Abstract

The luminescence properties of singly-doped Pr 3+ and Pr 3+ /Yb 3+ co-doped nanocrystalline gadolinium gallium garnet (GGG, Gd 3 Ga 5 O 12 ) are investigated. Dominant blue/green emission emanating from the 3 P 0 [arrow right] 3 H 4 and 3 P 0 [arrow right] 3 H 6 transitions was observed after excitation using a wavelength of 457.9 nm. The luminescence properties of the nanocrystals were compared to the bulk material (single crystal) with identical Pr 3+ concentrations (1 mol%) and no noticeable shift in peak position was observed. Increasing the Pr 3+ concentration in the nanocrystals resulted in a decrease in 3Po and 3P, emission to lower lying states via the [ 3 P 0 , 3 H 4 ] [arrow right] [ 3 H 6 , 1 D 2 ] cross relaxation (CR) mechanism. Furthermore, a decrease in the 1 D 2 emission was observed and was attributed to the [ 1 D 2 , 3 H 4 ] [arrow right] [ 1 G 4 , 3 F 3,4 ] CR mechanism. The increase in CR efficiency was attributed to the smaller interionic distances between the dopant ions. Continuous wave excitation into the 1 D 2 level of the Pr 3+ ion at 606.9 nm transition produced blue upconversion luminescence. Based on the increase in transition lifetimes, an energy transfer (ET) upconversion mechanism was proposed. Furthermore, weak blue, green and red upconversion emission was observed from the 3 P 0 , 3 P 1 and 1 D 2 states following excitation into the 1 G 4 energy level with 980 nm. Upconversion was determined to primarily occur through excited state absorption. Co-doping the nanocrystalline GGG:Pr 3+ (1 mol%) samples with Yb 3+ (1-10 mol%) results in a 3-fold increase in upconversion emission intensity relative to the singly doped samples excited under the same conditions (n exc = 980 nm). The observed lifetimes obtained using 457.9 nm excitation suggest back transfer from the Pr 3+ ion to neighboring Yb 3+ ions which results in decrease in room temperature visible emission and upconversion luminescence.