Wide Optical Band Gap Research Articles

Linear and nonlinear optical investigation of l-arginium adipate single crystal for photonic applications

The l-arginium adipate (LAA) single crystal, is an organic component material efficiently grown by a simple technique called slow evaporation solution technique at ambient temperature. The monoclinic crystal system with the space group of P21 is exhibited for LAA from the X-ray diffraction analysis. FTIR spectroscopy that designates different molecular vibrations existing in LAA crystal was studied. The absorbance spectrum from the UV profile proclaims very less cut-off wavelength down to 206 nm and its wide optical band gap is also calculated. The perfection of the crystal is shown from Urbach's energy determination. The extent of polarization phenomena was examined for selected temperatures at dissimilar frequencies from the dielectric studies. The double harmonic output and triple-order nonlinear response for LAA are inspected from Kurtz-Perry and Z-scan technique, respectively.

Influence of most reactive inorganic cation in the optical and biological activities of L-Lysine monohydrochloride crystal.

Slow evaporation method was used to grow the pure and K+ ion doped L-Lysine monohydrochloride (L-LMHCL) crystals which has optical and antibiotic applications. The space group, structure and slight shifting of peaks are confirmed using single crystal XRD and the powder XRD. The FTIR analysis also shows that the K+ doped L-LMHCL has a slight shifting in the spectrum which indicates the functional group of L-LMHCL and the interaction between the K+ ions. The existence of K+ ion in the doped crystal is assured by the presence of potassium in the EDAX spectrum. The wide optical band gap was found for pure and K+ doped crystal using UV spectra and these are utilized in optoelectronic and nonlinear applications. The Kurtz Perry technique specified the NLO property of grown crystals. The dielectric property crystals was studied by varying the temperature. As a result, the highest dielectric constant is observed in doped crystal. An antibacterial activity against certain bacteria like E-coli, pseudomonas aeruginosa and staphylococcus aureus are provided by mm range for the grown crystals.

Preparation, photoluminescence and semiconductive band gap of a gadolinium compound

A new compound [Gd(H2O)4(HIA)2(NO3)](2NO3) (1; HIA is isonicotinic acid) is reported. The Gd3+ cation is coordinated by eight oxygen atoms and exhibit a square antiprismatic GdO8 geometry. A three-dimensional (3-D) supramolecular framework is formed by hydrogen bond interactions. The photoluminescence absorption peak is ascribed to the 8S7/2→6I J , while the photoluminescence emission peaks are originated from the characteristic emission of the 6P5/2→8S7/2 and 6P7/2→8S7/2 transitions of Gd3+ ions. A solid-state UV/Vis diffuse reflectance spectrum reveals that it shows a wide optical band gap of 3.17 eV. A new gadolinium compound is reported. It features a 3-D supramolecular framework formed by hydrogen bond interactions. The photoluminescence absorption peak is ascribed to the 8S7/2→6I J , while the emission is originated from the characteristic emission of the 6P5/2→8S7/2 and 6P7/2→8S7/2 transitions of the Gd3+ ion. It possesses a wide optical band gap of 3.17 eV.

A Simulation Model for Narrow Band Gap Ferroelectric Materials

AbstractVarious ferroelectric simulation models have been developed in recent decades in order to study the mechanisms and predict the behaviors of ferroelectrics by simulating their hysteresis loops. Conventional ferroelectrics have wide optical band gaps (>2.7 eV), making them difficult to respond to visible light. Although their ferroelectricity can be affected by higher‐energy radiation like ultraviolet, little attention is paid to the development of their models incorporating light‐dependent factors. However, in recent years, narrow band gap (<2.5 eV) ferroelectrics have been discovered and are increasingly researched. These special ferroelectrics effectively absorb visible light and hence exhibit strongly light‐dependent ferroelectricity, triggering potentially a broad range of applications. Therefore, there is a need to develop a model for these ferroelectrics in order to predict their behavior under visible light. Such a model is also needed to improve the understanding of the interaction mechanisms between light and domains. In this paper, a ferroelectric simulation model based on the Jiles–Atherton theory considering light dependence is developed for the first time, and its accuracy is validated by experiments. The model shows an average error of 7.5% on polarization values compared to experimental results and thus can be employed to reliably predict photo‐induced ferroelectricity.

Hydrothermal Preparation, Crystal Structure, Photoluminescence and UV-Visible Diffuse Reflectance Spectroscopic Properties of a Novel Mononuclear Zinc Complex

A novel mononuclear zinc complex [ZnL(Phen)(H2O)]·H2O containing the mixed ligands of Phen (Phen = 1,10-phenanthroline) and 3-hydroxy-2-methylquinoline-4-carboxylic acid (HL) was prepared by hydrothermal synthesis and its crystal structure was characterized by X-ray single-crystal diffraction method. The title complex crystallizes in the orthorhombic systems and forms monomeric units. The molecules in the title complex are connected through the interactions of hydrogen-bonding and ????? interactions to give a three-dimensional (3D) supramolecular structure. The fluorescence result discovers a wide emission band in the violet blue region. Time-dependent density functional theory (TDDFT) calculations reveal that this emission can be attributed to ligand-to-ligand charge transfer (LLCT). Solid-state diffuse reflectance shows there is a wide optical band gap.

Optimized optical band gap energy and Urbach tail of Cr2S3 thin films by Sn incorporation for optoelectronic applications

In this study, the Cr2S3-based thin films were successfully prepared by a simple chemical spray pyrolysis method. The effect of Sn2+ incorporation at different contents (0 ≤ Sn2+ ≤ 0.25 mol) on the microstructural, optical, and optoelectrical properties of the thin films was investigated. The formation of high purity Cr2S3 and Sn-doped Cr2S3 thin films with a rhombohedral crystalline phase was confirmed by the grazing incident X-ray diffraction results and energy dispersive X-ray analysis. The surface morphology of thin films was observed using field emission scanning electron microscopy. The optical band gap energy and width of the Urbach tail were evaluated as a function of Sn2+ doping from the optical absorption coefficient of the samples. By increasing the Sn2+ content, a considerable narrowing of about 0.50 eV was observed in the optical band gap energy; while the Urbach energy was found to gradually increase up to 0.992 eV for the sample containing a high-content of Sn2+. A linear relationship between the optical band gap and Urbach energies was also proposed. Finally, the effect of optically changes on the photosensing performance and time-response switching of the pure Cr2S3 and Sn-doped Cr2S3 thin films was studied for the first time, in which the photosensitivity of the samples enhanced over 25 times, as the content of Sn2+ increased into the Cr2S3 host structure.

A brief study on structural, optical, and photovoltaic properties of lithium sulfate monohydrate single crystals

In the current study, single crystals of lithium sulfate monohydrate (LSMH) were grown by slow evaporation method. For structural analysis, these crystals were characterized by X-Ray diffraction, the optical properties were studied by UV–Vis–NIR and photoluminescence spectroscopy, and vibrational studies were studied by Fourier Transform Infrared spectroscopy. The XRD analysis reveals that this understudy crystal belongs to monoclinic system with P21/a space group. The FT-IR data indicate various functional groups associated with the established crystal structure of the crystal. From the optical absorption studies of these crystals, various parameters, such as optical band gap, disorder coefficient, disorder energy, nature of transition etc. These grown samples show good optical transmittance with wide optical band gap. This crystal shows PL emission lines in green, orange, and red part of visible spectrum when excited by the ultraviolet photons. Further, a simple diode of this crystal was also developed, and this prepared device was subjected to Current–voltage characterizations in dark and in the presence of various colors of light photons. The present material shows negative photoconductivity. Effect of light on photocapacitance of this prepared device was also studied. The defects or traps in the band structure of this material could be the best reason for this observed behavior. The present material also shows good thermal stability in the considerable range of temperature. A good interrelation among these various studied parameters was observed. The observed optical, electrical, and thermal properties of this crystal project it as a good candidate for modern electronic applications.

Negative dielectric behavior in tetragonal La0.8Co0.2-xEuxTiO3 (x = 0.01–0.04) nanorods

The La0.8Co0.2-xEuxTiO3 (x = 0.01, 0.02, 0.03 & 0.04)/LCET nanorods are synthesized via the hydrothermal technique. The tetragonal phases are detected by the X-ray diffraction (XRD) patterns. In addition, few minor orthorhombic α-Eu2TiO3 phases are noticed. The field emission scanning electron microscope (FESEM) and transmission electron microscope (TEM) pictures show the sequential evolution of nanorods as a function of Eu-content. The x = 0.04 content exhibits the complete formation of nanorods. The wide optical band gap (Eg) of x = 0.01, 0.03 & 0.04 contents is increased from 3.621 to 3.973 eV while the narrow Eg ~ 2.293 eV is observed for x = 0.02 content. Interestingly, the high negative dielectric constant (ɛ′) and dielectric loss (ɛ″) values of −78.68 and − 202.84, respectively, are recorded at 8 MHz frequency, for x = 0.04 content. This kind of metamaterials like behavior can offer the high frequency microwave device applications. Furthermore, the frequency dependency of dielectric constant, dielectric loss, ac-electrical conductivity, dielectric modulus, and impedance parameters is described.

Synthesis, Structure, Photoluminescent, and Semiconductor Properties of a Novel Hg–Pr Complex

A novel Hg-Pr compound [Hg3PrCl9(HIA)(IA)3]nnCl · 2nH3O · 4nH2O (I) (HIA = isonicotinic acid) is prepared through the hydrothermal reactions and structurally characterized by X-ray diffraction technique (CIF file CCDC no. 1831958). This compound is characterized by a 2D organic-inorganic hybrid layer structure. Solid-state photoluminescence measurement reveals that it exhibits a photoluminescence emission in the blue region. These photoluminescence emissions correspond to the characteristic emission 3H4–3PJ transitions (J = 2, 1, and 0, respectively) of Pr3+ ions. Solid-state UV−Vis diffuse reflectance spectrum discovers that the existence of a wide optical band gap of 3.39 eV.

Luminescence and Scintillation Properties of Dy3+ doped Li6Y(BO3)3 crystal

The orthoborate crystals with a wide optical bandgap allow different rare earth ions as an activator (Ce3+, Dy3+, Eu3+, etc.) to provide efficient luminescence. In the present study, Li6Y(BO3)3 pure and 4 mol% Dy3+ doped single crystals have been grown using the Czochralski method. The light emission of the grown crystals has been characterized by using X-ray luminescence, photoluminescence and thermoluminescence measurements. Intrinsic luminescence property has been observed for pure crystal at 330 nm and the characteristic emission of Dy3+ was observed in doped crystal under X-ray excitation. Photoluminescence study of the doped crystal at low temperature has shown the increased peak intensity with the decrease of temperature from 290 to 10 K. Decay time has been measured at the temperature ranging from 290 to 10 K which consists of three components in each stage. Thermally stimulated luminescence of both pure and 4 mol% Dy3+ doped LYBO crystals have been compared at low temperature from 320 K to 10 K. Scintillation β− counts measured from 300 K to 10 K. The performance of the doped crystal has been tested as a scintillator for thermal neutron imaging.

Phase transformation, nanorod-like morphology, wide bandgap, and dielectric properties of 1 − x (Al0.2La0.8TiO3) + x (BaTiO3) (x = 0.2–0.8) nanocomposites

A series of 1 − x (Al0.2La0.8TiO3) + x (BaTiO3) (x = 0.2, 0.4, 0.6, and 0.8)/ALTBT nanocomposites were prepared via the hydrothermal technique at 150 °C/6 h. The phase identification and structural transformation from tetragonal to cubic were confirmed using the X-ray diffraction pattern (XRD). Particularly, the low BaTiO3 contents (x = 0.2 and 0.4) revealed the tetragonal structure, while the high BaTiO3 contents (x = 0.6 and 0.8) showed the predominant cubic phases. Furthermore, the nanorod-like surface morphology was evidenced from the field emission scanning electron microscopy (FESEM) and transmission electron microscopy (TEM). The optical properties ensured the presence of metal oxide (M–O) bonds and wide optical bandgap (Eg ~ 3.975–3.899 eV) values. The frequency dependence of dielectric properties was described as a function of composition. The results expressed that the high dielectric constant (e′) of 260.8 was noticed at 10 kHz for x = 0.8 composite. The dc-electrical conductivity (σdc) and exponent (n) parameters were determined by applying power law fit to the log σac versus log ω plots. The temperature dependence of dielectric constant plots indicated the dielectric transition temperature from 723 to 623 K with the increase of ‘x’.

Deposition of boron-doped nanocrystalline silicon carbide thin films using H2-Ar mixed dilution for the application on thin film solar cells

Hydrogen-argon mixed dilution has been applied for the deposition of boron-doped nanocrystalline silicon carbide (nc-SiCx) thin films. The variations of structural, compositional, electrical and optical properties with the varying H2/Ar ratio are systemically investigated through various characterizations. It is shown that by using H2-Ar mixed dilution for deposition, B-doped nc-SiCx thin film possessing both wide optical band gap (∼2.22 eV) and high conductivity (∼1.9 S cm−1) can be obtained at the H2/Ar flow ratio of 360/140. In addition, the B-doped nc-SiCx thin films are fabricated as the window layers of a-Si thin film solar cells, and the highest conversion efficiency (8.13%) is obtained when applying the window layer with the largest optical band gap energy.

Synthesis, structure and photophysical properties of a new zinc compound

Under hydrothermal conditions, a new zinc compound, [Zn(2,2’-bpy)3]2S·16H2O·2OH (1) (2,2’-bpy = 2,2’-bipyridine) was synthesized and structurally characterized by using a single-crystal X-ray diffraction method. This compound is characteristic of an isolated (0-D) structure. A solid-state photoluminescence experiment revealed that it shows blue emission, in combination with molecular orbital (MO) calculations, lead us to conclude that the emission originates from the ligand-to-metal charge-transfer (LMCT) transition. Complex 1 possesses CIE chromaticity coordinates of (0.0782, 0.1973). A solid-state UV/Vis diffuse reflectance spectrum measurement unveiled that this compound features a wide optical band gap of 2.03 eV.

A wide-bandgap nonplanar small molecule acceptor having indenofluorene core for non-fullerene polymer solar cells

Recently, the nonplanar non-fullerene acceptors (NFAs) are attractive in active layers in highly efficient polymer solar cells (PSCs) because of their up-shifted energy levels, improved absorption as well as charge transportation performances. However, presently nonplanar NFAs always absorb the lights in the long-wavelength region and even to near-infrared (NIR) region, which limits their further utilization in low-bandgap polymer donor-based PSCs. To further probe the performances of nonplanar NFAs in low-bandgap polymer-based PSCs, a new twisted NFA (i-IF-4F) having indenofluorene derivatives as the electron-donating fused-ring core was synthesized. Due to the relatively weak electron-donating ability of the indenofluorene core, this newly designed NFA has wide optical bandgap (1.79 eV) with absorption spectrum ranged from 450 to 690 nm, suitable lowest unoccupied molecular orbital (LUMO, −3.71 eV) and highest occupied molecular orbital (HOMO, −5.55 eV) energy levels, which ensure its matching well with the typically low-bandgap polymer (PTB7-Th) to achieve complementary absorption and proper differences in energy levels. After thermal annealing treatment, the film morphologies, charge transfer properties and charge recombination performances of i-IF-4F:PTB7-Th-based device was improved to a certain degree, leading to an optimized power conversion efficiency (PCE) of 6.47%. The work in this manuscript demonstrates the applicability of wide-bandgap twisted acceptors in PSCs and the possible approach to further improve the performances of wide-bandgap nonplanar acceptors in PSCs.

Effect of Extended π-Conjugation of Central Cores on Photovoltaic Properties of Asymmetric Wide-Bandgap Nonfullerene Acceptors

Tremendous efforts have been dedicated to develop low-bandgap nonfullerene acceptors (NFAs) for organic solar cells (OSCs). In comparison, the NFAs with a wide bandgap (WBG) have received less attention. Here, three novel acceptor–donor–acceptor type WBG NFAs (TPT-T, TPTT-T, and TPTTT-T) have been designed and synthesized with different fused central cores by varying the π-conjugation length and molecular structures, which all exhibit wide optical bandgaps over 1.8 eV. The successive π-conjugation extension of electron-donating central cores (from TPT-T to TPTT-T and to TPTTT-T) induces red-shifted absorption spectra, lower optical bandgap, and enhanced electron mobility simultaneously. As a result, the optimized OSC devices based on TPTTT-T:PBT1-C achieved a power conversion efficiency of 7.42%, which was higher than those of PBT1-C:TPTT-T (6.93%) and PBT1-C:TPT-T (6.11%) based devices. These results indicate that extending the molecular π-conjugation structure is an effective strategy to design efficient NFAs for OSCs.

All-optical fiber modulator with a graphene interlayer

An all-optical fiber modulator with a graphene interlayer is proposed and calculated numerically. Graphene has excellent optical characteristics such as wide optical bandwidth, ultra-fast response and zero band gap, which makes the modulator cover the whole C and S band. Modulation rate is only limited by the inherent carrier relaxation time of graphene. We also deduced the mechanism of all-optical modulator based on graphene theoretically, and established a simple correspondence between the intensity of optical signal and the conductivity of graphene. The theoretical calculation results show that the slot structure can effectively improve the effect of graphene on the electric field distribution. The length of the slot structure is only 1.59 mm and the insertion loss can reach 1dB when modulation depth of 20 dB is achieved. The manufacturing tolerance of the structure is 35.42% of the whole device. The modulator based on a single-mode fiber that can be directly fused to the all-optical network and has broad application prospects.

Vacancy defect modulation in hot-casted NiO film for efficient inverted planar perovskite solar cells

Abstract Nickel oxide (NiOx) has exhibited great potential as an inorganic hole transport layer (HTL) in perovskite solar cells (PSCs) due to its wide optical bandgap and superior stability. In this study, we have modulated the Ni2+ vacancies in NiOx film by controlling deposition temperature in a hot-casting process, resulting the change of coordination structure and charge state of NiOx. Moreover, the change of the HOMO level of NiOx makes it more compatible with perovskite to decrease energy losses and enhance hole carrier injection efficiency. Besides, the defect modulation in the electronic structure of NiOx is beneficial for increasing the electrical conductivity and mobility, which are considered to achieve the balance of charge carrier transport and avoid charge accumulation at the interface between perovskite and HTL effectively. Both experimental analyses and theoretical calculations reveal the increase of nickel vacancy defects change the electronic structure of NiOx by increasing the ratio of Ni3+/Ni2+ and improving the p-type characteristics. Accordingly, an optimal deposition temperature at 120 °C enabled a 36.24% improvement in the power conversion efficiency compared to that deposited at room temperature (25 °C). Therefore, this work provides a facile method to manipulate the electronic structure of NiOx to improve the charge carrier transport and photovoltaic performance of related PSCs.

Defect dipole polarization mechanism in low-dimensional europium substituted Al0.8La0.2TiO3 nanostructures

Abstract Low-dimensional Europium substituted Al0.8La0.2TiO3 (Al0.8EuyLa0.2-yTiO3 (y = 0.01–0.04))/AELTO nanostructures were prepared via hydrothermal method. The X-ray diffraction (XRD) patterns revealed the mixed phase (tetragonal and orthorhombic) structure of AELTO. Furthermore, the surface morphology evidenced the formation of AELTO nanostructures. The wide optical band gap (Eg) was achieved for y = 0.01–0.04 contents and found to be varying from 3.371 to 3.399 eV. The high dielectric constant (e′) values of 2.84 × 108 at 10 kHz and 101608.8 at 1 MHz were obtained for y = 0.02 at room temperature due to defect dipoles. In addition, the high ac-electrical conductivity (σac) of 15.78 S/cm (at 10 kHz) was observed at room temperature. The frequency dependence of dielectric modulus and impedance parameters was elucidated. The reverse arc present in the Cole-Cole plot of y = 0.02 content clearly suggested the presence of defect dipoles in AELTO.

Preparation of SnO Nanoshells with Enhanced Lithium-Storage Properties.

Tin monoxide is a kind of IV-VI metal monoxides that has attracted great deal of attention due to its wide optical band gap and high field effect mobility in the past decade. On the other hand, nanoshell is a unique porous structure. Its curved shell provides a shelter for the hollow core, as well as a much bigger special surface area. We in this study systematically prepared SnO nanoshells through a facile self-assembly method under different annealing conditions. The lithium ion batteries were fabricated immediately based on the as prepared nanoshells. The capacity of as fabricated lithium ion batteries was 559.3 mAhg-1 at rate performance of 0.1 Ag-1 and 497.5 mAhg-1 at 1 Ag-1 in 30th cycle. This work exhibited high application performance of SnO nanoshells. We hope this work will help study similar structure and applications of IV-VI metal monoxides.

Effect of L-asparagine as dopant on the growth and characteristics of ammonium tetroxalate dihydrate single crystal

Abstract Single crystals of L-asparagine doped ammonium tetroxalate dihydrate were grown using slow evaporation solution growth technique with deionized water as a solvent. The shift and intensity of the peaks in the single crystal X-ray diffraction and Fourier transform infrared analyses confirmed the inclusion of L-asparagine in the ammonium tetroxalate dihydrate crystal structure. The optical transmission characteristics viz. optical band gap, optical conductivity, etc., were determined. Thermal studies revealed the occurrence of anomalies at 135.3 °C and 221.7 °C leading to the possibility of phase transitions and thereby, ferroelectric behavior. Vickers microhardness studies enabled determination of various microhardness parameters. Dielectric behavior was analyzed by varying the temperature and frequency. Anomalies were observed at 135 °C and 221 °C suggesting the existence of ferroelectric nature of the compound. Self-defocusing effect was observed. The polarization-electric field hysteresis loops showed a pinched effect due to defects induced by inclusion of dopant. The crystals were characterized by single crystal XRD, FT-IR, DRS, UV-Vis-NIR, Vickers microhardness test as well as thermal and dielectric techniques. In brief, L-asparagine as a dopant in ammonium tetroxalate dihydrate altered various physical properties of the crystals. They were highly transparent in the visible region with a wider optical band gap, softer material than the parent, higher phase transition temperature of 135 °C, negative nonlinearity and self-defocusing ability.