2004 Fiscal Year Final Research Report Summary
Time-resolved luminescence spectra of tungstates
| Project/Area Number |
15560005
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| Research Category |
Grant-in-Aid for Scientific Research (C)
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| Allocation Type | Single-year Grants |
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| Section | 一般 |
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| Research Field |
Applied materials science/Crystal engineering
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| Research Institution | Faculty of Engineering, Shinshu University |
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Principal Investigator |
ITOH Minoru Shinshu University, Faculty of Engineering, Professor, 工学部, 教授 (80126664)
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| Co-Investigator(Kenkyū-buntansha) |
USUKI Yoshiyuki Furukawa Co., Deputy Director, 素材総合研究所, 所長代理(研究職)
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| Project Period (FY) |
2003 – 2004
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| Keywords | Scintillator / Time-resolved measurement / Tungstate / Luminescence / Self-trapped exciton / Jahn-Teller effect |
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| Research Abstract |
Time-resolved luminescence spectra of lead tungstate (PbWO_4) were investigated in a wide temperature range of 8-300 K. For pulsed excitation, the sample was mounted in a vacuum chamber, and was irradiated by the fourth harmonics (266 nm) of a Q-switched Nd : YAG laser. The time-resolved luminescence was observed by means of a gated ICCD camera, with spectral resolution of 10 nm.
In undoped samples at 300 K, it was found that the peak position shifts from 2.88 eV to 2.55 eV when the delay time was increased from 0 to 1 ms. No appreciable shift was observed at low temperatures below 77 K.
In Mo-doped samples at 300 K, it was revealed that the peak position shifts from 2.86 eV to 2.32 eV when the delay time was increased from 0 to 500 μs. At 77 K, the luminescence peak shifted from 2.82 eV to 2.55 eV with the increase of the delay time from 0 up to 1 ms.
On the basis of these results, it was suggested strongly that the self-trapped exciton (STE) state responsible for the blue luminescence at 2.88 eV is slit into three sublevels by the Jahn-Teller effect. This is consistent with the well-known fact that the STE in PbWO_4 locates on the tetrahedral (WO_4)^<2-> ions. Furthermore, the green luminescence observed at 2.32 eV in Mo-doped PbWO_4 was ascribed to a radiative decay of the STE state perturbed by Mo ions. On the other hand, the blue-green luminescence observed at 2.55 eV in undoped samples was attributed to a radiative decay of the STE state perturbed by lattice imperfection, e.g., oxygen defect.
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