ZHANG Rui, GU Mu, LIU Xiao-lin, LIU Bing-jie. Theory Study of the Effect of Li<sup>+</sup> Doping Concentration on the Luminescence of Y<sub>2</sub>O<sub>3</sub>:Eu<sup>3+</sup> Phosphors[J]. Chinese Journal of Luminescence, 2007,28(5): 693-698
ZHANG Rui, GU Mu, LIU Xiao-lin, LIU Bing-jie. Theory Study of the Effect of Li<sup>+</sup> Doping Concentration on the Luminescence of Y<sub>2</sub>O<sub>3</sub>:Eu<sup>3+</sup> Phosphors[J]. Chinese Journal of Luminescence, 2007,28(5): 693-698DOI:
Yttrium oxide is one of the scintillation material used in X-ray imaging
in order to improve the light output of doped rare earth ions
Li
+
is always codoped with the luminescent center.However the mechanism for this codoping approach is still not quite clear except the common explanation of flux effect.Further research work shows the enhance effects of Li
+
doping is related with concentration of Li
+
and the lattice constants
but the implication of this kind of relationship is still not clear. Based on the model of cluster approximation
the influence of Li
+
doped concentration on defects formation and the effect of the change of YO bond length on electronic density of states are studied with molecular dynamics and density functional simulation with software package (ADF2005).Since the clusters we chosen are relatively small in order to save simulation time
the results of former simulation are adopted for the cluster charge value.The value of cluster charge is further readjusted so that the cluster with least bonding energy is used for discussion
by this way we can eliminate partly the effect caused by dangling bond.Furthermore
the simulation result by cluster approximation is compared with that of the supercell methods.From these results we can draw conclusion that the methods we adopted in the simulation is reliable. The results shows that firstly the Li
+
tender to occupy the interstitial position around the C
2
site
which producing the stretching of the YO bond
thus lower the phonon energy of the sample
and increase the quantum efficiency of the material
by this way the light yield of the sample is improved. From the results of simulation
with the increase of Li
+
the length of YO bond for C
2
sites changes with the tendency of decrease-increase-decrease
which may explain the similar emission change via Li
+
concentration for this type of material
thus explained the two maximum peaks in the Li
+
concentration-light yield curve.The stretching of the YO bond may also cause the narrowing of the band gap
which might be the cause of small shift of the absorption spectrum.