Du. Saenger et al., Optical and structural properties of doped ZnS nanoparticles produced by the sol-gel method, J SOL-GEL S, 13(1-3), 1998, pp. 635-639
Optical and structural properties of Mn2+-doped ZnS nanoparticles in an org
anic matrix are experimentally and theoretically studied. The nanoparticles
, which were produced by the sol-gel method, are nearly monodisperse with a
diameter of approximately 3 nm and show the characteristic orange-red lumi
nescence of Mn2+ centers in a crystalline ZnS matrix. The absorption spectr
um of the embedded ZnS nanoparticles is slightly blue shifted and broadened
compared to the reference system containing ZnS microparticles. This blue
shift is caused by quantum size effects, whereas the broadening is due to d
efects such as lattice distortions, and vacancies, which are probably locat
ed close to the surface in the case of small particles. With increasing tem
perature the absorption spectra shift to the red and are broadened due to t
hermal activated diffusion of ions close to the surface. In contrast, the s
pectral feature of the emission spectra via the Mn2+ center is nearly uncha
nged compared to the ZnS microparticles. Furthermore, the quantum efficienc
y is increased and the decay time of the electron-hole pairs is shortened t
o the nanosecond regime because of the enhanced probability of the electron
-hole pairs to "see" the Mn2+ center. Therefore, the only effect of doping
of ZnS nanoparticles with Mn2+ center is the suppression of the relaxation
of electron-hole pairs via surface defects generating a highly efficient an
d fast relaxation of the electron-hole pairs via the Mn2+ center.