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An environmentally safe chemical process was used to create the CdSe nanocomposite films in a polyvinyl alcohol (PVA) matrix. X-ray diffraction was used to analyze these composites, revealing the cubic zinc blend structure of CdSe/PVA nanocomposite with crystal sizes as small as a few nm. These composite films have had their photoluminescence (PL) properties examined. At 420nm, the PL peak of CdSe/PVA was detected. The CdSe/PVA nanocomposite’s mechanoluminescence properties were investigated. It is found that the impact velocity determines the ML intensities. When ML is produced impulsively by the impact of a moving piston on the nanocomposite, two peaks in ML intensity arise with time, and it is found that the mechanoluminescence intensity is dependent on the magnitude of impact velocity. ML peak intensities of the first and second peaks ($I_{m1}$ and $I_{m2})$ increase with increasing impact velocity. However, the time corresponding to the first and second maxima ($t_{m1}$ and $t_{m2})$ shifts towards shorter time values with greater impact velocity. We examined the voltage-brightness and voltage-current characteristics curves for our electroluminescence investigations of CdSe/PVA nanocomposite. At higher frequencies, EL with greater brightness at low threshold voltage has been seen.

‘Sequential potential field’ is a concept to produce a potential cascade by the organization of redox components, and to aim for an effective and vectorial electron and/or hole transfer. Construction of the sequential potential field is examined by double-layered thin film composed of two kinds of metallophthalocyanine having different oxidation potentials, i.e. copper phthalocyanine and zinc phthalocyanine. In the electrochromic device of double-layered metallophthalocyanine thin films, hole transfer can be controlled by the order of deposition, which suggests that the present system is suitable for the construction of a sequential potential field. Double-layered metallophthalocyanine thin films were also used as a hole transfer layer in all-solid organic electroluminescent devices. In the case of an indium-tin oxide/copper phthalocyanine/zinc phthalocyanine/tris(8-hydroxyquinoline)aluminum/Mg-Ag device for electroluminescence, a high brightness of more than 4000 cd m⁻² can be achieved. This double-layered hole transfer system is more effective than the corresponding single hole transfer system, which is due to the construction of a sequential potential field in the hole transfer layer.

Results obtained in recent studies of deep centers in 6H-, 4H-, and 3C-SiC are analyzed. The ionization energies and capture cross sections of centers formed by doping of SiC with different types of impurities or by irradiation, as well as the corresponding parameters of intrinsic defects, are presented. The involvement of these centers in radiative and nonradiative recombination is examined. Analysis of published data shows that a strong influence is exerted by intrinsic defects in the SiC crystal lattice both on the formation of deep centers and on the properties of the epitaxial layers themselves, such as their doping level and polytype homogeneity.

We analyze GaInN based light emitting diodes emitting in the range of 400-550nm using a new intensity-quantitative spectroscopic cathodoluminescence mapping method. Spectroscopic information of arbitrary sample locations is generated from sequences of quantitative image scans. From the temperature dependence of the intensity, we derive thermal activation energies of the dominant loss processes. Those compare well with the hole binding energies in the piezoelectric and quantized quantum well structures.

Optical properties of green emission Ga_0.80In_0.20N/GaN multi-quantum well and light emitting diode have been investigated by using photoluminescence, cathodoluminescence, electroluminescence, and photoconductivity. The temperature dependent photoluminescence and cathodoluminescence studies show three emission bands including GaInN/GaN quantum well emission centered at 2.38 eV (~ 520 nm). The activation energy of the non-radiative recombination centers was found to be ~ 60 meV. The comparison of photoconductivity with luminescence spectroscopy revealed that optical properties of quantum well layers are strongly affected by the quantum-confined Stark effect.

This review focuses on the interrelation between the influences of polymeric structure on the optical properties of polythiophene — a versatile polymer for opto-electronic applications. From the application's point of view, the polymer should either be melt- or solution-processible. Functionalization of polythiophenes really helps for the above. On the other hand, the functionalization at the 3 and/or 4 position of the thiophene ring modifies the band gap of the polymer, which in turn, modifies photo absorption, photo- and electro-emission characteristics of polythiophenes. The present work reviews the influence of the optical properties of polythiophene on the different functional groups present in the thiophene ring.

We propose a novel silicon structure, Hot Electron Emitting Substrate (HEES), which exhibits important effect of repeated tunneling at two different voltage ranges, which we refer to as double tunneling. In ambient atmosphere and room temperature, the $I$–$V$ characteristic of HEES shows two current peaks during voltage sweep from 2 to 15 V. These two peaks are formed by the Fowler–Nordheim (FN) tunneling effect and tunneling diode mechanism, respectively.

The role of the gate voltage in the regulation of electroluminescence (EL) of a molecular photodiode with asymmetric localization of electron density on the frontier highest occupied and lowest unoccupied molecular orbitals of the photochromic molecule is considered. It is shown that the gate voltage can have a significant effect on the formation of EL in devices where one of the orbital energy levels are outside the gap between the biased Fermi levels of the electrodes. The role of the gate voltage consists in shifting the position of the orbital energy levels until both frontier levels fall into the gap and thereby provide a resonant mechanism for the formation of EL. This leads to the inclusion of EL at a lower bias voltage than that which includes EL at zero gate voltage. In addition, the shift in energy levels caused by the gate voltage explains the mechanism for controlling the kinetics of bipolarity formation. The effect is carried out by turning on and off the resonant hopping’s of the electron between the conducting states of the electrodes and molecular orbitals localized at different distances from the electrode surfaces.

n-InSe single crystals were grown by the Bridgman method. Electroluminescence in undoped and rare-earth-doped (Dy and Er) crystals has been experimentally studied. It has been established that in both groups of crystals, electroluminescence is observed at $T\le$ 160–165K in the wavelength range $\lambda \approx 0.900$–1.150$\mu$m, regardless of the values of initial dark resistivity (${\rho }_{D0}$) and concentration (N). The volt-brightness characteristics and the dependence of brightness on the current strength have been investigated. It was found that the brightness also depends on the values of initial dark resistivity and concentration of the impurities. The highest luminescence brightness and the most stable and reproducible characteristics of electroluminescence are observed in doped crystals. The features of electroluminescence in undoped and rare-earth-doped crystals obey the criteria of theoretical concepts developed for spatially homogeneous crystalline semiconductors. All experiments were comparatively performed for both undoped and rare-earth-doped crystals.

The electroluminescence (EL) studies on the aluminum-doped nanoporous silicon (NPSi:Al) have been conducted. Nanoporous silicon (NPSi) layers have been prepared by anodically etching the unpolished p-type Si[100] wafer with surface resistivity of 4–8 Ω cm^-1 in hydrofluoric solution at 1:1 ratio of ethanol. Aluminum (Al) was doped on NPSi using cathodic electrodeposition composed of aluminum chloride (AlCl₃) and ethanol electrolyte. A diode structure has been fabricated comprising a semi-transparent Au/NPSi:Al/p-Si/Al ohmic contact electrode showing rectification on a forward bias I–V curve. EL from NPSi and NPSi:Al/p-Si has also been observed using the diode structure. The NPSi:Al/p-Si device shows increasing EL quantum efficiency at about 30%, and blue-shift EL spectra are observed. Possible reasons for the enhancement will be discussed.

For most practical applications, it is essential to fabricate micro- or nano-scale polymer electroluminescent (EL) devices and pixel arrays. Microcontact printing, which uses a patterned elastomer (usually PDMS) as the mold to generate or transfer the pattern offers immediate advantages. Here we describe a method of patterning polymeric EL materials based on microcontact printing using PDMS mold. In this technique, we use the self-assembled monolayer (SAM) system of alkanephosphonic acids on ITO substrate, and patterned EL polymer is formed on the SAM-modified ITO substrate.

Blue light-emitting polymer/dielectric nanolayer nanocomposites were fabricated by solution intercalation method and the photoluminescence data showed that these nanolayers act as separation layers to isolate polymer chains. Furthermore the dielectric nanolayers whose aspect ratio is about 500, also acted as efficient barriers to oxygen resulting in low keto-type emission and photo-oxidation.

We synthesized and characterized novel highly phenyl-substituted spirobifluorene and carbazole derivatives such as 3,6-bis[(2,3,4,5-tetraphenyl)phenyl]-9-ethylcarbazole (BTPEC); 3,6-bis(7,10-diphenyl-fluoranthene)-9-ethylcarbazole (BDFEC); 2,7-Bis[(2,3,4,5-tetraphenyl)phenyl]-9,9′-spirobifluorene (BTPSF); and 3,6-bis(7,10-diphenyl-fluo-ran-thene)-9,9′-spirobifluorene (BDFSF), through Diels–Alder reaction. BDFEC showed sky blue PL spectrum at 481 nm and BTPSF showed ultra-violet PL spectrum at 374 nm in chloroform solution. Also BTPEC and BDFSF exhibited PL spectrum at around the UV region, 390 and 467 nm.

We have synthesized N-alkylated carbazole with a variation of alkyl size such as ethyl, hexyl, dodecyl and octadecyl group and have made thin film by using the spin-coating method. When N-octadecyl carbazole (NOC) film is made on ITO, the surface of the ITO/NOC layer becomes flatter compared to ITO and ITO/other N-alkylated carbazole layer. As the pendent alkyl chain length of carbazole becomes longer, the PL spectrum of the carbazole derivative becomes smooth and the PL maximum value is slightly shifted to long wavelength. ITO/NOC (100 nm)/LiF (1 nm)/Al (200 nm) device showed typical I-V characteristics and very weak blue EL light.

A novel light-emitting aluminum complex (PAl) containing the dihydroxy derivative of trans-1,2-dipyridylethene, α-pyridoin, was synthesized and its electroluminescent (EL) properties characterized. The chemical structure of the complex was elucidated by FT-IR, UV-Vis and XPS. The complex showed thermal stability up to 350°C under nitrogen flow by TGA. The photoluminescence (PL) was measured from PAl cast film on quartz plate. Electroluminescent device having the structure of ITO/TPD/PAl/Al was fabricated by vacuum deposition, where N,N-bis(3-methylphenyl)-N,N′-diphenylbenzidine (TPD) was used as a hole transporting layer. The device emitted blue-green light of around 480 nm. The maximum luminance of 38 cd/m² and current density of 0.09 mA/cm² were observed at 34 V.

While exciplex formation is considered to have a negative impact on the performance of organic light-emitting devices (OLEDs), it can be utilized as a simple means for manipulating the emission colors. Here, we explore various important factors influencing the exciplex formation in order to provide a simple way for tailoring the emission color of OLEDs involving exciplex emission. In addition to the well-known effects of the energy difference between electron affinity and ionization potential (I_P) of organic materials used, we found that electron mobility and I_P of electron-transporting layer (ETL) are also critical factors in controlling the intensity of exciplex emission via the influence on charge accumulation intensity at the organic/organic interface. Interestingly, devices with green, blue, and white electroluminescence colors can be attained by simply replacing different ETL materials in contact with the same blue fluorophore underneath. The underlying mechanism for the color change in OLEDs will be discussed.

Tb₂O₃:Er light-emitting diodes were prepared by radio-frequency magnetron sputtering method and the EL performance of the devices were studied. The crystal structure and morphology of the annealed films were investigated by XRD and SEM, respectively. The EL spectrum was achieved and the EL principle was discussed. Six emission peaks of Er${}^{3+}$ located at 402, 517, 548, 649, 691, and 1,538nm were observed, achieving energy transfer from Tb${}^{3+}$ to Er${}^{3+}$. In order to study the effect of Er⁺ doping concentration, the doping concentrations of Tb₂O₃:Er films were from 5at.% to 20at.%. The effect on electroluminescence intensity of doping concentration was investigated and the optimal doped concentration was 15at. %.

A possibility of the formation of light emitting devices, containing GaAs:Mn layers, by the MOCVD epitaxy process was demonstrated. It was shown that produced GaAs:Mn layers exhibit ferromagnetic properties at room temperature. Luminescent and electrical properties of the In(Ga)As/GaAs quantum-size heterostructures with incorporated GaAs:Mn layers were studied.

Here we adopt a convenient green chemical route for synthesis of CdSe quantum dots, their characterization by UV/Vis absorption spectroscopy, X-ray diffraction study and transmission electron microscopy. We carry out photoluminescence and electroluminescence spectroscopy to investigate the variation in electro-optical property with size. By UV/Vis spectroscopy, blue shift is revealed and bandgap is also calculated. X-ray diffraction spectrum reveals cubic structure and transmission electron micrographs show quantum dots of different size distributions (in the range 2–8 nm). Both the luminescence spectroscopies reveal green-orange luminescence depending upon the size distribution and indicate the possibility of using CdSe quantum dots as light emitting devices with better compatibility and faster response.

The electroluminescence (EL) and photoluminescence (PL) of five porphyrin compounds have been investigated. Each of the porphyrin derivations were doped with different concentrations in a PVK(polyvinyl carbazole):PBD(2-(4-biphenyl)-5-(4-t-butyl-phenyl)-1,3,4-oxadiazole) blend as the host. The effect of the porphyrin type on the variation of the peak wavelength, FWHM (wavelength peak of emission spectra), CIE (1931 color Space standard) Coordinate, I–V characteristics have been studied in the same host, and the PL and EL spectra for all porphyrins were compared. It has been shown that the electrical and optical properties of the fabricated device can be controlled by altering the structure and concentration of the dopant.