Luminescent spectra of PbI2 single crystals doped by 3d-metal impurities

Investigations of an influence of 3d-metal dopants (Mn, Ni and Fe) on lumin escent properties of layered PbI2 single crystals are presented. We have sh own that different dopants lead to different local defect electronic charge density distributions in the layered crystals of PbI2. Electron-phonon int eractions and impurity levels should influence the nature of the luminescen t spectra. To interpret the obtained spectra we have essentially modified e xisting to date one-electron methods of band energy calculations, particula rly LCAO and pseudopotential (PP) ones. The measurements carried out at liq uid helium temperature (LHeT) show existence of the luminescent maxima near 490 nm for PbI2-Fe (PI-Fe) that corresponds to optical transitions from hi gher 3d-Fe states to valence states. Due to a high localization of the Fe-d opant we expect a weak interaction between the continuous band and discrete 3d-Me states. Theoretical calculations show a discrepancy between absolute values of theretical and experimental luminescence. The latter could be ca used by a contribution of low-frequency interlayer membrane vibrations. In the case of Mn-doping, one can observe an essential charge density delocali zation in the vicinity of the impurities. As a consequence, the correspondi ng electron-phonon interaction leads to the appearance of new electron-vibr ational states and a redistribution of the luminescent intensities between the intra-center 3d and the electron-vibrational energy levels at 473 and 4 21 nm, respectively. The influence of the electron-phonon interaction can b e manifested for PbI2-Ni crystalline systems. Without taking into account t he electron-phonon interaction, the discrepancy between the experimental an d theoretical maxima is higher than 30 nm (440 and 471 nm, respectively). H owever, such a difference is probably caused by a difference between electr ostatic fields near the impurity and the host due to the relatively high di fferences of the electronic charge density distributions. (C) 1998 Elsevier Science B.V. All rights reserved.