Band edge photoluminescence of undoped and doped TlInS 2 layered crystals

Abstract

Intrinsic photoluminescence (PL) of undoped and of B-, Ag-or Er-doped TlInS 2 layered single crystals was investigated by confocal spectroscopy. It is found that position and intensity of PL spectral peak at 2.4 eV is vastly dependent on the excitation light incidence and polarization relative to crystallographic directions. For the normal incidence to the layer plane k||c, a significant Stokes shift between the PL peak in respect to exciton absorption energy is highlighted. The shift increases to 80 meV around the crystal phase transformations region of 200 K. We show that presence of B and Ag impurity do not diminish the intrinsic PL emission while Er atoms incorporation enhances it substantially and modifies a fine excitonic line structure in the ferroelectric phase at low T. The obtained results imply out-of-layer plain oriented 2D excitons in TlInS 2 existing at various crystal phases which are influenced by related interlayer stresses.& 2017 Elsevier B.V. All rights reserved. the TlInS 2 exhibit formation a new shallow donor-acceptor pair (DAP) photoluminescence band after low temperature thermocycling [6]. In addition, an imprint of photoactive trap self-polarization in the external electric field under different temperatures was observed and attributed to the dipolar origin of some Contents lists available at ScienceDirect

Carrier dynamics in highly excited TlInS2: evidence of 2D electron–hole charge separation at parallel layers

“…[7] Furthermore, we obtained that in TlInS 2 the excitonic PL exhibit a large Stokes shift from the direct exciton absorption. [24] Also, we detected enhancement of the PL intrinsic intensity in TlInS 2 crystals with small additions of B, Ag and Er dopants. The most pronounced enhancement was discovered in crystals doped by Erbium.…”

“…Both crystals (pristine and with Er) were yellow in color and demonstrated a sharp drop in optical transparency at the indirect gap threshold. [24] By the energy-dispersive X-ray analysis, we determined the same ratio of the main elements (Tl, In, Se) in both type of the samples. The micro-Raman spectra recorded with Nanofinder-HE apparatus are shown in Supplementary file (Fig.…”

“…[16,21] It is known that pristine TlInS 2 crystal is an inefficient PL emitter, particularly for normal to layers excitation, at k||c. [23,24] This is attributed to presence of the indirect optical band gap. The energies for lowest direct exciton and indirect band gap at RT are E x d = 2.44 eV and E g i = 2.26 eV, respectively.…”

“…The energies for lowest direct exciton and indirect band gap at RT are E x d = 2.44 eV and E g i = 2.26 eV, respectively. [24,25] Besides, the direct exciton absorption is relatively low, and absorption is restricted to the values of about 10 3 cm -1 . [3,26] In our previous work, it was discovered that polarization of the emitting light from TlGaSe 2 is outof-layer plane, suggesting the e-h emitting dipoles (excitons) are orthogonal to the crystal layer.…”

“…The most pronounced enhancement was discovered in crystals doped by Erbium. [24] This result is unexpected, since extrinsic impurity in ionic semiconductors usually reduces the intrinsic radiation due to charge trapping. [27] In the current work, we provide comprehensive study of the charge carrier dynamics in TlInS 2 crystals after short laser pulses under diverse excitation conditions.…”