CdS CoreâShell Quantum

Subscriber access provided by HACETTEPE UNIVERSITESI KUTUPHANESI

Article

Single-Mode Lasing from “Giant” CdSe/CdS CoreShell Quantum Dots in Distributed Feedback Structures Lei Zhang, Chen Liao, Bihu Lv, Xiaoyong Wang, Min Xiao, Ruilin Xu, Yufen Yuan, Changgui Lu, Yiping Cui, and Jiayu Zhang ACS Appl. Mater. Interfaces, Just Accepted Manuscript • DOI: 10.1021/acsami.7b01669 • Publication Date (Web): 30 Mar 2017 Downloaded from http://pubs.acs.org on April 2, 2017

Just Accepted “Just Accepted” manuscripts have been peer-reviewed and accepted for publication. They are posted online prior to technical editing, formatting for publication and author proofing. The American Chemical Society provides “Just Accepted” as a free service to the research community to expedite the dissemination of scientific material as soon as possible after acceptance. “Just Accepted” manuscripts appear in full in PDF format accompanied by an HTML abstract. “Just Accepted” manuscripts have been fully peer reviewed, but should not be considered the official version of record. They are accessible to all readers and citable by the Digital Object Identifier (DOI®). “Just Accepted” is an optional service offered to authors. Therefore, the “Just Accepted” Web site may not include all articles that will be published in the journal. After a manuscript is technically edited and formatted, it will be removed from the “Just Accepted” Web site and published as an ASAP article. Note that technical editing may introduce minor changes to the manuscript text and/or graphics which could affect content, and all legal disclaimers and ethical guidelines that apply to the journal pertain. ACS cannot be held responsible for errors or consequences arising from the use of information contained in these “Just Accepted” manuscripts.

ACS Applied Materials & Interfaces is published by the American Chemical Society. 1155 Sixteenth Street N.W., Washington, DC 20036 Published by American Chemical Society. Copyright © American Chemical Society. However, no copyright claim is made to original U.S. Government works, or works produced by employees of any Commonwealth realm Crown government in the course of their duties.

Page 1 of 32

1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 28 29 30 31 32 33 34 35 36 37 38 39 40 41 42 43 44 45 46 47 48 49 50 51 52 53 54 55 56 57 58 59 60

ACS Applied Materials & Interfaces

Single-Mode Lasing from “Giant” CdSe/CdS Core-Shell Quantum Dots in Distributed Feedback Structures †

†

‡

‡

‡

†

Lei Zhang, Chen Liao, Bihu Lv, Xiaoyong Wang,*, Min Xiao, Ruilin Xu, Yufen Yuan,

†

Changgui Lu,† Yiping Cui,† and Jiayu Zhang*,† †

Advanced Photonics Center, School of Electronic Science & Engineering, Southeast University, Nanjing 210096, China

‡

National Laboratory of Solid State Microstructures, School of Physics, and Collaborative Innovation Center of Advanced Microstructures, Nanjing University, Nanjing 210093, China

ABSTRACT: “Giant” semiconductor quantum dots (GQDs) have tremendous potential for the applications in laser devices. Here, CdSe/CdS core-shell GQDs (11 MLs) are synthesized as lasing gain material. The photoluminescence decay of the GQDs ensemble is of singleexponential, and the two-photon absorption cross section is above 105 GM. This article presents that a versatile method for fabrication of CdSe/CdS GQDs distributed feedback lasers by laser interference ablation. The high-quality surface relief grating structure can be readily created on the GQDs thin films, and that the relationship between laser beam intensity and surface modulation depth is studied. With appropriate periods, the single-mode lasing emission has been detected from these devices under excitation wavelength of 400 and 800 nm. The laser thresholds are as low as 0.028 and 1.03 mJ cm−2 with the lasing Q-factor of 709 and 586, respectively. The lasing operation is realized from the directly laser interference ablated QDs distributed feedback structures for the first time. KEYWORDS: Giant quantum dots, optical gain, laser interference ablation, surface relief grating, discributed feedback lasers

ACS Paragon Plus Environment

1


1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 28 29 30 31 32 33 34 35 36 37 38 39 40 41 42 43 44 45 46 47 48 49 50 51 52 53 54 55 56 57 58 59 60

Page 2 of 32

1. INTRODUCTION Colloidal semiconductor quantum dots (QDs) have obtained widespread attention because of the size-dependent bandgaps that promote a broad range of applications in solid-state lighting,

1

lasers2-4 and biotechnology.5 So far, various colloidal QD-based materials have been shown as optical gain medium for lasers, 2-4,6,7 the lasing emission can be precisely controlled within the scope of entire visible and near-infrared region.6-8 However, the fast nonradiative Auger recombination (AR) and surface/interface defect states have been aware to be the dissipating approach of population inversion in the nanometer-sized QDs.9,10 Auger recombination process could severely reduce optical gain lifetime and bandwidth,11 thus restrains the optical amplification. In order to solve these problems, the heterostructures quantum dots have been extensively researched. Particularly, for CdSe/CdS core−shell structure, the features of both giant CdS shells12-14 and alloyed interfacial layers with smooth confinement potential15,16 have been proved as an efficient way to suppress AR. If the shell thickness is increased towards 10 monolayers, core-shell QDs could be called as giant quantum dots (GQDs).13,14 The GQDs with quasi-type-II band alignment concurring strong electron delocalization efficiently decrease the rate of AR and simultaneously reduce or even suppress blinking.13,14,17,18 Moreover, the surface passivation can be also preferably improved with coating a larger bandgap material, hence decreasing surface nonradiative channel and increasing photoluminescence quantum yields (PL QYs).19 Only if non-radiative processes, for instance surface defects and extremely fast AR rates, are eliminated under higher pump intensities, which afford longer excited state lifetime than optical gain build-up times.12,20 Therefore, the amplified stimulated emission (ASE) regime will be realized in GQDs with a lowered gain threshold. The ASE has been also acquired based on two-photon absorption mechanism21-24 on account of the coated shell with relatively large two-


2

Page 3 of 32

1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 28 29 30 31 32 33 34 35 36 37 38 39 40 41 42 43 44 45 46 47 48 49 50 51 52 53 54 55 56 57 58 59 60


photon absorption cross sections, which could supply a lower photodamaging and the applications in the field of biophotonics. Besides, the CdSe based QDs have been provided with almost temperature-independent optical gain performance because of the well-separated electronic states.11,25 All of these properties clearly state that the CdSe/CdS GQDs have many incomparable merits as a superior laser gain medium. Several optical microarchitectures have been applied as resonant cavities for laser devices. Such as microring, 26 microsphere resonators 2,4,27 and distributed feedback (DFB) grating,22,23,2831

that have been used as optical feedback structures in QDs lasers. With the assistance of these

resonant cavities, the laser performance can be improved markedly. Among such alternatives, the DFB structures have the advantages of single-mode emission, low-threshold, high quality factor and tunable lasing wavelength by changing the grating period and the thickness of the gain layer.29,30 The nanoimprint lithography and soft lithography are common approaches to construct DFB grating.22,23,30-33 However, the masks in these lithography methods involve inflexible and high cost fabrication. With the characteristics of excellent repeatability and facile process, the laser interference ablation (LIA) has been employed to fabricate polymer or single crystals DFB lasers.34,35 In addition, it has not been reported yet that the fabrication of periodic nanostructures on the QDs film by LIA, as far as we know. In this study, the laser interference ablation has been used to fabricate distributed feedback lasers based on giant CdSe/CdS core-shell QDs. The optical gain characteristics of GQDs and the properties of the amplified stimulated emission in GQDs film were studied in detail. The grating surface modulation depth was approximately proportional to the laser beam intensity. Significantly, we detected laser emission from these devices via one- and two-photon absorption (OPA and TPA) pumping that displayed single-mode operation and the low thresholds of 0.028


3


1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 28 29 30 31 32 33 34 35 36 37 38 39 40 41 42 43 44 45 46 47 48 49 50 51 52 53 54 55 56 57 58 59 60

Page 4 of 32

and 1.03 mJ cm−2, respectively. Finally, on the basis of the improved film-forming performance by means of water soluble GQDs, the LIA may open up a new way for high-yield fabrication of semiconductor quantum dots DFB lasers.

2. EXPERIMENTAL SECTION 2.1. Synthesis of Giant CdSe/CdS Core-Shell QDs. Giant CdSe/CdS core-shell QDs were synthesized in two steps: Synthesis of CdSe cores

36

and the coating of the CdS shell 14 (see the

Supporting Information for details). 2.2. Preparation of Water Soluble GQDs. The water soluble GQDs were prepared by a conventional ligand exchange method employing mercaptopropionic acid (MPA).37 The detailed processes were briefly described as follows: purified GQDs (0.2 µmol) was poured into 40 mL of hexane and then added 4 mL tetramethyl ammonium hydroxide (TMAH), MPA of 0.8 mL was added dropwise into the solution with continuous stirring. The solution was kept at 50 °C in a water bath by another 1 h of stirring to complete the ligand exchange reaction. In the process, the solvent of GQDs turned from hexane to water. The precipitate was collected and centrifuged with the use of acetone and methanol to remove the residual MPA. Then, the MPA-GQDs were dissolved in deionized water (0.5 mL), which has high-concentration dispersions (0.4 mM). For the following measurements, the polyvinyl pyrrolidone (PVP) aqueous solution of 10 wt% was added into above solution according to the actual situation, and the volume fractions of GQDs and PVP were about 47 % and 53 % in the final solution, respectively. 2.3. Fabrication of DFB Structures. In the laser interference ablation process, a single-mode Nd: YAG laser (532 nm, 200 mW) was used as the light source. The laser intensity could be controlled by a neutral density filters. A spatial filter was employed at the beam path for achieving uniform intensity in the interference region. The two beams with equal intensity were


4

Page 5 of 32

1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 28 29 30 31 32 33 34 35 36 37 38 39 40 41 42 43 44 45 46 47 48 49 50 51 52 53 54 55 56 57 58 59 60


obtained by a non-polarizing beamsplitter, and the interfered beams were guided to overlap directly on the surface of drop-casted GQDs film. After about 15 minutes, the grating structure would be created on the film. The fabricated DFB gratings were transparent and uniform. The grating period could be accurately adjusted by tuning the angle between two beams. And it is necessary to point out that the grating’s area can be also changed by using balsaming lens with different focal length. All experiments were carried out on an isolation optical platform under ambient conditions. 2.4. Materials Characterization. The PL emission spectrum and the PL decay trace were recorded with Edinburgh F900 luminescence spectrometer at room temperature, and the PL decay trace was monitored with a single photon counting system at the PL peak wavelength. The PL QYs of samples were measured in comparison to standard dye (Rhodamine B (QYs, 50 %)) at identical optical density. The UV–visible absorption data was collected with SHIMADZU (UV3600) spectrophotometer. The exciton recombination dynamics measurements were performed in solution, PL signal was collected by an electrically triggered streak camera system (Hamamatsu C5680). The TPIF experiments were measured by a tunable Ti: Sapphire amplifier system (Coherent Mira 900-F, 150 fs, 76 MHz). Single QD PL measurements were performed on a confocal microscope. The diluent solution of QDs was spin-casted onto a quartz coverslip. The picosecond supercontinuum fiber laser (NKT Photonics EXR-15, 490 nm, 4.9 MHz) was employed as the excitation source. For the blinking measurements, the laser power density used for exciting a single QD was ∼1 W cm−2, and the PL emission from a single QD collected by the same objective was sent to a single-photon counting system. Transmission electron microscopy (TEM) image was obtained by a FEI TecnaiG2 electron microscope at an acceleration voltage of 200 kV. Optical image was taken on a metallographic


5


1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 28 29 30 31 32 33 34 35 36 37 38 39 40 41 42 43 44 45 46 47 48 49 50 51 52 53 54 55 56 57 58 59 60

Page 6 of 32

microscope (OLYMPUS BX51M). The thickness and refractive index for GQDs film was measured using a prism coupling device (Metricon Model 2010) at a wavelength of 632.8 nm. AFM images were obtained by using BioScope Resolve™ in the tapping mode. 2.5. ASE and Lasing Investigation. The excitation pulses were from an amplified femtosecond Ti: Sapphire laser system (Legend-F-1k, 800 nm, 1 kHz, 100 fs). The 400 nm beam was obtained by a β-barium borate (BBO) crystal. A stripe pumping configuration (with dimension of 3 mm × 0.4 mm) was acquired by a 10-cm focal length cylindrical lens. The pump pulse energy could be continuously varied with a half-wave plate. The modal gain was characterized by the variable stripe length (VSL) method on the surface of a GQDs film, and all samples with the uniform thickness (~1 µm, n= 1.67) used for VSL and ASE measurements. The optical gain coefficients (g) were determined by the equation: I = A (egL-1)/g, where I is the ASE intensity dependent on the length of stripe (L), A is a constant. Pump intensity was chosen to be three times of the corresponding OPA- or TPA-pumped ASE threshold, respectively. For ASE measurements, the stripe pump pulses were perpendicular to the films. The sample’s edge emitted beam was collected from the lateral parallel to the films by a fast optical multichannel analyzer (OMA, SpectraPro-300i) and an optically triggered streak camera system for steady and transient spectra, respectively. For lasing measurements, the pumping stripe was orthogonal to the grating grooves. The lasing emission was detected by the OMA in a plane at an angle of 30 °.

3. RESULTS AND DISCUSSION 3.1. Linear and Nonlinear Optical Characteristics. In this work, we employed giant CdSe/CdS core-shell quantum dots with 11 monolayers of CdS shell (11 MLs) as active material for lasing. The CdS shell provides an improved surface modification and reduces the interface trapping rates, thus help to enhance chemical- and photostability. Figure 1a presents TEM image


6

Page 7 of 32

1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 28 29 30 31 32 33 34 35 36 37 38 39 40 41 42 43 44 45 46 47 48 49 50 51 52 53 54 55 56 57 58 59 60


of GQDs with excellently narrow size distribution and highly crystal quality, resulting from the controlled shell-growth process with slow crystal growth at high temperature.14 To exhibit the recombination dynamics of QDs based on shell thickness, the PL lifetimes of the samples were measured and fitted, as shown in Figure 1b. The PL decay traces demonstrate an increasingly longer lifetimes because of the reduced wavefunction overlap. In the case of PL decay fitting of CdSe core QDs, the trace cannot be greatly fitted with the single exponential dynamics. It is likely that the surface-related defects induced the increasing probability of nonradiative carrier losses.38, 39 With the increase of shell thickness, the trace is better conformed to single-exponent behaviour. When the shell thickness reaches up to 11 MLs, the decreased chi-square χ2 value is below 1.2, which is an acceptable value with regard to the PL decay fitting operated under single photon counting system. The results suggest that the surface defects can be sufficiently inhibited after coating with an epitaxial thick CdS shell in the higher growth temperatures, isolating the exciton from the CdSe cores surface and the solution. The dramatically enhanced absorption values ( 40 ns, showing clearly that multiexcitons possess a long lifetime.


10

Page 11 of 32

1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 28 29 30 31 32 33 34 35 36 37 38 39 40 41 42 43 44 45 46 47 48 49 50 51 52 53 54 55 56 57 58 59 60


(b) The biexciton dynamics shows that the biexciton lifetime (τxx) of GQDs is 10.8 ns, which is consistent with the result extracted from red curve (19 µJ cm−2) by subtraction procedure (see Figure S4, Supporting Information), and the single exciton lifetime τx is 44 ns. Time dependent PL intensity traces of a single CdSe/CdS core-shell QD with different shell thickness 11 MLs (c), 7 MLs (d) and 4 MLs (e). The measurements are performed with a bin size of 20 ms. The dextral diagrams reveal the statistical distribution of intensity in the trace. “On” states and “Off” states are separated by a predefined intensity threshold shown as the dashed line. To verify the suppression of Auger recombination, the photoluminescence from single QD was measured by a time-correlated single photon counting system, as shown in Figure 2c-e. The time dependent PL intensity trace of single GQD (11 MLs) was continuously on states, the off-states fraction far below 1 % during the timescales of 500 s. It is in striking contrast to a typical CdSe/CdS (4 MLs) QD, which displays several obvious off periods with an off-time fraction of ~10 %. When the thickness of CdS shell achieves 7 MLs, it just has some independent off states and the off-time fraction further reduced to ~1 %. The photoluminescence blinking behavior may arise from the high efficiency of nonradiative Auger recombination and surface traps.46 So, the thick shell structures exhibit more efficient suppression of AR and sufficient surface passivation than medium-shell QDs, thus confirming the suppressed Auger process in GQDs. Table 1. ASE and gain parameters of GQDs film under one- and two-photon pumping. Excitation Wavelength (nm)

ASE Peak (nm)

FWHM (nm)

Threshold (mJ cm−2)

Gain (cm−1)

One-Photon

400

642

8.3

0.108

108

Two-Photon

800

644

8.8

2.67

102

3.3. Amplified Stimulated Emission Properties. For exploring the gain performance in GQDs film, the amplified stimulated emission properties of GQDs film (GQDs volume fraction of ~47 %) was studied under both one- and two-photon excitation (Table 1). At pump intensities


11


1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 28 29 30 31 32 33 34 35 36 37 38 39 40 41 42 43 44 45 46 47 48 49 50 51 52 53 54 55 56 57 58 59 60

Page 12 of 32

above threshold values of 0.108 mJ cm−2 for 400 nm and 2.67 mJ cm−2 for 800 nm optical pumping, the amplified stimulated emission peaked at 642 and 644 nm was detected with a narrow FWHM of about 8-9 nm (Figure 3a, c), respectively. Due to the mixture of PVP in GQDs film, the QDs’ packing density is lower than that in the pure QDs films, thus resulting in the higher ASE threshold compared to some reported values (6-53 µJ cm−2). 12, 21, 47, 48 And the ASE spectra displays that the areas of the optical gain occupy a broad bandwidth across the PL spectrum. Notably, the blue-shifted ASE peak with respect to the PL maximum can be distinctly viewed under one-photon pumping, which is accordant to the repulsive exciton-exciton interactions in GQDs as aforesaid and thus effectively demonstrates the biexcitonic gain mechanism in our GQDs.9,20,49 In the condition of two-photon pumping, the spectral position of ASE relative to PL peak is analogous to that under one-photon pumping, which affirms that twophoton induced ASE is similarly rooted in the optical amplification of biexciton recombination. The effective modal gain is measured by variable stripe length technique 50 at the ASE peak (Figure 3b, d). These high gain coefficients (108 cm−1 and 102 cm−1 corresponding to one- and two-photon pumping, respectively) are comparable to the conventional semiconductor QDs, 50, 51 but were achieved here at films with the reduction of packing density and the giant shell volume. The high modal gain relies on an optical structure while offering minimal modal loss, 52 thus highlight their potential lasing applications as optical gain layers within microcavity lasers.


12

Page 13 of 32

1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 28 29 30 31 32 33 34 35 36 37 38 39 40 41 42 43 44 45 46 47 48 49 50 51 52 53 54 55 56 57 58 59 60


Figure 3. (a) The ASE spectra of the GQDs film under stripe excitation at 400 nm, measured with increasing pump intensities. (b) The VSL measurement for the GQDs film excited at 400 nm (108 cm −1, pumped intensity of 0.32 mJ cm−2). (c) The ASE spectra of the GQDs film under stripe excitation at 800 nm, measured with increasing pump intensities. (d) The VSL measurement for the GQDs film excited at 800 nm (102 cm −1, pumped intensity of 8 mJ cm−2). Fitting of the data is performed according to a linear amplifier model (see relative Experimental Section for details). Besides, the transient PL dynamics of GQDs thin films was also studied for deeper insights under excitation at 400 nm with different excitation intensities. Figure 4a displays the timeresolved PL spectrogram under pump intensity of 0.18 mJ cm−2, which is slightly above ASE threshold. As shown in Figure 4b, the narrow ASE peak dominates the transient PL spectra for


13


1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 28 29 30 31 32 33 34 35 36 37 38 39 40 41 42 43 44 45 46 47 48 49 50 51 52 53 54 55 56 57 58 59 60

Page 14 of 32

that within the initial 75 ps. Meanwhile, it decays much faster than the corresponding broad spontaneous emission, indicating the signature of ASE.53 Finally, the transient PL spectra is dominated by the spontaneous emission for long delay times (75-2000 ps), which suggests that the ASE only takes place within a much shorter time. Figure 4c presents the time-resolved PL spectrogram measured at progressively increasing excitation intensities and exhibits a transition from spontaneous emission to amplified stimulated emission. The corresponding evolution of PL decay dynamics is illustrated in Figure 4d. For excitation intensity (0.08 mJ cm−2) of lower than the threshold, spontaneous emission was dominated by a fast decay with a lifetime of 410 ps, which could be produced by a small fraction of ASE emission energy.50, 54 When the pump intensities (0.12 mJ cm−2) increased to slightly larger than the threshold, a much-faster decay component appeared and corresponded to the ASE, the measured lifetime was 130 ps. As the pump intensities (0.51 mJ cm−2) far above the threshold, the fast PL decay lifetime was further reduced to 16 ps and near the temporal resolution of streak camera system, which was more than thousand-fold faster than Auger decay, as well signified highly efficient ASE. Ultimately, we can come to the conclusion that the lifetime of ASE action is measured to be less than 16 ps, clearly indicates that the decay process is dominated by the ultrafast ASE and enough fast to compete with the intrinsic Auger recombination.


14

Page 15 of 32

1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 28 29 30 31 32 33 34 35 36 37 38 39 40 41 42 43 44 45 46 47 48 49 50 51 52 53 54 55 56 57 58 59 60


Figure 4. (a) Time-resolved PL spectrogram of a close-packed GQDs film under pump intensity of 0.18 mJ cm−2. (b) Transient PL spectra extracted from the spectrogram (a) with different integrated time range. To quantify the temporal distribution of PL/ASE spectra, the dashed lines show the fitting by Gaussian curves. (c) Time-resolved PL spectrogram of a close-packed GQDs film under excitation intensities of 0.08, 0.12 and 0.51 mJ cm−2, respectively. (d) PL decay traces of GQDs film with the pump intensities vary from lower than the ASE threshold (0.08 mJ cm−2) to far above the ASE threshold (0.51 mJ cm−2). The time-resolved PL measurements are monitored at excitation wavelength of 400 nm. 3.4. Fabrication of Grating on the GQDs Thin Films. Figure 5 shows the schematic illustration for fabricating distributed feedback grating. The dashed frame describes the process of LIA. Firstly, the GQDs-based thin films were obtained by drop-coating GQDs-PVP solution


15


1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 28 29 30 31 32 33 34 35 36 37 38 39 40 41 42 43 44 45 46 47 48 49 50 51 52 53 54 55 56 57 58 59 60

Page 16 of 32

onto a cleaned quartz substrate (n= 1.46). Next, the prepared films were exposed to the laser interference pattern about 15 minutes, and their surfaces were structured to acquire periodic relief patterns due to the laser induced ablation effect. Finally, the fabricated DFB gratings have a circular effective area with a diameter of 1 cm (thickness of ~1 µm). The PVP component is partially removed at the bright interference fringes whereas survived in the dark interference region. Additional areas between the bright and the dark interference fringes constitute sinusoidal nanostructures, which should be attributed to the LIA effect along with the distribution of laser intensity.55, 56 Experiments show that the laser intensity of about 200 mW is sufficient to realize LIA at the bright interference regions. To sum up, the LIA is an efficient way to fabricate GQDs grating with highly consistent morphology.

Figure 5. Schematic of experimental setup for fabricating distributed feedback grating based on GQDs film by LIA, where NPBS denotes the non-polarizing beamsplitter. The dashed frame shows the forming process of surface relief structures. 3.5. Optical Properties of GQDs Gratings. On account of the scattering and diffraction of


16

Page 17 of 32

1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 28 29 30 31 32 33 34 35 36 37 38 39 40 41 42 43 44 45 46 47 48 49 50 51 52 53 54 55 56 57 58 59 60


periodic nanostructures, the bright iridescence on the grating surface is clearly observed by our eyes (Figure 6a). The uniform color changes from red to the short wavelength purple under different viewed angles. Moreover, the well-proportioned transmission diffraction spot is shown in Figure 6b. They all imply that the LIA treated GQDs gratings possess uniform grating structures and put up extremely admirable optical-quality, as well as the LIA is a high-efficiency fabrication technics with advantages of excellent reproducibility and easy realization. We know that the ablation depth can be adjusted by controlling the laser intensity and LIA time. Figure 6c shows the relationships between modulation depth and the laser beam intensity. The ablation depth is positively related to the laser intensity, which intuitively manifest that the higher laser intensity, the greater depth. The modulation depth is larger than 140 nm. Furthermore, it should be noted that the LIA process produces large amounts of spininess and potholes on the surface of the GQDs grating (Figure 6d) at the low laser intensity (96 mW cm−2), that would induce scattering losses due to surface roughness imperfections. Nevertheless, the grating surface becomes smooth with increasing laser intensity (223 mW cm−2), which maybe result from the laser induced thermal effect.57 The tendency reveals the higher laser intensity brings about more smooth surface (see Figure S6a-e, Supporting Information), and will decrease the level of loss within the structures. Consequently, the higher laser intensity is necessary to ensure the high-quality of grating structures, showing enormous potential for proving to be the high performance DFB laser devices.


17


1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 28 29 30 31 32 33 34 35 36 37 38 39 40 41 42 43 44 45 46 47 48 49 50 51 52 53 54 55 56 57 58 59 60

Page 18 of 32

Figure 6. (a) Optical photograph of the GQDs grating. The iridescence is caused by the grating diffraction, seven colors from red to purple are successively observed under different viewed angles. (b) Diffraction pattern of the prepared grating. (c) The relationships between surface modulation depth and the laser intensities (1.5 µm period). Experiment data is obtained by averaging the ablation depth throughout the whole measurement areas. (d) AFM images (10 µm × 10 µm) of grating structures under different laser intensities. The laser intensity is 96, 159 and 223 mW cm−2, respectively. In the process of fabricating grating, the GQDs film was exposed to the lasers with high power intensity. In order to study the damage of LIA to the GQDs, the PL spectra of the GQDs film before and after laser ablation was contrastively investigated. Using laser intensity 223 mW cm−2, both of the emission maximums are located in 646 nm. The PL intensity has hardly any decrease after the LIA process last for 30 min (see Figure S6f, Supporting Information), which conceivably confirms that the continuous exposure under high laser intensity does not result in


18

Page 19 of 32

1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 28 29 30 31 32 33 34 35 36 37 38 39 40 41 42 43 44 45 46 47 48 49 50 51 52 53 54 55 56 57 58 59 60


the degradation of GQDs and exhibits excellent photostability. For this reason, the GQDs’ optical performance is not nearly affected by LIA. 3.6. DFB Laser Performance. The distributed feedback lasers were directly fabricated on the GQDs (11 MLs) film by laser interference ablation. The integrated effect of surface modulation depth and grating period enables essential impacts on the laser’s output properties within the gain mode.

58

Figure 7a-c shows the AFM images of the DFB structures. The devices have the

smooth surface with a period of 800 nm, and the average modulation depth is estimated to be 50nm (Figure 7b). Figure 7d shows the optical microscope image of the DFB structures, indicating the uniformity and high quality of grating over a large scale. With the proposed grating configuration, the above excellent photonic structures afford strong DFB mechanisms according to theoretical calculations, which points out that the laser emission wavelength centered near 640-650 nm within the optical gain emission spectrum.

Figure 7. (a-c) AFM images of the DFB structures fabricated by LIA with laser intensities 210 mW cm−2, the period is 800 nm. (b) Height profile of the DFB structure along the direction of line in (a). (d) Optical microscope image of the DFB structures. To investigate the performance of DFB laser devices, the measurements were carried out under optical pumping in the OPA and TPA regime. The lasing emission was collected at an angle of 30 ° by an OMA (see Figure S7, Supporting Information), where the coupled emission


19


1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 28 29 30 31 32 33 34 35 36 37 38 39 40 41 42 43 44 45 46 47 48 49 50 51 52 53 54 55 56 57 58 59 60

Page 20 of 32

angle of lasing wavelength was defined as reported by previous work.34 The laser emission spectra were then recorded at different pump intensities (Figure 8a, b). At the lower excitation intensities (below the thresholds), only the PL emission is observed. As the excitation intensities increase above the lasing thresholds, the single-mode lasing emission are completely detected under excitation at 400 and 800 nm (summarized in Table 2). The emission intensity shows a steep linear growth, a further trend characteristic of lasing (Figure 8c, d). Both of the lasing peaks are located at 645 nm with a FWHM of ~1 nm. The lasing threshold is 0.028 and 1.03 mJ cm−2, respectively, which is a third of the corresponding ASE thresholds. More importantly, operated under either one- or two-photon excitation, the devices show quite low laser threshold among previously reported CdSe-based DFB structures.22,23,28,29 In addition to the suppression of Auger decay and nonradiative recombination defects, the low thresholds can be also ascribed to the large absorption cross sections dominated by the thick CdS shells, 11,12 which accounts for ∼95 % of the GQD’s volume. Furthermore, the smooth surface of grating would reduce intrinsic optical losses among the surface relief structures, which could availably enhance the overall coupling efficiency of the amplified mode. Table 2. A summary of laser parameters in GQDs distributed feedback structures based on oneand two-photon excitation. Excitation Wavelength (nm)

Laser Peak (nm)

FWHM (nm)

Threshold (mJ cm−2)

Q-factor

One-Photon

400

645

0.91

0.028

709

Two-Photon

800

645

1.1

1.03

586

The results are accorded with the calculated laser’s output wavelength (λBragg) by the Bragg condition: N·λBragg = 2·neff·Λ, where Λ is the grating period, N is the grating order, and neff is the effective refractive index of the DFB structure. We obtain that neff = 1.61 and the N= 4, the laser output coming from a fourth-order diffraction. Therefore for a DFB structure in this work, the


20

Page 21 of 32

1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 28 29 30 31 32 33 34 35 36 37 38 39 40 41 42 43 44 45 46 47 48 49 50 51 52 53 54 55 56 57 58 59 60


free spectral range (FSR) is 215 nm. This large FSR is sufficient to ensure single-mode operation inside the GQDs’ optical gain band.12, 59 The Q-factor is connected with the lasing emission wavelength as well as the linewidth (∆λ) of each lasing mode, Q = λBragg/∆λ, giving a high Qfactor of 709 and 586, respectively. Hence, it demonstrates that the high-quality DFB lasers can be directly prepared by LIA on QDs films. At the same time, the GQDs have been also proved to be promising frequency up-converted gain-medium for laser applications.

Figure 8. Lasing emission spectra of the DFB devices under different excitation intensities pumped at 400 nm (a) and 800 nm (b). Lasing emission intensity as a function of increasing excitation intensities pumped at 400 nm (c) and 800 nm (d). The insert shows that the FWHM of lasing emission peak is 0.91 nm and 1.1 nm, respectively.


21


1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 28 29 30 31 32 33 34 35 36 37 38 39 40 41 42 43 44 45 46 47 48 49 50 51 52 53 54 55 56 57 58 59 60

Page 22 of 32

4. CONCLUSION In summary, GQDs distributed feedback lasers have been successfully fabricated by laser interference ablation. The GQDs exhibit remarkable gain properties in view that the quantum dots with thick CdS shells effectively suppress Auger recombination and PL blinking. Furthermore, GQDs have the potential as an outstanding frequency up-converted material for lasers because of high TPA cross sections ~1.1×105 GM and attractive two-photon gain. The single-mode lasing emission have been observed from these DFB structures operated in the oneand two-photon absorption regime, the lasing thresholds are reduced to one third of the corresponding ASE threshold. In general, the water soluble system can be as a means to greatly improve the film-forming performance of GQDs materials, it still remains excellent optical characterizations after ligand exchange. On this basis, the fabrication of GQDs distributed feedback lasers start the way to a facile production in view of solution-based method by LIA, which provides a kind of processable technical-approach for future applications of semiconductor quantum dots DFB laser devices.

■ ASSOCIATED CONTENT *S Supporting Information The Supporting Information is available free of charge on the ACS Publications website at DOI:. Additional details are available, including Experimental section, PL and absorption characterization of MPA-GQDs, nonlinear optical characterization, time resolved fluorescence spectroscopy, morphology and optical properties of GQDs grating and lasing measurements (PDF)

■ AUTHOR INFORMATION Corresponding Authors *E-mail: [email protected]


22

Page 23 of 32

1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 28 29 30 31 32 33 34 35 36 37 38 39 40 41 42 43 44 45 46 47 48 49 50 51 52 53 54 55 56 57 58 59 60


*E-mail: [email protected] ORCID Jiayu Zhang: 0000-0001-7868-6346 Notes The authors declare no competing financial interest.

■ ACKNOWLEDGMENTS This work was supported by the National Basic Research Program of China (973 Program, 2012CB921801) and the Science and Technology Department of Jiangsu Province (BE2016021).

■ REFERENCES (1) Dai, X. L.; Zhang, Z. X.; Jin, Y. Z.; Niu, Y.; Cao, H. J.; Liang, X. Y.; Chen, L. W.; Wang, J. P.; Peng, X. G. Solution-Processed, High Performance Light-Emitting Diodes Based on Quantum Dots. Nature 2014, 515, 96−100. (2) Chan, Y.; Steckel, J. S.; Snee, P. T.; Caruge, J. M.; Hodgkiss, J. M.; Nocera, D. G.; Bawendi, M. G. Blue Semiconductor Nanocrystal Laser. Appl. Phys. Lett. 2005, 86, 073102. (3) Zavelani-Rossi, M.; Lupo, M. G.; Krahne, R.; Manna, L.; Lanzani, G. Lasing in SelfAssembled Microcavities of CdSe/CdS Core/Shell Colloidal Quantum Rods. Nanoscale 2010, 2, 931−935. (4) Snee, P. T.; Chan, Y.; Nocera, D. G.; Bawendi, M. G. Whispering-Gallery-Mode Lasing from a Semiconductor Nanocrystal/Microsphere Resonator Composite. Adv. Mater. 2005, 17, 1131−1136. (5) Wegner, K. D.; Hildebrandt, N. Quantum Dots: Bright and Versatile in Vitro and in Vivo Fluorescence Imaging Biosensors. Chem. Soc. Rev. 2015, 44, 4792−4834. (6) Wang, Y.; Leck, K. S.; Ta, V. D.; Chen, R.; Nalla, V.; Gao, Y.; He, T.; Demir, H. V.; Sun, H. Blue Liquid Lasers from Solution of Cdzns/Zns Ternary Alloy Quantum Dots with QuasiContinuous Pumping. Adv. Mater. 2015, 27, 169−175.


23


1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 28 29 30 31 32 33 34 35 36 37 38 39 40 41 42 43 44 45 46 47 48 49 50 51 52 53 54 55 56 57 58 59 60

Page 24 of 32

(7) Xing, G.; Kumar, M. H.; Chong, W. K.; Liu, X.; Cai, Y.; Ding, H.; Asta, M.; Gratzel, M.; Mhaisalkar, S.; Mathews, N.; Sum, T.C. Solution-Processed Tin-Based Perovskite for NearInfrared Lasing. Adv. Mater. 2016, 28, 8191−8196. (8) Dang, C.; Nurmikko, A. Beyond Quantum Dot LEDs: Optical Gain and Laser Action in Red, Green, and Blue Colors. MRS Bull. 2013, 38, 737−742. (9) Klimov, V. I.; Mikhailovsky, A. A.; McBranch, D. W.; Leatherdale, C. A.; Bawendi, M. G. Quantization of Multiparticle Auger Rates in Semiconductor Quantum Dots. Science 2000, 287, 1011−1013. (10) Robel, I.; Gresback, R.; Kortshagen, U.; Schaller, R. D.; Klimov, V. I. Universal SizeDependent Trend in Auger Recombination in Direct-Gap and Indirect-Gap Semiconductor Nanocrystals. Phys. Rev. Lett. 2009, 102, 177404. (11) Klimov, V. I.; Mikhailovsky, A. A.; Xu, S.; Malko, A.; Hollingsworth, J. A.; Leatherdale, C. A.; Eisler, H. J.; Bawendi, M. G. Optical Gain and Stimulated Emission in Nanocrystal Quantum Dots. Science 2000, 290, 314−317. (12) García-Santamaría, F.; Chen, Y.; Vela, J.; Schaller, R. D.; Hollingsworth, J. A.; Klimov, V. I. Suppressed Auger Recombination in “Giant” Nanocrystals Boosts Optical Gain Performance. Nano Lett. 2009, 9, 3482−3488. (13) Chen, Y.; Vela, J.; Htoon, H.; Casson, J. L.; Werder, D. J.; Bussian, D. A.; Klimov, V. I.; Hollingsworth, J. A. Giant” Multishell CdSe Nanocrystal Quantum Dots with Suppressed Blinking. J. Am. Chem. Soc. 2008, 130, 5026−5027. (14) Ghosh, Y.; Mangum, B. D.; Casson, J. L.; Williams, D. J.; Htoon, H.; Hollingsworth, J. A. New Insights into the Complexities of Shell Growth and the Strong Influence of Particle Volume


24

Page 25 of 32

1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 28 29 30 31 32 33 34 35 36 37 38 39 40 41 42 43 44 45 46 47 48 49 50 51 52 53 54 55 56 57 58 59 60


in Nonblinking “Giant” Core/Shell Nanocrystal Quantum Dots. J. Am. Chem. Soc. 2012, 134, 9634−9643. (15) García-Santamaría, F.; Brovelli, S.; Viswanatha, R.; Hollingsworth, J. A.; Htoon, H.; Crooker, S. A.; Klimov, V. I. Breakdown of Volume Scaling in Auger Recombination in CdSe/CdS Heteronanocrystals: The Role of the Core-Shell Interface. Nano Lett. 2011, 11, 687−693. (16) Climente, J. I.; Movilla, J. L.; Planelles, J. Auger Recombination Suppression in Nanocrystals with Asymmetric Electron-Hole Confinement. Small 2012, 8, 754−759. (17) Mahler, B.; Spinicelli, P.; Buil, S.; Quelin, X.; Hermier, J. P.; Dubertret, B. Towards Nonblinking Colloidal Quantum Dots. Nat. Mater. 2008, 7, 659−664. (18) Heyes, C. D.; Kobitski, A. Y.; Breus, V. V.; Nienhaus, G. U. Effect of the Shell on the Blinking Statistics of Core-Shell Quantum Dots: A Single-Particle Fluorescence Study. Phys. Rev. B: Condens. Matter Mater. Phys. 2007, 75, 125431−125438. (19) Cretí, A.; Anni, M.; Rossi, M. Z.; Lanzani, G.; Leo, G.; Della Sala, F.; Manna, L.; Lomascolo, M. Ultrafast Carrier Dynamics in Core and Core/Shell CdSe Quantum Rods: Role of the Surface and Interface Defects. Phys. Rev. B 2005, 72, 125346. (20) Klimov, V. I. Mechanisms for Photogeneration and Recombination of Multiexcitons in Semiconductor Nanocrystals: Implications for Lasing and Solar Energy Conversion. J. Phys. Chem. B. 2006, 110, 16827−16845. (21) Guzelturk, B.; Kelestemur, Y.; Gungor, K.; Yeltik, A.; Akgul, M. Z.; Wang, Y.; Chen, R.; Dang, C.; Sun, H.; Demir, H. V. Stable and Low-Threshold Optical Gain in CdSe/CdS Quantum Dots: An All Colloidal Frequency Up-Converted Laser. Adv. Mater. 2015, 27, 2741−2746.


25


1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 28 29 30 31 32 33 34 35 36 37 38 39 40 41 42 43 44 45 46 47 48 49 50 51 52 53 54 55 56 57 58 59 60

Page 26 of 32

(22) Todescato, F.; Fortunati, I.; Gardin, S.; Garbin, E.; Collini, E.; Bozio, R.; Jasieniak, J. J.; Della Giustina, G.; Brusatin, G.; Toffanin, S.; Signorini, R. Soft-Lithographed Up-Converted Distributed Feedback Visible Lasers Based on CdSe-CdZnS-ZnS Quantum Dots. Adv. Funct. Mater. 2012, 22, 337−344. (23) Signorini, R.; Fortunati, I.; Todescato, F.; Gardin, S.; Bozio, R.; Jasieniak, J. J.; Martucci, A.; Della Giustina, G.; Brusatin, G.; Guglielmi, M. Facile Production of Up-Converted Quantum Dot Lasers. Nanoscale 2011, 3, 4109−4113. (24) Xing, G.; Liao, Y.; Wu, X.; Chakrabortty, S.; Liu, X.; Yeow, E. K. L.; Chan, Y.; Sum, T. C. Ultralow-Threshold Two-Photon Pumped Amplified Spontaneous Emission and Lasing from Seeded CdSe/CdS Nanorod Heterostructures. Acs Nano 2012, 6, 10835−10844. (25) Moreels, I.; Raino, G.; Gomes, R.; Hens, Z.; Stoeferle, T.; Mahrt, R. F. Nearly Temperature-Independent Threshold for Amplified Spontaneous Emission in Colloidal CdSe/CdS Quantum Dot-in-Rods. Adv. Mater. 2012, 24, OP231−OP235. (26) Kiraz, A.; Chen, Q.; Fan, X. Optofluidic Lasers with Aqueous Quantum Dots. ACS Photonics 2015, 2, 707−713. (27) Grivas, C.; Li, C.; Andreakou, P.; Wang, P.; Ding, M.; Brambilla, G.; Manna, L.; Lagoudakis, P. Single-Mode Tunable Laser Emission in the Single-Exciton Regime from Colloidal Nanocrystals. Nat. Commun.2013, 4, 2376. (28) Roh, K.; Dang, C.; Lee, J.; Chen, S.; Steckel, J. S.; Coe-Sullivan, S.; Nurmikko, A. Surface-Emitting Red, Green, and Blue Colloidal Quantum Dot Distributed Feedback Lasers. Opt. Express 2014, 22, 18800−18806.


26

Page 27 of 32

1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 28 29 30 31 32 33 34 35 36 37 38 39 40 41 42 43 44 45 46 47 48 49 50 51 52 53 54 55 56 57 58 59 60


(29) Dang, C.; Lee, J.; Roh, K.; Kim, H.; Ahn, S.; Jeon, H.; Breen, C.; Steckel, J. S.; CoeSullivan, S.; Nurmikko, A. Highly Efficient, Spatially Coherent Distributed Feedback Lasers from Dense Colloidal Quantum Dot Films. Appl. Phys. Lett. 2013, 103, 171104. (30) Saliba, M.; Wood, S. M.; Patel, J. B.; Nayak, P. K.; Huang, J.; Alexander-Webber, J. A.; Wenger, B.; Stranks, S. D.; Horantner, M. T.; Wang, J. T.-W.; Nicholas, R. J.; Herz, L. M.; Johnston, M. B.; Morris, S. M.; Snaith, H. J.; Riede, M. K. Structured Organic−Inorganic Perovskite toward a Distributed Feedback Laser. Adv. Mater. 2016, 28, 923−929. (31) Sundar, V. C.; Eisler, H. J.; Deng, T.; Chan, Y.; Thomas, E. L.; Bawendi, M. G. SoftLithographically Embossed, Multilayered Distributed-Feedback Nanocrystal Lasers. Adv. Mater. 2004, 16, 2137−2141. (32) Xiong, Z.; Liao, C.; Wang, X. Reduced Graphene Oxide Diffraction Gratings from Duplication of Photoinduced Azo Polymer Surface-relief-gratings Through Soft-lithography. J. Mater. Chem. C 2015, 3, 6224−6231. (33) Camposeo, A.; Del Carro, P.; Persano, L.; Cyprych, K.; Szukalski, A.; Sznitko, L.; Mysliwiec, J.; Pisignano, D. Physically Transient Photonics: Random versus Distributed Feedback Lasing Based on Nanoimprinted DNA. Acs Nano 2014, 8, 10893−10898. (34) Fang, H.-H.; Ding, R.; Lu, S.-Y.; Yang, J.; Zhang, X.-L.; Yang, R.; Feng, J.; Chen, Q.D.; Song, J.-F.; Sun, H.-B. Distributed Feedback Lasers Based on Thiophene/Phenylene CoOligomer Single Crystals. Adv. Funct. Mater. 2012, 22, 33−38. (35) Zhai, T.; Zhang, X.; Pang, Z.; Dou, F. Direct Writing of Polymer Lasers using Interference Ablation. Adv. Mater. 2011, 23, 1860−1864.


27


1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 28 29 30 31 32 33 34 35 36 37 38 39 40 41 42 43 44 45 46 47 48 49 50 51 52 53 54 55 56 57 58 59 60

Page 28 of 32

(36) Liao, C.; Fan, K.; Xu, R.; Zhang, H.; Lu, C.; Cui, Y.; Zhang, J. Laser-Annealing-Made Amplified Spontaneous Emission of “Giant” CdSe/CdS Core/Shell Nanocrystals Transferred from Bulk-Like Shell to Quantum-Confined Core. Photonics Res. 2015, 3, 200−205. (37) Bae, W. K.; Char, K.; Hur, H.; Lee, S. Single-Step Synthesis of Quantum Dots with Chemical Composition Gradients. Chem. Mater. 2008, 20, 531−539. (38) van Embden, J.; Jasieniak, J.; Mulvaney, P. Mapping the Optical Properties of CdSe/CdS Heterostructure Nanocrystals: The Effects of Core Size and Shell Thickness. J. Am. Chem. Soc. 2009, 131, 14299−14309. (39) Zhang, J.; Zhang, X.; Zhang, J. Y. Dependence of Microstructure and Luminescence on Shell Layers in Colloidal CdSe/CdS Core/Shell Nanocrystals. J. Phys. Chem. C 2010, 114, 3904−3908. (40) Sundar, V. C.; Eisler, H.-J.; Bawendi, M. G. Room-temperature, Tunable Gain Media from Novel II-VI Nanocrystal-titania Composite Matrices. Adv. Mater. 2002, 14, 739−743. (41) Cihan, A. F.; Kelestemur, Y.; Guzelturk, B.; Yerli, O.; Kurum, U.; Yaglioglu, H. G.; Elmali, A.; Demir, H. V. Attractive versus Repulsive Excitonic Interactions of Colloidal Quantum Dots Control Blue- to Red-Shifting (and Non-shifting) Amplified Spontaneous Emission. J. Phys. Chem. Lett. 2013, 4, 4146−4152. (42) Pu, S. C.; Yang, M. J.; Hsu, C. C.; Lai, C. W.; Hsieh, C. C.; Lin, S. H.; Cheng, Y. M.; Chou, P. T. The Empirical Correlation Between Size and Two-Photon Absorption Cross Section of CdSe and CdTe Quantum Dots. Small 2006, 2, 1308−1313. (43) Klimov, V. I.; McGuire, J. A.; Schaller, R. D.; Rupasov, V. I. Scaling of Multiexciton Lifetimes in Semiconductor Nanocrystals. Phys. Rev. B 2008, 77, 195324.


28

Page 29 of 32

1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 28 29 30 31 32 33 34 35 36 37 38 39 40 41 42 43 44 45 46 47 48 49 50 51 52 53 54 55 56 57 58 59 60


(44) Sampat, S.; Karan, N. S.; Guo, T.; Htoon, H.; Hollingsworth, J. A.; Malko, A. V. Multistate blinking and scaling of the recombination rates in individual silica-coated CdSe/CdS nanocrystals. ACS Photonics 2015, 2, 1505−1512. (45) Zavelani-Rossi, M.; Lupo, M. G.; Tassone, F.; Manna, L.; Lanzani, G. Suppression of Biexciton Auger Recombination in CdSe/CdS Dot/Rods: Role of the Electronic Structure in the Carrier Dynamics. Nano Lett. 2010, 10, 3142−3150. (46) Hu, F.; Yin, C.; Zhang, H.; Sun, C.; Yu, W.W.; Zhang, C.; Wang, X.; Zhang, Y.; Xiao, M. Slow Auger Recombination of Charged Excitons in Nonblinking Perovskite Nanocrystals without Spectral Diffusion. Nano Lett. 2016, 16, 6425−6430. (47) Park, Y.; Bae, W. K.; Baker, T.; Lim, J.; Klimov, V. I. Effect of Auger Recombination on Lasing in Heterostructured Quantum Dots with Engineered Core/Shell Interfaces. Nano Lett. 2015, 15, 7319−7328. (48) Stasio, F. D.; Polovitsyn, A.; Angeloni, I.; Moreels, I; Krahne, R. Broadband Amplified Spontaneous Emission and Random Lasing from Wurtzite CdSe/CdS “Giant-Shell” Nanocrystals. ACS Photonics 2016, 3, 2083−2088. (49) Saba, M.; Minniberger, S.; Quochi, F.; Roither, J.; Marceddu, M.; Gocalinska, A.; Kovalenko, M. V.; Talapin, D. V.; Heiss, W.; Mura, A.; Bongiovanni, G. Exciton−Exciton Interaction and Optical Gain in Colloidal CdSe/CdS Dot/Rod Nanocrystals. Adv. Mater. 2009, 21, 4942−4946. (50) Dang, C.; Lee, J.; Breen, C.; Steckel, J. S.; Coe-Sullivan, S.; Nurmikko, A. Red, Green and Blue Lasing Enabled by Single-Exciton Gain in Colloidal Quantum Dot Films. Nat. Nanotechnol. 2012, 7, 335−339.


29


1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 28 29 30 31 32 33 34 35 36 37 38 39 40 41 42 43 44 45 46 47 48 49 50 51 52 53 54 55 56 57 58 59 60

Page 30 of 32

(51) Malko, A. V.; Mikhailovsky, A. A.; Petruska, M. A.; Hollingsworth, J. A.; Htoon, H.; Bawendi, M. G.; Klimov, V. I. From Amplified Spontaneous Emission to Microring Lasing Using Nanocrystal Quantum Dot Solids. Appl. Phys. Lett. 2002, 81, 1303−1305. (52) Adachi, M. M.; Fan, F.; Sellan, D. P.; Hoogland, S.; Voznyy, O.; Houtepen, A. J.; Parrish, K. D.; Kanjanaboos, P.; Malen, J. A.; Sargent, E. H. Microsecond-Sustained Lasing from Colloidal Quantum Dot Solids. Nat. Commun. 2015, 6, 8694. (53) Wang, Y.; Ta, V. D.; Gao, Y.; He, T. C.; Chen, R.; Mutlugun, E.; Demir, H. V.; Sun, H. D. Stimulated Emission and Lasing from CdSe/ CdS/ZnS Core-multi-shell Quantum Dots by Simultaneous Three-photon Absorption. Adv. Mater. 2014, 26, 2954−2961. (54) Yakunin, S.; Protesescu, L.; Krieg, F.; Bodnarchuk, M. I.; Nedelcu, G.; Humer, M.; De Luca, G.; Fiebig, M.; Heiss, W.; Kovalenko, M. V. Low-Threshold Amplified Spontaneous Emission and Lasing From Colloidal Nanocrystals of Caesium Lead Halide Perovskites. Nat. Commun. 2015, 6, 8056. (55) Jiang, H. B.; Zhang, Y. L.; Han, D. D.; Xia, H.; Feng, J.; Chen, Q. D.; Hong, Z. R.; Sun, H. B. Bioinspired Fabrication of Superhydrophobic Graphene Films by Two-Beam Laser Interference. Adv. Funct. Mater. 2014, 24, 4595−4602. (56) Cai, B.; Hattori, T.; Deng, H.H.; Komatsu, K.; Zawadzki, C.; Keil, N.; Kaino, T. Refractive Index Control and Grating Fabrication of 4′-N,N-dimethylamino-N-methyl-4stilbazolium Tosylate Crystal. Jpn. J. Appl. Phys. 2001, 40, 964−966. (57) Bian, S.; Williams, J. M.; Kim, D. Y.; Li, L.; Balasubramanian, S.; Kumar, J.; Tripathy, S. Photoinduced Surface Deformations on Azobenzene Polymer Films. J. Appl. Phys.1999, 86, 4498−4508.


30

Page 31 of 32

1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 28 29 30 31 32 33 34 35 36 37 38 39 40 41 42 43 44 45 46 47 48 49 50 51 52 53 54 55 56 57 58 59 60


(58) Holzer, W.; Penzkofer, A.; Pertsch, T.; Danz, N.; Brauer, A.; Kley, E. B.; Tillmann, H.; Bader, C.; Horhold, H. H. Corrugated Neat Thin-film Conjugated Polymer Distributed-feedback Lasers. Appl. Phys. B: Lasers Opt. 2002, 74, 333−342. (59) Liao, C.; Xu, R.; Xu, Y.; Zhang, C.; Xiao, M.; Zhang, L.; Lu, C.; Cui, Y.; Zhang, J. Ultralow-Threshold Single-Mode Lasing from Phase-Pure CdSe/CdS Core/Shell Quantum Dots. J. Phys. Chem. Lett. 2016, 7, 4968−4976.


31


1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 28 29 30 31 32 33 34 35 36 37 38 39 40 41 42 43 44 45 46 47 48 49 50 51 52 53 54 55 56 57 58 59 60

Page 32 of 32

Table of contents


32

CdS CoreâShell Quantum

Recommend Documents

CdS CoreâShell Quantum