The optical band gap of ZnO thin films deposited on fused quartz by metal-organic chemical-vapor deposition was studied. The optical band gap of as-grown ZnO blueshifted from 3.13 to 4.06 eV as the growth temperature decreased from 500 to 200°C. After annealing, the optical band gap shifted back to the single-crystal value. All the ZnO thin films studied show strong band-edge photoluminescence. X-ray diffraction measurements showed that samples deposited at low temperatures ͑Ͻ450°C͒ consisted of amorphous and crystalline phases. The redshift of the optical band gap back to the original position after annealing was strong evidence that the blueshift was due to an amorphous phase. The unshifted photoluminescence spectra indicated that the luminescence was due to the crystalline phase of ZnO, which was in the form of nanocrystals embedded in the amorphous phase.

We have studied the spectral (UV−vis absorption and fluorescence) and thermally spectral stability of seven fluorene-based blue-light-emitting polymers in film states. These polymers have different side chain and backbone structure. Spiro-functionalization at the C-9 bridge position of fluorene unit could significantly improve the emission spectral quality (narrower spectrum and shorter tail extended to longer wavelength direction) and thermally spectral stability of 9,9-disubstituted polyfluorene derivatives. A glass transition temperature dependence for excimer emission in the polymers was demonstrated, and the improvement of thermally spectral stability by the spiro-functionalization is attributed to the increase of glass transition temperature. The backbone structural modification for 9,9-disubstituted polyfluorenes by alternatively inserting substituted phenylene units could provide blue emission with the spectral quality and thermally spectral stability even better than spiro-functionalized polyfluorenes, and no glass transition temperature dependence for excimer formation was observed in the backbone-modified polymers. The spectral properties of the polymers are dependent on the substitution on the phenylene ring. Thermotropic liquid crystallization was observed in the polymers bearing long alkoxy substituents. The good thermally spectral stability of the polymers is attributed to the poor planar configuration of the backbone and the efficient separation of the side chains on phenylene units for backbones.

The recent developments and trends of electrochromic conjugated polymers and their devices are highlighted in this review.

Atomically thin Mo(1-x)W(x)S2 (0 ≤ x ≤ 1) ternary compounds have been grown on 2-inch c-plane sapphire substrates with high uniformity by sulfurizing thin Mo(1-x)W(x) layers that were deposited at room temperature using a co-sputtering technique. Atomic force microscopy (AFM), Raman scattering, and optical absorbance spectroscopy (OAS) studies reveal that the Mo(1-x)W(x)S2 films consist of crystallites of two-to-four monolayers in thickness. X-ray photoelectron spectroscopy (XPS) shows that the core levels of Mo3d and W4f shift to lower binding energies while that of S2p shifts to higher ones with the increase in W compositions, which can be related to the larger electron affinity of W (0.8163 eV) than that of Mo (0.7473 eV). OAS has also shown that the direct bandgap of Mo(1-x)W(x)S2 is tuned from 1.85 to 1.99 eV by increasing x from 0 to 1. Both E(1/2)(g) and A(1g) phonon modes of the Mo(1-x)W(x)S2 films exhibit a two-mode behavior. The bandgap tuning and the two-mode phonon behaviors are typically the same as those recently observed in monolayer Mo(1-x)W(x)S2 obtained by mechanical exfoliation, thus shedding light on the bottom-up growth of large-scale two-dimensional Mo(1-x)W(x)S2 ternary alloys.

The transport properties of GaN nanobelts (NBs) are tuned using a piezotronic effect when a compressive/tensile strain is applied on the GaN NB. This is mainly due to a change in Schottky barrier height (SBH). A theoretical model is proposed to explain the observed phenomenon.

A novel series of well-defined amphiphilic block copolymers containing conjugated poly(fluorene) (PF) block and coillike poly(2-(dimethylamino)ethyl methacrylate) (PDMAEMA) were successfully synthesized through atom transfer radical polymerization (ATRP) initialized by a 2-bromoisobutyrate end-capped PF macroinitiator using CuCl/HMTETA (1,1,4,7,10,10-hexamethyltriethylenetetramine) as the catalyst. The first-order kinetics plot indicated a constant number of active species present in the polymerization. The molecular weight and molecular weight distribution were well controlled, implying well-defined block structure of the prepared block copolymers. The chemical structures of the copolymers were confirmed by 1H NMR studies. The copolymers could be successfully quanternized, and the final conjugated−ionic block copolymers were found to form PF aggregates in water as confirmed by 1H NMR, UV−vis, and photoluminescence (PL) spectra. PL spectra and quantum efficiency measurement also suggested the formation of excimers within the PF aggregates.

A quantum dot infrared photodetector (QDIP) consisting of self-assembled InGaAs quantum dots has been demonstrated. Responsivity of 3.25 mA/W at 9.2 μm was obtained for nonpolarized incident light on the detector with a 45° angle facet at 60 K. The QDIPs exhibit some unique electro-optic characteristics such as a strong negative differential photoconductance effect and blueshift of the response peak wavelength.

We present the results of a depth-resolved cathodoluminescence (CL) and transmission electron microscopy study of autodoped GaN grown on sapphire. Depth-resolved CL analysis can be used for depth profiling of the yellow luminescence (YL) center concentration which was found to increase with depth. The results are consistent with the (ON–VGa)2− complex model of YL centers [J. Neugebauer and C. G. Van de Walle, Appl. Phys. Lett. 69, 503 (1996) and T. Mattila and R. M. Nieminen, Phys. Rev. B 55, 9571 (1996)]. Depth profiling of the near-edge emission in GaN layers thicker than ∼0.5 μm is not possible due to strong self-absorption.