Blue to red color-tunable Eu-doped AlPO4 mesoporous glass

A tunable luminescence from red to blue in Eu-doped mesoporous AlPO4 glass is achieved by adjusting the annealing temperature. With increasing annealing temperature, the increased Eu3+ions reduction changes the luminescence of the obtained glass. The abnormal reduction of Eu3+to Eu2+occurs in AlPO4 mesoporous glass at relative low annealed temperatures from 600 to 800 ℃ in air. The presence of Eu2+ions, which are reduced from Eu3+by hole-electron pairs, is revealed by XPS spectra. Our results indicate the mesoporous AlPO4 glass is a suitable matrix to incorporate Eu ions as the tunable luminescent light sources or LEDs.     

Synthesis and characterization of MnWO4 nanoparticles encapsulated in mesoporous silica SBA-15 by fast microwave-assisted method

The MnWO₄ nanoparticles encapsulated in mesoporous silica (MnWO₄/SBA-15) was successfully synthesized by a fast microwave-assisted method. The products were characterized by X-ray diffraction (XRD), transmission electron microscopy (TEM), nitrogen absorption–desorption isotherm, and Fourier transform infrared spectroscopy (FTIR). Our results showed that the MnWO₄/SBA-15 nanocomposites have the ordered hexagonal meso-structure of SBA-15, indicating MnWO₄ nanoparticles were successfully distributed into the channels of SBA-15. The size of MnWO₄ nanoparticles in SBA-15 is significantly smaller than the size of MnWO₄ nanoparticles prepared without SBA-15, indicating that the MnWO₄/SBA15 nanocomposites would be very promising for improving photocatalytic activity of MnWO₄ nanoparticles.     

Intense orange emission in Pr3+ doped lead phosphate glass

Spectroscopic properties of one mol% Pr₂O₃ embedded in 40%PbO–60%P₂O₅ glass have been investigated at room temperature. From the absorption spectra energy levels of the observed bands are assigned. Using free ion Hamiltonian theoretical values of energy of 13 multiplets of Pr³⁺ are calculated. Judd–Ofelt intensity parameters have been estimated by including and excluding the hypersensitive transition (³H₄→³P₂). The best set of Judd–Ofelt parameters are obtained by omitting ³H₄→³P₂ transition from the calculation. These parameters are used to evaluate the important laser parameters for various emission lines. Our investigation reveals that the present glass may be utilized as a laser active medium corresponding to ³P₀→³H₄ and ¹D₂→³H₄ transitions respectively, for 484.6 nm (blue) and 599.5 nm (strong orange) emissions. Indirect and direct optical band gap energies of Pr³⁺ doped lead phosphate glass matrix have also been reported.     

Laser-excited fluorescence of perylene by using self-induced second-harmonic and sum-frequency radiation emanating from high-power AlGaAs double hetero-type diodes

High-power (12 W) pulse-operated AlGaAs double-heterostructure lasers with a large thickness of the active layer (1.5 µm) are able to produce internal second-harmonic and sum-frequency generation with a peak power of 10 mW. The corresponding portion of the electroluminescence spectra has a maximum at 405 nm. Clearly resolved mode structures of the fundamental and harmonic radiation are analysed in detail. Particular transverse modes exhibit different conversion efficiencies. Violet resonances without modal precursors in the infrared spectrum make a marked contribution to the light intensity. The harmonic signal serves as an excitation source in photoluminescence studies. A technique of single-photon counting is applied in order to perform spectral measurements under weak-intensity levels. Bright fluorescence spectra of saturated solution of perylene ino-xylene are presented. The spectrum obtained when the solution is illuminated with a gas discharge lamp shows no differences with respect to the positions of the intensity peaks. This allows us to suggest that AlGaAs high-power lasers can be used as convenient excitation sources in photophysics, in particular in time-resolved experiments.     

Anomalous behavior of the fluorescence spectra of perylene in n-octane under pressure and temperature variations

Pressure-induced transformations of the vibronic spectra of perylene in n-octane were studied. An increase in pressure from normal to 10 kbar caused a sharp change in the multiplet structure of the spectra. An anomalous, almost linear temperature dependence of spectral line widths was observed in the temperature range 4.2–15 K. Both temperature and baric effects were explained in terms of the same model of a two-well adiabatic potential of impurity centers, which caused the appearance of low-frequency splittings in the ground and excited electronic level regions.     

Quenching of perylene fluorescence by Co2+ ions in dipalmitoylphosphatidylcholine (DPPC) vesicles

We report the fluorescence quenching of perylene by CoCl₂·6H₂O in small unilamellar DPPC vesicles via energy transfer. At the probe-to-lipid ratio of 1200 and quencher to lipid ratios of 12.51, donor-donor energy transfer between clustered perylene molecules was observed as well as energy transfer from the perylene molecules to cobalt ions bothabove andbelow the main phase transition temperature of the lipid. The fluorescence quenching of perylene by CoCl₂·6H₂O in the lipid gel state is shown to be well described by Förster long-range energy transfer when both donor-donor and donor-acceptor energy transfer are considered. In the liquid crystalline phase diffusion of the molecules is described as well as energy transfer. The interaction radiusR ₀ for energy transfer from perylene to Co²⁺ is found to be 13.4±1.1 Å in the gel phase at 303 K, in good agreement with the theoretical value forR ₀ of 13.9 Å. In the liquid crystalline phase at 323 K the lower value obtained forR ₀, 11.3±1.6 Å, is attributed to saturation of the Co²⁺ ions at the interfacial region of the bilayer. A diffusion coefficient of (1.06±0.15)×10^–6 cm² s^–1 is obtained for perylene-cobalt diffusion in the liquid crystalline phase at 323K.     

Observation of anti-stokes fluorescence cooling in thulium-doped glass

We report the first observation of anti-Stokes fluorescence cooling in a thulium-doped solid with pump excitation at 1.82 &mgr;m相似文献   

Preparation method: structure–bioactivity correlation in mesoporous bioactive glass

In perovskite oxide materials, because of the insertion of multiple valence states ions (e.g., Mn in manganites) at atomic A-site (i.e., at the center of perovskite cubic cell), an enhancement of the ferromagnetic metallic state together with a strong orbital order of Mn-ions is established. Such a feature goes beyond the conventional theoretical framework for which the kinetic energy of the free charge carriers prevents the occurrence of a long-range orbital order. We do provide a complete physical characterization of these so-called A-site manganites by comparing transport and structural properties of La_0.7Sr_0.3MnO₃ and LaMnO₃ thin films with different excess Mn content and different oxygen content. A viable route to successfully grow such class of materials as a function of temperature and oxygen environment is provided. The observed multi-order phase coexistence opens unexplored perspectives toward the synthesis of new intrinsic multi-functional materials.     

Monochromic orange emission of Pr~(3+) ions in phosphate glass

Zinc strontium phosphate glasses doped with different trivalent praseodymium ion(Pr3t) concentrations are presented and their photoluminescence properties are investigated upon 442 nm excitation. With the Pr3tconcentration decreasing, the orange emission of Pr3t(1D2-3HJ) is enhanced steadily at the cost of its blue emission(3P1;0-3H4). Monochromic orange emission of Pr3tions is obtained when the Pr3tdoping is reduced to 0.05 mol.%. The mechanism controlling the monochromatic characteristic of Pr3temissions is supposed to be associated with the phonon-aided nonradiative relaxation process of Pr3t:3Pj→1D2, which depends on the Pr3tconcentration as well as the phonon energy of the glass matrix. Sodium zinc tellurite and barium gadolinium germinate glasses with the lower phonon energy are used as reference hosts to clarify this mechanism, and the results obtained support this suggestion.     

Performance characteristics of a Nd: glass laser amplifier from fluorescence emission studies

The dependence of cavity transfer efficiency of a Nd: glass laser amplifier on flashlamp current density is obtained from the analysis of amplified fluorescence. The cavity transfer efficiency decreases as the current density through the flashlamps is increased. The use of the fluorescence method in optimizing the flashlamp pulse duration for achieving maximum gain in the amplifier is illustrated.     

Efficient generation of orange light in a quasi-periodically poled LiTaO3 crystal

We present an approach to generating a tunable orange laser from 0.601 to 0.604 μm based on a quasi-periodically poled superlattice in LiTaO₃ and a Q-switched 1.064 μm Nd:YVO₄ laser as pump. The orange laser was generated in a cavity by a parametric process cascaded by a frequency mixing with a maximum output of 310 mW using 15 W pump power.     

Efficient phosphors based on organic dyes encapsulated in nanoporous nickel phosphate VSB-1

Different dyes were introduced into the channels of nanoporous material of nickel phosphate VSB-1 (Versailles Santa Barbara-1) by a wet-chemistry method. Narrower absorption and large blue-shift of photoluminescence bands as well as 50, 45, and 57 times enhanced intensities were obtained after being encapsulated in the channels of VSB-1 for dye 1, 2, and 3, respectively. The three dyes selected for encapsulation in VSB-1 emit red, green, and blue lights, respectively, which favor their application in optical devices. Thus, the narrower FWHM and higher emission efficiency for dyes encapsulated in VSB-1 materials make them good candidates for tricolor lamps, light-emitting diode, or miscellaneous materials.     

Efficient dual-wavelength Nd:YVO4 laser at 1085 and 1342 nm and sum-frequency mixing for an orange emission

We report on the efficient continuous-wave (CW) dual-wavelength operation of a Nd:YVO₄ laser at 1085 and 1342 nm. An output power of 1.72 W for the dual-wavelength was achieved at the incident pump power of 17.4 W. Intracavity sum-frequency mixing at 1085 and 1342 nm was then realized in a KTP crystal to reach the orange range. A maximum output power of 146 mW in the orange spectral range at 600 nm has been achieved. The orange output stability is better than 3.8%. The orange beam quality M ² value is about 1.41 and 1.25 in both horizontal and vertical dimensions, respectively.     

The mechanisms for dye laser fluorescence from 4-methylumbelliferone

The laser fluorescence emitted from solutions of 4-methylumbelliferone has been studied and it has been shown that not all of the observations are explained adequately by models proposed recently in which the various fluorescence bands are associated with different excited state structures for the 4-methylumbelliferone molecule. It is found that the observations may be explained if the structural model is extended to account for the effect of solvent environment on the emissions from the various excite stated structures. Mechanisms are proposed to account for the formation of the excited state structures associated with the emission of each of the fluorescence bands.     

Morphology and photocatalysis of mesoporous titania thin films annealed in different atmosphere for degradation of methyl orange

The effect of different annealing atmosphere on the morphology and photocatalytic activity of mesoporous TiO₂ thin films by dip-coating technique is investigated. The annealing temperature and atmosphere causes significant change of the morphology, thermal stability, photoluminescence, and photocatalytic properties of mesoporous TiO₂ films. As-prepared mesoporous thin films have an amorphous structure that is transformed to crystalline TiO₂ with well-maintained mesoporous structure at 450°C in various annealing atmosphere except that the mesoporous structure is fully destroyed for films annealed in air. Films annealed in N₂ show the enhanced UV photodegradation of methyl orange (MO) resulting from the enhanced crystallinity in these films evidenced by XRD and Raman spectra. These findings can be used to tailor the structure and morphology of mesoporous TiO₂ films and thus improve their photocatalytic activity for efficient removal of dye effluents in wastewater.     

Two-photon-excited fluorescence from silicate glass containing tantalum ions pumped by a near-infrared femtosecond pulsed laser

We report a novel phenomenon in sodium-calcium-silicate glass doped with Ta(5+). Under irradiation with a 780 nm femtosecond pulsed laser, strong blue emission centered at about 420 nm could be observed. The spectral characteristics are similar to those pumped by ultraviolet photons. The log-log correlation between integrated emission intensity and pump power reveals that a two-photon absorption process is involved in the phenomenon. It is suggested that the presence of localized Ta(5+)5d(0) energy levels is responsible for the appearance of the blue emission. The results indicate that transition metal ions without d electrons play an important role in fields of optics when embedded into glass hosts.     

Effect of CdS nanoparticles on fluorescence from Sm doped SiO2 glass

Sm³⁺ doped CdS nanoparticles have been prepared by sol-gel method. The effect of annealing temperatures and doping concentrations of CdS on the photoluminescence spectra of Sm³⁺ were studied. From the measurement of its optical absorption, three phenomenological Judd-Ofelt intensity parameters (Ω₂, Ω₄, and Ω₆) have been computed and used to parameterize the radiative properties. The influences of CdS on Sm³⁺ ions were studied by fluorescence spectroscopy. The fluorescence spectra revealed that the emission intensity of samarium increased considerably in the presence of CdS nanoparticles. The evaluation of radiative properties of Sm³⁺ containing CdS showed that the ⁴G_5/2→⁶H_7/2 transition in silica matrix had the potential to be a laser transition.     

Absorption and fluorescence of Nd3+ ion in lanthanum-borate glass

The optical properties of lanthanum-borate glass having the composition B₂O₃.La₂O₃.SrO. BaO.ThO₂ with the addition of neodymium, i.e. their absorption and infra-red emission, luminescence decay and quantum yield, were measured. A study was also made of the concentration quenching of luminescence, the optimum concentration for use in a laser and the influence of the composition of the glass (content of thorium and exchange of bivalent ion). Compared with silicate glasses, these borates exhibit higher absorption, a lower quantum yield and decay that is an order of magnitude shorter. Of the chemical composition, only the thorium content plays a role.The paper follows on from an analogical paper on silicate glasses (Phys. Stat. Sol.9 (1965), 525) and measurements on a series of lithium-calcium-borate glasses are being prepared.     

Mechanisms of fluorescence enhancement in rare earth sol-gel glass containing Al

Analysis of glasses containing Eu and Tb dopants yields new insights about the role of Al³⁺ co-doping in improving fluorescence yield of glasses containing rare earth (RE) dopants. Our work suggests that Al co-doping enhances fluorescence by two important mechanisms. (1) At low Al:RE ratio the site symmetry is lowered, allowing more admixture of opposite parity wavefunctions and increased transition probability. (2) At high Al:RE ratio, the highest frequency phonons are of lower energy; so nonradiative decay rates are reduced. In addition, a new technique - post-annealing immersion - is introduced, which allows the study of RE location in the sol-gel matrix. Al co-doping is observed to increase the tendency for RE ions to reside on pore surfaces.