INFRARED TO VISIBLE UP-CONVERSION IN CS3YB2CL9-TM3+

Tm3+ doped Cs3Yb2Cl9 and Cs3Y2Cl9 was synthesized and single crystals were grown using the Bridgman technique. Absorption, upconversion luminescence and excitation spectra are presented as well as power- and concentration-dependent measurements. Under near-infrared (NIR) CW excitation of the (2)F7/2 --> F-2(5/2) transition of Yb3+, Tm3+ doped Cs3Yb2Cl9 exhibits intense NIR (H-3(4) --> H-3(6)), red (F-3(3) --> H-3(6)), blue ((1)G(4) --> H-3(6) and D-1(2) --> F-3(4)) and near-UV (D-1(2) --> H-3(6)) upconversion luminescence. It is a stepwise energy transfer with a very pronounced power and concentration dependence. The unusual (compared to fluoride and oxide systems) red upconversion luminescence, assigned to a F-3(3) --> H-3(6) transition, is due to the low-energy phonons (less than or equal to 280 cm(-1)) in this lattice. The power dependence and the dependence of the excitation spectra upon the detection wavelength are reproduced by simple models.