Erratum to: Study of the structural, electrical and optical properties of Ge-Pb-Te nanocrystals Iman A. Mahdy, Manal A. Mahdy and S. M. El Sheikh Eur. Phys. J. D, 71 2 (2017) 33 Published online: 14 February 2017 DOI: 10.1140/epjd/e2017-70801-y