Photoluminescence spectroscopy of Er3+/Yb3+ co-activated silica-alumina monolithic xerogels

Two Er3+/Yb3+ monolithic silica-alumina xerogels doped with different Yb3+ concentrations were prepared by sol-gel route. The samples were thermally treated in air at 950 degrees C for 120 h. and Raman and UV-visible-NIR spectroscopy were used to monitor the degree of densification of the glasses and the residual OH content. Back energy transfer from Er3+ to Yb3+ was demonstrated by measurement of Yb3+ emission upon Er3+ excitation at 514.5 nm. Photoluminescence excitation spectroscopy over the 880-1010 nm wavelength range, spanning the energy range of the Yb3+-F-2(5/2) and Er3+-I-4(11/2) excited states, was used to obtain information about the effective excitation efficiency of Er3+ ions by co-doping with Yb ions. The emission of I-4(13/2) --> I-4(15/2) of Er3+ ion transition with a 47 nm bandwidth was observed upon excitation at 514.5 nm and a lifetime of the I-4(13/2) metastable state of 8.7 ms was measured.