Journal
OPTICAL MATERIALS
Volume 60, Issue -, Pages 431-437Publisher
ELSEVIER
DOI: 10.1016/j.optmat.2016.08.024
Keywords
Mn4+; Pyrochlore; E-2 level energy; Vibronic structure; Temperature quenching
Categories
Funding
- Technologiestichting STW, Nederlandse Organisatie voor Wetenschappelijk Onderzoek (NWO)
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Red emitting Mn4+-doped crystalline materials have potential for application in light emitting devices and therefore it is important to understand how the optical properties of Mn4+ are influenced by the host lattice the Mn4+ ions are situated in. In this work we investigate the effect of the host cations in the second coordination sphere on the Mn4+ emission by studying the luminescence of Mn4+ ions doped into three isostructural rare earth (RE) stannate RE2Sn2O7 pyrochlores (RE3+ = Y3+, Lu3+ or Gd3+). It is found that the energies of the Mn4+ T-4(1) and T-4(2) states significantly increase with decreasing Mn4+-O2- distance, whereas the energy of the E-2 level shows a small shift to higher energies from RE3+ = Gd3+ to Lu3+ to Y3+. The observed trend for the E-2 level energy is not related to the size of the RE3+ ion and is not in line with theoretical calculations reported previously. Low temperature emission spectra of the RE2Sn2O7:Mn4+ phosphors reveal that only asymmetrical vibronic modes couple to the E-2 -> (4)A(2) transition and furthermore show there is significant and unexpected local disorder for Mn4+ in Gd2Sn2O7 that is not observed for Mn4+ in the other hosts. Photoluminescence decay measurements demonstrate that the luminescence of RE2Sn2O7:Mn4+ is strongly quenched below room temperature which is assigned to non-radiative relaxation via a low-lying O2- -> Mn4+ charge-transfer state. (C) 2016 Elsevier B.V. All rights reserved.
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