Alq3 Sample Research Articles

Solid-state nuclear magnetic resonance study of polymorphism in tris(8-hydroxyquinolinate)aluminium.

Tris(8-hydroxyquinolinate)aluminium (Alq3 ) is a metal-organic coordination complex, which is a widely used electroluminescent material in organic light-emitting diode technology. Crystalline Alq3 is known to occur in five polymorphic forms (denoted α, β, γ, δ, and ε), although the structures of some of these polymorphs have been the subject of considerable debate. In particular, the structure of α-Alq3 , which is a model for the local structure in amorphous films used in devices, is highly complex and has never been conclusively solved. In this work, we use solid-state nuclear magnetic resonance (NMR) and density functional theory (DFT) calculations to investigate the local structure of four Alq3 samples. We find that the first structure proposed for α-Alq3 is inconsistent with all of the samples studied, and DFT calculations further suggest that this structure is energetically unfavourable. Instead, samples containing the meridional (mer) isomeric form are found to contain local structures consistent with ε-Alq3 , and a sample containing the facial (fac) isomeric form is consistent with a mixture of γ-Alq3 and δ-Alq3 . We also investigate the influence of different strategies for dispersion correction in DFT geometry optimisations. We find that a recently proposed modified semiempirical dispersion correction scheme gives good agreement with experiment. Furthermore, the DFT calculations also show that distinction between mer and fac isomers on the basis of ηQ that has been assumed in previous work is not always justified.

Synthesis and characterization of hybrid organic–inorganic nanocomposite for photocatalytic application

We report a simple precipitation method for the synthesis of organic–inorganic hybrid composite Alq3–WO3 materials. The incorporation of WO3 into Alq3 samples was demonstrated using different techniques. The surface morphology signifies the aggregation in the particles. Conversely, the decrease in the photoluminescence, band gap, prolonged excited-state lifetimes, and the higher conductivity in the impedance measurements suggest a much lower recombination rate in the final composite. Overall, the present finding demonstrates an enhanced separation and transfer efficiency of the photo-generated charge carriers upon combing WO3 semiconductor with Alq3 organic complex. The photocatalytic degradation property of Alq3–WO3 composite has been studied using methylene blue (MB) as a model organic pollutant. The Alq3–WO3 composite analysis possesses good catalytic activities. From the photocatalytic degradation experiment, it is found that the data fit well with the pseudo-first-order equation for the whole range of irradiation time with a high correlation coefficient.

The influence of synthesis conditions on the stability of tris(8-hydroxyquinoline) aluminum organometallic luminophore

Single-phase crystalline luminophore tris(8-hydroxyquinoline) aluminum (Alq3) has been synthesized at Т = 483 K and a partial pressure of 8-hydroxyquinoline vapor from 0.15 to 6.12 Torr. The influence of P8-Hq on the luminescent characteristics of crystalline Alq3 samples has been studied. It has been found that an increase in P8-Hq led to a shift of the photoluminescence-band maximum and to a change in the photoluminescence-decay kinetics. It has been shown that Alq3 synthesized at Т = 483 K and P8-Hq = 6.12 Torr had the most stable spectral-luminescent characteristics. The results obtained are discussed taking into account defect formation in crystalline Alq3.

Efficient, Scalable, and Solvent-free Mechanochemical Synthesis of the OLED Material Alq3 (q = 8-Hydroxyquinolinate)

The aluminum complex Alq3 (q = 8-hydroxyquinolinate), which has important applications in organic light-emitting diode materials, is shown to be readily synthesized as a pure phase under solvent-free mechanochemical conditions from Al(OAc)2OH and 8-hydroxyquinoline by ball milling. The initial product of the mechanochemical synthesis is a novel acetic acid solvate of Alq3, and the α polymorph of Alq3 is obtained on subsequent heating/desolvation of this phase. The structure of the mechanochemically prepared acetic acid solvate of Alq3 has been determined directly from powder X-ray diffraction data and is shown to be a different polymorph from the corresponding acetic acid solvate prepared by solution-state crystallization of Alq3 from acetic acid. Significantly, the mechanochemical synthesis of Alq3 is shown to be fully scalable across two orders of magnitude from 0.5 to 50 g scale. The Alq3 sample obtained from the solvent-free mechanochemical synthesis is analytically pure and exhibits identical photoluminescence behavior to that of a sample prepared by the conventional synthetic route.

Studies on the Fluorescence of Tris-(8-hydroxyquinoline)Aluminum and the Effect of Light Exposure

Organic Tris-(8-hydroxyquinoline)aluminum (Alq3) thin films, one of the most widely used electron transport as well as emissive materials in the organic electroluminescent (EL) devices, have been deposited on glass substrates by thermal evaporation process. The deposited Alq3 thin films were exposed to light in the normal ambient. The effect of light exposure on the fluorescence of Alq3 sample and formation of luminescent quencher has been studied using cyclic voltammeter and 3D contour emission spectroscopy. It is observed that the luminescent quencher can be formed in the Alq3 during the light exposure, quenching the emission of light exposed sample. It is found that the energy of excitons in the Alq3 molecule in the light exposed Alq3 thin films can be non-radiatively transferred to its neighbouring luminescent quencher, quenching the emission of light exposed Alq3 thin films.

Tris(8-hydroxyquinoline)aluminum (III) (Alq3) nanowires templated from an eggshell membrane

One to 2-µm long, ≤ 400-nm wide amorphous tris(8-hydroxyquinoline)aluminum (III) (Alq3) nanowires (NWs) grown from the 15-min boiled outer shell membrane (OSM) of the hen's egg and from the OSM solution cast film via thermal evaporation with a source temperature of 260 °C and a substrate temperature of 138 °C under 6.7 × 10 − 2 Pa gave about 1.4 to 1.7 times more photoluminescence emission than the control Alq3 sample did, which was grown from the plain glass surface. The characteristic bonding energies of C 1s X-ray photoelectron signal at 282 eV, O 1s signal at 529 eV and N 1s signal at 397 eV suggested that the relatively high NW density for the 15-min boiled OSM and the OSM solution cast film, was mainly caused by the formation of the O═C–O–C═O anhydride moiety and the C═N group in the proteinaceous OSM at high temperature of 90 °C to 100 °C. Therefore, we proposed that the 15-min boiled OSM and the OSM solution cast film apparently served as good templates by providing nano-regions of high concentration of the O═C–O–C═O anhydride groups and the C═N groups for nesting the Alq3 gas molecules to form nano-conical Alq3 nuclei for the growth of long and narrow NWs.

Deep-Level Characterization of Tris(8-hydroxyquinoline) Aluminum with and without Quinacridone Doping

We have investigated band gap states in tris(8-hydroxyquinoline) aluminum (Alq3) with and without quinacridone (Qd) doping on fabricated indium–tin-oxide (ITO)/Alq3(:Qd)/LiF/Al devices by a deep-level optical spectroscopy (DLOS) technique. A nondoped Alq3 sample shows a discrete trap level located at ∼1.39 eV below the lowest unoccupied molecular orbital band in addition to near-band-edge transitions at 2.2–3.6 eV. This pronounced 1.39 eV level is attributable to the intrinsic nature of Alq3 and can be activated as an efficient generation-recombination (GR) center that may affect photophysical properties. On the other hand, a Qd-doped Alq3 sample exhibits a new deep level at ∼2.40 eV with increasing double-carrier injection rate, corresponding to the highest occupied molecular orbital band of Qd. Simultaneously, this GR center is subject to charge up positively owing to the presence of holes injected into the Qd doping level of the Qd-doped Alq3 sample.

Characterization of molecular disorder in vapor-deposited thin films of aluminum tris(quinoline-8-olate) by one-dimensional Al27 NMR under magic angle spinning

Aluminum tris (quinoline-8-olate) (Alq3) is used as an electron-transport layer in organic light-emitting diodes. The material can be obtained in a wide range of different solid phases, both crystalline and amorphous, by deposition from the vapor phase or from solution under controlled conditions. While the structure of the crystalline polymorphs of Alq3 has been investigated thoroughly by x-ray diffraction as well as solid-state NMR, very little information is currently available on the amount of structural disorder in the amorphous forms of Alq3. In the present contribution, we report the use of 27Al NMR spectroscopy in the solid state under magic angle spinning to extract such information from amorphous vapor deposits of Alq3. The NMR spectra obtained from these samples exhibit different degrees of broadening, reflecting distributions of the electric-field gradient tensor at the site of the aluminum ion. These distributions can be obtained from the NMR spectra by solving the corresponding inverse problem. From these results, the magnitude of structural disorder in terms of molecular geometry has been estimated by density-functional theory calculations. It was found that the electric-field gradient anisotropy delta follows a bimodal distribution. Its majority component is centered around delta values comparable to the meridianal alpha crystal polymorph and has a width of about 10%, corresponding to distortions of the molecular geometry of a few degrees in the orientation of the ligands. Alq3 samples obtained at higher deposition rates exhibit higher degrees of disorder. The minor component, present at about 7%, has a much smaller anisotropy, suggesting that it may be due to the facial isomer of Alq3.

Deep-Level Optical Spectroscopy Investigation of Trap Levels in Tris(8-Hydroxyquinoline) Aluminum

ABSTRACTWe have investigated band gap states in tris(8-hydroxyquinoline) aluminum (Alq3) with and without quinacridone (Qd) doping on fabricated indium-tin-oxide (ITO)/Alq3(:Qd)/LiF/Al devices by using a deep-level optical spectroscopy (DLOS) technique. Non-doped Alq3 sample shows a discrete trap level located at ∼1.39 eV below the lowest unoccupied molecular orbital band in addition to near-band-edge transitions at 2.2 - 3.6 eV. The pronounced 1.39 eV level is attributable to an intrinsic nature of Alq3 and can be active as an efficient generation-recombination (GR) center that may impact the photophysical properties. On the other hand, Qd-doped Alq3 sample exhibits a new deep level at ∼2.40 eV with increasing the double carrier injection rate, corresponding to the highest occupied molecular orbital band of the Qd. Simultaneously, this GR center is subject to charge up positively due to the presence of holes injected into the Qd doping level for Qd-doped Alq3.

Dielectric studies of Alq 3 and transport mechanisms

From dielectric measurements in the 20 Hz–1 MHz frequency range and between 150 and 320 K, we deduced a relaxation energy we attribute to the depth of traps filled with remaining electrons. The mean activation energy is around 0.20 eV, value in good agreement with previous determinations by other techniques. This value seems independent of the Alq3 sample preparation. The proof of the level existence around 0.20 eV confirms the transport mechanism scheme by way of these intermediate levels. Nevertheless, the experimental measurements are disturbed by other phenomena, in particular, by electrical contacts. The intensification by UV light of the dielectric absorption, that is to say the photodipolar effect, becomes hidden by the photoconductivity component.

Characterization and luminescence properties of Alq3 films grown by ionized-cluster-beam deposition, neutral-cluster-beam deposition and thermal evaporation

Tris-(8-hydroxyquinoline) aluminum (Alq3) films have been grown on silicon substrates by several techniques: neutral-cluster-beam deposition; thermal evaporation; and ionized-cluster-beam deposition technique. The films were characterized by low angle X-ray reflectivity, atomic force microscopy, Fourier transformed infrared (FTIR) spectroscopy and photoluminescence. According to the FTIR spectroscopy measurement, the spectra of all the Alq3 samples show almost the same signals of atomic binding regardless of the process conditions. However, the photoluminescence intensities of the films are different. When all the films are adjusted to the same thickness, neutral-cluster-beam deposition films show more intense photoluminescence than the thermal-evaporated ones, while ionized-cluster-beam deposition samples are found to be inferior in intensity. Since the photoluminescence intensity of the 8-hydroxyquinoline aluminum layers is one of the important factors for the performance of organic light emitting devices, the neutral-cluster-beam deposition seems to be a promising method for the film deposition of organic electroluminescence materials.