UP-CONVERSION LUMINESCENCE OF TM3-DOPED FLUOROPHOSPHATE GLASSES UNDER683-NM EXCITATION( IN YB3+)

The upconversion properties of Tm3+ ions have been studied in fluoroph osphate glasses having the composition: 2.67AlPO(4) . 37.33AlF(3) . 27 PbF(2) . (33 - x - y) CaF2 . xTmF(3) . yYbF(3) under 683 nm light whic h corresponds to the ground state absorption of the (Tm) F-3(3) level. The absorption, luminescence, excitation and time-resolved spectra an d the decay patterns were measured as function of TmF3 and YbF3 concen trations at room temperature. Three upconverted emissions centered at 363 (D-1(2) --> H-3(6) transition), 451 (D-1(2) --> H-3(4) transition) and 478 ((1)G(4) --> H-3(6) transition) nm were observed. The emissio n centered at 478 nm was enhanced in the codoped sample. Two-photon ab sorption processes are responsible for the upconverted emissions origi nating from the D-1(2) and D-1(4) levels in both singly and codoped sa mples, respectively. The upconversion mechanism governing the stepwise excitation of 683 nm light was attributed to the (Tm) F-3(4) --> (Yb) F-2(5/2) and (Yb) F-2(5/2) --> (Tm) (1)G(4) energy transfer processes between Tm3+ and Yb3+ ions in the codoped sample. According to the ti me-resolved spectra of the blue emissions, the time at which the upcon verted emission reaches its maximum value depends on the Tm concentrat ion. However the (Tm) F-3(4) -->(Yb) F-2(5/2) transfer rate is indepen dent of the Tm3+ concentration and is equal to 8.8 x 10(3) s(-1).