The photoluminescence of Er3+ in borosilicate glass is strongly enhanced by the presence of silver. Samples prepared by a combination of erbium ion implantation and Na+«Ag+ ion exchange show an increase of the Er3+ excitation efficiency of up to a factor 70 when excited at 488 nm. Excitation of Er3+ is possible over a broad wavelength range in the near ultraviolet and visible. Our data suggest that absorption of light occurs at a silver ion/atom pair or similar defect, followed by energy transfer to Er3+. We can exclude that silver nanocrystals are part of the dominant excitation mechanism, neither via local field enhancement effects due to their surface plasmon resonance nor via absorption and subsequent energy transfer to Er3+.