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Praseodymium-doped ZrO 2 photoluminescent (PL) powders have been prepared by a co-precipitation process. Different doping concentrations in the start mixture and annealing temperatures for the precipitated were studied. It is observed that the crystalline structure and the crystallinity of the powders depend on the annealing temperature. For temperatures higher than 750˚C, the material presents the monoclinic phase with an average crystalline grain size of 100 nm. Measurements on photoluminescence show excitation and emission spectra. For an excitation wavelength of 294 nm, all the PL emission spectra show the peaks located at 490

ZrO2 : Pr films were synthesized by the ultrasonic spray pyrolysis process. X-ray diffraction studies, as a function of the deposition temperature, indicate a tetragonal crystal structure of zirconia as the substrate temperature was increased. Luminescence (photo- and cathodoluminescence) properties of the films were studied as a function of growth parameters such as the substrate temperature and the praseodymium concentration. For an excitation wavelength of 290 nm, all the photoluminescent emission spectra show peaks located at 490, 510, 566, 615, 642, 695, 718, 740 and 833 nm, associated with the electronic transitions 3 P0 → 3H4, 3P0 → 3 H4, 3P1 + 1I6 → 3H5, 1D2 → 3H4, 3 P0 → 3H6, 1D2 → 3 H5, 1D2 → 3H5, 3 P0 → 3F3,4 and 1D2 → 3 F2 of the Pr3+ ion. As the deposition temperature is increased, an increasing intensity of the luminescence emission is observed. Also, quenching of the luminescence, with increasing doping concentration, is observed. The chemical composition of the films as determined by energy dispersive spectroscopy is reported as well. In addition, the surface morphology characteristics of the films, as a function of the deposition temperature, are presented.

Cathodoluminescent (CL) powders of zinc aluminate activated with samarium ions have been prepared by a co‐precipitation chemical process. Different doping concentrations in the start mixture and sintering temperatures for the precipitated powder were studied. It was observed that the crystalline characteristics of the powders depend upon the sintering temperature. For temperatures higher than 450 °C, the powders presented the cubic spinel phase with a lattice parameter value of 8.0756 Å, and grain sizes from 50 to 100 nm with semispherical shape. The CL emission spectra showed broad bands localized at 564, 602, 644, and 703 nm associated with 4G5/2 → 6H5/2, 4G5/2 → 6H7/2, 4G5/2 → 6H9/2, and 4G5/2 → 6H11/2 transitions in the Sm3+ ions, respectively. Concentration quenching of the cathodoluminescence occurred at about 4.26 at% of the activator (Sm) concentration inside the sintered powders. (© 2005 WILEY‐VCH Verlag GmbH & Co. KGaA, Weinheim)

Praseodymium doped zirconia powder (ZrO 2 : (0.53 at%) Pr 3+ ) was prepared by a co-precipitation technique and annealed in air at a temperature T a = 950 • C. The x-ray diffraction pattern shows a nanocrystalline structure composed of 29.6% monoclinic and 70.4% cubic-tetragonal phases. Medium infrared and Raman analysis confirms the monoclinic/cubic-tetragonal crystalline structure and proves the absence of praseodymium aggregates in the material. Photoluminescent spectroscopy over excitations of 457.9 and 514.9 nm (at 20 K), shows two emission spectra composed of many narrow peaks in the visible-near infrared region (VIS-NIR) of the electromagnetic spectrum, associated with 4f inter-level electronic transitions in praseodymium ions incorporated in the zirconia. Excitation and emission spectra show the different mechanisms of the direct and non-direct excitation of the dopant ion (Pr 3+ ), and the preferential relaxation of the material by charge transfer from the host (zirconia) to the 4f5d band and the 4f inter-level of the dopant ion (Pr 3+ ). No evidence of energy transfer from the host to the dopant was observed.

Al2O3:Ce3+:Mn2+ films deposited by the spray pyrolysis technique show blue and red emissions under ultraviolet light excitation. The blue emission is due to the de-excitation of Ce3+ ions from their excited state 5d to the split ground state 2F. The usually weak red emission attributed to 3d  3d de-excitation of Mn2+ is enhanced through an efficient energy transfer from Ce3+ to Mn2+ ions. The most probable mechanism of energy transfer is found to be electric dipole–quadrupole interaction. The quantum efficiency of this transfer was estimated as being near to 100%, which makes these films interesting phosphors for the design of luminescent layers in flat-panel displays with two-colour emission.

Europium doped Al2O3 photoluminescent coatings have been prepared by an ultrasonic spray pyrolysis process, using a solution of 0.05M of AlCl3 · 6H2O as starting material and EuCl3 as doping. These films were deposited on Pyrex glass substrates at atmospheric pressure using purified air as a carrier gas. All films were amorphous in structure. The photoluminescence spectra were measured at room temperature as a function of substrate temperature and doping concentration. For an excitation wavelength of 395 nm, all the photoluminescent spectra show bands located at 587, 600, 612 and 648 nm, characteristics of the trivalent europium ion. We observed a concentration quenching of the photoluminescence at values of activator concentration above 10 at% in the starting solution.

The leaves of Agave tequilana Weber variety Blue represent a viable, inexpensive, and renewable source of lignocellulosic biomass and fructans for the production of second generation biofuels. The objective was to study the effect of drying temperature on the release of reducing sugars for the agave leaves. It was found that with pretreatment‐drying at 100°C for 30.5 ± 1.0 min had a maximum of the release of reducing sugars with a 66% increment compared to 60°C. An aqueous extract obtained from the powder of the leaves after drying did not show the presence of furfural and hydroxymethylfurfural compounds. Phenolic compounds were detected in order of 120.8 ± 1.0 mg L−1 below 1 g L−1 reported to cause inhibition of the alcoholic fermentation. In addition the drying of the leaves also can be used as preservation of agave leaf for biomass storing. The results show that pretreatment‐drying allow increase the release of reducing sugars, avoids thermal degradation and does not produce significant concentrations of fermentation inhibitors. Practical Applications The research in industrial waste materials has received special attention worldwide because it is potential for production of biofuels. This study propose a simple method of drying that acts as a thermal pretreatment of Agave tequilana Weber variety Blue leaves that increases the release of reducing sugars, avoids thermal degradation, not produce significant concentrations of fermentation inhibitors for ethanol production and can be used as a preservation method for storing biomass of the agave leaves. The results would be useful not only in the energy field but also in the alimentary and pharmaceutical industry. Fructans and phenolic compounds found in the agave are used as functional ingredients in the food industry and also bioactive compounds that by themselves promotes future research for the Agave tequilana.