EXCITED-STATE ABSORPTION MECHANISMS OF RED TO UV AND BLUE CONVERSION LUMINESCENCE IN TM3+ DOPED FLUOROPHOSPHATE GLASS

Characteristics and ion-ion interaction processes important in the opt ical dynamics of UV and blue upconversion luminescence in Tm3+ doped f luorophosphate glass have been investigated by exciting Tm3+ ions into the F-3(2) level with a DCM dye laser tuned at 657 nm. Two emission b ands centered at 363, 451 nm from the 1D2 level and one emission band centered at 478 nm from the 1G4 level were observed. The 451 nm emissi on was stronger than the 478 nm emission. The excitation power depende nce of all the upconverted emissions were found to be quadratic, confo rming the two photon nature of these transitions. The mechanism leadin g to these emissions was attributed to the excited state absorption (E SA) from the F-3(4) and H-3(4) levels for the emissions the 1D2 and 1G 4 levels, respectively. The loss mechanism due to ion-ion interaction in the F-3(4) level therefore was studied as function of temperature b y measuring the spectral overlap between emission and absorption spect ra of this level. From this data relevant microscopic interaction para meters that give a measure of Tm-Tm coupling have been calculated. Opt ical properties of the intermediate and the final levels involved in t he upconversion processes were studied using the Judd-Ofelt theory. Th is theory was also used to determine radiative transition rates and th e fluorescence quantum efficiencies of the excited levels, and the exc ited state absorption coefficient for the F-3(4) --> 1D2 and H-3(4) -- > 1G4 transitions when the excitation was fixed at 657 nm. Lower excit ed state absorption coefficient of the former transition explains why the 478 nm emission intensity is weaker than 451 nm emission intensity in this glass. According to the rate equation model temperature depen dence of the upconverted emission intensities from the 1D2 level was c ontrolled by the temperature dependence of the excited state absorptio n coefficient corresponding to the F-3(4) --> 1D2 transition.