Rotationally induced luminescence of nanoclusters immersed in superfluid helium
P.T. McColgan1, S. Sheludiakov1, P.M. Rentzepis2, D.M. Lee1, and V.V. Khmelenko1
1Texas A&M University, Department of Physics and Astronomy, Institute of Quantum Science and Engineering 4242 TAMU, 77843-4242 College Station, Texas, United States
2Texas A&M University, Department of Electrical and Computer Engineering 3127 TAMU, 77843-3127, College Station, Texas, United States
Received October 24, 2018
We studied the influence of rotation speed of a beaker containing superfluid helium (He II) on the intensity of luminescence of collections of nanoclusters immersed in He II. We observed an increase in the α-group emission of nitrogen atoms (2D → 4S transition) in nanoclusters which correlated with the increasing of rotational speed ofthe beaker. Increasing luminescence was also observed by increasing the concentration of molecular nitrogen in the nitrogen-helium gas mixtures used for the formation of the molecular nitrogen nanoclusters. We suggest that this effect is caused by the change of the density of quantum vortices in He II initiated by variation of rotational speed of the beaker. When the density of the vortices is increased, the probability for the nanoclusters to become trapped in the vortex cores is also increased. The collisions in the vortex cores of trapped nanoclusters with nitrogen atoms stabilized mostly on the surfaces of the nanoclusters initiate the recombination of nitrogen atoms resulting in luminescence.
Key words: luminescence, quantized vortices, optical spectroscopy, nanoclusters.