I. Levchuk, L. Römling, M. Steimle, A. Osvet, M. Batentschuk, A. Winnacker, C.J. Brabec
University of Erlangen-Nuremberg,
Keywords: co-precipitation, nanoparticles, storage phosphor, medical diagnostics
Summary:Biological and medical imaging is a key-stone for in-vivo and in-vitro monitoring necessary for basic research and for medical diagnostics. Inorganic nanoparticles have already been established as fluorescence markers due to their high stability and excellent optical properties. A future development would be markers with afterglow (phosphorescence) or photostimulable luminescence (PSL). An advantage of such phosphors would be background-free detection due to the absence of autofluorescence of the samples under infrared or red excitation. Phosphorescence often shows a rapid decay of the emission intensity immediately after the charging. The PSL, in contrast, can be stimulated at a desired time after charging the phosphor and its intensity may be controlled by adjusting the stimulation intensity. Herein we present efficient photostimulated luminescence (PSL) in nanosized SrAl2O4:Eu2+, Sm3+ phosphor, synthesized via a novel fatty acid assisted co-precipitation method. Oleic and other fatty acids were successfully utilized to form metal precipitate resulting particles ~100 nm in size after calcination in H2/N2 atmosphere. However, due to hydrolysis, SrAl2O4 is an unstable compound in water environment which harms the luminescence properties of the material and hinders the application for bio-imaging.The hydrolysis reactions is described by the following equation: SrAl2O4 +4H2O → Sr2+ +2OH− +2Al(OH)3↓. To improve the stability, we have modified the surface of the SrAl2O4:Eu2+, Sm3+ nanoparticles with a uniform ZrO2 shell by wet chemical processing at low temperature which efficiently protects the material against water, enabling to use these particles in biological environment for several hours.