MARTIN, A. A., RUF, T., CARDONA, M., JANDL, S., BARBA, D., NEKVASIL, Vladimír, DIVIŠ, M., WOLF, T. Infrared study of crystal-field excitations in NdBa_2Cu3O_{6. Physical Review B. 1999, 59(9), 6528-6534. ISSN 0163-1829.}