Resonance Raman Scattering at the Forbidden Yellow Exciton inCu2O

Abstract

We report strong resonance enhancement in the 220-cm" i Raman line of Cu 2 0 at the r 12 "-phonon-assisted absorption threshold of the forbidden Is yellow exciton. A consistent theoretical interpretation is presented. It shows that the line is due to scattering of two r 12 " phonons and the resonance enhancement is strongly affected by the exciton lifetime. The latter effect has never been considered or observed before in resonance Raman scattering.

Biexcitonic behavior of 1s yellow exciton in Cu 2 O microcrystallites embedded in solution-derived nano-zirconia film matrix

“…Two more exciting wavelengths at 350 nm and 400 nm were also selected for observing the interactions of excitons with photons. These were possibly due to the energy differences, in E(F12) -E(F25) and E(F1) -E(F15) of Cu20 exciton which corresponded to the energies of 350 nm and 400 nm excitonic transitions respectively [11,13,16]. Three distinct emissions a (yellow, weak), 13 (green) and 'y (red) excitons were observed (scheme shown in Fig.…”

“…We also presumed earlier [13] that the other two bands at 53O nm and 625 nm were due to biexciton formation; these two transitions generated from two different sublevels above and below the r-7 and F8 to ]Tt But it would be prudent to consider all these bands as a, 3 and y forms of ls yellow exciton respectively due to the splitting of valence band, generating two more sublevels (S-L) ( Fig. 4) in addition to f and F8 for the anisotropic nature of is yellow exciton [11,13,16] as 53O mn band does not belong to green excitonic transition. The microcrystallite size (Table 1) ; NIR spectra due to intra-valence band transition in Cu20 excitons prepared at djfferent annealing temperatures [13].…”

Exciton-phonon interaction in PbI2 revealed by Raman and photoluminescence studies using excitation light overlapping the fundamental absorption edge

“…The previously reported low-temperature enhancement of the A 1g band has been presented as a specific feature of the resonant optical excitation [8,35] without clarifying whether it originates from an electron-phonon interaction or an exciton-phonon interaction that occurs in nanostructured materials [18][19][20][21][22][23][24][25]. The high value of the ratio I 88K /I 300K observed in the case of C and CS samples could be explained by the dependence of the enhancement of the A 1g band on the staking of the I-Pb-I layers along the c axis, which is manifested as quantum well structures that are able to host quantum confining effects [14].…”

“…Another inciting issue, but with little published data regarding the Raman studies on PbI 2 , concerns the enhancement of certain Raman lines at low temperature and the occurrence of overtones when the excitation light is close to the excitonic states [5,8]. Known as resonance Raman scattering, this phenomenon has been the subject of numerous theoretical and experimental studies [18][19][20][21][22][23][24][25], albeit without considering that the PbI 2 layer structure can be an ideal candidate in the studies of quantum wells structures.…”

Exciton Enhanced Raman Scattering of LO Phonons in Trigonal Se

“…Resonant Raman scattering (RRS) has been recently applied successfully to study properties of phonons [1], electrons [2], and their interaction.with each other in solids [3]. In particular, LO phonons have been found to show strong enhancement at excitons due to Frohlich-type exciton-phonon interaction [4].…”