OPTICAL PROPERTIES OF Cr3+ ION IN LaMgAl11O19 and La1-x Ndx MgAl11O19 B. VIANA, V. PONCON, C. GARAPON, A.M. LEJUS, D. VIVIEN et G. BOULON J. Phys. Colloques, 48 C7 (1987) C7-505-C7-507 DOI: 10.1051/jphyscol:19877120