Photoinduced effects in γ-glycine nanocrystallites embedded in polymer matrices

We have established a principal role of the polarity of polymer matrices on the piezooptical dispersion of the γ-glycine nanocrystallites embedded into the polymethymethacrylate (PMMA) and polycarbonate (PC) matrices. We found that the optical treatment by bicolor two laser beams at 1064 nm and 532 nm which are originating from the same 10 ns Nd:YAG laser, causes occurrence of the piezooptical effects. The optimal content of the γ-glycine nanocrystallites with respect to the magnitude of piezooptical coefficients was within the range of size 50-80 nm, corresponding to the 6.5 wt.%. We studied relaxation and spectral dependence of the corresponding coefficients of the piezooptic tensor.     

Optical operation by elastooptical dispersion of Nd-containing oxide crystals

The dispersion of the piezooptical coefficients induced by external light for neodymium-containing NdGaO₃, K₅Nd(MoO₄)₄, α-RbNd(WO₄)₂, and NdAl₃(BO₃)₄ crystals was discovered. As a pumping laser we have used Nd:YAG laser possessing power density varying from 0.2 up to 1 GW/cm², pulse duration 15 ns and frequency repetition 10 Hz. The dispersion of the piezooptical coefficients was evaluated in the spectral range 450-910 nm. We have found that illumination by the laser pulses with power density up to 1 GW/cm² cause substantial changes of the piezooptical coefficients in these crystals. However, behaviour of the obtained dependences is substantially different for all the compounds. The possible origins of the observed effects are considered.     

Piezooptical effects in the tellurite glasses doped by europium and gold

We present the temperature dependence of piezooptical coefficients for three samples of TeO₂-GeO₂-PbO glasses doped with 0.5% of Eu₂O₃, 0.5% and 1% of Au₂O₃, after different thermoannealing times. We have established that there exist two temperatures singularities - minima in the range 655-695 K and maxima - at 850 K. It is crucial that for the glasses annealed during 61 h, at temperatures about 850 K, the anomaly of piezooptical coefficient disappears. Simultaneously the minima within the range 655-695 K changed depending on the duration of the thermoannealing which leads to low temperature shift of the minima. Towards lower temperature the piezooptical maxima occurs around 850 K and disappears after the increase of the annealing time. It is also crucial that the values of the piezooptical coefficients decrease with the enhancement of the thermoannealing. The observed temperature dependence with the piezooptical coefficients has a good correlation with the temperature dependences of the DSC. We have found that the pure glasses and glasses doped only by Au₂O₃ and Eu₂O₃ possess the piezooptical coefficients one order less with respect to the samples possessing simultaneously Au₂O₃ and Eu₂O₃.     

Synergistic upconversion effect in NaYF4:Yb,Tm nanorods under dual excitation of 980 nm and 808 nm

NaYF₄:Yb³⁺,Tm³⁺ nanorods are prepared with hydrothermal method. The upconversion luminescent properties are investigated under dual excitation of 980 nm and 808 nm. The blue emission is observed at about 475 nm under dual excitation. The intensity is 2.6 times higher than the total intensity of the two corresponding single wavelength excitations, showing a synergistic upconversion effect occurring there. The dual wavelength excitation not only effectively decreases non-radiative relaxation pumped by 980 nm but also reduces the rate of the back energy transfer from Tm³⁺ to Yb³⁺ pumped by 808 nm. The result provides a possible new way to further improve the upconversion efficiency of rare earth doped phosphor.     

Dependence of intermediated noble metals on the optical and electrical properties of ITO/metal/ITO multilayers

Sn doped In₂O₃ (ITO) single layer and a sandwich structure of ITO/metal/ITO (IMI) multilayer films were deposited on a polycarbonate substrate using radio-frequency and direct-current magnetron sputtering process without substrate heating. The intermediated metal films in the IMI structure were Au and Cu films and the thickness of each layer in the IMI films was kept constant at 50 nm/10 nm/40 nm. In this study, the ITO/Au/ITO films show the lowest resistivity of 5.6 × 10⁻⁵ Ω cm.However the films show the lower optical transmission of 71% at 550 nm than that (81%) of as deposited ITO films. The ITO/Cu/ITO films show an optical transmittance of 54% and electrical resistivity of 1.5 × 10⁻⁴ Ω cm. Only the ITO/Au/ITO films showed the diffraction peaks in the XRD pattern. The figure of merit indicated that the ITO/Au/ITO films performed better in a transparent conducting electrode than in ITO single layer films and ITO/Cu/ITO films.     

Sol-gel preparation and enhanced photocatalytic performance of Cu-doped ZnO nanoparticles

Cu-doped ZnO nanoparticles were prepared by a sol-gel method for the first time. XRD, XPS, UV-vis and FS techniques were used to characterize the Cu-doped ZnO samples. The photocatalytic activity was tested for methyl orange degradation under UV irradiation. The results show that the crystal sizes of ZnO and 0.5% Cu/ZnO nanoparticles with wurtzite phase are 32.0 and 28.5 nm, indicating that Cu-doping hinder the growth of crystal grains. The doped Cu element existed as Cu²⁺. The optimal Cu doping concentration in ZnO is 0.5%. The optimal calcination condition is at 350 °C for 3 h. The MO degradation rate of 0.5% Cu/ZnO reaches 88.0% when initial concentration of MO is 20 mg/L, exceeding that of undoped ZnO. The enhanced charge carrier separation and increased surface hydroxyl groups due to Cu-doping contributed to the enhanced photocatalytic activity of 0.5% Cu/ZnO.     

Near-infrared luminescence of OH and Cl doped Bi4Ge3O12 crystals

OH⁻ and Cl⁻ doped Bi₄Ge₃O₁₂ (BGO) single crystals had been grown by Vertical Bridgman (VB) method. The structure of these crystals was determined by XRD, the transmittance and emission spectra in near infrared region (NIR) were measured at room temperature. 5% OH⁻ doped BGO shows a significant emission band peaking around 1181 nm under 808 nm laser diodes (LDs) excitation, and the 5% Cl⁻ doped BGO exhibits a relatively weak emission band as well. 100% and 5% OH⁻ doped BGO show noticeable emission band centered at about 1346 nm under 980 nm LDs excitation.     

Spectroscopic properties of OH doped and Bi-rich Bi4Ge3O12 crystals by vertical Bridgman method

OH⁻ doped and Bi-rich Bi₄Ge₃O₁₂ (BGO) single crystals were grown by Vertical Bridgman (VB) method. The structure of these crystals was determined by XRD, and the emission spectra in visible and near infrared region (NIR) were measured at room temperature. The emission spectrum of Bi-rich BGO has extra peaks at 385, 367 and 357 nm, Bi-rich BGO after annealing in Ar at 500 °C for 5 h shows a significant emission band peaking around 1170 nm under 808 nm laser diodes (LDs) excitation, and OH⁻ doped BGO shows a noticeable emission band centered at about 1346 nm under 980 nm LDs excitation. A brief discussion is presented.     

Synthesis and fluorescence properties of pure and metal-doped spherical ZnS particles from EDTA-metal complexes

Monodispersed spherical ZnS particles as well as doped with Cu, Mn ions were synthesized from metal-chelate solutions of ethylenediamine tetraacetate (EDTA) and thioacetamide (TAA). The characterizations of the ZnS-based particles were investigated via TEM, SEM, XRD, TG/DTA and PL measurements. The sphere size was controlled from 50 nm to 1 μm by adjusting the nucleation temperatures and molar ratio of Zn-EDTA to TAA. The emission intensity continuously increased with the increase of the particle size. When the ZnS microspheres were annealed at 550-800 °C, there were two specific emission bands with the centers at 454 nm and 510 nm, which were associated with the trapped luminescence arising from the surface states and the stoichiometric vacancies, respectively. When Cu²⁺ was introduced into ZnS microspheres, the dominant emission was red-shifted from 454 to 508 nm, fluorescence intensity also sharply increased. However, for the Mn²⁺-doped ZnS, the emission intensity was significantly enhanced without the shift of emission site.     

Radiation response behaviour of Al codoped germano-silicate SM fiber at high radiation dose

Radiation response behaviour of Ge + Al doped SM fiber fabricated by the solution doping process has been studied at room temperature with respect to 1310 nm transmission wavelength under three different dose rates of 200, 400 and 600 Rad/min to compare with that of standard Er doped as well as Ge doped SM fibers. Their radiation sensitivity has been observed with variation of dose rates, transmission wavelength along with their recovery nature. Radiation response behaviour of Al doped SM fiber is found to be slightly non-linear in nature with very low dose rate dependency. No saturation level was found upto 13 Krad cumulative dose. Thermobleaching as well as photobleaching phenomena have also been studied. Gamma irradiated Al doped preform shows an absorption peak at around 300 nm due to generation of Al (E′) defect center and gets annihilated after thermobleaching process. Gamma irradiated Al doped SM fiber shows prominent photobleaching effect on their optical attenuation with respect to the 850 nm transmission wavelength. From ESR study resonance signals for Al³⁺ related radiation-induced defect centers are not clearly observed in this study. A very weak hyperfine pattern has been observed for gamma irradiated Al doped preform sample. The high radiation sensitivity along with linear response behaviour, low recovery and almost dose rate independence behaviour of the material system of Ge + Al codoped SM core optical fiber under gamma radiation shows their potential for application as fiber optic radiation sensor in comparison to the universal standard erbium doped SM fiber.     

Electron beam induced green luminescence and degradation study of CaS:Ce nanocrystalline phosphors for FED applications

Green luminescence and degradation of Ce³⁺ doped CaS nanocrystalline phosphors were studied with a 2 keV, 10 μA electron beam in an O₂ environment. The nanophosphors were synthesized by the co-precipitation method. The samples were characterized using X-ray diffraction, Transmission electron microscopy, Scanning electron microscopy/electron dispersive X-ray spectroscopy and Photoluminescence (PL) spectroscopy. Cubic CaS with an average particle size of 42 ± 2 nm was obtained. PL emission was observed at 507 nm and a shoulder at 560 nm with an excitation wavelength of 460 nm. Auger electron spectroscopy and Cathodoluminescence (CL) were used to monitor the changes in the surface composition of the CaS:Ce³⁺ nanocrystalline phosphors during electron bombardment in an O₂ environment. The effect of different oxygen pressures ranging from 1 × 10⁻⁸ to 1 × 10⁻⁶ Torr on the CL intensity was also investigated. A CaSO₄ layer was observed on the surface after the electron beam degradation. The CL intensity was found to decrease up to 30% of its original intensity at 1 × 10⁻⁶ Torr oxygen pressure after an electron dose of 50 C/cm². The formation of oxygen defects during electron bombardment may also be responsible for the decrease in CL intensity.     

Nonlinear refraction and photoinduced birefringence in chlorophosphonazo I doped polymer thin films

The nonlinear refraction and photoinduced birefringence of chlorophosphonazo I (CPA I ) doped PVA thin films were investigated. The single-beam Z-scan measurement showed that CPA I doped PVA thin film possessed a large value of nonlinear refractive index (n₂=1.82×10⁻¹² cm²/W) under a pulse 532 nm excitation, and the mechanism accounting for the process of nonlinear refraction was discussed in term of resonant electronic effect. Moreover, fast and stable molecular reorientation was observed when investigating the photoinduced birefringence of CPA I doped PVA thin film with a CW 532 nm laser as pump light and a CW 650 nm laser as probe light.     

Sm-doped polymer optical waveguide amplifiers

Trivalent samarium ion (Sm³⁺) doped SU8 polymer materials were synthesized and characterized. Intense red emission at 645 nm was observed under UV laser light excitation. Spectroscopic investigations show that the doped materials are suitable for realizing planar optical waveguide amplifiers. About 100 μm wide multimode Sm³⁺-doped SU8 channel waveguides were fabricated using a simple UV exposure process. At 250 mW, 351 nm UV pump power, a signal enhancement of ∼7.4 dB at 645 nm was obtained for a 15 mm long channel waveguide.     

Effect of gamma ray irradiation on optical properties of Nd doped phosphate glass

The effect of gamma irradiation in the dose range of 5-500 kGy on the optical absorption and luminescence spectra of Nd doped phosphate glass is reported. The spectral absorption of this glass before and after gamma irradiation was measured in the spectral range 300-900 nm at room temperature using spectrophotometer and synchrotron beamline. Drastic increase in absorption was noted below 600 nm after gamma irradiation, which was dependent on the dose of irradiation. Additional absorption (AA) spectra of irradiated sample shows generation of two absorption bands below 600 nm, which finally became one very broad band peak with increased intensity at irradiation dose of 500 kGy. AA spectra also show the presence of negative peaks at the location of absorption peaks of Nd³⁺. Photoluminescence of Nd doped phosphate glass shows two strong bands which decreases to a very low intensity with a red shift after gamma irradiation. These results indicate that irradiation produces different kinds of defects in the glass material along with conversion of valence state of Nd³⁺ to Nd²⁺. This change was found irreversible at room temperature.     

Synthesis and characterization of Cu doped ZnS nanoparticles using TOPO and SHMP as capping agents

Undoped and Cu²⁺ doped (0.2-0.8%) ZnS nanoparticles have been synthesized through chemical precipitation method. Tri-n-octylphosphine oxide (TOPO) and sodium hexametaphosphate (SHMP) were used as capping agents. The synthesized nanoparticles have been analyzed using X-ray diffraction (XRD), transmission electron microscope (TEM), Fourier transform infrared spectrometer (FT-IR), UV-vis spectrometer, photoluminescence (PL) and thermo gravimetric-differential scanning calorimetry (TG-DTA) analysis. The size of the particles is found to be 4-6 nm range. Photoluminescence spectra were recorded for ZnS:Cu²⁺ under the excitation wavelength of 320 nm. The prepared Cu²⁺-doped sample shows efficient PL emission in 470-525 nm region. The capped ZnS:Cu emission intensity is enhanced than the uncapped particles. The doping ions were identified by electron spin resonance (ESR) spectrometer. The phase changes were observed in different temperatures.     

Enhanced field emission from Si doped nanocrystalline AlN thin films

Si doped and undoped nanocrystalline aluminum nitride thin films were deposited on various substrates by direct current sputtering technique. X-ray diffraction analysis confirmed the formation of phase pure hexagonal aluminum nitride with a single peak corresponding to (1 0 0) reflection of AlN with lattice constants, a = 0.3114 nm and c = 0.4986 nm. Energy dispersive analysis of X-rays confirmed the presence of Si in the doped AlN films. Atomic force microscopic studies showed that the average particle size of the film prepared at substrate temperature 200 °C was 9.5 nm, but when 5 at.% Si was incorporated the average particle size increased to ∼21 nm. Field emission study indicated that, with increasing Si doping concentration, the emission characteristics have been improved. The turn-on field (E_to) was 15.0 (±0.7) V/μm, 8.0 (±0.4) V/μm and 7.8 (±0.5) V/μm for undoped, 3 at.% and 5 at.% Si doped AlN films respectively and the maximum current density of 0.27 μA/cm² has been observed for 5 at.% Si doped nanocrystalline AlN film. It was also found that the dielectric properties were highly dependent on Si doping.     

Transfer and backtransfer processes in Yb-Er codoped Strontium Barium Niobate glass-ceramics

The forward and backward energy transfer processes in Strontium Barium Niobate glass-ceramics double doped with Yb³⁺ and Er³⁺ ions have been studied. In these samples the rare earth ions are incorporated into the nanocrystals with an average size of 50 nm. Using laser excitation at 950 nm is possible to excite selectively the Yb³⁺ ions and detect emission due to these ions (at 1040 nm) or combined with the Er³⁺ ions (at 980 nm). In previous works, the energy transfer processes between these ions in different matrices have been analyzed in order to improve the emission at 1550 nm, but these analyses are restricted to fast migration processes among ions. In this fast migration regimen the results are valid only for larger concentrations. However, in this work the dynamics of these transfer processes has been carried out using a general method called “transfer function model”. The parameters which characterize these processes have been obtained and it has been possible to explain the important increase of the emission at 1550 nm due to the co-doping with Yb³⁺ ions. This analysis is valid for any range of doping concentrations.     

Luminescence characterization and electron beam induced chemical changes on the surface of ZnAl2O4:Mn nanocrystalline phosphor

Luminescence characteristics and surface chemical changes of nanocrystalline Mn²⁺ doped ZnAl₂O₄ powder phosphors are presented. Stable green cathodoluminescence (CL) or photoluminescence (PL) with a maximum at ∼512 nm was observed when the powders were irradiated with a beam of high energy electrons or a monochromatic xenon lamp at room temperature. This green emission can be attributed to the ⁴T₁ → ⁶A₁ transitions of the Mn²⁺ ion. Deconvoluted CL spectra resulted in two additional emission peaks at 539 and 573 nm that may be attributed to vibronic sideband and Mn⁴⁺ emission, respectively. The luminescence decay of the Mn²⁺ 512 nm emission under 457 nm excitation is single exponential with a lifetime of 5.20 ± 0.11 ms. Chemical changes on the surface of the ZnAl₂O₄:Mn²⁺ phosphor during prolonged electron beam exposure were monitored using Auger electron spectroscopy. The X-ray photoelectron spectroscopy (XPS) was used to determine the chemical composition of the possible compounds formed on the surface as a result of the prolonged electron beam exposure. The XPS data suggest that the thermodynamically stable Al₂O₃ layer was formed on the surface and is possibly contributing to the CL stability of ZnAl₂O₄:Mn phosphor.     

Laser operated elasto-optical features of La2CaB10O19:Pr3+ polymer nanocomposites

We have discovered a principal role of the polymer matrices on the spectral dependences of piezooptical coefficients of La₂CaB₁₀O₁₉:Pr³⁺ (LCBO:Pr) nanocomposites formed by polymethylmethacrylate (PMMA) and polycarbonate (PC) matrices. It was established that the optical treatment by the 10 ns Nd:YAG laser can cause substantial changes of the dispersion of the piezooptical coefficients within the spectral wavelength 1400–1600 nm. The optimal content of the LCBO:Pr with sizes ranging from 40 to 110 nm corresponds to 4–6% in weighing units. Following the performed quantum chemical simulations, the observed changes are caused by different polarizabilities of the polymer matrices.     

Failure behavior of ITO diffusion barrier between electroplating Cu and Si substrate annealed in a low vacuum

A structure of Cu/ITO(10 nm)/Si was first formed and then annealed at various temperatures for 5 min in a rapid thermal annealing furnace under 10⁻² Torr pressure. In Cu/ITO(10 nm)/Si structure, the ITO(10 nm) film was coated on Si substrate by sputtering process and the Cu film was deposited on ITO film by electroplating technique. The various Cu/ITO(10 nm)/Si samples were characterized by a four-point probe, a scanning electron microscope, an X-ray diffractometer, and a transmission electron microscope. The results showed that when the annealing temperature increases near 600 °C the interface between Cu and ITO becomes unstable, and the Cu₃Si particles begin to form; and when the annealing temperature increases to 650 °C, a good many of Cu₃Si particles about 1 μm in size form and the sheet resistance of Cu/ITO(10 nm)/Si structure largely increases.