Stability against crystallization and spectroscopic properties of Tm3+ doped fluorophosphate glasses

Fluorophosphate glasses with various content of Al(PO3)3 were prepared. With the increment of Al(PO3)3 content, density decreases while refractive index increases, and transition temperature, crystallization peak temperature and melt temperature increase which were suggested by differential scanning calorimetry. These glasses exhibit the best stability against crystallization with 7-9 mol% Al(PO3)3 content. Normalized Raman spectra were used to analyze structure and phonon state. The increment of Al(PO3)3 content does not affect phonon energy but results in the augment of phonon density. Absorption spectra were measured. 3H6 → 3F4 transition exhibits absorption at L band of the third communication window. Compared with the energy of Tm3+ excited states in other glass system, 3F4 energy of Tm3+ in these glasses is considerable higher and 3H4 energy is considerable lower, and it can be predicted that emission band of 3H4 → 3F4 transition is close to the amplified band of gain-shift Tm3+ doped fiber amplifier. Analyses of Judd-Ofelt theory suggest when Al(PO3)3 content is no more than 7 mol%, Judd-Ofelt parameters Ωt and the lifetime of 3H4 energy level of Tm3+ vary little with the increment of Al(PO3)3 content, and when Al(PO3)3 content is more than 7 mol%, Ω2 and Ω6 increase and radiative lifetime of 3H4 energy level of Tm3+ drops sharply with the increment of Al(PO3)3 content.