The dielectric function of PbS quantum dots in a glass matrix

Moreels, Iwan; Kruschke, Detlef; Glas, P.; Tomm, Jens W.

doi:10.1364/ome.2.000496

Cited by 52 publications

(46 citation statements)

References 12 publications

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“…The PbS:Glass samples were grown as described in details elsewhere 17 with the following compositions: SiO 2 : 59.1, Al 2 O 3 : 4.2, Na 2 O: 11.5, NaF: 4.3, ZnO: 11.5, ZnS: 4.0, PbO: 2.9, PbS: 1.0, with percentage of mass. A two-stage process of 475 • C/23 h plus 525 • C/1.5 h was employed for annealing.…”

Section: Methodsmentioning

confidence: 99%

Spontaneous and stimulated emission dynamics of PbS quantum dots in a glass matrix

2013

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Optical properties and relaxation mechanisms of PbS quantum dots in glass matrix (PbS:Glass) have been systematically investigated by transmission and (steady-state and transient) photoluminescence spectroscopy. Key parameters are determined by combining the data with semiempirical expressions, based on which the recombination mechanisms including spontaneous and stimulated emissions have been discussed as a function of temperature by referring to a multilevel model including intrinsic (or band-to-band transition), bright, dark, and ground states. The results disclose that (i) the existence of a dark exciton state is the main reason for thermal quenching of the emission even at low temperatures due to the strong multiacoustic phonon coupling, (ii) the "intrinsic" spontaneous emission related to the intrinsic state is observed with an approximately nanosecond lifetime, in contrast to the "regular" spontaneous emission from the bright exciton state with an approximately microsecond lifetime, and (iii) stimulated emission, which has a lifetime of 20-40 ps and shows power-dependence of excitation density (or temperature), only appears from the intrinsic state but not the (bright) exciton state when enough accumulation of photogenerated carriers is reached. Furthermore, we find that the thermal conductivity will become crucial for future PbS:Glass related optoelectronic device applications.

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Section: Methodsmentioning

confidence: 99%

Spontaneous and stimulated emission dynamics of PbS quantum dots in a glass matrix

2013

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“…This results in increased amount of residual positive charge in the QD layer at a given light intensity. Using a simple model, we obtain the following expression for the photoresponsivity is the corresponding absorption coeffi cient, [ 31 ] s ≈ 50nm is the QD layer thickness, [ 32 ] -------…”

Section: Lumomentioning

confidence: 99%

Ligand‐Induced Control of Photoconductive Gain and Doping in a Hybrid Graphene–Quantum Dot Transistor

Turyanska

Makarovsky

Svatek

et al. 2015

Adv Elect Materials

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concentration can be modifi ed, and photoresponsivity of SLG can be signifi cantly enhanced by the choice of ligands. By reducing the length of capping ligands, hence the thickness of the dielectric barrier between the QDs and the SLG, and by preserving the integrity of the ligand layer, we achieve the efficient transfer of photogenerated carriers from the QDs to the graphene before recombining, resulting in enhanced photoresponsivities of up to ≈10 9 A W −1 .Single layer graphene grown by low-pressure chemical vapor deposition (LP-CVD) [ 14,15 ] was processed into a planar transistor and deposited onto a SiO 2 /n-Si substrate with oxide layer thickness t = 300 nm, as shown schematically in Figure 1 a (see also the Supporting Information, Figure S1). The length, L , and width, w , of the graphene channel are 6 and 10 µm, respectively. The n-Si layer serves as a gate electrode. Colloidal quantum dots with an average PbS core diameter of d = 4.5nm QD (Figure 1 b) were stabilized using the following capping ligands of different length, l , which determines the effective separation between the PbS nanocrystals and graphene: polyethylene glycol H (O CH 2 CH 2 ) n OH with n = 2000 for QD p2000 and n = 500 for QD p500 [ 16 ] and corresponding length of l ≈ 10 nm and l ≈ 5 nm, respectively; [ 17 ] a mixture of thioglycerol (TGL) and 2,3-dimercapto-1-propanol (DTG), l ≈ 0.5 nm for QD TGL , [ 18 ] see Table 1 . We note that the ligand size is estimated for extended molecules and does not include any effects that could arise from compression of the ligand layer upon drying under vacuum. The interparticle distances observed on TEM images are comparable with the theoretical estimate of the ligand length (see the Supporting Information, Figure S2). The QDs were dropcast from aqueous solution (5 mg mL −1 ) to produce continuous thick (>100 nm) coverage of the graphene layer, followed by drying for 12 h in vacuum at room temperature. The size of the QDs and their room temperature photoluminescence spectra (with a peak at photon energy ≈1.1eV) are similar in all three structures, i.e., they are not affected by the ligand. All measured devices demonstrate stable and reproducible behavior during the measurement period of at least 14 days. All samples were stored in dry nitrogen cabinet and all electrical measurements were performed at room temperature T = 300 K in vacuum (≈10 −6 mbar). The I V ( ) g characteristics were measured using slow sweeping rate, r , of the gate voltage, i.e., r ≤ 0.02 V s −1 .The pristine monolayer graphene devices show a linear dependence of current, I , on bias voltage, V s , and a minimum conductance at a gate voltage, V ≈ +30V g min corresponding to p-type doping with hole concentration, p ≈ 2 × 10 12 cm −2

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“…In addition, we observe excited and "intrinsic" states having a lifetime of sub-100-ps and ∼ns, respectively. Moreover, we also find that the split structure can be described by a phonon-assisted exciton relaxation model.Samples were grown with the compositions SiO 2 : 51.5, Al 2 O 3 : 7.5, B 2 O 3 : 15.3, Na 2 O: 11.4, PbS: 1.6, PbO: 0.9, ZnO: 0.8, ZnS: 0.8, CaO: 4.8, K 2 O: 5.4 (mass %), and followed by a two-stage annealing process (the first stage for crystallization and the second stage for tuning the QD size) [10,11]. Sample plates were polished with thicknesses from ∼50 μm to 3 mm.…”

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“…The volume fraction f of these QDs in glass matrix is deduced to ∼0.07% by referring to the absorption coefficient of 400 nm at 300 K [see the inset in Fig. 1(b)] [11]. The average distance between QDs is then estimated tod ≈ 70 nm assuming a cubic arrangement of QDs in the glass matrix.…”

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confidence: 99%

Experimental observation of exciton splitting and relaxation dynamics from PbS quantum dots in a glass matrix

2014

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Multiple optical transitions from PbS quantum dots (QDs) in glass matrix are observed. Energy separations between them amount up to ∼200 meV. Instead of being due to a size distribution of QDs, they are found to be related to a splitting of the lowest exciton levels. Systematic analysis of the relaxation dynamics reveals the lifetimes of the split states ranging from sub-100-ns to ∼μs. Moreover, we observe excited and "intrinsic" states having a sub-100-ps and ∼ns lifetime, respectively. The behavior of the split structure can be modeled by a phonon-assisted relaxation mechanism. This investigation offers a conclusive interpretation for the wide distribution of experimentally observed nonequilibrium carrier lifetimes in PbS QDs.Lead salt (e.g., PbS) quantum dots (QDs) have been widely investigated for applications in optoelectronic devices [1,2]. The QDs are either colloidal or embedded into a glass matrix. The latter provides substantial advantages in terms of longterm stability [3]. In order to evaluate and improve the properties of materials or devices, the QD size and its distribution as well as the excitonic lifetime are major issues, which should be accurately characterized, e.g., directly by optical methods including steady-state (SS) or transient absorption and photoluminescence (PL) spectroscopy at room temperature [4].However, in rock salt PbS QDs the dimension of the excitonic manifold is theoretically 64 because both the valence-band maximum and the conduction-band minimum originate from the 8-fold (including spin) L valleys in the first Brillouin zone of bulk PbS. The degeneracy of these L valleys becomes lifted due to, e.g., intervalley coupling, interband coupling, and electron-hole Coulomb and exchange interaction [5]. Another mechanism potentially acting into this direction is external forces such as pressure as well as a special chemical surrounding, e.g., in a matrix. The split structure makes the optical transition in QDs complex and affects the characterization of QD features including the lowest excitonic transition energy (for simplicity called E g ) and subsequently the size and distribution of QDs as well as the nonequilibrium carrier recombination mechanism. In spite of the fact that asymmetric-or multi-PL (or absorption) peaks from these kinds of QDs have been observed even at room temperature, no direct reports involve these split states. Typically extrinsic assumptions are made including size distribution (e.g., multimodal QDs) [6], temperature/excitation-induced broadening [7], or defect states [8,9].In this Rapid Communication, PbS QDs embedded in a borosilicate glass matrix are prepared and characterized by SS-or transient-PL spectroscopy at low excitation densities and temperatures. A three-transition structure from the QDs is observed with an energy separation up to 200 meV, in dependence of growth conditions including annealing. The * yue@mbi-berlin.de intrinsic mechanism for this three-transition structure that seems to be sensitive to the host matrix, e.g., with borosilicate b...

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The dielectric function of PbS quantum dots in a glass matrix

Cited by 52 publications

References 12 publications

Spontaneous and stimulated emission dynamics of PbS quantum dots in a glass matrix

Spontaneous and stimulated emission dynamics of PbS quantum dots in a glass matrix

Ligand‐Induced Control of Photoconductive Gain and Doping in a Hybrid Graphene–Quantum Dot Transistor

Experimental observation of exciton splitting and relaxation dynamics from PbS quantum dots in a glass matrix

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