Optical properties of ultrathin PbI2 microcrystallite in polymer

2019-10-10 13:03:21

energy optical Raman shift exciton

责任者: Goto, T.;Saito, S. 单位: Dept. of Phys., Tohoku Univ., Sendai, Japan 来源出处: Journal of Luminescence(J. Lumin. (Netherlands)),1996/10/,70(1-6):435-47 摘要: We have prepared PbI2 microcrystallites embedded in polymer, which have a layer structure and are ultrathin crystals consisting of two to nine monolayers. A very large energy shift of the exciton absorption band has been observed in these microcrystallites and interpreted in terms of size confinement of the translational motion of excitons in the c-direction perpendicular to the crystal surface. The simple effective mass approximation is broken down in 2,3,4 layer crystallites, because the crystal thickness is smaller compared to the exciton Bohr radius. Secondly, in the Raman spectrum where the excitation energy is resonant to the exciton energy, there appears a new line in the energy region below 20 cm-1 which is characteristic of a ultrathin crystal. The Raman shift increases with decreasing the crystal thickness. This line is assigned as due to a longitudinal mode of a rigid-layer phonon. Thirdly, the confinement of the internal motion is studied by measuring a diamagnetic shift of the exciton energy in the magnetic field up to 150 T and a bound exciton luminescence in the ultrathin microcrystallites. Much larger binding energy of the exciton compared to the bulk value is estimated. This fact suggests that the envelope function of the exciton shrinks not only by a strong spacial restriction in the c-direction but also by the dielectric screening from the surrounding polymer. Fourthly, the exciton-phonon interaction is studied by the hole-burning measurement 关键词: binding energy;bonds (chemical);lead compounds;light polarisation;magneto-optical effects;nanostructured materials;optical hole burning;phonon-exciton interactions;piezo-optical effects;polymer films;Raman spectra;semiconductor materials;semiconductor thin films;spectral line shift;visible spectra;lead diiodide;microcrystallites;polymer embedding;optical properties;crystallite layer structure;monolayer number;exciton absorption energy shift;size confinement;exciton c axis translation;effective mass approximation;exciton Bohr radius;Raman spectrum;Raman exciton energy resonance;rigid layer phonon mode;exciton binding energy;exciton envelope function;dielectric screening;exciton phonon interaction;hole burning measurement;exciton energy diamagnetic shift;exciton defect scattering;exciton energy pressure dependence;atomic bonding size effect;covalent ionic bonding change;sample preparation techniques;optical conductivity spectrum;transmission electron microscopy;optical phonons;exciton surface interaction;0 to 0.41 GPa;15 to 300 K;2.5 to 9 eV;0 to 150 T;PbI2