1. Y. Shimizu: Rare Earths: The Rare Earth Society of Japan 40 (2002) 150.
2. W.-T. Chien, C.-C. Sun, and I. Moreno: Opt. Express 15 (2007) 7572.
3. S. Tanabe, S. Fujita, S. Yoshihara, A. Sakamoto, and S. Yamamoto: Proc. SPIE 5941 (2005) 594112.
4. H. J. Cornelissen, S.-L. Hsiao, and N.-H. Hu: OSA Conf. Pap. Solid-State and Organic Lighting (SOLED), 2012, LM2B.1.
5. C.-Y. Chen, C.-C. Sun, Y.-N. Peng, and T. Yang: OSA Conf. Pap. Solid-State and Organic Lighting (SOLED), 2012, LM2B.4.