Effect of Ga and Gd ions substitution on the structural and optical properties of Ce -doped yttrium aluminium garnet phosphor nanopowders.

The structural and optical properties of commercially obtained Y Al O :Ce phosphor were investigated by replacing Al with Ga and Y with Gd in the Y Al O :Ce structure to form Y (Al,Ga) O :Ce and (Y,Gd) Al O :Ce . X-Ray diffraction (XRD) results showed slight 2-theta peak shifts to lower angles when Ga was used and to higher angles when Gd was used, with respect to peaks from Y Al O :Ce and JCPDS card no. 73-1370. This could be attributed to induced crystal-field effects due to the different ionic sizes of Ga and Gd compared with Al and Y . 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 Y Al O :Ce arising from the 5d → 4f transition of Ce . PL revealed a blue shift for Ga substitution and a red shift for Gd substitution. UV-Vis showed two absorption peaks at 357 and 457 nm for Y Al O :Ce , with peaks shifting to 432 nm for Ga and 460 nm for Gd substitutions. Changes in the trap levels or in the depth and number of traps due to Ce were analysed using thermoluminescence (TL) spectroscopy. This revealed the existence of shallow and deep traps. It was observed that Ga substitution contributes to the shallowest traps at 74 °C and fewer deep traps at 163 °C, followed by Gd with shallow traps at 87 °C and deep traps at 146 °C. Copyright © 2016 John Wiley & Sons, Ltd.