Enhanced Tm3+ blue emission in Tm, Yb, co‐doped fluorophosphate glasses due to back energy transfer processes

Up‐conversion emission spectra of fluorophosphate glasses doped with Tm3+ and co‐doped with Tm3+ and Yb3+ ions were obtained under two different excitation wavelengths (657 and 683 nm). Both samples show a stronger emission centered at 450 nm than the ones centered at 478 and 363 nm when 3F2 level of Tm3+ is excited at 657 nm. If 3F3 level of Tm3+ is excited with the 683 nm light the 478 nm emission of the double doped sample becomes much stronger (about 200 times) than the same emission of the single doped sample. We propose an up‐conversion mechanism to explain the spectra which is in agreement with quadratic dependence of the emission intensities on the excitation power under both excitations.