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PL spectra of QDs in SU-8 solution (solid line-right) and in solid SU-8 composite film (dash line-left).
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Commercially available CdSe/ ZnS and PbSe colloidal semiconductor quantum dots were employed to produce both an electron beam sensitive polymethyl methacrylate PMMA-quantum-dot QD positive composite via a prepolymerization processing and an electron beam and ultraviolet UV light sensitive SU-8-QD negative composite via a direct dispersion procedure...
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... composite was prepared by spin coating the solution onto a substrate followed by a soft bake in a 90 ° C oven for 5 min. The PL in the SU-8-QD composites was measured as shown in Fig. 6 with the same setup as in Sec. II A. The quantum dots used to make the SU-8 composite are from a different batch bought from the same company. Their central emission wavelength was slightly different from the one used in making the PMMA-QD composite. However, the trend of the PL after the solidification is the same. The PL blueshifts ...Citations
... The PL results showed an organized reduction based upon modification of its surface chemistry. Moreover, the PL results in [26] indicated the presence of an oxidation layer on the quantum dots by shifting the peaks to the blue side. In addition, a study of the optical features of curing SU-8 included Raman scattering, where its intensity changed by 1 wt% for the photoinitiators and induced the heating and cross-linking of photopolymers. ...
SU-8 polymers are promising materials for various applications due to their low cost, excellent thermal stability, and outstanding mechanical properties. Cross-linking of SU-8 is a crucial process that determines the properties of the materials. This study investigates the effect of cross-linking of free-standing SU-8 films on optical transmission and PL emission under various curing conditions. Our findings show that an increase in the cross-linking density reduces optical transmission and causes a red shift of the PL emission band peaks. By directly measuring the optical response of the isolated SU-8, we remove any uncertainty due to the substrate’s presence. Moreover, we show that optical transmission and PL spectroscopy are two non-distractive techniques that can be employed to monitor the curing of the SU-8. This finding enhances our understanding of the cross-linking process in SU-8 and paves the way to further enhance the properties of the SU-8 polymer for various electronics and optoelectronics applications.
... The latter is more desirable for integrated photonics due to improved performances, such as high compactness and low signal cross-talk. 51,[85][86][87]95 In this sense, nanocomposites by doping CQDs into photoresist or e-beam resist, such as SU-8, 45,87,142 PMMA, 95,142,143 and HSQ, 144 are of great advantage as compared to CQD solids, which, up to now, still lack high-quality fabrication methods without material damage. 145 Note that, due to the employment of special solvents and additives, commercially available resists maybe a poor solvent for CQDs, and one of the possibilities is to use the ligand exchange method to enhance their solubility. ...
... The latter is more desirable for integrated photonics due to improved performances, such as high compactness and low signal cross-talk. 51,[85][86][87]95 In this sense, nanocomposites by doping CQDs into photoresist or e-beam resist, such as SU-8, 45,87,142 PMMA, 95,142,143 and HSQ, 144 are of great advantage as compared to CQD solids, which, up to now, still lack high-quality fabrication methods without material damage. 145 Note that, due to the employment of special solvents and additives, commercially available resists maybe a poor solvent for CQDs, and one of the possibilities is to use the ligand exchange method to enhance their solubility. ...
... 45 However, to keep the intrinsic properties of the resists, the loading density of CQDs must be maintained at a low level, which inevitably leads to low equivalent refractive indexes for the nanocomposite stripe waveguides (e.g., n eq = 1.51 by doping CQDs in SU-8 45 and n eq = 1.49 by doping CQDs in PMMA 95 ). As a result, low-index substrates are needed, and the lateral sizes of the stripe waveguides are usually designed to be big enough (e.g., 4 Â 2.5 mm 2 for CQDdoped SU-8 waveguides 45 and 2.5 Â 3.5 mm 2 for CQD-doped PMMA waveguides 142 ) in order to achieve an effective mode confinement. Besides, due to the large cross-sections of the stripe waveguides, higher-order waveguide modes, such as the fundamental transverse magnetic mode (TM, electric field perpendicular to the substrate), can also be supported. ...
Colloidal quantum dots (CQDs), semiconductor nanocrystals capped with surfactant ligands and dispersed in solution, have provided a powerful platform for the achievement of numerous classes of solution-processed photonic and optoelectronic devices over recent years. They exhibit a plethora of outstanding properties, such as cost-effective synthesis, wide size-tunable emission (or absorption), large-scale solution-processable fabrication, and impressive photostability. Based on these properties achieved by novel material and structure engineering, these CQD-based photonic and optoelectronic devices are appealing alternatives to costly semiconductor products. Furthermore, a combination of these devices enables the construction of CQD-based nanophotonic circuits, which are generally composed of various components for light generation, guiding, manipulation, and detection in a single chip. In this review, we firstly summarize optical properties of CQDs, and then CQD-based passive and active nanophotonic devices, and nanophotonic circuits are also introduced and discussed. Lastly, further developments and challenges of CQD-based nanophotonic devices and circuits are outlined.
... Although QDs are well dissolved and suspended in chloroform solutions showing good photoluminescence (PL) properties, the liquid QD solutions are impractical for fabrication of solid shape photonic and optoelectronic devices [18]. Without wrapped in a non-toxic polymer, QDs cannot be used for most biomedical applications [19], due to their toxicity. ...
... The use of PMMA is however not desirable due to limitation of Ebeam lithography which can only typically produce 2D geometry. UV lithography fabrication is more preferred because in general it can provide less rough surface and higher quality optical devices than Ebeam fabrication on PMMA material [18]. Besides, UV curable materials can be used to produce various 3D device structures including complex microelectromechanical systems [24]. ...
We present for the first-time light emitting ultraviolet (UV) curable active PbS quantum dots-polymer composite optical waveguides fabricated by vacuum assisted microfluidic (VAM) soft lithography technique. PbS quantum dots were synthesized by colloidal chemistry methods with tunable sizes resulting in light emissions in near infrared wavelengths. UV curable polymer of selective refractive index were synthesized facilitating waveguide mode confinement and good PbS quantum dots solubility. Photoluminescence of the composite exhibited ∼30 times better brightness than PbS-SU-8 composites. Light emitting multi-mode waveguides of about 50×42μm cross-sectional dimension were successful demonstrated. Light emitting single-mode waveguides were fabricated by VAM technique with sectional flow tapers.
... However, such synthesis methods not always allow one to achieve a high nanoparticles concentration, which is often required in the creation of thin-film optical composites. To attain this aim, joint synthesis of nanoparticles and their matrix or modification of grown nanoparticles with surfactant molecules for compatibility with their matrix is used [7,8]. ...
Colloidal solutions (~0.3 mol/L) of CdSe nanoparticles in xylene have been synthesized by the electrochemical method from an acid electrolyte based on HNO3 + HCl (2:1) mixture using extraction into xylene. It has been found that CdSe nanoparticles of small size (2–5 nm) synthesized on the cathode are readily extractable in xylene, whereas nanoparticles of larger size (20–100 nm) remain in the aqueous electrolyte and dissolve in the nitric–hydrochloric acids mixture. An X-ray phase analysis of powders of 2–5 nm CdSe nanoparticles showed them have a mixed cubic/hexagonal crystal structure. It has been found from measurements of absorption and photoluminescence spectra that the CdSe nanoparticles of this structure have a broad photoluminescence band (λmax = 500 nm) at a narrow absorption peak (λmax = 420 nm), which may be due to stacking fault formation in nanoparticles of mixed cubic/hexagonal structure. Using this electrolyte with a xylene surface layer under continuous electrolysis conditions and extraction of 2–5 nm CdSe nanoparticles with a content of up to 0.05 g in 1 cm3 xylene (~0.3 mol/L) was obtained. Such colloidal solution can be used to obtain optical nanocomposites by incorporation CdSe nanoparticles into a liquid–crystalline cadmium caprylate matrix. The spectral characteristics such of composites have been studied by adsorption spectroscopy and fluorescence.
... However, their technological processing is restricted, and hence, their application in integrated optics is limited. To overcome this issue, the incorporation of colloidal QDs in polymers is found to be a more suitable approach [5], [8]. ...
In this paper, active nanocomposite waveguides based on the dispersion of CdS, CdTe, and CdSe colloidal quantum dots (QDs) in PMMA are proposed. Their propagation properties are studied as a function of the concentration of nanoparticles in the polymer using the variable length stripe method. When the three nanostructures are dispersed in the same film, the structure is able to waveguide the three basic colors: red (CdSe), green (CdTe), and blue (CdS), it being possible to engineer any waveguided color by an appropriate choice of the filling factor of each QD in the PMMA matrix. For this purpose, it is important to take into account reabsorption effects and the Förster energy transfer between the different QDs families. As a final application, white waveguided light at the output of the structure is demonstrated. This energy transfer can be also the origin of the surprising observation that initial gain (losses) are much higher (smaller) in these active multinanopaticle waveguides than in single-loaded ones.
... Beside their luminescent properties 7 (excitation /emission spectra, phosphorescent decay time) a very important characteristic, is the long term stability in various environmental conditions 8,9 . In the case of the above mentioned compounds the phosphorescence phenomenon is possible only in crystalline phase so, preserving their structural characteristics is essential for any practical approach including the above mentioned applications. ...
Solar energy-powered solutions for various applications, including utilitarian and emergency lightning, could have a significant contribution in decreasing the human impact on the environment. Besides the solar energy conversion in electrical or thermal energy, a possible way for solar energy conversion and storage is the development of new phosphorescent compounds able to provide long-term phosphorescence with reasonable delivered light intensity. These phosphorescent compounds could be used in various applications like highway traffic lights, signs, emergency guidance in buildings in case of power failures, etc. Given the targeted applications, the phosphorescent compounds should meet some specific characteristics, among them the most important are: longterm, constant behaviour in harsh environmental conditions, more than 5 h phosphorescence decay time, constant luminescence over a long period of time and low production costs. In this paper a new developed phosphorescent composite will be presented, based on poly-ethyleneterephthalate (PET) as polymer matrix and copper-doped zinc sulphide nanocrystals as luminescent compound. The described preparation method could stay on the basis of a scaled up procedure for large quantities production and the composite characteristics should recommend it for the above-mentioned applications.
... These fundamental approaches can be easily combined to attain multi-color patterns from only one batch of QDs. The methods presented here are also compatible with other micro-fabrication technologies of QDs embossed emission patterns, such as stamp mold [19, 20], e-beam lithography [21, 22] and flow coating [23]. The combination of PA, LSPR and annealing undoubtedly provides an effective way of precisely tuning the colors of light-emitting materials and devices that use colloidal CdSe QDs.Figure 8 shows perspectives on the potential applications of the combined methods. ...
Localized surface plasmon resonance (LSPR) and photoactivation (PA) effects are combined for the tuning of fluorescent colors of colloidal CdSe quantum dots (QDs). It is found that LSPR with QD emitters intensely enhances surface state emission, accompanied by a remarkable red-shift of fluorescent colors, while PA treatment with colloidal QDs leads to a distinct enhancement of band-edge emission, accompanied by a peak blue-shift. Furthermore, the LSPR effect on QD emitters can be continuously tuned by the PA process. The combination of the post-synthetic approaches allows feasible realization of multi-color patterns from one batch of QDs and the approaches can also be compatible with other micro-fabrication technologies of QD embossed fluorescent patterns, which undoubtedly provides a way of precisely tuning the colors of light-emitting materials and devices that use colloidal QDs.
... The polymerization was then continued to obtain polymer-QD composites. With this method, CdSe/ZnS and PbSe QDs were incorporated into electron beam sensitive PMMA [181] and photonic structures with embedded QDs were fabricated by using e-beam and UV light sensitive resists [182]. ...
Quantum dots (QDs) are nanocrystals made of semiconductors, which exhibit intriguing electronic transitions that resemble single atom behavior. Due to their unique, size-tunable optical and electronic properties, QDs are increasingly applied in biology, bioanalytics and optoelectronics. Many of these applications require a combination of the QDs with polymers. The development of methods to obtain well-defined polymer–QD hybrid materials with tunable optical properties is an active field of research. In this review we first describe progress in the synthesis and fabrication of polymer–QD hybrid materials of various architectures. In particular, embedding methods of semiconductor nanocrystals into bulk polymers, polymer thin films, micro- and nanospheres are presented. Direct surface modification of the nanocrystals with polymers using a number of strategies ranging from multivalent surface passivation to functionalized chain-end attachment, as well as layer-by-layer assembly are also reviewed. Finally, we provide examples for applications of QD/polymer materials in the fields of biodiagnostics, bioanalytics, photonics and optoelectronics.
... Recently there have been several attempts to achieve this goal by embedding QDs in variety of photonic structures and hosts123456789101112131415. A significant challenge here is the incorporation of QDs into transparent host matrices without affecting their optical properties161718. In addition, it is also desirable to achieve monodispersity, high fill factor and efficient charge injection. ...
... The passive structures such as waveguides, resonators and couplers are fabricated in silicon and thus permit smaller footprint devices. The active medium for emission, amplification and detection is colloidal QD composite consisting of QDs in a polymer host matrix161718. Currently we are working on efficient passive to active couplers. In a different version of the vertically integrated devices, the passive structures are made using polymer – SU8, a negative photoresist. ...
We discuss our work on light emitters and photonic circuits realized using colloidal quantum dot composites. Specifically we will report our recent work on flexible microcavity laser, microdisk emitters and integrated active – passive waveguides. The entire microcavity laser structure was realized using spin coating and consisted of an all-polymer distributed Bragg reflector with a poly-vinyl carbazole cavity layer embedded with InGaP/ZnS colloidal quantum dots. These microcavities can be peeled off the substrate yielding a flexible structure that can conform to any shape and whose emission spectra can be mechanically tuned. The microdisk emitters and the integrated waveguide structures were realized using soft lithography and photo-lithography, respectively and were fabricated using a composite consisting of quantum dots embedded in SU8 matrix. Finally, we will discuss the effect of the host matrix on the optical properties of the quantum dots using results of steady-state and time-resolved luminescence measurements. In addition to their specific functionalities, these novel device demonstrations and their development present a low cost alternative to the traditional photonic device fabrication techniques.
... Polymers are attractive candidates to be blended with NCs for such applications as they are easily processable materials and are readily transparent in the near UV and visible region provided they do not quench the NC luminescence and keep them in a uniform distribution. Surface modification can be applied to make the NCs compatible with most relevant organic materials [5], but poly(methyl methacrylate) (PMMA) was first reported as a matrix for as-received NCs [6]. Spectral shifting in the photoluminescence was a major drawback in the latter case which has subsequently been addressed using a pre-polymerized polymer [7,8]. ...
We report on the integration of monodisperse semiconductor nanocrystal (NC) color converters onto gallium nitride ultraviolet micro-pixelated light-emitting diodes ('micro-LEDs'). Integration is achieved in a 'self-aligned' process by forming a nanocomposite of the respective NCs in a photocurable epoxy polymer. Blue, green, yellow and red NC/epoxy blend microstructures have been successfully integrated onto micro-pixelated LEDs by this technique and utilised for color conversion, resulting in a five color emission single chip. Optical output power density of up to about 166 mW/cm2 is measured; spectral emission at 609 nm gives an estimated optical-to-optical conversion as high as 18.2% at 30 mA driving current.
