By incorporating low weight percentages of graphene in our precursor solution and using a technique derived from spray pyrolysis, we obtained a low cost TCO with excellent properties, characterized by AFM, UV-VIS and Hall Effect. The film roughness was calculated to be ~7.49-12.7 nm, while band gap was determined to be ~4.0-4.2 eV. The material’s optical transparency ranges from 84-86% and its resistivity was measured to be ~5.5-8.5 x10-3 Ω cm. With these results, we suggest that the obtained material is a proper candidate for use in photovoltaic applications, such as Grätzel solar cells, which will be our main focus.
A technique to fabricate dye (rhodamine B) sensitized solar cells based on Titanium Oxide (TiO2) and Zinc Oxide (ZnO) nanoparticles are reported. The TiO2 was synthesized using the sol-gel method and the ZnO was synthesized by hydrolysis method to obtain nanoparticles of ~ 5 nm and 150 nm respectively. ZnO was doped with Al3+ in order to enhance the photovoltaic efficiency to promote the electrons mobility. The photovoltaic conversion characterization of films of TiO2, ZnO and ZnO:Al3+ nanoparticles is also reported. The generated photocurrent was measured by two methods; one of those uses a three electrode electrochemical cell and the other use an electronic array where the cells were exposed to UV lamp and the sun light. The role of the TiO2, ZnO and Al3+ doped ZnO nanoparticles is discussed to obtain a better efficiency in the generation of photocurrent (PC). The results exhibited by the electrochemical cell method, efficiencies of 0.55 (PC=187 μA/cm2) and 0.22 (PC=149 μA/cm2) for TiO2 and undoped ZnO respectively. However, when ZnO is doped with Al3+ at the higher concentration the efficiency was 0.44. While using the electronic array the results exhibited efficiencies of 0.31 (PC=45 μA/cm2) and 0.09 (PC=16 μA/cm2) for TiO2 and undoped ZnO respectively. However, when ZnO is doped with Al3+ at the higher concentration the efficiency was 0.44 and 0.48 for electrochemical cell and electronic array respectively. This shows that Al3+ enhances the photogenerated charge carriers increasing the mobility of electrons.
This work reports the synthesis, structural characterization, and optical properties of ZrO2:Yb3+-Er3+ (2–1 mol%) nanocrystals. The nanoparticles were coated with 3-aminopropyl triethoxysilane (APTES) and further modified with biomolecules, such as Biotin-Anti-rabbit (mouse IgG) and rabbit antibody-AntiKi-67, through a conjugation method. The conjugation was successfully confirmed by Fourier transform infrared, zeta potential, and dynamic light scattering. The internalization of the conjugated nanoparticles in human cervical cancer (HeLa) cells was followed by two-photon confocal microscopy. The ZrO2:Yb3+-Er3+ nanocrystals exhibited strong red emission under 970-nm excitation. Moreover, the luminescence change due to the addition of APTES molecules and biomolecules on the nanocrystals was also studied. These results demonstrate that ZrO2:Yb3+-Er3+ nanocrystals can be successfully functionalized with biomolecules to develop platforms for biolabeling and bioimaging.
Raman spectroscopy is in the scientific community an accepted and applied noninvasive technique, which can be used to
identify many classes of potentially explosive materials, based on vibrational molecular information. This technique has
demonstrated to be a useful tool for the identification and characterization of explosives that are of interest for forensic
services and security, and is used due to the necessity for a fast identification of potentially explosive materials of
homemade manufacture, which can be made using chemical agents available in the market. This technique allows the
identification of precursory substances, without direct handling, nor exposure to any potentially harmful environment,
providing high personal security in the process.
In this work, the analysis of some commonly used precursors for explosives' production was done, by means of a
portable Raman spectrometer, in a fast way and using transparent sample-containers.
The Photoluminescence (PL), FFTIR, Raman characterization, XRD and TEM of Er doped nanocrystals (Y3Al5O12:Er)
prepared by glycolate method modified with PVA and UREA is reported. Irregular morphology was observed but for
some concentration of PVA and UREA nanorods was observed, being PVA dominant in final morphology. XRD patterns
show the presence of hexagonal phase of YAG (YAH) when the UREA was used but pure YAG crystalline structure was
obtained with only PVA. Raman spectroscopy confirms the crystalline phase and in combination with infrared
spectroscopy the presence of oxygen deficiency was observed. Strong green emission was observed as a result of the
upconversion mechanism due to the two photon process. Luminescence results show that both PVA and UREA do not
modify the emission properties but control the morphology.
The thermoluminescence (TL) characterization of undoped and Lu3+ doped nanocrystalline ZrO2 under β-ray irradiation
is presented. The average crystallite size was 40 nm and the crystalline structure was monoclinic although for doped
samples 5 wt% of tetragonal was observed. The TL results show a typical second order kinetic with four TL peaks
centered around 120, 170, 240 and 280 °C when the sample is exposed to β-ray irradiation. The presence of dopant ion
induces changes in the trapping process and recombination efficiency in the TL response. The result is that dominant
peak typically centered at 120 °C was quenched while the peak centered at 240 °C was enhanced. This shifting to higher
temperature of the dominant peak induces important changes in the dosimetric properties of nanocrystals. The dosimetric
behavior for TL method and the TL fading of the samples under β-irradiation was systematically characterized as
function of the dopant concentration. The high efficiency of the TL suggest a good potential of this nanophosphor as β-
irradiation dosimeter.
Erbium doped, SiO2 - TiO2 powders were fabricated using the sol gel technique. The Er3+ concentrations were 2%, 5% and 10% (mol), and 10%, 25%, 50%, 70% for the TiO2. A strong, green up-conversion luminescence was found in the samples when exciting at 1532 nm and 978 nm. The recorded spectra showed less intense emissions at 410 nm and 675 nm. The excitation and emission mechanisms proposed were supported on experimental results, such as the absorption and emission spectra, the decay times and the luminescence intensity versus pump power.
Nanocrystalline yttrium aluminum garnet doped with Cerium (YAG:Ce3+), was synthesized by means of a modified sol-gel method that consists of a mixture of salts in an aqueous media. Structure and morphology were characterized by X-ray diffraction and Transmission Electron Microscopy. Single crystalline phase were obtained and the crystallite size range from 26 nm to 96 nm depending on the annealing temperature (from 800 to 1150 °C, respectively). The photoluminescence dependence on the crystallite size and ion concentration was performed. The experimental results show that the best ion concentration where the highest luminescence was obtained correspond to 0.1 mol% and that increases as the crystallite size increases. The feasibility of the modified sol-gel method for the preparation of nanocrystalline YAG is discussed.
Nanocrystalline ZrO2:Sm3+ doped at 2 mol% was prepared by sol-gel process and the structure and photoluminescence characterization as function of the annealing temperature were performed. Strong visible fluorescence emission produced by transitions 4G5/2→4H5/2,7/2,9/2 of Sm3+ was obtained by energy transfer process exciting the host at 320 nm and by direct excitation at 408 nm. The experimental results show a quenching of the emission bands by reducing the annealing temperature that is associated with a high content of tetragonal structure. Furthermore, an important change in the structure of the signal emitted was observed when ion was excited directly and the annealing temperature was reduced. These results suggest the possibility to tune the emission of ZrO2:Sm3+ nanophosphor.
The photoluminescence and crystalline structure characterization of undoped and several samarium and erbium doped ZrO2 samples are reported. Strong visible fluorescence emission produced by the transitions 4G5/2→6H5/2,7/2,9/2 of Sm3+ was obtained by the excitation of the host at 320 nm (downconversion). Green (545 nm) and red (680 nm) emissions bands were observed under 962 nm excitation (upconversion). Experimental results showed that the emission bands could be tuned by controlling the Er3+ concentration. In particular, for the highest Er3+ concentration, the red band is enhanced under 962 nm excitation. The nature of this behavior is discussed taking into account the concentration dependent non-radiative energy transfer (4I13/2 + 4I11/2) → (4F9/2 + 4I15/2) and cross-relaxation (2H11/2 + 4I15/2) → (4I9/2 + 4I13/2) process.
The photoluminescence (PL) and thermoluminescence (TL) characterization of undoped and cerium and terbium doped nanocrystalline Y3Al5O12 (YAG) prepared by the sol-gel method is reported. The experimental results of the PL show the typical emission bands centered at 490, 543 and 590 nm for YAG:Tb3+ and 530 nm for YAG:Ce3+ when excited with 325 and 345 nm light, respectively. The TL signal was obtained after exposure to UV-, X- and β- irradiation. The thermoluminescence results indicate that YAG:Tb3+ sample is very sensitive to all type of irradiation used, being highly sensitive for UV-irradiation. The high efficiency of the TL and PL suggests a good potential of this material as radiation dosimeter as well as active optical windows and new generation television screen.
Polystyrene dye doped plastic optical fiber was prepared and used to detect gamma and beta radiation from I151 and TeO4 gamma tracers typically used to get images of tumor areas within the human body. Absorption and fluorescence emission of TMQ, PBDBD365, POPOP styrene doped was performed under gamma and UV-irradiation. The fluorescence efficiency of the binary system PBDBD365-POPOP and the ternary TMQ- PBDBD365-POPOP was compared and according to the experimental results it was shown that the presence of the TMQ dye enhance the fluoresce obtained under I151 radiation. Systematic characterization of the binary system was performed as function of primary dye concentration .
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