This review covers the recent progress made in the nanophotonic devices-based daytime passive radiative coolers. The radiative cooling capabilities along with the structural description of various natural species are discussed. The design principle along with key characteristics of the omnidirectional solar reflectors as well as thermal adiators is discussed in detail. Several analogues planner one-dimensional and two-dimensional photonic nanostructures and their current state-of-the-art techniques have been discussed. For each kind of the photonic structure, the novelty, measurement principle, and their respective daytime radiative cooling capability are presented. The reported works and the corresponding results predict the possibility to realize an efficient and commercially viable radiator for passive radiative cooling applications.

A quasicontinuously wavelength tuned self-injection locked blue laser diode system employing a prism is presented. A rigorous analysis of the injection ratio (IR) in the form of three systems, namely high (HRS, ∼  −  0.7  dB IR), medium (MRS, ∼  −  1.5  dB IR), and low (LRS, ∼  −  3.0  dB IR) reflection systems, showed a direct relationship with the wavelength tunability whereas the usable system power exhibited an inverse correlation. In particular, MRS configuration demonstrated a concurrent optimization of tuning window and system power, thus emerging as a highly attractive candidate for practical realization. Moreover, a comprehensive investigation on two distinct MRS configurations employing different commercially available InGaN/GaN blue lasers, i.e., MRS-1 and MRS-2, displayed a wavelength tunability (system power) of ∼8.2  nm (∼7.6  mW) and ∼6.3  nm (∼11.6  mW), respectively, at a low injection current of 130 mA. In addition, both MRS configurations maintained high-performance characteristic with corresponding average optical linewidths of ∼80 and ∼58  pm and a side-mode-suppression-ratio of ≥12  dB. Lastly, a thorough stability analysis of HRS and MRS configurations, which are more prone to system instabilities due to elevated IRs, is performed at critical operation conditions of a high injection current of ≥260  mA and a temperature of 40°C, showing an extended stable performance of over 120 min, thus further substantiating the promising features of the prism-based systems for practical applications.

The issues faced by CMOS technology in the nanoregime have led to research for other possible technologies that can operate with the same functionalities but with higher speed and lower power dissipation. One such technology is quantum-dot cellular automata (QCA). A 3  ×  3 reversible universal and multifunctional gate is presented that is reversible, universal, and multifunctional in nature. The gate is then used as a building block to design an ultra-efficient 1-bit full adder and 1-bit full subtractor in QCA. Based on the performance analysis, it is concluded that the proposed designs are efficient in respect to cell count, area, delay, and quantum cost and achieve performance improvements over existing designs in the literature. Hence, the proposed designs can be efficiently utilized in various digital logics requiring minimal area and ultra-low-power consumption such as central processing units, microcontrollers, etc.

We theoretically investigate the enhancement of the evanescent waves near the surface of a prism coated with several layers of metals, graphene, and double negative materials. The thicknesses of the metals and double negative material films along with the number of graphene layers are optimized to achieve the highest enhancement factor. We show that the intensity of the evanescent wave in the proposed resonance structure is about 10⁹ times higher than that of a bare prism. A comparison between our results and those reported in the literature indicates a 10⁴ times amplification of the evanescent field intensities. This amplification can open a new window to manipulate attached biological cells, design perfect atom mirrors, and apply an effective force on nano- and microparticles for the purpose of manipulation and trapping. The effect of the optimization of the involved parameters on the results shows the importance of these theoretical and simulation results, which leads to the reduction in time and costs of experimental works.

Tumor necrosis factor-alpha (TNF-α) is a signaling protein of inflammatory processes. TNF-α overexpression triggers inflammatory processes related to various diseases such as rheumatoid arthritis, Crohn’s disease, Chagas, and others. For this reason, the TNF-α has been used as an important biological biomarker for prognosis, understanding, and disease treatment. Surface plasmon resonance (SPR)-based biosensors are a good alternative for TNF-α detection because they are more sensitive than other techniques and have the ability to be developed miniaturized systems. Then we developed a nanohole array on gold nanofilm-based SPR biosensor for TNF-α detection. A biological biorecognition system (cysteamine/biotin/streptavidin/TNF-α antibody) was formed and TNF-α antigen was detected by transmitted light intensity monitoring. TNF-α antigen at 17  pg mL^−  1 was detected from fungus Paracoccidioides brasiliensis-infected rat blood serum. This concentration is far below those found in similar studies in the literature. This plasmonic device opens new opportunities for TNF-α detection.

A terahertz graphene tunable absorber consisting of monolayer graphene on a dielectric grating and a substrate separated by a waveguide layer is designed and investigated. The absorber exhibits polarization-independent absorption enhancement at resonance for fully conical light incidence, which is attributed to the simultaneous excitation of two identical guided modes in the waveguide layer. Moreover, the absorber possesses an ultranarrow absorption profile with an ultrahigh quality factor. To intuitively confirm the potential physical mechanism of such phenomena, the electromagnetic field distributions for both polarized light are described. Finally, the influences of Fermi level and relaxation time on the absorption properties are investigated, which present the flexible tunability of the proposed device. It is believed that the conclusions will enable the development of optoelectronic devices by simply combining graphene with a guided-mode resonance structure.

We report energy transfer (ET) from two dyes: Alexa Fluor 514 (AF514) and Alexa Fluor 532 (AF532) to gold nanoparticles (AuNPs) of three different sizes (10, 30, and 53 nm) employing steady-state and time-resolved fluorescence measurements. The results show that the fluorescence intensity and fluorescence lifetimes of donor (D) molecules AF514 and AF532 decrease with increase in the concentration of acceptor (A) AuNPs (2 to 10  μM) upon interaction with AuNPs, thereby confirming the occurrence of ET between D and A. This clearly suggests that these two Alexa Fluor molecules act as efficient donors and AuNPs as excellent acceptors. Interestingly, the Forster distance (R_o) determined for these dyes varies from 212 to 550 Å with increasing size of AuNPs and suggests that the ET from AF514 and AF532 to AuNPs is essentially obeying surface energy transfer (SET) process following 1  /  d⁴ distance dependence. As is well known, Forster resonance energy transfer is efficient for separation distances of up to 100 Å, beyond which its efficiency decreases. Thus, the present results follow dipole-surface type ET from molecule dipole (AF514 and AF532) to nanometal (Au) surface. The influence of size and distance on the SET from AF514 and AF532 to AuNPs is discussed. Further, the quenching of donor fluorescence in the presence of AuNPs and nonradiative ET are analyzed using Stern–Volmer plots. Our study is an experimental quest to explore the potential of such dye–noble metal NPs pairs performing as sensitive chemical and biosensors.

We study the near-infrared properties of spherical multishell nanoparticles comprising a loss-less dielectric core enclosed by a concentric layering of metallic–dielectric–metallic nanoshells. The coupling between the metallic shells induces plasmon resonance redshifts and peak splitting in the absorption spectra of the layered particle relative those of the metallic constituents. We use full-wave electromagnetic analysis to investigate changes in the absorption spectra as a function of key parameters including the material properties of the inner and outer metallic shells and the aspect ratio of their inner and outer radii. We systematically vary the aspect ratios and quantify the degree of plasmonic coupling between the metallic nanoshells. Our analysis reveals conditions under which the spectral resonance peaks blueshift and/or redshift. We consider bimetallic particles with gold and silver nanoshells and determine the dependency of plasmon resonance peak shifting and splitting as a function of the order of these material layers, i.e., as inner or outer shells.

A metallic microcones array-based plasmonic strcture is presented as an example for the purpose of experimentally exploring the dependence of ambient temperature and incident angle on resonance and absorption properties. The microcones array is fabricated using the technique of heavy ion tracking. The technique has advantages of large-area patterning, high-aspect ratio of unit dimension, controllable length, and multichoice of materials. Fabrication steps, mathematical fitting, and experimental measurements of optical absorption spectra are presented. To analyze the experimental data regarding thetemperature-dependence effect, a theoretical formula, a quasi-Gauss model, is applied to describe the relationship between temperature (T) and plasmonic wavelength (λ_SP). Our experimental results demonstrate that the variation of temperature and incident angle strongly affect the sensitivity of λ_SP and its absorption properties. Our experimental results indicate that this structure is capbale of acting as an optical sensor for detection of temperature and angular denpendence.

In the framework of effective mass envelope function approximation, the impurity states are calculated in InGaAsP/InP core–shell quantum dots by plane wave expansion method, and the effect of electric field is considered. The impurity binding energies in 1s and 2p  ±   states, and the impurity transition energy between 1s state and 2p  ±   state are calculated and analyzed in detail with the change of shell thickness, core radius, impurity position, and electric field strength. The results show that the impurity states in the core are stable when the shell thickness is more than 0.4a^*. The binding energies and transition energies decrease with the increase of core radius. The applied electric field destroys the symmetrical distribution of binding energy and transition energy about the core center. The increase or decrease of the binding energy and transition energy depend upon the position of impurity and the direction of electric field.

We design and numerically investigate an all-dielectric metasurface, constructed of four open resonant rings described by the group C_s and located with a cross-shaped resonator between them, that realizes double toroidal switching, in which switching from a toroidal dipole to a quadrupole response occurs in two separate frequency regimes. It is shown that the toroidal dipole can be dynamically switched on, whereas the pronounced toroidal quadrupole can be switched off simultaneously at orthogonal orientations from same metasurface, and vice versa, through changing the polarization of the incident light. The maximum value of modulation depth for the toroidal dipole and quadrupole responses reached 76% and 83%, respectively. Active switching of a toroidal dipole into a quadrupole has potential applications in designing efficient filters and modulators.

Quantum-dot cellular automata (QCA) is a potential upcoming nanotechnology for designing digital circuits with high performance. A subtractor is an important arithmetic circuit used in many digital circuits. An efficient multilayer full subtractor design is proposed using majority logic in QCA. The proposed design has only 53 cells and occupies a small area of about 0.03  μm². Using the proposed subtractor, a 4-bit ripple borrow subtractor with 256 cells and an area of about 0.20  μm² is realized. Verification and simulation are done using QCADesigner. Defect analysis is also done for the proposed subtractor. Energy dissipation of the proposed designs is done using QCADesignerE tool.

A simple, low-cost, and ecofriendly method of obtaining silver nanoparticles was obtained from AgNO₃ in dilution for the first time with a habanero pepper infusion. Two sets of experiments were carried out. The samples obtained in the first experiment were analyzed by SEM and TEM. Results showed that the samples prepared using 0.001 M and 0.005 M of AgNO₃ and particles with an average size of 19.3 and 26.4 nm were obtained. Furthermore, the nanoparticles prepared with 0.005 M showed an absorption peak shifted toward a larger wavelength, and according to its distribution, it also exhibited larger particle sizes. In the second experiment, different concentrations of habanero pepper (10, 50, and 100 mL) were explored and the pH and oxidation reduction potential were monitored. The sample with 100 mL concentration showed the most intense absorption peak and the highest decrease in pH, which is explained by biomolecules deprotonation.

A compact and broadband transverse electric (TE)-pass power splitter using triple-guide directional couplers (TGDCs) is proposed and analyzed in detail, where the TGDCs are formed by two outside subwavelength grating (SWG) waveguides and a central strip waveguide with segmented hybrid plasmonic waveguides (HPWs) on its top. For input transverse magnetic (TM) mode, it is transmitted along the central strip waveguide, gradually transferred from the strip waveguide into the horizontal slots formed by strip waveguide and HPWs, and finally radiated into the claddings since the HPWs are segmented. As to the TE mode, by choosing suitable structural parameters, phase-matching condition is only satisfied for TE mode so that it is evenly coupled from the central waveguide into the outside SWG waveguides, effectively preventing the coupling of the residual TM mode in the TGDC. Consequently, a TE-pass power splitter is realized. Moreover, efficient transitions between the SWG and strip waveguides are used at the end of the outside SWG waveguides. Results show that, with the number of the segments of the HPWs being 6, a compact device of ∼9  μm in length is achieved with an insertion loss (IL) of 0.56 dB (TE), an extinction ratio (ER) of 23.74 dB, and a reflection loss of −30.6  dB (−4.94  dB) for TE (TM) mode at 1.55  μm. Also, the bandwidth is up to 150 nm when ER  >  15  dB and IL  <  0.9  dB. In addition, fabrication tolerances to the key structural parameters are investigated and field evolution through the present device is also presented.

Due to the dire need to monitor, sense, and control useful and harmful chemicals for industrial, environmental, and biomedical purposes, chemical sensing has become an eminent topic among researchers. Hence, we focus mainly on a modified kagome design with a relatively high sensitivity of 99.8%, effective material loss of 0.000263  cm^−  1 for constant absorption loss, and 0.0004204  cm^−  1 for variable absorption loss and low confinement loss of 2.117  ×  10^−  17  cm^−  1 investigated with the help of the full vector finite element method in Comsol multiphysics using water, ethanol, and benzene as analytes while considering other parameters, such as nonlinearity, dispersion, numerical aperture, and effective area which are equally investigated and discussed. The results obtained are tabulated and compared with recent works published.

Photocatalysis is a new advanced oxidation process based on the irradiation of semiconductors such as TiO₂ and ZnO for photodegradation of contaminants. In this process, the semiconductor absorbs the photon energy of ultraviolet radiation, generating highly reactive species for the degradation of organic compounds. It has been reported that doping of transition metals (e.g., Cu, Ni, Co, and Mn) into the structure of oxide semiconductors can reduce the band gap and expand their adsorption properties to the visible solar spectrum. Accordingly, a new hybrid photocatalyst of Mn-doped TiO₂  /  ZnO with an Mn content of 1 to 5 wt. % was synthesized via the sol–gel process followed by thermal calcinations in air at 500°C. The prepared photocatalyst powder was characterized in terms of crystalline structure, thermal property, surface morphology, and band gap energy level. Its photocatalytic performance was then assessed based on photodegradation of methylene orange under visible light irradiation. Compared with the pure TiO₂  /  ZnO, the lattice of Mn-doped TiO₂  /  ZnO was found to be more thermally stable, and thus phase transformation of anatase to rutile was postponed to a higher calcination temperature. The photocatalysis evaluation showed an increased activity of Mn–ZnO  /  TiO₂ compared with pure TiO₂ and TiO₂  /  ZnO under visible light irradiation. Accordingly, the highest degradation of 98% was obtained by the Mn–ZnO  /  TiO₂ with 3 wt. % Mn.

We propose the use of metal nanoparticles (NPs) [(silver (Ag)] embedded heterogeneous composite material made of titanium dioxide (TiO₂) for antireflection coating (ARC) while partially blocking the transmission of near-ultraviolet (UV) radiation across the thin-film arrangement. The proposed structure consists of two layers of porous TiO₂ thin film of specific thickness and volume fraction to attain antireflection property with Ag NPs embedded in the upper layer to optimize the UV blocking potentiality within the range of 320 to 400 nm. The calculations indicate that 10-nm Ag NPs with volume fraction of 0.01 and film thickness (51-nm top layer and 102-nm bottom layer) give the best results for blocking of near-UV radiation. Decreasing the aspect ratio of the prolate nanospheriod gives better UV blocking intensity.