4. Conclusion
In conclusion, we have observed blue, green and red upconversion
emission from nanocrystalline Yb/Er co-doped Y2O3
particles synthesized by spray pyrolysis at 900 1C. The Yb3þ
concentration, crystallinity and the distribution of active ions in the
host material affect the final up-conversion efficiency. The most
intense green up-conversion emission with a decay time of 550 ms
occurs in the Y1.97Yb0.02Er0.01O3 powders thermally treated at
1100 1C for 24 h, having the crystallite size of 70 nm and the
mean particle size of 950 nm. The long emission lifetimes are
the consequence of the achieved purity of the materials, homogeneous
doping and the particle composite structure, i.e. persistence
of nano-building units in the annealed samples. The rather
narrow particle size distribution, the spherical geometry of particles
and their un-agglomerated state make them attractive for the
manufacturing of display panels, while the observed emission
temperature dependence indicates that they also may be used for
temperature sensing. Additionally, their composite substructure
makes them suitable for the functionalization and surface modification
towards more specific application in bioimaging.
Acknowledgment
The financial support for this work was provided by the
Ministry of Education and Science of the Republic of Serbia,
Project no. 172035.
Appendix A. Supplementary materials
Supplementary data associated with this article can be found
in the online version at http://dx.doi.org/10.1016/j.ceramint.
2013.10.002