NANOMETER-SIZED PARTICLES OF PBI2 EMBEDDED IN SIO2-FILMS

Nanometer-sized particles of lead iodide layered semiconductors were e mbbeded in SiO2 films. X-ray diffraction and photoluminescence (PL) sp ectroscopy showed the preservation of the hulk layered structure and s ymmetry. The PL and PL excitation (PLE) spectroscopy exhibited a blue- shift due to quantum size effect. The bulk lead iodide showed exciton transition with an exceptionally small Bohr radius (a(B) = 19 Angstrom ) and a large Rydberg constant (R = 70.8 meV). In addition, the lead i odide represents a special case in which m(e) >> m(h). The prepared sa mples contained particles with mean radii, a, in-the range a(B) < a < 3a(B). In this limit (with m(e) >> m(h)) the experimental results are in agreement with a model in which the electron is localized nearly at the center of the particle, enabling the hole to move around it. Acco rding to this model, the localization of the electron is further enhan ced due to the confinement of the hole motion by the particle boundari es; Thus, the size confinement permits the creation of an acceptor-lik e exciton. The simulated blue-shift of this acceptor-like exciton has been determined, utilizing a variational method. The PL spectrum revea led additional states, associated with stoichiometric and structural d efects. These defects were created during the growth process.