Up-conversion Fluorescence Properties Of Rare Earth Doped Sample Based On Bi₂O₃ And SrF₂ Compounds

With the rapid development of techniques, rare-earth doped up-conversion materials have became valuable in the fields of display devices, lighting storage, optical materials, anti- faker industry, solid-state lasers and so on. At present, the most important task is to improve the efficiency of up-conversion. In this paper, a series of samples have been prepared by rare earth single-doped or co-doped to hosts according to the fundamental principles of up- conversion materials. The influences of the microstructures, the compositions of host materials and the rare earth concentrations on the up-conversion luminous efficiency were studied by metalography, XRD and SEM. And the up-conversion spectrum was measured by R-500. The results are shown as follows:1. Er³⁺-doped Bi₂O₃ glasses have been fabricated through the high temperature solid-state reaction method. Under exitation of 980 nm LD, the glass emits strong red emission (⁴F_9/2→⁴I_15/2) and green emission (²H_11/2→⁴I_15/2, ⁴S_3/2→⁴I_15/2). But the red emission becomes too weak to be detected under excitation of 808 nm LD which shows that the electron population of 4F9/2 level is mainly achieved by energy transfer..2. The Judd–Oflet intensity parametersΩ_t (t =2,4,6), were found to beΩ₂ =3.35×10^-20cm²,Ω₄ =1.34×10^-20cm² ,Ω₆ =0.67×10^-20cm² calculated basing on the measured absorption spectrum according to the Judd-Oflet theory The stimulated emission cross-section of ⁴I_13/2→⁴I_15/2 transition was calculated by Mc- Cumber theory. The value of FWHM×σ_e^peak is found to be 6.0×10^-21cm², which accounts for that the band-width property of the Bi₂O₃ glasses is better than those of silicate, phosphate and germinate glasses.3. A set of SrF₂:Yb³⁺/Er³⁺ co-doped samples were also prepared by high temperature solid- state reaction method. Under the excitation of 980 nm LD, The ratio of blue emissionâ… (480 nm) to blue emission bandâ…¡(449nm) and the ratio of red to green reduced with increasing the Yb³⁺/Er³⁺ ions ratio, this is due to that the blue emissionâ… was originated from the co- operative sensitization of Yb³⁺- Yb³⁺ pair, while the blue emissionâ…¡was originated from the co- operative sensitization of Er³⁺- Yb³⁺ pairs. The ratio of blue emissionâ… toâ…¡decreases with the decreasing of the Er³⁺ concentration. The red/green ratio becomes smaller due to the increase of Yb³⁺ ions, which lead to the increasing of the electron population of ⁴F_9/2 and the electron population in ⁴S_3/2/²H_11/2 increasing faster than in⁴F_9/2,4. According to the XRD and SEM, with the increasing of SrF2 concentration, the volume of phase of SrF₂ crystal has increased and the fluorescence intensity of the samples has became stronger. It can be concluded that SrF₂ are the fairly good choice as a host for up-conversion materials because cubic phase SrF₂ is beneficiary to hence the fluorescence efficiency.