Ultraviolet upconversion in Pr3+:Y2SiO5 crystal by Ar+ laser (488 nm) excitation C. L. Sun, J. F. Li, C. H. Hu, H. M. Jiang and Z. K. Jiang Eur. Phys. J. D, 39 2 (2006) 303-306 Published online: 18 May 2006 DOI: 10.1140/epjd/e2006-00102-7