Key Engineering Materials Vols. 368-372

Abstract: Position-sensitive photodetectors, a useful class of sensor with a wide range of applications in automatization and measuring techniques, on the basis of a La0.7Sr0.3MnO3/Si heterojunction have been developed. Thin p-La0.7Sr0.3MnO3 films were grown on n-Si substrates by laser molecular beam epitaxy. The large lateral photovoltaic effect has been observed in response to excitation by ultraviolet laser spot irradiation. The position characteristics are symmetric to the zero and linear between the contacts. The devices work well under unbiased conditions and so are simple to configure for practical applications.

Abstract: In this paper, the application of new functional nano-material films prayed on transmission display screen is studied. Optical properties, such as luminance gain and scattering angle, of the screens are measured to investigate the particle size effects on the properties. The results show that the optical properties of screen sprayed with nano-material film improve notably compared with those screens with films of conventional particle sizes. When the particle size is less than 100nm, the gain is high and the viewing angle low. With increasing particle sizes, the characteristics of screens vary with particle sizes. In order to solve the contradictory relationship between gain and viewing angle and to obtain screens with desirable optical properties, suitable nano-particle sizes ranging from 400nm to 700nm should be chosen for the spraying film. The scattering mechanisms between nano-particles and light are also discussed.

Abstract: We successfully developed a novel elasticoluminescent (EML) material with water resistance, CaAl2Si2O8:Eu2+ (CAS). The crystal structure, photoluminescence (PL) and EML properties were characterized for both CAS and the typical EML material SrAl2O4:Eu2+(SAO). Contrary to SAO, CAS showed superior water resistance property. No changes were found in the XRD patterns, and the PL, EML intensities, during the whole examination of water immersion test.

Abstract: Europium-doped strontium aluminate is a famous green phosphor that can give luminescence under a mechanical stress that is named elastico-luminescence. This paper reports a modified reverse micelles process for preparing the europium-doped strontium aluminate nanoparticles. A polymeric matrix was coated on the surface of the precursor formed in the reverse micelles. The polymeric matrix is considered to prevent the particle agglomeration by forming a carbon layer while the precursor was heat-treated. Consequently, the luminescent nanoparticles were achieved after removing the carbon layer and forming the luminescent center under a reducing atmosphere. The processing and properties of the luminescent nanoparticles were discussed in this paper.

Abstract: We have revealed that SrCaMgSi2O7:Eu phosphors emits blue-greenish light under the application of a mechanical stress, called as mechanoluminescence (ML). The ML showed a similar spectrum as photoluminescence, which indicated that ML is emitted from the same center of Eu2+ ions as PL. Such a blue-greenish light of ML emission can be seen by the naked eye when pressing the sample. In addition, the ML intensity of SrCaMgSi2O7:Eu proportionally increased with the increase of mechanical load.

Abstract: Eu2+ activated strontium silicate (Sr3SiO5:Eu2+) yellow phosphor was prepared by the conventional solid-state reaction technique in reduction atmosphere with starting materials SrCO3, SiO2 and Eu2O3. The phase, morphology and luminescence property of the samples were analyzed. The X-ray diffraction analysis showed the main phase in all samples is tetragonal Sr3SiO5. With Eu2+ ions doped into the host lattice, the Sr3SiO5:Eu2+ phosphors absorb light energy in the UV-visible spectrum region and show an intense broad emission band in the yellow colour range (around 570 nm) and a weak band in the blue region (around 470 nm). The excitation and the emission bands are originated from the 4f−5d transition of Eu2+ ions. When the concentration of Eu2+ ions increases, the emission peaks of phosphors shift to longer wavelengths. The effective emission in the yellow colour indicates that phosphor as potential candidates for white light-emitting-diodes.

Abstract: A series of phosphor of MBPO7:Tm3+, and MBPO7:Tm3+, Gd3+ (M= Mg, Sr, Ca) were prepared and studied. The XRD data showed Tm3+, Gd3+ didn’t affects the lattice parameters. Excitation spectra exhibited high absorption in vacuum ultraviolet (VUV) region. There existed strong emission peaking at 453nm and 363nm correspond to the 1D2 →3HJ (J=4, 6) emission transition of Tm 3+ when excited under VUV. With the changes of cation in the samples, the excitation spectra changed greatly, and lead a great change in its emission spectra. The crystal lattice parameters affect the ratio of intensity of the peak at 454nm and 312nm.

Abstract: The excitation spectrum of BaZr(BO3)2:Eu3+ is composed of two broad bands. One band in the range from 120 nm to 170 nm is attributed to the borate groups, and the other band at 230 nm is due to the charge-transfer state (CTS) of the Eu3+ ion. The excitation spectrum of BaZr(BO3)2:Tb3+consists of one broad band in the range from 120 nm to 170 nm and the bands peaking at 226 nm, 245 nm and 272 nm respectively. The former is also attributed to the absorption of the BO3 groups. The latter correspond to the 4f8-4f75d transition of Tb3+.Main peak of the host absorption moves about 30 nm to high energy region as Sr2+ replaces Ba2+ partially.

Abstract: New phosphors of Tm3+ doped Re2SiO4 (Re=Mg, Ba, Sr) were prepared by the solid-state reaction and their luminescent properties were investigated. X-ray powder diffraction analysis confirmed the formation of Re2SiO4: Tm3+ (Re=Mg, Ba, Sr). The excitation spectra indicated that this phosphor can be effectively excited by 161nm. It consists of peaked at 175nm and a broad excitation band from 184nm to 300nm, corresponded to the absorption of the host lattice and the O−Tm3+ charge transfer transitions. The emission peaks at about 357nm, 459nm, 485nm is separately corresponds to the 1D2 → 3H6, 1D2 → 3H4, 1G4 → 3H6 transitions of Tm3+. As the radius of alkali earth ion in Re site increases, the main emission peaks changed to 478nm from 459nm.

Abstract: Zn2SiO4:Mn2+ was synthesized via a dipping method. Stoichiometric high pure SiO2 was put into the solution of zinc nitrate and manganese nitrate. The mixture was milled while being heated until the water was vaporized completely. The as-received mixture was added into the ethanol, and dispersed well, then the mixture was milled and heated to remove the ethanol thoroughly by evaporation. The precursor were dried for several hours at 60°C, and annealed in a reducing atmosphere of active carbon at 1000°C for 4 h. As-prepared powders of Zn2SiO4:Mn2+ was tested by XRD and SEM. Its luminescent properties were characterized by excitation and emission spectra. The results are compared with those of Zn2SiO4:Mn2+ prepared by a general solid state reaction.