Submitted on: 17 October 2011.
Revised on: 22 November 2011.
Accepted on: 16 December 2011.
Optoelectronics and Advanced Materials-Rapid Communications
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Submitted on: 05 February 1999.
Revised on: 20 February 1999.
Accepted on: 02 March 1999.
Optoelectronics and Advanced Materials-Rapid Communications
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Submitted on: 03 September 2001.
Revised on: 18 September 2001.
Accepted on: 23 September 2001.
Optoelectronics and Advanced Materials-Rapid Communications
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