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To develop high-performance organic light-emitting organic field-effect transistors (LE-OFETs), a fundamental problem in organic semiconductors is to compromise light luminescent efficiency for high carrier mobility and vice versa. Therefore, LE-OFETs can avoid this problem by separating the light-emission and carrier-transport functions. Here, a bilayer LE-OFET composed of a tetracene crystal as a carrier transporter (bottom crystal) and a 4-(dicyanomethylene)-2-methyl-6-( p-dimethylaminostyryl)-4 H-pyran (DCM1)-doped tetracene crystal as a light emitter (top crystal) was fabricated. Red light-emission color, which is distinct from the green emission color of tetracene, was detected in the top crystal. Light emission from the top layer was prohibited when an insulating thin film was inserted between the two crystals. These observations indicate that excitons are formed in the bottom crystal and transferred to the top crystal, emitting reddish light. Bilayer LE-OFETs have the advantage of providing both high current density and a bright emission for high-performance light-emitting FETs.

Direct x-ray detectors using thermally evaporated pentacene thin-films are fabricated in Schottky and coplanar configurations and are analysed for low x-ray dose rates. In both configurations, the x-ray induced photocurrent is found to be five orders of magnitude greater than the theoretically evaluated threshold value that may reflect possible internal gain mechanism. Coplanar detectors showed unstable x-ray photocurrent characteristics; on the other hand, Schottky photodiode structure showed stable response and thus allowed to proceed for x-ray sensitivity measurements. Pentacene-based Schottky detector presented a decent volume sensitivity of 162.3 μC/mGy/cm3. The high x-ray sensitivity of pentacene Schottky detector can be due to the complete depletion of the thin-film at the operating reverse bias, revealed by transfer characteristics of fabricated pentacene MESFET. Such a reasonably good x-ray photoconversion in low-Z organic semiconducting materials uncovers the possibility of implementing them in x-ray medical dosimetry applications and in wearable electronic technology.

A theoretical study was carried out to understand the geometrical, electronic and optical properties of bipheylyl/thiophene based molecular system. For that, density functional theory along with classical Marcus charge transfer theory and time-dependent potentials were used. The results indicate that the structure-property relationship between the molecular parameters and ionization energy, electron affinity, reorganization energy, charge transfer integrals, mobility, energy gap, optical absorption and transition dipole moments. Low lying HOMO values and lower bandgaps of the molecules offer a higher charge transport in the systems and 5,5″-bis(4-biphenylyl)-2,2′:5′,2″-terthiophene (BP3T) molecule shows the maximum hole and electron mobility, 0.81 cm2 V−1 S−1 and 0.17 cm2 V−1 S−1, respectively. The results have shown that all the title compounds can be fabricated as ambipolar organic semiconductor materials and can be considered for the fabrication of efficient organic light emitting transistors.

Organic semiconductors have attracted much attention for low-cost, flexible and human-friendly optoelectronics. However, achieving high electron-injection efficiency is difficult from air-stable electrodes and cannot be equivalent to that of holes. Here, we present a novel concept of electrode composed of a bilayer of tetratetracontane (TTC) and polycrystalline organic semiconductors (pc-OSC) covered by a metal layer. Field-effect transistors of single-crystal organic semiconductors with the new electrodes of M/pc-OSC/TTC (M: Ca or Au) show both highly efficient electron and hole injection. Contact resistance for electron injection from Au/pc-OSC/TTC and hole injection from Ca/pc-OSC/TTC are comparable to those for electron injection from Ca and hole injection from Au, respectively. Furthermore, the highest field-effect mobilities of holes (22 cm2 V–1 s–1) and electrons (5.0 cm2 V–1 s–1) are observed in rubrene among field-effect transistors with electrodes so far proposed by employing Ca/pc-OSC/TTC and Au/pc-OSC/TTC electrodes for electron and hole injection, respectively., One of technological challenges building organic electronics is efficient injection of electrons at metal-semiconductor interfaces compared to that of holes. The authors show an air-stable electrode design with induced gap states, which support Fermi level pinning and thus ambipolar carrier injection.

We theoretically analyze the optoelectronic properties of single crystals of 2,5-bis(4-biphenylyl) bithiophene (BP2T) and 2-(4-biphenyl)-5-[5- (4-biphenyl)-2-thienyl] furan (BPFT) molecules, aiming to provide a guiding principle for the material design of organic light-emitting transistors. The X-ray structure analysis and the density functional theory (DFT) calculations indicate that half of the BPFT molecules bend the π-conjugation plane in the crystal. The Marcus theory parametrized by the DFT calculations indicates anisotropic charge mobilities. The emission spectra of the BP2T and BPFT crystals are analyzed by the time-dependent DFT calculations in conjunction with the Frenkel exciton model and the vibronic coupling analysis. We revealed that the high photoluminescence efficiency of the BPFT crystal originates from the symmetry breaking of the H-aggregate, where the transition dipole of the dark state does not cancel out.

Three organic semiconductors consisting of thiophene, furan, and phenylene groups showed either one or two gain-narrowed emission peaks by excitation with a laser pulse. The two gain-narrowed emission peaks are optically studied and assigned to 0 → 1 and 0 → 2 vibronic transitions. The number of gain-narrowed emission peaks is determined by a degree of overlap of the vibronic emissions with ground-state and excited-state absorption of the material. Dependence of the gained emission intensity both on the total input energy and the density of the excited states shows that the two gain-narrowed peaks are attributed to two different decay processes: amplified spontaneous emission (ASE) and superfluorescence (SF). The input energy to be conserved in total is distributed between ASE and SF processes strongly dependent on the transition probability and the self-absorption of organic semiconductors as a gain media.

Two new regiospecific biphenyl end-capped bithiazole co-oligomers, BP2Tz(in) and BP2Tz(out), have been synthesized for application in thin film field effect transistors (TFTs). BP2Tz(in) with a 2,2'-bithiazole central unit exhibits a field effect hole mobility as high as 3.5 cm(2) V(-1) s(-1). Green light emission is demonstrated for highly balanced ambipoar TFTs based on both BP2Tz(in) and BP2Tz(out).

(0.5 mol%) Dysprosium (Dy) doped bismuth silicon oxide (BSO) single crystals were grown by the Czochralski technique under air atmosphere. Detailed analysis of Dy-doped BSO with pure BSO has been studied through optical analysis. The absorption edges of pure and Dy-doped BSO crystals are found to be 405 nm and 415 nm, respectively. The shift in the absorption edge is contributed to the defect centers created in the crystal with Dy-doping. The shifts observed in the Raman spectra on doping Dy are found to be lower, when compared with the pure BSO crystal. This effect can be correlated to the lattice distortion induced by the Dy doping. The oxide formation and intrinsic defects in the BSO crystal have been identified by photoluminescence analysis. Dielectric measurements reveal that higher permeability value in the BSO sample is due to the presence of charged defects, which can be related to the space charge polarization. There is a slight decrease in dielectric constant on doping with Dy. The piezoelectric value explains the defects formed in the crystal. On poling, d 33 value of BSO and Dy-doped BSO are 32 pC/N and 40 pC/N, respectively.

In this report, the modifications in the structural, optical, mechanical, electrical and nonlinear properties of 70 MeV Li3+ and 100 MeV Ag7+ ion irradiated M-Nitroaniline single crystals are studied. The irradiation induced defect structures at the crystal surface which becomes more prominent at higher irradiation fluences, leading to the enhancement in the optical absorption behaviour and the nonlinear property of the irradiated crystals. The mechanism leading to the enhanced nonlinearity and the blue shift of the irradiated M-NA crystals has been discussed.

The 50 MeV silicon ion irradiation induced modifications on structural, optical and dielectric properties of solution grown glycine monophosphate (GMP) crystals were studied. The high-resolution X-ray diffraction study shows the unaltered value of integrated intensity on irradiation. The dielectric constant as a function of frequency and temperature was studied. UV–visible studies reveal the decrease in bandgap values on irradiation and presence of F-centers. The fluorescence spectrum shows the existence of some energy levels, which remains unaffected after irradiation. The scanning electron micrographs reveal the defects formed on irradiation.

Organic nonlinear optical crystal dimethyl-amino-pyridinium-4-nitrophenolate-4-nitro-phenol was subjected to 100 MeV Ag8+ ions and 50 MeV Si8+ ions. The radiation effects are studied in terms of processes observed with the pristine samples and in comparison with them. The dielectric properties of the crystals were studied before and after irradiation from 100 Hz to 5 MHz at various temperatures (308–383 K). A drastic increase in the dielectric constant is seen due to irradiation. The dielectric constant and conductivity increases with the increase of irradiation fluence for the samples. The observed results are discussed in detail.

This report presents the growth and characterization of l-valinium picrate (LVAP) single crystals. Density functional theory at the B3LYP/ HF6-31G (d,p) level has been used to compute the first order hyperpolarizabilty of LVAP. The second harmonic generation (SHG) efficiency of the title compound is reported for the first time in the literature and is found to be very high. Planar molecular structure and better conditions for electron conjugation and charge transfer result in larger values of β for this title crystal.

The organic nonlinear optical crystal of N-Bromosuccinimide (NBS) was grown by slow cooling solution growth technique using methanol as solvent. Single crystal and powder X-ray diffraction (XRD) and Fourier transform infrared (FTIR) spectral analyses were carried out to confirm the NBS crystals. The ultra violet (UV)–Visible and photoluminescence spectral studies were carried out, the green band at 2.02 eV can be attributed to radiative recombination between deep donors and shallow acceptors. The second harmonic generation (SHG) behaviour of NBS was tested by Kurtz–Perry powder technique. The hardness behaviour, laser damage threshold and dielectric characteristics of NBS crystals were studied.

The NLO properties of L-asparaginium picrate (LASP) crystals have been measured. The measurements were performed using a SHG diode-pumped laser at 532-nm wavelengths by employing the Z-scan technique. The nonlinear refractive index is found to be on the order of 10−8 cm2/W. The magnitude of the third-order susceptibility is on the order of 10−5 esu.

Pure and o-nitroaniline (O-NA) doped benzil single crystals were grown by the slow cooling solution growth method. The doping of O-NA is associated with the strong interaction between the guest and host molecules by the hydrogen bonding. Incorporation of O-NA in the lattice enhances the crystallinity. The nonlinearity increases due to the inductive nitro group added to the benzil. The values of nonlinear absorption coefficient (β) and nonlinear refractive index (n2) of benzil are −78 × 10−3 cm/W and −22 × 10−3 cm/W, while the corresponding values for O-NA doped benzil are −9.4 × 10−9 and −6 × 10−7 cm2/W, respectively. The figure of merit values of benzil and O-NA doped benzil are 2265 and 4990, respectively. The increase in hardness on doping of O-NA to benzil is due to the strong hydrogen bond.

Glycinium oxalate (GOX) single crystals were grown by slow cooling solution growth method. The X-ray diffraction and Fourier transform infra red studies confirm the grown crystal. The hardness values of GOX are found to be higher than glycine. The increase in hardness may be due to the C–H---O bonding. The UV–Visible studies show that GOX crystals can be used for nonlinear applications. The dielectric measurement indicates that the GOX crystals have domains of varying sizes and varying relaxation time. The SHG output of GOX was 210 mV at given pulse energy of 5 mJ/s and KDP was 240 mV.

The nicotinium dihydrogenphosphate crystals were grown by the low temperature solution growth technique. The grown crystals were confirmed by the powder X-ray diffraction and Fourier transform infrared spectroscopy studies. The optical properties were analyzed by the UV–visible and the photoluminescence studies. The mechanical hardness anisotropy of the nicotinium dihydrogenphosphate has been analyzed by the Vickers microhardness tester. The second harmonic generation in the nicotinium dihydrogenphosphate crystals was analyzed by the Kurtz–Perry powder technique. The dielectric properties of the nicotinium dihydrogenphosphate crystals were analyzed.

Pure single crystals of glycine lithium sulphate (GLS) were irradiated at room temperature with 100 MeV silver ions at fluences varying from 10 10 to10 12 ions/cm 2 from the 15 UD Pelletron facility at Inter University Accelerator Center (IUAC), New Delhi. The virgin as well as irradiated GLS single crystals were characterized by photoluminescence at room temperature under 2.55 eV blue excitation and UV–Vis absorption to study the radiation induced defects. The ion-induced changes have also been studied with respect to their mechanical response using Vicker’s micro hardness technique. The structural changes were analyzed by means of powder X-ray diffraction analysis. The effect of swift heavy ion beam on dielectric dispersion is explained in detail.

The 50 MeV Si ion irradiation-induced modifications on structural, chemical, optical and thermal properties of Vertical Bridgman grown benzimidazole (BMZ) crystals have been studied. The FTIR studies have been used to analyze the variation in various bonds that are associated with the functional groups in the native and the irradiated sample. X-ray diffraction studies reveal the compressive strains that are generated due to irradiation. The effect of irradiation on the conductivity of BMZ crystals has been studied. The fluorescence spectrum shows the existence of some energy levels, which remains unaffected after irradiation. The thermal analysis reveals that the melting point remains unaffected and the sample does not decompose as a result of irradiation.

The induced damage in single crystals of Sodium sulphanilate dihydrate (SSDH) irradiated at IUAC, New Delhi with 15 MV Pelletron accelerator with 100 MeV Ag7+ and 70 MeV Li3+ ions has been studied by optical measurements, mechanical hardness measurements, Electrical and ERDA measurements. Optical absorption measurements increase with the increase in fluence. The mechanical hardness of the crystal decreases on irradiation. The dielectric constant of SSDH increases on irradiation.

The 50 MeV Si7+ ion irradiation induced modifications on structural, dielectric, optical and mechanical properties of Vertical Bridgman grown benzimidazole (BMZ) crystals were studied. The high resolution X-ray diffraction studies show the quality of as grown BMZ and irradiated BMZ crystals. The dielectric constant and dielectric loss as a function of frequency and temperature was studied in detail. The ion induced mechanical behaviour of both as grown BMZ and irradiated BMZ crystals has been explained with the indentation effects using Vickers microhardness tester. UV-VIS. studies reveal the decrease in bandgap values and defects on irradiation. The above results are discussed in detail. (© 2007 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim)

Metastable zonewidth and induction period measurements of Benzimidazole (BMZ) are presented. The nucleation parameters such as interfacial tension, radius of the critical nucleus and critical free energy change have been calculated for the solution grown Benzimidazole (BMZ) single crystals at different supersaturation ratios. The grown BMZ crystals were characterized by the differential scanning calorimetric studies for analysis of thermal properties. The dielectric behaviour of the crystal was studied at different temperature and frequency. The laser damage threshold studies show that BMZ crystal has higher laser damage threshold. (© 2007 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim)

The organic nonlinear optical crystal of sodium sulfanilate dihydrate (SSDH) was grown by slow cooling solution growth technique using water as solvent. Single-crystal X-ray diffraction and Fourier transform infrared (FTIR) spectral analyses were used to confirm the SSDH crystals. The UV–visible and photoluminescence studies were carried out. The second-harmonic generation of SSDH was tested by Kurtz–Perry powder technique. The hardness and laser damage threshold on the (0 0 1) and (0 1 0) planes were analyzed.

Nucleation parameters such as radius of critical nucleus, critical free energy change and interfacial tension were evaluated for Sulphanilic acid (SAA) single crystals. Metastable zone width and induction period values were determined to optimize the growth parameters. The interfacial tension values estimated using the experimentally determined induction period is found to be comparable with theoretical values. SAA crystals were grown with the optimized growth parameters. The formation of SAA crystals was confirmed by powder X-ray diffraction and FT-IR studies. The density measurements were carried out by both theoretical and experimental methods. The NLO behaviour of SAA crystals was tested by Kurtz- Perry technique. The mechanical hardness was studied by Vickers Microhardness tester. The UV-Vis spectral analysis was carried out on the SAA crystals to study the optical properties. The laser damage threshold values of the SAA crystals are found to be 7.6 and 6.6 GW/cm2 for single and multiple shots, respectively. (© 2007 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim)

Organic nonlinear optical crystal l -asparaginium picrate was subjected to 100 MeV Ag 8+ ions and 100 MeV Si 8+ ions. The dielectric properties of the crystals were studied before and after irradiation from 100 Hz to 5 MHz at various temperatures (308 K to 358 K). A drastic increase in the dielectric constant is seen due to irradiation. The dielectric constant and dielectric loss increase with increasing irradiation fluence. The UV–vis spectra of the pristine and irradiated samples were recorded and quantified. There is a small shift in absorption edge towards lower wavelength for the irradiated crystals due to the decrease in bandgap of the material. The observed results are discussed in detail.

Good transparent single crystals of N -(2 chlorophenyl)-(1-propanamide) have been grown by slow cooling solution growth technique. From the crystal structure analysis we infer that the crystal belongs to monoclinic system. The grown crystals were subjected to FT-IR and FT-Raman analyses for vibrational assignments, UV–Vis spectral studies for optical transmission and band gap determination, dielectric studies for the study of dependence of capacitance, dielectric constant, and conductivity with frequency and temperature and Laser damage threshold studies.

The potential organic NLO crystal of benzimidazole (BMZ) has been successfully grown by slow evaporation solution growth technique at room temperature. The crystalline perfection has been verified by High resolution X-ray diffraction (HRXRD) analysis. The very low angle boundary obtained for this solution-grown specimen may be attributed to the segregation of solvent molecules (methanol), which were entrapped within the crystal during growth. The laser damage threshold has been measured by using high intensity Q-switched Nd:YAG laser. The observed value is greater than that of KDP and lesser than that of melt grown benzimidazole. The NLO efficiency has been determined and it is compared with the KDP crystal. The thermal behaviour has been assessed by TG/DTA analysis. (© 2006 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim)

Good quality single crystals of l-asparaginium picrate have been grown by a low-temperature solution growth technique. The UV−visible−NIR absorption spectra were recorded for the grown crystal and relative second harmonic generation (SHG) efficiency was investigated to explore the NLO characteristics of the material for the first time in the literature. The relative SHG efficiency of the material is 66.5 times greater than that of KDP and 10 times higher than that of urea. The dielectric and mechanical behavior of the specimen were also studied. The structural perfection of the grown crystals has been analyzed by high-resolution X-ray diffraction (HRXRD) rocking curve measurements. Fourier transform infrared (FTIR) spectroscopic studies were also performed for the identification of different modes present in the compound.

The bulk single crystals of 2,4,6-trinitrophenol (TNP) have been grown by slow cooling solution growth technique using acetone and ethanol as solvents. Good-quality crystals were obtained from ethanol as solvent. The solubility in acetone and ethanol was studied. The X-ray diffraction and mass spectrum studies were performed for material confirmation. FT-IR and FT-Raman measurements were carried out for spectral analyses. The factor group analysis was carried out for TNP which predicts that there are 453 vibrational optical modes. Relative second harmonic generation (SHG) efficiency of TNP was compared with that of urea and KDP. TNP exhibit SHG efficiency over 1.4 order of magnitude higher than that of urea and 13.4 order of magnitude higher than that of KDP. The melting point, hardness and UV–Vis spectral studies were carried for the grown crystals.

Single crystals of m-Nitroaniline (mNA) were grown by slow cooling solution growth technique. Induction period, interfacial energy and metastable zonewidth have been evaluated. The solubility of mNA has been estimated at different temperatures in acetone and ethanol. Interfacial energy has been estimated using the experimentally determined induction period values. It is observed that the nucleation rate increases with the increase of supersaturation. (© 2005 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim)

Carrier injection from Au electrodes to organic thin-film active layers can be greatly improved for both electrons and holes by nano-structural surface control of organic semiconducting thin films using long-chain aliphatic molecules on a SiO2 gate insulator. In this paper, we demonstrate a stark contrast for a 2,5-bis(4-biphenylyl)bithiophene (BP2T) active semiconducting layer grown on a modified SiO2 dielectric gate insulator between two different modifications of tetratetracontane and poly(methyl methacrylate) thin films. Important evidence that the field effect transistor (FET) characteristics are independent of electrode metals with different work functions is given by the observation of a conversion of the metal-semiconductor contact from the Schottky limit to the Bardeen limit. An air-stable light emitting FET with an Au electrode is demonstrated.

Optoelectronic devices based on layered materials such as graphene have resulted in significant interest due to their unique properties and potential technological applications. The electric and optoelectronic properties of nano GaTe flakes as layered materials are described in this article. The transistor fabricated from multilayer GaTe shows a p-type action with a hole mobility of about 0.2 cm(2) V(-1) s(-1). The gate transistor exhibits a high photoresponsivity of 10(4) A/W, which is greatly better than that of graphene, MoS2, and other layered compounds. Meanwhile, the response speed of 6 ms is also very fast. Both the high photoresponsivity and the fast response time described in the present study strongly suggest that multilayer GaTe is a promising candidate for future optoelectronic and photosensitive device applications.

The factor group analysis and the hyperpolarizability study were carried out for the l -asparaginium picrate (LASP) single crystals to explore the possible vibrational modes and the microscopic nonlinearity by the density functional triply parameter hybrid model DFT/B3LYP using GAUSSIAN 98W, respectively. The HF/6-31G (d,p) basis set has been employed. The calculated first order hyperpolarizability of LASP is 4.815 × 10 −29 esu. The Fourier transform infrared (FTIR) spectroscopic studies were performed for identifying different functional groups present in the compound.

We report the synthesis and characterization of two new furan-based biphenyl end-capped oligomers, 2-([1,1′-biphenyl]-4-yl)-5-(5-([1,1′-biphenyl]-4-yl)thiophen-2-yl)furan (BPFT) and 5,5′-di([1,1′-biphenyl]-4-yl)-2,2′-bifuran (BP2F) as candidate semiconductors for organic light-emitting field effect transistors (OLETs). Differential scanning calorimetry (DSC) and thermogravimetric analysis (TGA) showed the high thermostability of these furan-based semiconductors. X-Ray crystallography of single crystals grown by physical vapor transfer (PVT) method revealed a complicated herringbone packing of BPFT stacking with unusual flat and bent structures, which is different from that of BP2F and the bithiophene-based analogue 5,5′-di([1,1′-biphenyl]-4-yl)-2,2′-bithiophene (BP2T). BPFT single crystal showed a higher absolute quantum yield (51%) compared to that of BP2F and BP2T. Density Functional Theory (DFT) calculations showed that the different excitation energies between flat and bent structures led to the asymmetric transition dipoles in dark state of BPFT H-aggregates, which explains the highest PLQY of BPFT single crystal. Single crystal FET based on BPFT showed an ambipolar characteristic with high hole and electron mobilities, while single crystal FET based on BP2F exhibited p-type characteristic with a high hole mobility. Light emission was observed from the single-crystal FET based on BPFT.