  We theoretically investigate the electronic and magneto-optical properties of
rectangular, hexangular, and triangular monolayer phosphorene quantum dots
(MPQDs) utilizing the tight-binding method. The electronic states, density of
states, electronic density distribution, and Laudau levels as well as the
optical absorption spectrum are calculated numerically. Our calculations show
that: (1) edge states appear in the band gap in all kinds of MPQDs regardless
of their shapes and edge configurations due to the anisotropic electron hopping
in monolayer phosphorene (MLP). Electrons in any edge state appear only in the
armchair direction of the dot boundary, which is distinct from that in graphene
quantum dots; (2) the magnetic levels of MPQDs exhibit a Hofstadter-butterfly
spectrum and approach the Landau levels of MLP as the magnetic field increases
. A "flat band" appears in the magneto-energy spectrum which is totally
different from that of MLP; (3) the electronic and optical properties can be
tuned by the dot size, the types of boundary edges and the external magnetic
field.
