Basal dislocations in anthracene crystals

Abstract

The low‐temperature fluorescence spectra (T = 4.2 K) and etching patterns of anthracene crystals grown from a benzene solution (BSAC) are investigated. It is shown that these spectra exhibit a new series as compared with the fluorescence spectrum of vapour‐grown crystals. The series is red‐shifted by 130 cm−1 from the exciton band bottom. Its vibrational intervals coincide with the intramolecular vibrations of anthracene. The series is ascribed to basal dislocations of (001) [010] type. After annealing of such crystals for 1 h at T = 398 K basal dislocations vanish and non‐basal dislocations of (100) [010] or (201) [010] type appear. This phenomenon is partly reversible: in annealed crystals kept for a week at room temperature nonbasal dislocations vanish and basal appear again, i.e. relaxation processes occur.

Absorption and emission in oligo-phenylene vinylene nanoaggregates: The role of disorder and structural defects

“…In reality organic molecular crystals and aggregates are disordered due to point and structural defects. [45][46][47][48][49][50][51] Defects have the most profound affect on emission ͑see Sec. VI͒; in absorption they are manifest primarily in the form of inhomogeneously broadened line shapes.…”

“…In organic molecular crystals, point defects due to misaligned molecules and impurities as well as structural defects, such as dislocations, stacking faults, and grain boundaries are common, and are responsible for continuous and quasi-discrete emission bands. [45][46][47][48][49][50][51] FIG. 11.…”

“…Such defects have long been identified as exciton traps in anthracene and naphthalene molecular crystals. [45][46][47][48][49][50][51] We also consider the effect of adding orientational point defects to aggregates with stacking faults and dislocations.…”

“…Such defects have been identified with structured trap emission some 150 cm Ϫ1 -300 cm Ϫ1 below the bottom of the exciton band in anthracene. [45][46][47]50,51 A basal ͑001͓͒010͔ dislocation is depicted in Fig. 14.…”

“…We employ the noninteracting domains model ͑NDM͒ to approximate spatially correlated site-energy disorder in evaluating the nanoaggregate absorption spectrum. In order to account for the aforementioned Stokes shift structural disorder, including stacking faults and dislocations, [45][46][47][48][49][50][51] is investigated.…”