Quantum dots coated dust as a main source of molecular clouds abnormal reddening?

Silica dust particles are naturally present in dusty environments such as interstellar clouds, protoplanetary disks and comets. Quantum dots in form of nanometer-scale semiconductor crystals can be formed on surfaces of these dust particles due to supernova explosions, shock waves, low-temperature condensation or cosmic radiation alteration. An abnormal extended red emission with a color shift dependent on the size of the dust particles in dominant UV light regions are usually observed by astronomers for nebulas or interstellar clouds.

In this study, we present a laboratory investigation of the light re-emission by 6.5 nm CdSe/ZnS core-shell quantum dots present on the surface of micrometer-sized silica dust particle. The dust particle captured in an electrodynamic trap is irradiated by a blue laser at a specific wavelength of 405 nm. The re-emitted light produced by quantum dots with main wavelength of 650 nm is collected by optical lens attached to the trap and guided by optical fiber to wavelength spectrometer. The macroscopic charge of the dust particle is determined from its motion in the trap. This charge can be controlled by 1 keV protons within a range of up to 6 C/kg.

Initial tests indicate that the measured spectrum of the emitted light shifts towards the red end of spectra as the amount of charge on the surface of grain increases.