Variable ratio blue/red upconversion in Yb3+-Tm3+ codoped fluorosilicate glasses.

Simultaneous blue-red emission in a fiber pumped by a single wavelength source is perceived as a great challenge because of the large energy difference of the emitted photons. This Letter reports the dependence of the blue-to-red upconversion (UC) emission ratio in Yb3+-Tm3+ codoped fluorosilicate glasses (FSGs) under the excitation of a 980-nm laser on the host glass silica content. Photoluminescence spectra and SEM-EDS are used to clarify the UC mechanism, indicating that the probability of the cross-relaxation (CR) process 1G4 + 3F2→3H6 + 3F4 is key to the dominance of the blue or red emissions. This research can provide a new platform for variable UC luminescence.