Spectroscopic properties of 1.6 mum emission from Ho3+-doped sulfide glass were evaluated for their potential use as U-band fiber-optic amplifiers. Emission from the I-5(5) --> I-5(7) transition showed a peak wavelength of 1670 nm and a full width at half maximum of similar to65 nm with a cross-section of similar to7.1 x 10(-21) cm(2). Ho3+ concentration in glass should be limited to 0.08 mol% due to energy transfers between Ho3+ ions which lead to a decrease in the I-5(5) level lifetime. Co-doping of Tb3+ effectively decreased terminal I-5(7) level lifetimes via the energy transfer of Ho3+:I-5(7) --> Tb3+:F-7(0, 1, 2). (C) 2003 Elsevier B.V. All rights reserved.