Investigation of upconversion luminescence in antimony-germanate double-clad two cores optical fiber co-doped with Yb3+/Tm3+ and Yb3+/Ho3+ ions

In the paper double-clad optical fiber with two off-set cores co-doped with 1Yb2O3-0.1Tm2O3 and 1Yb2O3-0.5Ho2O3 has been investigated. Antimony-germanate glass was melted as a matrix for active cores. The concentration of lanthanides and their ratio have been optimized to achieve maximum upconversion emission intensity at 478 nm (1G4→3H6) and 650 nm (1G4→3F4) in glasses doped with Tm3+ ions and 545 nm and 655 nm, corresponding to the 5F5→5I8 and 5F4→5I8 transitions in holmium ions. The energy transfer efficiency in glasses used as optical fiber cores was ηTm=56% (0.1 mol% Tm2O3) and ηHo=85% (0.5 mol% Ho2O3), respectively. As a result of excitation of the fabricated optical fiber (λexc=976 nm), a UC luminescence spectra was obtained. Superposition of three emission bands at the wavelengths of 481 nm (Tm3+: blue), 545 nm (Ho3+:green) and 665 nm (Tm3+, Ho3+: red) from two separated cores was measured. Influence of fiber length and excitation power on the color coordinates (CIE-1931) have been also investigated.