Optical absorption and photoluminescence spectra (PL) of the glasses possessing compositions (49 − x ) Li 2 O− x Y 2 O 3 −50 SiO 2 :1.0 Ce 2 O 3 /1.0Yb 2 O 3 and (49 − x ) Li 2 O− x Y 2 O 3 −50 SiO 2 :(0.5 Ce 2 O 3 + 0.5 Yb 2 O 3 ) with x varying from 5 to 15 mol% were studied. The PL spectra of Ce 3+ doped glasses excited at 360 nm exhibited two broad parity allowed 5d( 2 D) → 4f( 2 F 5/2 , 7/2 ) bands in the blue spectral region, whereas the spectra of Yb 3+ doped glasses excited at 900 nm exhibited a broad emission band centered at about 980 nm due to 2 F 5/2 → 2 F 7/2 transition. A significant enhancement in the intensity of NIR emission is observed due to the sensitization with Ce 3+ ions. The increase in the rate of energy transfer from Ce 3+ to Yb 3+ could be observed with increasing Y 2 O 3 content. The reasons for such improvement have been discussed within a framework of structural modifications taking place in the vicinity of Yb 3+ ions.