[1] [1] M. S. Sajna, Sunil Thomas, K. A. Ann Mary, Cyriac Joseph, P. R. Biju and N. V. Unnikrishnan, Journal of Luminescence 159, 55 (2015).

[2] [2] Y. Hu, S. Jiang, G. Sorbello, T. Luo, Y. Ding, B. C. Hwang and N. Peyghambarian, Journal of the Optical Society of America B-Optical Physics 18, 1928 (2001).

[3] [3] M. elikbilek, A. E. Ersundu, E.O. Zayim and S. Aydin, Journal of Alloys and Compounds 637, 162 (2015).

[4] [4] W. J. Zhang, J. Lin, M. Z. Cheng, S. Zhang, Y. J. Jia and J. H. Zhao, Journal of Quantitative Spectroscopy and Radiative Transfer 159, 39 (2015).

[5] [5] R. Anthony, R. Lahiri and S. Biswas, Microwave and Optical Technology Letters 125, 2463 (2014).

[6] [6] A. Pandey, S. Som, V. Kumar, V. Kumar, K. Kumar, V. K. Rai and H. C. Swart, Sensors and Actuators B-Chemical 202, 1305 (2014).

[7] [7] S. C. Zheng, Y. W. Qi, S. X. Peng, D. D. Yin, Y. X. Zhou and S. X. Dai, Optoelectronics Letters 9, 461 (2013).

[8] [8] G. Dantelle, M. Mortier, D. Vivien and G. Patriarche, Optical Materials 28, 638 (2006).

[9] [9] T. Sasikala, L. R. Moorthy, K. Pavani and T. Chengaiah, Journal of Alloys and Compounds 542, 271 (2012).

[10] [10] B. R. Judd, Physical Review 127, 750 (1992).

[11] [11] G. S. Ofelt, Journal of Chemical Physics 37, 511 (1962).

[12] [12] M. R. Dousti, R. J. Amjad and Z. A. S. Mahraz, Journal of Molecular Structure 1079, 347 (2015).

[13] [13] P. Y. Wang, H. P. Xia, J. T. Peng, H. Y. Hu, L. Tang, Y. P. Zhang, B. J. Chen and H. J. Jiang, Optoelectronics Letters 9, 285 (2013).

[14] [14] G. R. Khan, Optical Fiber Technology 18, 421 (2012).

[15] [15] Y. X. Zhou, D. D. Yin, S. C. Zheng and X. C. Xu, Journal of Quantitative Spectroscopy and Radiative Transfer 129, 1 (2013).

[16] [16] D. E. McCumber, Physical Review 136, 954 (1964).