Optical and paramagnetic properties of titanium centres in ZnS |
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Authors: | J Dziesiaty MU Lehr P Peka A Klimakow S Müller H-J Schulz |
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Institution: | Humboldt-Universit?t zu Berlin, Institut für Physik, Invalidenstrasse 110, 10099 Berlin, Germany, DE Fritz-Haber-Institut der Max-Planck-Gesellschaft, Faradayweg 4-6, 14195 Berlin, Germany, DE
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Abstract: | ZnS:Ti crystals grown by different methods are investigated at low temperatures (2 K K) by electron paramagnetic resonance (EPR) and optical spectroscopies, mainly with regard to their photoluminescence properties,
including excitation and sensitisation spectra. The more familiar lattice-neutral Ti2+(d
2
) ion on a cubic site (AN) presents an isotropic EPR signal with g=1.928 observable up to 80 K. Signals of axial PN and AS sites are detected in the same temperature range. This Ti2+ ion exhibits the transition in emission, structured by no-phonon lines (NPL) of centres in various environments, with the AN site represented
at 3613 cm-1, and the 3
T
1
(F) and 3
T
1
(P) bands in excitation spectra. Substitutional Ti3+(d
1
) is identified by an anisotropic EPR spectrum at T = 3.5 K, indicating a quasistatic Jahn-Teller effect at the doubly degenerate 2
E(D) ground state, while in the first excited vibronic state a quasidynamic JT effect in the strain-split vibronic 2
E/2
A
2
manifold is found. A new luminescence band centred at 4500 cm-1 with NPL structures near 5000 cm-1 represents AN, PN and AS sites in the transition. Charge-transfer processes are described in a one-particle model, depicting the Ti3+/Ti2+ donor level at 12 900 cm-1 below the conduction-band edge.
Received: 3 October 1997 / Revised: 17 December 1998 / Accepted: 18 May
1998 |
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Keywords: | PACS 71 70 -d Level splitting and interactions- 76 30 Fc Iron group (3d) ions and impurities (Ti-Cu)- 78 55 Et II-VI semiconductors |
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