Introductory Chapter: The Fame of Quantum Dots in Space-age Improvements for Multifunctional Application

1. Introduction

The word “‘Quantum dot (QD)” is a precisely trifling structure (ranging between 1 and 10 nm wide), for instance, a semiconductor-made nanocrystal implanted in alternative semiconductor-based materials, in which the electrons or other charge carriers can be confined in all the three dimensions along with reference to the respective electronic physiognomies contingent on its shape and size. Over the past three decades, quantum dots (QDs) had well established in connection with numerous remarkable applications. Amid the supreme contemporary machineries are typically built on their attractive optical and electronic properties and their part in light absorption, emission, conversion, and detection have a massive volume of innovative day-to-day applications, and gratifying ever more controllable and accustomed to the societal nature. In 1981, Alexey I. Ekimov is a Russian solid-state physicist invented the semiconductor nanocrystals well known as quantum dots in glass matrix, while he was working at the Vavilov State Optical Institute [1]. Further, systematic progress in the remarkable science and technology of the QDs was determined in 1985, when Louis E. Burs at Columbia University come up with a relationship between size and a degree of bandgap relies on the semiconductor base nanoparticles which relates a particle of kind in a sphere model approximations to the respective wave function ideologies for the aforesaid bulk semiconductors [2, 3, 4, 5] and the QDs were discovered from the colloidal mixture of semi-conductor nanocrystals [6]. Also, spin qubits in semiconductor quantum dots signify a prominent family of solid-state qubits, which provides greater efforts to build a quantum computer [7].

Murray et al. have efficaciously synthesized the colloidal state CdX (X = S, Se, Te) QDs along with a tunable size of band-edge absorption as well as emissions and it took more than a decade for the preparation of new-fangled QD material [4]. Owing to its outstanding optical and electrochemical physiognomies, the CdX QDs had widely investigated. In the infancy of core-shell QD research, CdSe/ZnS and CdSe/CdS are the utmost exhaustively examined materials [5, 8, 9, 10]. A decade back, increasingly new “core-shell” QDs were synthesized, such as CdSe/ZnSe [11], CdTe/CdS [12], CdSe/ZnS, and CdTe/ZnS [13], and at even multilayer CdTe/CdS/ZnS “core/shell/shell” QDs [14]. By employing zinc stearate as a zinc source, bright luminescent and low toxic, CdSeTe@ZnS-SiO2 QDs would be made with ZnS-like clusters packed into the SiO2 shell through a microwave-assisted process [15]. Hypersensitive type photosensors were prepared with respect to the cesium lead bromide (CsPbBr3) perovskite quantum dots (QDs) with ample amount of higher sensitivity for chemiluminescence based immunoassays [16]. Vastly luminescent all-inorganic cesium lead bromide (CsPbBr3-QDs/CuPc) heterostructures of perovskite natured quantum dots (QDs) had been comprehensively in the usage as a photosensitizer in the known optoelectronic devices, while p-type small-organic-molecule comprised of copper phthalocyanine (CuPc) would greatly use as a photoactive material in solar cells and organic field-effect transistors (OFETs) [17].

In the year 1988, Mark Reed investigated electronic transport via a three-dimensional confined semiconductor quantum well (“quantum dot”). In 2013, the first commercial deliverance of a product employing the quantum dots would be the Sony XBR X900A series of flat panel televisions. In the year 2013, the Kindle Fire HDX is released covering quantum dot technology, and a blue glow bleeding in from the edge of the display. Followed by in the year 2015, the quantum dots would be a featured innovation at the consumer electronics show, projects that, the quantum dots have been flaunted to be the next breakthrough visual technology to enhance the LED TV picture quality. In recent years, the focus is based on the development of effectual and stable lead-free wise perovskite solar cells (PSCs) and also the prospect of reaching 20% power conversion efficiency (PCE) for tin PSCs. These issues concern the enlargement of the cell size and apprehending scalable production in the future [18] (Table 1).

Field	Application with examples
Engineering/Processing	scale-up engineering development: Trap engineering in PbSe quantum dots for photodetectors [19] Wave function engineering—Type—I/II Excitons [20] Large-scale production of quantum dots for energy storage applications [21] Efficient calibration of crosstalk in a quadruple quantum dot array [22]
Photonic devices	Quantum dot—Si photonic integrated circuits [23] High-quality quantum dot laser/waveguide [24] QDs and nano-photonic waveguides [25]
Optoelectronics	Semiconductor quantum dot for photovoltaic applications [26] Quantum dot optoelectronics [27] Quantum dot semiconductor optical amplifiers (QD-SOA) [28] Flexible quantum dot light-emitting diodes [29]
Electronics	Single-electron transistors with quantum dots [30] High-Performance quantum dot thin-Film transistors [31] Integrated circuits (VLSI, hybrid integrated) [32] Single quantum emitter detection with amateur CCD [33]
Electricity (without semiconductors)	Insulating matrices [34] - e.g., for resistors, capacitors Piezoelectric energy harvester [35]
Cryotechnics	Cryogenic-temperature thermodynamically Suppressed and strongly confined quantum dots [36] SQUIDS (superconducting quantum interference devices) [37]
Mechanics	Quantum-dot array with self-aligned electrodes [38] Reversible adhesion via quantum dots [39] Reduction of friction [40]
Magnetics	Quantum-dot cellular automata [41] Multimodal imaging [42]
Sensorics	Data acquisition in antagonistic surroundings and media [43] Telemetry monitoring via PDA [44] Optical and electrochemical (bio)analytical sensors [45]
Chemistry	Drift-diffusion [46] Carbon dots are in contrast to corrosion inhibitors [47] Resistive-based gas sensors [48]
Biomedicine	Biocompatible implant coating [49] Neurological sensors [50]
New materials	Metastable phases/metallic glasses: Mn^2+- doped CdS quantum dots in a silicate glass [51]; Metal-doped PbSe quantum dots in silicate glasses [52]; Low-noise GaAs quantum photonics [53] Ultra-stable carbon quantum dots [54]
(Alternative) Energies	Digital light processing to inkjet 3D printing [55] Quantum Dots as potential electrode materials for Supercapacitors application [56]

Table 1.

Reviews some major state-of-the-art development in technology connected to the applications of quantum dots in a diverse spectrum.

2. Recent automated advancements in quantum dots for multifunctional application

With due diligence to the nano-size regime, quantum dots (QDs) had demonstrated unique physicochemical properties which are prosperous for multifunctional applications. Exclusively, owing to the respective quantum size effect, remarkable optoelectronic properties have been perceived. These substantial growths have not only elevated the systematic practice of QDs but also fortified to formulate numerous hybrid manners of materials to accomplish higher efficacy by eradicating definite inadequacies. Such problems can be overwhelmed by amalgamating QDs with potential applications, including single-electron transistors, solar cells, LEDs, lasers, single-photon sources, quantum computing, second-harmonic generation, cell biology research, medical imaging, microscopy. In addition, the next-Generation QDs can be lingering further into developing technologies, such as (i) quantum dots of very high-quality optical applications, light guide plate (LGP) with QDs, (ii) quantum dot white light-emitting diodes (QD-WLED), (iii) quantum dot-based photodetectors (QDPs), perovskite QDs, (iv) quantum dot solar photovoltaics, (v) biological applications (to study in-vivo & in-vitro observation of subcellular trafficking, drug delivery, and high-resolution cellular imaging), (vi) quantum computers (qubits), and (vii) the future of quantum dots (magnetic quantum dots & graphene quantum dots) owing to the unique physicochemical characteristics. A typical QD color enrichment scheme by including fluorescent QDs into a polycarbonate (PC) LGP, has been also established to broadcast quite homogeneous planar lighting and might be likely for the new-generation backlighting as well as display devices [57]. Outlook on stability of Quantum dots, patterning, and deposition which yield dare of micro-LED displays provide progressive development in the field of QD-based micro-LED displays, exhibiting the optimistic future prospects of the same kind of spelled technology [58]. The device on blue LED exhibited that efficacy levels of various 230 lm/W are achievable using ultra-revolutionized blue LED pumps. By employing liquid injection fabrication, high performance of white LEDs using QD liquids indicates a high potential for future prospects on lighting devices [59]. Perovskite quantum dots (PQDs) have captured an innovative impression that is exploited to improve the photovoltaic performance of numerous kinds of solar cells and summarized some challenges and perspectives concerning of PQDs [60]. The latest innovations in perovskite technology via diverse schemes, such as the amplify its functionality of methodological procedures, surface amendments, and solid QD inks near the device manner engineering for accomplishing sophisticated PV efficiency and enhanced longstanding steadiness [61]. Quantum dots (QDs) make available a multipurpose component to aid the most precise investigative tools and fluoroimmunoassays, dual imaging, multiplexed imaging, therapeutic platforms, real-time in vivo and cellular process imaging, and so on. With the extensive augmented interest in researchers to report these challenges and endure to move forward toward the clinical translation of QDs [62]. The team Krause P et al., have successfully modeled the simulations exposed in what way the quantum dot duos absorb, exchange, and store light energy. Similarly, it is of interest how size and geometry variations of three Ge/Si nanocrystals impact the transfer times and thus the efficacy of laser-driven populations of the said electron-hole pair states paid to a wide range of applications for quantum dots including quantum bits (qubits) [63]. Tajik S, et al., reviewed the applications of carbon-based QDs (GQDs and CQDs) in biological and sensing areas, and then covers sensing features of key neurotransmitters [64]. In conclusion, in recent years, quantum dots play a major role in multifunctional applications to make acquainted with the novel techniques of semiconductor nanocrystals, and advanced devices which favor the outcomes from translational research, a convenient collaboration lined by the research scientists of extreme necessity for the societal benevolent.

3. Conclusion

The endorsement of quantum dots (QDs) has led to swift developments in multifunctional QDs applications over the early few years throughout the world amidst the advanced scientific improvements, though confirmations, moreover, validate that it has been more extensive and extremely significant in the way of innovative examination in contradiction of novel applications for the societal prerequisite. Amongst the major noteworthy progress in diverse fields of QDs the roadmap for next-generation QDs points to the advent of single-electron transistors, single-photon sources, solar cells, μ-LEDs, lasers, quantum computing, second-harmonic generation, microscopy, cell biology research, and medical imaging, etc., highly necessary for the societal benign. However, a probable drawback when utilized in biological applications is the fact that owing to their large physical size, they could not prolix across cellular membranes. Also, the delivery process may essentially be hazardous for the cell and even affect in destroying it. In other cases, a QD may be venomous for the cell and not suitable for any biological application. The dispute on the degradation of quantum dots inside the living organism has to be explored in the near future. Thus, studies on superior QDs hi-tech vicinities might pay way to atoms/molecules that might perchance turn out to be the upcoming policies of multifunctional prospects in the forthcoming outline.

Acknowledgments

All authors contributed toward data analysis, drafting, and revising the paper and agree to be accountable for all aspects of the work.

The authors apologize for inadvertent omission of any pertinent references.

Conflict of interest

The authors declare that there is no conflict of interests regarding the publication of this paper.