Highly monodisperse ZnO:Eu3+ nanocrystals have been synthesized by modified sol-gel method from ethanolic solutions. The effect of Eu3+ ions (x=0.05-0.30) concentration on the structural, optical and luminescent properties has been evaluated. No other than the ZnO-wurtzite phase was observed at all dopant levels, which was confirmed by FT-IR and Raman spectroscopy techniques. A blue shift of the exciton peak and the increase on the corresponding band gap were observed at increasing Europium contents, which would indicate an interaction between Eu3+ ions and the development of the ZnO host structure. The luminescence properties were also dependent on Europium contents; a systematic blue shift and enhancement of the intensity of visible luminescence peak, attributed to an increment of surface defects, was observed by a rising Europium concentration. The red luminescence band, representing the 5D0→7F2 transition, was clearly observed in nanocrystals after annealing at 300oC for one hour. The presence of this band could be considered as an evidence of the effective energy transfer from ZnO to Eu3+ ions.

The present work addresses the synthesis and characterization of red emitting Gd2-xEuxO3 nanocrystalline phosphors by a modified sol-gel based method. The effects of the annealing temperature and atomic fraction of Eu3+ ions, ‘x’, on the structural and luminescence properties of the produced oxides have been systematically investigated. X-ray diffraction analyses revealed that crystalline cubic-Gd2O3 host structure was obtained when the intermediates (x=0.01-0.30) were annealed at different temperatures in air. Photoluminescence spectra of doped Gd2O3 powders showed all transitions of Eu3+ species, being the5D0→7F2 transition the most intense. On a common sample-weight basis, the highest photoluminescence intensity was obtained at ‘x’ = 0.15. The energy transfer from host to dopant was verified for all evaluated ‘x’ values, which suggest the actual incorporation of Eu species into the Gd-oxide lattice. It was also found that the photoluminescence intensity was strongly dependent on the annealing temperature and dopant concentration.

In the present work, nanocrystalline Gd2-xEuxO3 phosphors have been synthesized by sol-gel method. The effect of Eu3+ concentration and annealing temperature on structural and luminescence properties of nanocrystalline powders were investigated. X-ray diffraction analyses showed that cubic Eu-doped Gd2O3 was formed and exhibited an average crystallite size ranging from 29nm to 41nm when the annealing temperature varied from 750 to 950 degrees C, respectively. Photoluminescence (PL) measurements verified the presence of all transitions of Eu3+ dopant, being the D-5(0) to F-7(2) transition the most intense. It was also found that, on a common weight basis, the PL intensity was strongly dependent on both the annealing temperature and dopant concentration. The highest PL intensity was observed for `x'=0.15. The observed quenching in luminescence would result from exchange interactions. Preliminary results on the PL characterization of nanocrystalline Gd2-xEuxO3 thin films are also presented.

Highly crystalline and transparent Eu-doped Gd2O3 thin films were produced through a modified sol-gel method that did not require the use of any chelating agent. The effect of the atomic fraction of Eu3+ ions ('x' =0.05-0.30) on the structural, optical and luminescent properties has been studied. X-ray diffraction studies showed the preferential growth of Gd2-xEuxO3 thin films along the (400) plane corresponding to the cubic phase. UV-vis measurements revealed the high film transparency of the films in the visible region and a band gap value of 5.3eV. It has also been observed that the luminescence properties of the films were strongly dependent on both, the excitation wavelength and Eu concentration; the most efficient excitation conducive to red luminescence was achieved at the absorption band of Gd2O3 host (229nm). Under this condition all films exhibited strong red emission that is characteristic of Eu3+ ions. The emission intensity was also dependent on the doping level; the most intense luminescence was obtained at 'x'=0.15. The drop in the luminescence intensity observed for 'x' values higher than 0.15 was attributed to quenching concentration effect.

Laser-induced ultrafast nonlinear optical (NLO) response was observed in transient absorption, reflection and NLO measurements in VO2 thin films. The films were prepared using pulsed laser deposition technique with metallic vanadium and V2O5 powder employed as target material. The obtained thin films exhibit a thermal, as well as a laser-induced phase transition (PT) from semiconductor state at room temperature to metallic state. A typical hysterisis was observed for electric resistivity and optical reflectance verses temperature T. For the laser-induced PT in femtosecond pump–probe experiment, the PT was found to be ultrafast, immediately upon laser excitation. Kinetics study suggests that the PT is realized via an intermediate state, presumably a Wannier–Mott exciton (WME) state, followed by a resonant transition to the metallic phase state. The presence of the intermediate state is responsible for an extremely large third-order susceptibility observed in a nonlinear holographic experiment. In a 80nm thick VO2 thin amorphous film, the value of χ(3) was measured to be 1.3×10−8esu which is four orders of magnitude greater than a standard reference sample of CS2. In addition, the nonlinear response was further enhanced with diffraction signal increased by a factor of 4 after the laser excitation. A signal dip at ∼1.2ns was repeatedly observed, which is presumably due to the excitation process associated with the intermediate state. Finally, the resonant transition from the intermediate state to the metallic state, giving rise to a maximum diffraction signal intensity from the formed transient grating.

As a kind of phase transition functional material, Vanadium dioxide (VO2) thin films deposited on fused quartz substrate were fabricated using pulsed laser deposition (PLD) technique. Europium was introduced for structure study. By laser excitation at 526nm, VO2 thin film undergoes a reversible and ultrafast phase transition from semiconductor to metallic state, which results in a change of optical properties. In fluorescence measurement, Eu emission was found severely quenched in all as-grown thin films. After annealing the sample in air, a red Eu-emission appeared. The emission spectrum is characterized by a pronounced twin peak, centered at 617nm (5D0–7F2), surrounded by a set of broad, but relatively weaker bands (emission from 5D0 to 7Fj manifold). The emission lifetime increased when the sample annealed at higher temperature for longer time. Each spectral component is actually a doublet which is the spectral overlap of emissions from Eu3+ situated in two sites with different configurations. One is a linear h-Eu3+-h, where h stands for holes. Another is a right-angle configuration of h-Eu3+-h with Eu3+ in the corner. In as-grown VO2 film, Eu3+ ions can either substitute V4+, leaving a negative charge around (Eu3+–O)–, or substitute V5+, leaving two negative charges around (Eu3+–O)−−. Due to trapped electrons in a large radius state, it covers Eu3+V4+–V5+ complexes. It suggests that the screening by degenerate electronic gas may result in switching off the Eu-related optical response for a wide spectral region, causing emission quenching in VO2 films.

VO 2 thin films deposited on fused quartz substrates were successfully fabricated by the pulsed-laser-deposition (PLD) technique. The obtained samples were examined by microscopy and x-ray diffraction (XRD). The films show a fast, passive thermochromic effect of semiconductor-to-metal phase transition (PT) with a characteristic hysterisis at ∼68°C. The thermochromic effect was measured as resistivity, optical transmission, and reflection versus temperature. Under pulsed laser excitation, an optically induced ultrafast PT of VO 2 thin film was observed. Using the degenerate-four-wave-mixing (DFWM) technique, it was found that excited state dynamics is responsible for the induced lattice reorientation polarization, which results in the ultrafast PT.

For potential ultrafast optical sensor application, both VO2 thin films and nanocomposite crystal-Si enriched SiO2 thin films grown on fused quartz substrates were successfully prepared using pulsed laser deposition (PLD) and RF co-sputtering techniques. In photoluminescence (PL) measurement c-Si/SiO2 film contains nanoparticles of crystal Si exhibits strong red emission with the band maximum ranging from 580 to 750 nm. With ultrashort pulsed laser excitation all films show extremely intense and ultrafast nonlinear optical (NLO) response. The recorded holography from all these thin films in a degenerate-four-wave-mixing configuration shows extremely large third-order response. For VO2 thin films, an optically induced semiconductor-to-metal phase transition ( PT) immediately occurred upon laser excitation. it accompanied. It turns out that the fast excited state dynamics was responsible to the induced PT. For c-Si/ SiO2 film, its NLO response comes from the contribution of charge carriers created by laser excitation in conduction band of the c-Si nanoparticles. It was verified by introducing Eu3+ which is often used as a probe sensing the environment variations. It turns out that the entire excited state dynamical process associated with the creation, movement and trapping of the charge carriers has a characteristic 500 ps duration.

VO2 thin films deposited on fused-quartz substrates were prepared by a pulsed laser deposition technique. Vanadium dioxide shows an ultrafast, passive phase transition (PT) from a monoclinic semiconductor phase to a metallic tetragonal rutile structure when the sample temperature is above 68°C. The fast PT can also be optically induced by laser excitation. In this paper, we report the optical properties of prepared thin films by absorption and photoluminescence (PL) measurements. In addition, a degenerate-four-wave-mixing measurement was also conducted using a 30ps YAG pulsed laser operated at 532nm. It is the first time, to our knowledge, that a large polarizability and relatively slow nanosecond excited state dynamical processes have been identified in VO2. The polarizability is found to be ∼300 times greater than the χ(3) value of a CS2 reference. The mechanism for slow process is believed to be associated with the structural change.

Optical quality SrxBa1−xNb2O6 (SBN) thin films doped with Pr3+ ions were successfully grown on fused quartz substrates using a pulsed laser deposition technique. Both as-grown and annealed samples were studied at either room temperature or at 10K. Luminescence measurements show that most 4f2→4f2 emissions from Pr3+ centers were efficiently quenched in the films. Strong red emission from 1D2 to 3H4 at ∼610nm accompanied by weak emission to other 3Hj multiplets could be observed only by UV excitation into the SBN conduction band. At 10K, the main emission peak splits into four components. In addition, a broadband SBN-host luminescence was identified at ∼560nm in the annealed sample, associated with the charge-transfer vibronic exciton. As an interstitial ion, Pr3+ may occupy a 15-, 12-, 9- or 6-fold cage surrounded by oxygen and was found to occupy all four possible sites in SBN thin films. This behavior is different from Eu3+- SBN where Eu3+ only occupies a 6-fold site.

VO 2 thin films deposited on MgO and fused silica glass substrates were prepared by the pulsed laser deposition (PLD) technique, which shows phase transition (PT) from the monoclinic semiconductor phase to a metallic tetragonal rutile structure at temperatures over 68°C. The observed PT is reversible, showing a typical hysteresis. The PT can also be induced through optical pumping by laser excitation. In this case, it was found that the optically induced PT is ultrafast and passive, but not thermally initiated. In order to understand the PT mechanism, a study of transient holography using degenerate-four-wavemixing (DFWM) measurement was conducted. A Nd:YAG pulsed laser with pulse duration of 30 psec operating at 532 nm was employed as the coherent light source. This showed that the observed transient holography in VO 2 thin film is associated with the excited state dynamical process, which essentially causes the structural change, or so-called optically induced PT. The observed extremely large polarizability is believed to relate to the large offset in the potential well minimum between the ground state and excited state. Through an unidentified intermediate state, the transient lattice distortion triggered the structural change.