Upconversion emission in antimony–germanate double-clad optical fiber co-doped with Yb3+/Tm3+ ions

• The upconversion luminescence in antimony–germanate glasses co-doped with Yb3+/Tm3+ was measured.
• UC luminescence in double-clad off-set core optical fiber was obtained.
• Blue/red emission ratio of the optical fiber decreases with increasing optical fiber length.

In the paper upconversion luminescence properties in Yb3+/Tm3+ co-doped antimony–germanate glass and double-clad optical fiber were studied. The concentration of lanthanides, which has shown the highest upconversion emission intensity at 478 nm (1G4 → 3H6) and 650 nm (1G4 → 3F4), is 1Yb2O3/0.1Tm2O3 (mol%) as a result of exciting with a laser diode (976 nm). The lifetime of 2F5/2 (Yb3+) level decreases from 781 μs to 71 μs in the presence of Tm3+ 0.1–0.75 mol% respectively. Luminescence decay curve of glass co-doped with 1Yb2O3/0.75Tm2O3 suggests donor–donor fast migration followed by Tm3+ → Yb3+ energy transfer. Glass characterized by highest intensity of upconversion luminescence (1Yb2O3/0.1Tm2O3 mol%) was used as core of double-clad optical fiber made by modified rod-in-tube method. Mechanisms influencing differences in upconversion amplified spontaneous emission of the fabricated optical fiber and bulk glass were discussed. Reabsorption of the amplified spontaneous emission signal along the fibre resulting from Tm3+:3H6 → 1G4, transition was observed.

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