Absorption and Luminescence Spectroscopy of MnO42--Doped Crystals of BaSO4
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- 作者：Thomas C. Brunold and Hans U. Gü ; del
- 刊名：Inorganic Chemistry
- 出版年：1997
- 出版时间：April 23, 1997
- 年：1997
- 卷：36
- 期：9
- 页码：1946 - 1954
- 全文大小：298K
- 年卷期：v.36,no.9(April 23, 1997)
- ISSN：1520-510X
文摘
The first polarized low-temperature absorption and luminescencespectra of manganese-doped crystals of BaSO4containing essentially MnO42- arereported. By using a flux composed of NaCl, KCl, and CsCl we wereable togrow BaSO4:Mn6+ crystals below 620 
C.This prevents the simultaneous presence ofMnO43- besidesMnO42-,which was mainly responsible for the erroneous assignments of theabsorption spectrum in the literature. In theBaSO4 host the MnO42-ion occupies a site of Cs symmetry,and the orbital degeneracies of the E and T statesare thus lifted. Above 16 000 cm-1 theabsorption spectra consist of a series of intense ligand-to-metalchargetransfer (LMCT) excitations. Their marked polarization dependenceallows an unambiguous band assignment inthe parent Td symmetry. Thethree origins of the 2E 
2T2ligand-field (LF) transition peak at 11 074, 11 570,and 11 790 cm-1. The lowest-energycomponent of 2T2 serves as the initial statefor broadband luminescence inthe near-infrared (near-IR) region with a maximum at 9300cm-1. Below 100 K the quantum yield isunity andthe radiative lifetime is 2.75 
s, and at 300 K the quantum yield isstill 20%. In both the 2E 
2T2 (d d)absorption and luminescence spectra the vibrational structure isdominated by progressions in O-Mn-O bendingmodes whereas coupling to the totally symmetric Mn-O stretching modeis less pronounced. The luminescenceband shapes for the transitions to the two orbital components of2E are strikingly different; the Huang-Rhysparameters for the bending-mode progressions obtained from fits ofsimulated band shapes to the experimentalspectra are 1.3 and 3.7, respectively. This is due to weakE
e and stronger T2eJahn-Teller (JT) effects in theground and excited LF states, respectively. The linear vibroniccoupling constants are fE 
180cm-1 and fT-730 cm-1 and the corresponding JTstabilization energies EJT(2E) 50 cm-1 andEJT(2T2) 780cm-1,respectively.
C.This prevents the simultaneous presence ofMnO43- besidesMnO42-,which was mainly responsible for the erroneous assignments of theabsorption spectrum in the literature. In theBaSO4 host the MnO42-ion occupies a site of Cs symmetry,and the orbital degeneracies of the E and T statesare thus lifted. Above 16 000 cm-1 theabsorption spectra consist of a series of intense ligand-to-metalchargetransfer (LMCT) excitations. Their marked polarization dependenceallows an unambiguous band assignment inthe parent Td symmetry. Thethree origins of the 2E 2T2ligand-field (LF) transition peak at 11 074, 11 570,and 11 790 cm-1. The lowest-energycomponent of 2T2 serves as the initial statefor broadband luminescence inthe near-infrared (near-IR) region with a maximum at 9300cm-1. Below 100 K the quantum yield isunity andthe radiative lifetime is 2.75 s, and at 300 K the quantum yield isstill 20%. In both the 2E 2T2 (d d)absorption and luminescence spectra the vibrational structure isdominated by progressions in O-Mn-O bendingmodes whereas coupling to the totally symmetric Mn-O stretching modeis less pronounced. The luminescenceband shapes for the transitions to the two orbital components of2E are strikingly different; the Huang-Rhysparameters for the bending-mode progressions obtained from fits ofsimulated band shapes to the experimentalspectra are 1.3 and 3.7, respectively. This is due to weakEe and stronger T2eJahn-Teller (JT) effects in theground and excited LF states, respectively. The linear vibroniccoupling constants are fE 180cm-1 and fT-730 cm-1 and the corresponding JTstabilization energies EJT(2E) 50 cm-1 andEJT(2T2) 780cm-1,respectively.