. For Er 3+ and Tm 3+ both spin-allowed and spin- forbidden fd emission is observed. A decrease of the matrix element for the fully allowed fd transitions through the lanthanide series is observed and explained by lanthanide contraction. Finally it is shown how the new information on the VUV levels of lanthanides can be used to obtain luminescent materials with a quantum efficiency of more than 100 % via downconversion. This gives new hope for the applications which triggered this research.
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