Luminescence of Fe3+ doped NaAlSiO4 prepared by gel to crystallite conversion

Nayak, M and Kutty, TRN (1998) Luminescence of Fe3+ doped NaAlSiO4 prepared by gel to crystallite conversion. In: Materials Chemistry and Physics, 57 (02). pp. 138-146.

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Abstract

The polymorphs of NaAlSiO4, namely low-carnegieite, nepheline and high-carnegieite, are prepared through gel to crystallite conversion. As-prepared compound has the composition, NaAlSiO4. 1 . 5H(2)O (nepheline hydrate), and acts as a precursor for low-carnegieite. The latter is obtained by decomposing the nepheline hydrate at 800 degrees C, which has an orthorhombic structure and the X-ray diffraction pattern is indexed based on the space group Pmaa. Low-carnegieite is metastable and can be rehydrated to form nepheline hydrate. At 950 degrees C, low-carnegieite transforms to nepheline which, in turn, transforms to high-carnegieite at 1300 degrees C. Low-carnegieite and nepheline do not show any luminescence when doped with Fe3+, whereas the high-carnegieite exhibits the red emission. Non-emissivity of Fe3+ is correlated to the higher site symmetry in low-carnegieite and nepheline having D-2 and C-3v, symmetry, respectively, according to infrared spectral analysis. Whereas, the high-carnegieite has the C-2v site symmetry, due to the rhombic distortion of the tetrahedral sites during the phase transformation that accompanies the polyhedral rotation. Ferric ion doped high-carnegieite shows strong emission band maximising around 684 nm, due to the T-4(1) ((4)G) --> (6)A(1) (S-6) transition of Fe3+ (3d(5)). A weak emission around 714 nm arises from the cooperative vibronic transition and another band around 674 nm is attributed to the Fe3+ ion associated with the hole centre to form a complex centre of the type Fe3+-O--Si4+ as shown by the EPR spectra. The presence of the defect centre in the vicinity of Fe3+ changes the crystal field.

Item Type:	Journal Article
Publication:	Materials Chemistry and Physics
Publisher:	Elsevier Science
Additional Information:	Copyright of this article belongs to Elsevier Science.
Keywords:	gel to crystallite conversion;sodium alumino silicate; photoluminescence;defect centres.
Department/Centre:	Division of Chemical Sciences > Materials Research Centre
Date Deposited:	24 Dec 2009 09:12
Last Modified:	19 Sep 2010 05:25
URI:	http://eprints.iisc.ac.in/id/eprint/18887

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