Spectroscopic investigation on the properties of visible and near infraredemissions in Tm3+, Ho3+Co-doped YVO4 crystals

With the help of absorption and fluorescence spectra, the spectroscopic pro perties of Tm3+, Ho3+:YVO4 crystals have been investigated under different dopant concentrations. The absorption results show that the maximum absorpt ion in the spectral range of currently available powerful laser diodes (LD) is at 796 nm, corresponding to the transition H-3(6) --> H-3(4) Of Tm3+ in the crystals. Upon the excitation with a LD at 808 nm, we have detected te n fluorescence bands in the spectral range spanning from visible to infrare d. In visible region 4 upconversion bands have been observed centered at 47 5, 547, 660, and 701nm. Discussions of the energy transfer processes sugges t that cross relaxations and excited absorptions with the involvement of Tm 3+ F-3(4), H-3(5) and Ho3+ 7I(5) states are responsible for the four upconv ersion emissions. Comprising the relative integrated intersities of 2 mu m (Ho3+: I-5(7) --> I-3(8)) and 1.8 mu m (Tm3+:F-3(4) --> H-3(6)) bands we ha ve observed an efficient energy transfer from Tm3+ (F-3(4)) to Ho3+ (I-5(7) ). Examination of the ratios of the intensity of 2 mu m band to that of 1.8 mu m band as a function of the ratios of Tm3+ concentration (c(Tm)) to Ho3 + concentration (c(Ho)) indicates that small concentration ratios (c(Tm)/c( Ho)) lead to high efficient energy transfers of Tm3+(F-3(4)) --> Ho3+(I-5(7 )).