Optical properties of Tm3+ in the gehlenite matrix and sensitization of Ho3+ luminescence in potential Tm/Ho lasers N. BRITOS, B. VIANA, A.M. LEJUS and D. VIVIEN J. Phys. IV France, 04 C4 (1994) C4-513-C4-516 DOI: 10.1051/jp4:19944123