Stark effect and Franz-Keldysh effect of a quantum wire realized by conjugated polymer chains of a diacetylene 3NPh2

Abstract

Conjugated polymer chains diluted in monomer single crystals of a novel diacetylene, 1,10-bis(diphenylamino)-4,6-decadiyne, represent quantum wires of long range coherence. They di¤er from most polydiacetylenes by their repeat unit that consists of two C 4 units with twisted molecular planes. The resulting modi…cation of exciton and band states is studied by electroabsorption which resolves an increase of the exciton transition energy to 2.399 eV and of the free electron gap to 3.158 eV. The Stark shift of the exciton reveals a signi…cant reduction of the exciton radius by about 40 % to 6 1 Å which is consistent with a similar increase of the exciton binding energy to 759 meV. The lineshape of electroabsorption spectra at the free electron gap is for …elds larger than 30 kV/cm in accordance with the one-dimensional Franz-Keldysh e¤ect and yields a reduced mass of 0.07 m 0 larger than in other PDA. Spectra at smaller …elds are distorted by contributions of a weak dipole allowed and a forbidden exciton 38 and 12 meV, respectively below the bandgap.Coherent coupling of free electrons and vibrational modes leads to replicas of the Franz-Keldysh e¤ect. Since light polarized parallel to the conjugated chain excites two propagating modes in the monomer crystals the quantitative analysis was restricted to EA spectra taken with perpendicular polarization in samples which transmit only the weakly absorbed polariton mode.

Twisted polydiacetylene quantum wire: Influence of conformation on excitons in polymeric quasi-one-dimensional systems

“…In addition, a weak broad band is present at ∼ 3.12 eV, which does not belong to these vibronic progressions. It is shown in the companion paper [38] that this structure corresponds to a weakly bound exciton close to the dissociation threshold, which can be observed here because the larger exciton binding energy displaces farther from the gap energy the overall vibronic progression of the lower energy exciton. Between ambient temperature and 13 K all absorption lines are red-shifted by ∼ 80 meV.…”

“…Moreover, it will be shown that the chains in this material have the optical properties of highly luminescent quasi-1D systems, as isolated red poly-3BCMU chains do [8,10,37]. But in the DA studied in this paper these properties are shared by all chains in the crystal and are not restricted to a small minority of chains, so studies that were not possible on poly-3BCMU such as electroabsorption as in the attendant paper [38], non linear absorption or pump-probe spectroscopies become feasible. The spectroscopic properties of these chains will be described and discussed in two companion papers, this one and another [38] essentially dealing with the study of electroabsorption.…”

“…But in the DA studied in this paper these properties are shared by all chains in the crystal and are not restricted to a small minority of chains, so studies that were not possible on poly-3BCMU such as electroabsorption as in the attendant paper [38], non linear absorption or pump-probe spectroscopies become feasible. The spectroscopic properties of these chains will be described and discussed in two companion papers, this one and another [38] essentially dealing with the study of electroabsorption. The present paper deals with absorption and luminescence spectra, luminescence temporal decay, all as a function of temperature.…”

Anisotropic exciton Stark shift in black phosphorus

“…[9] Strong exciton binding energies are also observed in conjugated polymer chains, [10] where exciton Stark shifts for high electric fields have been investigated as well. [11,12] In recent sudies on single or few-layer semiconductors, such as transition metal dichalcogenides and black phosphorus, exciton binding energies are found to be on the order of hundreds of meV, [13][14][15][16] which brings the possibility of experimentally observing the Stark effect of their excitons. In this context, the case of black phosphorus, [17][18][19][20][21] a layered material that has recently been fabricated in few-layer form [13] and has a strong potential for technological applications, [19,[22][23][24][25][26] is of special interest.…”

Rabi-Bloch oscillations in spatially distributed systems: Temporal dynamics and frequency spectra

“…which follows from (10), (13)- (16). We present the required wave function as a superposition of Wannier functions…”