Thulium is investigated as a sensitizing ion for the mid-infrared transitions of praseodymium and neodymium doped into low-phonon energy crystals. Pumping thulium with 800 nm laser diodes enhances emission of mid-infrared fluorescence between 4000 and 5500 nm in potassium lead chloride co-doped with Tm3+ - Pr3+ and Tm3+ - Nd3+.

© 2004 Optical Society of America

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