M. García-Hipólito

Characterization of europium doped zinc aluminate luminescent coatings synthesized by ultrasonic spray pyrolysis process

Abstract Europium doped zinc aluminate (ZnAl 2 O 4 ) photoluminescent films have been deposited by ultrasonic spray pyrolysis deposition process. Different substrate temperatures and doping concentrations in the start spraying solution were studied. It is observed that the crystalline structure of this material depends on the substrate temperature during deposition of the films. For low substrate temperatures, the deposited films are amorphous. When the substrate temperature is increased at 500 °C some peaks corresponding to hexagonal phase of ZnO (zincite) appears. At substrate temperatures of 550 °C, the crystalline structure of the ZnAl 2 O 4 :Eu films presents the close-packed face centered cubic phase. The excitation and emission spectra were obtained; for an excitation wavelength of 260 nm, all the photoluminescence (PL) spectra show peaks located at 589, 615, 652 and 700 nm. Concentration quenching of the PL occurs at activator concentrations greater than 0.85 at.% inside the deposited films. The PL intensity increases as the substrate temperature rises. In addition, the surface morphology features of the films, as a function of the deposition temperature, are shown.

Preparation and characterization of photoluminescent praseodymium-doped ZrO 2 nanostructured powders

Praseodymium-doped ZrO2 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 750uC, 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, 505, 536, 567, 589,

Characterization of luminescent samarium doped HfO2 coatings synthesized by spray pyrolysis technique

Trivalent samarium (Sm3+) doped hafnium oxide (HfO2) films were deposited using the spray pyrolysis deposition technique. The films were deposited on Corning glass substrates at temperatures ranging from 300 to 550 °C using chlorides as raw materials. Films, mostly amorphous, were obtained when deposition temperatures were below 350 °C. However, for temperatures higher than 400 °C, the films became polycrystalline, presenting the HfO2 monoclinic phase. Scanning electron microscopy of the films revealed a rough surface morphology with spherical particles. Also, electron energy dispersive analysis was performed on these films. The photoluminescence and cathodoluminescence characteristics of the HfO2 : SmCl3 films, measured at room temperature, exhibited four main bands centred at 570, 610, 652 and 716 nm, which are due to the well-known intra-4f transitions of the Sm3+ ion. It was found that the overall emission intensity rose as the deposition temperature was increased. Furthermore, a concentration quenching of the luminescence intensity was also observed.

Characterization of ZrO2:Mn, Cl luminescent coatings synthesized by the Pyrosol technique

Abstract Manganese doped zirconia luminescent films have been deposited at temperatures ranging from 250 to 500 °C using the Pyrosol technique. The material obtained is in an amorphous state up 400 °C. For higher temperatures a polycrystalline material is obtained with a cubic and/or tetragonal crystalline zirconia phase. The photoluminescence and cathodoluminescence spectra show the bands associated with the electronic transitions 4 T 1 ( 4 G )→ 6 A 1 ( 6 S ) of the Mn2+ ions. A decrease of the luminescence, as a function of the doping concentration, substrate temperature and electron accelerating voltage is observed. The presence of chlorine seems necessary for the red luminescence. The surface morphology of the films is also presented.

Photoluminescent spectroscopy measurements in nanocrystalline praseodymium doped zirconia powders

Praseodymium doped zirconia powder (ZrO2: (0.53 at%) Pr3+) was prepared by a co-precipitation technique and annealed in air at a temperature Ta = 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 (Pr3+), 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 (Pr3+). No evidence of energy transfer from the host to the dopant was observed.

Characterization of luminescent praseodymium-doped ZrO2 coatings deposited by ultrasonic spray pyrolysis technique

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 → 3 H4, 3 P0 → 3 H4, 3 P1 + 1 I6 → 3 H5, 1 D2 → 3 H4, 3 P0 → 3 H6, 1 D2 → 3 H5, 1 D2 → 3 H5, 3 P0 → 3 F3,4 and 1 D2 → 3 F2 of the Pr 3+ 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.

Blue and red photoluminescence from Al2O3:Ce3+:Mn2+ films deposited by spray pyrolysis

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.

Structural and luminescent properties of europium doped TiO 2 thick films synthesized by the ultrasonic spray pyrolysis technique

The structural and luminescent properties of trivalent europium-doped titanium dioxide films synthesized by the ultrasonic spray pyrolysis technique at several substrate temperatures are reported. These films are nanocrystalline and present a mixture of tetragonal (anatase and rutile) crystal structures of the titania as determined by x-ray diffraction. The rutile crystal structure became predominant as the substrate temperature during deposition was increased. Under UV and electron beam excitation, these coatings showed strong luminescence due to f–f transitions and the dominant transition was the hypersensitive 5 D0 → 7 F2 red emission of Eu 3+ . The photo- and cathodoluminescence characteristics of these films were studied as a function of growth parameters such as substrate temperature and europium concentration. Excitation with a wavelength of 396 nm resulted in photoluminescent emission peaks located at 557, 580, 592, 615, 652 and 703 nm, associated with the electronic transitions of the Eu 3+ ion. The photoluminescence (PL) intensity as a whole is observed to decrease as the deposition temperature is increased. Also, with increasing doping concentration, a quenching of the PL is observed. The chemical composition and surface morphology characteristics of the films are also reported.

Cathodoluminescent and Photoluminescent Properties of Al2O3 Powders Doped with Eu

Eu-doped Al 2 O 3 powders were made by a coprecipitation technique using aluminum nitrate and europium chloride as precursors at annealing temperatures of 500, 700, and 900°C. Room temperature cathodoluminescence and photoluminescence characteristics of Al 2 O 3 :Eu powders as a function of the dopant concentration and annealing temperature have been studied. The emissions from Eu-doped powders have the spectral characteristics typical of radiative transitions among the electronic energy levels associated with the 3 + ionized state of this ion. The X-ray diffraction patterns show a broad peak that tends to become narrower as the annealing temperature is raised. Energy dispersive spectroscopy indicates that the powders are oxygen-rich, which may indicate a low density or porous material. Finally, scanning electron microscopy images show a variety in the shape and size of the powder particles associated with the milling procedure implemented in order to obtain the powders.

Photoluminescent characteristics of hafnium oxide layers activated with trivalent terbium (HfO2:Tb+3)

Hafnium oxide layers doped with trivalent terbium ions have been synthesized using the ultrasonic spray pyrolysis technique. Photoluminescence properties were studied as a function of growth parameters such as the substrate temperature and the terbium concentration. The films were grown starting from aqueous solution of Hafnium and Terbium chlorides. The results show that crystalline structure of HfO2:Tb+3 films depends on the temperature. Emission and excitation spectra were obtained for the HfO2:Tb+3 films using 262 nm as the excitation wavelength. All emission spectra show bands centered at 488, 542, 584 and 621 nm, which correspond to the electronic transitions: 5D4→7Fj (j=3, …, 6) characteristic of trivalent terbium ion. The dominant emission intensity corresponds to the green color, which depend on the terbium concentration incorporated inside the host matrix.