Effect of Ga3+ and Gd3+ ions substitution on the structural and optical properties of Ce3+ -doped yttrium aluminium garnet phosphor nanopowders.

The structural and optical properties of commercially obtained Y3 Al5 O12 :Ce3+ phosphor were investigated by replacing Al3+ with Ga3+ and Y3+ with Gd3+ in the Y3 Al5 O12 :Ce3+ structure to form Y3 (Al,Ga)5 O12 :Ce3+ and (Y,Gd)3 Al5 O12 :Ce3+ . X-Ray diffraction (XRD) results showed slight 2-theta peak shifts to lower angles when Ga3+ was used and to higher angles when Gd3+ was used, with respect to peaks from Y3 Al5 O12 :Ce3+ and JCPDS card no. 73-1370. This could be attributed to induced crystal-field effects due to the different ionic sizes of Ga3+ and Gd3+ compared with Al3+ and Y3+ . The photoluminescence (PL) spectra showed broad excitation from 350 to 550 nm with a maximum at 472 nm, and broad emission bands from 500 to 650 nm, centred at 578 nm for Y3 Al5 O12 :Ce3+ arising from the 5d → 4f transition of Ce3+ . PL revealed a blue shift for Ga3+ substitution and a red shift for Gd3+ substitution. UV-Vis showed two absorption peaks at 357 and 457 nm for Y3 Al5 O12 :Ce3+ , with peaks shifting to 432 nm for Ga3+ and 460 nm for Gd3+ substitutions. Changes in the trap levels or in the depth and number of traps due to Ce3+ were analysed using thermoluminescence (TL) spectroscopy. This revealed the existence of shallow and deep traps. It was observed that Ga3+ substitution contributes to the shallowest traps at 74 °C and fewer deep traps at 163 °C, followed by Gd3+ with shallow traps at 87 °C and deep traps at 146 °C.