Luminescence Spectral Properties of CdS Nanoparticles.

We examined the steady state and time resolved luminescence spectral properties of two types of CdS nanoparticles. CdS nanoparticles formed in the presence of an amine-terminated dendrimer showed blue emission. The emission wavelength of these nanoparticles depended on the excitation wavelength. The CdS/dendrimer nanoparticles displayed polarized emission with the anisotropy rising progressively from 340 to 420 nm excitation, reaching a maximal value in excess of 0.3. To the best of our knowledge this is the first report of a constant positive polarized emission from luminescent nanoparticles. We also examined a second type of nanoparticle, polyphosphate-stabilized CdS. These polyphosphate-stabilized nanoparticles displayed a longer wavelength red emission maximum and displayed a zero anisotropy for all excitation wavelengths. Both nanoparticles displayed strongly heterogeneous intensity decays with mean decay times of 93 ns and 10 s for the blue and red emitting particles, respectively. Both types of nanoparticles were found to be severalfold more photostable upon continuous illumination than fluorescein. Despite the long decay times, the nanoparticles are mostly insensitive to dissolved oxygen but were quenched by iodide. These results suggest that nanoparticles can provide a new class of luminophores for use in chemical sensing, DNA sequencing, high throughput screening and other biotechnology applications.