共查询到20条相似文献,搜索用时 15 毫秒
1.
C.D. Pinheiro E. Longo E.R. Leite F.M. Pontes R. Magnani J.A. Varela P.S. Pizanni T.M. Boschi F. Lanciotti 《Applied Physics A: Materials Science & Processing》2003,77(1):81-85
We discuss the nature of visible photoluminescence at room temperature in amorphous strontium titanate in the light of the
results of a recent experimental and quantum mechanical theoretical study. Our calculation of the electronic structure involves
the use of first-principles molecular calculations to simulate the variation of the electronic structure in the strontium
titanate crystalline phase, which is known to have a direct band gap, and we also make an in-depth examination of amorphous
strontium titanate. The results of our simulations of amorphous strontium titanate indicate that the formation of five-fold
coordination in the amorphous system may introduce delocalized electronic levels in the highest occupied molecular orbital
and the lowest unoccupied molecular orbital. These delocalized electronic levels are ascribed to the formation of a tail in
the absorbance-spectrum curve. Optical absorption measurements experimentally showed the presence of a tail. The results are
interpreted by the nature of these exponential optical edges and tails associated with defects promoted by the disordered
structure of the amorphous material. We associate them with localized states in the band gap.
Received: 15 January 2002 / Accepted: 7 August 2002 / Published online: 4 December 2002
RID="*"
ID="*"Corresponding author. Fax: +55-16/2615-215, E-mail: derl@power.ufscar.br 相似文献
2.
L.E.B. Soledade E. Longo E.R. Leite F.M. Pontes F. Lanciotti Jr. C.E.M. Campos P.S. Pizani J.A. Varela 《Applied Physics A: Materials Science & Processing》2002,75(5):629-632
Room-temperature photoluminescence (PL) was observed in undoped and 2 mol % Cr-, Al- and Y-doped amorphous SrTiO3 thin films. Doping increased the PL, and in the case of Cr significantly reduced the associated PL wavelength. The optical
bandgaps, calculated by means of UV–vis absorption spectra, increased with crystallinity and decreased with the doping level.
It was considered that yttrium and aluminum substituted Sr2+, whereas chromium replaced Ti4+. It is believed that luminescence centers are oxygen-deficient BO6 complexes, or the same centers with some other defects, such as oxygen or strontium vacancies, or BO6 complexes with some other defects placed in their neighborhood. The character of excitation and the competition for negatively
charged non-bridging oxygen (NBO) among numerous types of BO6 defect complexes in doped SrTiO3 results in various broadband luminescence peak positions. The results herein reported are an indicative that amorphous titanates
are sensitive to doping, which is important for the control of the electro-optic properties of these materials. The probable
incorporation of Cr into the Ti site suggests that the existence of a double network former can lead to materials displaying
a more intense photoluminescence.
Received: 20 November 2001 / Accepted: 22 November 2001 / Published online: 27 March 2002 相似文献
3.
A novel electrochemical approach for fabrication of photoluminescent erbium-doped porous silicon 总被引:2,自引:0,他引:2
M.L. Gong J.X. Shi W.K. Wong K.K. Shiu W.H. Zheng K.W. Cheah 《Applied Physics A: Materials Science & Processing》1999,68(1):107-110
21 /cm3. After this new ECD treatment, PS:Er was found to emit much more intense room-temperature visible photoluminescence than
both the porous silicon control and the PS:Er prepared by constant-current ECD. Room-temperature IR photoluminescence around
1.54 μm was observed for the first time without any post-doping annealing.
Received: 3 September 1998/Accepted: 9 September 1998 相似文献
4.
E.R. Leite N.L.V. Carreño L.P.S. Santos J.H. Rangel L.E.B. Soledade E. Longo C.E.M. Campos F. Lanciotti Jr. P.S. Pizani J.A. Varela 《Applied Physics A: Materials Science & Processing》2001,73(5):567-569
Photoluminescence (PL) at room temperature has been achieved in amorphous thin films and powders of the TiO2–PbO system. They were prepared by the polymeric precursor method with [PbO]/[TiO2] molar ratios ranging from 0.0 to 1.0. The energy position of maximum PL emission and the PL intensity showed dependence
on Pb concentration. The Pb addition suggests an increase in the number of non-bridging oxygens (NBO) in the amorphous TiO2 network. These results support the relationship between photoluminescence and structure in TiO2-based amorphous materials.
Received: 7 February 2001 / Accepted: 8 February 2001 / Published online: 27 June 2001 相似文献
5.
W.X. Que Y. Zhou Y.L. Lam C.H. Kam J. Zhou K. Pita Y.C. Chan S. Buddhudu L.H. Gan G.R. Deen 《Applied Physics A: Materials Science & Processing》2001,73(4):485-488
Neodymium (III) oxide nanocrystal/titania/organically-modified silane (ormosil) composite thin films have been prepared using
a chemical approach consisting of a combination of inverse microemulsion and sol-gel techniques at low temperature. Transmission
electron microscopy shows that the neodymium (III) oxide nanoparticles have a needle-like nanocrystal structure. A strong
room temperature emission at 1064 nm, corresponding to the 4
F
3/2?4
I
11/2 transition, has been observed as a function of the heat treatment temperature used for the production of the composite thin
films. In addition to this emission, two other main emissions at 890 nm and at 1336 nm have also been observed. In particular,
there was a clear shoulder peak at 1145 nm, probably be due to the host matrix, which was observed in all the measured samples
and this shoulder peak gave a maximum intensity after heat treatment at 300 °C.
Received: 6 September 2000 / Accepted: 15 November 2000 / Published online: 20 June 2001 相似文献
6.
J.H RangelN.L.V Carreño E.R Leite E LongoC.E.M Campos F Lanciotti Jr.P.S Pizani J.A Varela 《Journal of luminescence》2002,99(2):85-90
Pb1−XLaXTiO3 thin films, (X=0.0; 13 and 0.27 mol%) were prepared by the polymeric precursor method. Thin films were deposited on Pt/Ti/SiO2/Si (1 1 1), Si (1 0 0) and glass substrates by spin coating, and annealed in the 200-300°C range in an O2 atmosphere. X-ray diffraction, scanning electron microscopy and atomic force microscopy were used for the microstructural characterization of the thin films. Photoluminescence (PL) at room temperature has been observed in thin films of (PbLa)TiO3. The films deposited on Pt/Ti/SiO2/Si substrates present PL intensity greater than those deposited on glass and silicon substrates. The intensity of PL in these thin films was found to be dependent on the thermal treatment and lanthanum molar concentration. 相似文献
7.
W. Que Y. Zhou Y.L. Lam K. Pita Y.C. Chan C.H. Kam 《Applied Physics A: Materials Science & Processing》2001,73(2):209-213
Luminescence properties from erbium (III) oxide nanocrystals dispersed in titania/organically modified silane composite thin
films were studied. Erbium oxide nanocrystals were prepared by an inverse microemulsion technique. A strong room-temperature
photoluminescence was observed at 1.531 μm, with the full width at half maximum (FWHM) of 22 nm due to intra-atomic transitions
between 4
I
13/2 and 4
I
15/2 levels in the erbium (III) ion. The shape, peak position, and FWHM of the photoluminescence signals from the composite thin
films were quite comparable to those prepared by other methods. The photoluminescence peak of the composite thin films showed
a maximum intensity at the heat-treatment temperature of 300 °C. A room-temperature green up-conversion emission at 543 nm
(4
S
3/2?4
I
15/2) was observed for the composite thin films with different heat-treatment temperatures upon excitation at 993 nm. The up-conversion
emission mechanism was explained by means of an energy-level diagram and the lifetime of the visible up-conversion emission
was measured.
Received: 10 July 2000 / Accepted: 11 July 2000 / Published online: 5 October 2000 相似文献
8.
Strong enhancement of spontaneous emission in amorphous-silicon-nitride photonic crystal based coupled-microcavity structures 总被引:1,自引:0,他引:1
M. Bayindir S. Tanriseven A. Aydinli E. Ozbay 《Applied Physics A: Materials Science & Processing》2001,72(1):125-127
We investigated photoluminescence (PL) from one-dimensional photonic band gap structures. The photonic crystals, a Fabry–Perot
(FP) resonator and a coupled-microcavity (CMC) structure, were fabricated by using alternating hydrogenated amorphous-silicon-nitride
and hydrogenated amorphous-silicon-oxide layers. It was observed that these structures strongly modify the PL spectra from
optically active amorphous-silicon-nitride thin films. Narrow-band and wide-band PL spectra were achieved in the FP microcavity
and the CMC structure, respectively. The angle dependence of PL peak of the FP resonator was also investigated. We also observed
that the spontaneous emission increased drastically at the coupled-cavity band edge of the CMC structure due to extremely
low group velocity and long photon lifetime. The measurements agree well with the transfer-matrix method results and the prediction
of the tight-binding approximation.
Received: 8 March 2001 / Accepted: 17 March 2001 / Published online: 23 May 2001 相似文献
9.
Strong blue photoluminescence from aligned silica nanofibers 总被引:1,自引:0,他引:1
L. Dai X.L. Chen J.K. Jian W.J. Wang T. Zhou B.Q. Hu 《Applied Physics A: Materials Science & Processing》2003,76(4):625-627
Photoluminescence (PL) and infrared spectra of aligned silica nanofibers are investigated. Two striking strong blue luminescence
emissions have been found at room temperature. This suggests that the silica nanofibers could be a candidate material for
a blue-light emitter. The intensity of the PL emission decreases after annealing, which can be interpreted as the decrease
of the oxygen deficiency resulting in the reduction of radiative recombination centers. Infrared spectra provide further evidence
of this conclusion, where the enhancement of Si–O absorption is observed in annealed samples.
Received: 2 October 2002 / Accepted: 7 October 2002 / Published online: 8 January 2003
RID="*"
ID="*"Corresponding author. Fax: +86-10/8264-9531, E-mail: ldai@vip.sina.com 相似文献
10.
R.M. Xie H.B. Fu X.H. Ji Z.H. Chen J.N. Yao 《Applied Physics A: Materials Science & Processing》2002,74(2):239-242
4,4′-dibromobiphenyl nanocrystals with different sizes in the range from 20 nm to 300 nm were prepared by the reprecipitation
method. It was found that their absorption peaks experienced a red shift while the size of the nanocrystals increased. Through
analyzing these spectra of the nanocrystals with different sizes, it is suggested that this size-dependent optical property
is contributed by two factors, the size effect and the J-aggregate formation.
Received: 28 August 2000 / Accepted: 2 March 2001 / Published online: 23 May 2001 相似文献
11.
We report on germania/organically modified silane (ormosil) hybrid materials produced by the sol–gel technique for photonic
applications. Acid-catalyzed solutions of γ-glycidoxypropyltrimethoxysilane mixed with germanium isopropoxide have been used
as precursors for the hybrid materials. Planar waveguide films with a thickness of about 2 μm have been prepared by a single
spin-coating process and low-temperature heat treatment from these high germanium content hybrid materials. Atomic force microscopy,
thermal gravimetric analysis, UV–visible spectroscopy, and Fourier-transform infrared spectroscopy have been used to investigate
the optical and structural properties of the films. The results have indicated that a dense, low absorption, and high transparency
(in the visible range) waveguide film could be achieved at a low temperature. A strong UV-absorption region at short wavelengths
∼200 nm, accompanied by a shoulder peaked at ∼240 nm, has been noticed due to the neutral oxygen monovacancy defects. The
propagation mode and loss properties of the planar waveguide films have also been investigated by using a prism-coupling technique.
Received: 5 November 2002 /
Revised version: 27 December 2002 / Published online: 19 March 2003
RID="*"
ID="*"Corresponding author. Fax: +65-67909081, E-mail: ewxque@ntu.edu.sg 相似文献
12.
A phosphor Tb3+-doped ZnWO4 (ZWO:Tb) phosphors were prepared by a hydrothermal method. X-ray powder diffraction (XRD) analysis revealed that the as-obtained sample is pure ZnWO4 phase. The excitation and emission spectra indicated that the phosphor could be well excited by ultraviolet light (272 nm) and emit blue light at about 491 nm and green light at about 545 nm. Significant energy transfer from WO42− groups to Tb3+ ions has been observed. Two approaches to charge compensation are investigated: (a) 2Zn2+ = Tb3+ + M+, where M+ is a monovalent cation like Li+, Na+ and K+ acting as a charge compensator; (b) 3Zn2+ = 2Tb3+ + vacancy. Compared with two charge compensation patterns in the ZnWO4:Tb3+, it has been found that ZnWO4:Tb3+ phosphors used Li+ as charge compensation show greatly enhanced bluish-green emission under 272 nm excitation. 相似文献
13.
Two bands in the photoluminescence excitation spectra have been studied for the red, blue, and IR emission of oxidized porous silicon (PS) and PS with Er3+- and Yb3+-containing gadolinium oxychloride complex (PS:Er,Yb), introduced by thermal diffusion. These two spectral bands were shown to reflect contributions of two different mechanisms of excitation-emission processes. The UV band for the IR emission of PS:Er,Yb rose sharply at about 290 nm and was explained by the direct photoemission of carriers from the valence band of Si crystallites into the conduction band of the oxide shell. The second band was found to be common for the red and blue emission and assosiated with the carriers photoexcitation inside the Si crystallites. Lifetimes for both bands were measured and the structure of the blue emission from PS:Er,Yb with peaks at 416, 440, 466, and 500 nm from PS:Er,Yb was observed. 相似文献
14.
J. Gonzalo O. Sanz A. Perea J.M. Fernández-Navarro C.N. Afonso J. García López 《Applied Physics A: Materials Science & Processing》2003,76(6):943-946
Heavy metal oxide thin films of the ternary system Nb2O5–GeO2–PbO have been prepared by pulsed laser deposition in an O2 environment from either glassy or crystalline bulk samples. The range of ([Pb]+[Nb]) content in which the films are optically
homogeneous and transparent is much broader (0.5–1.0) than that of the bulk samples considered in the present work (0.55–0.62).
The imaginary part of the refractive index is very low in all cases (k<10-3), whereas the real part increases linearly with the ([Pb]+[Nb]) content up to values as high as 2.35. The optical energy
gap has been found to be strongly dependent on [Pb], whereas it is almost independent of [Nb]. This dependence is discussed
in terms of the role of Pb and Nb as network modifiers or formers.
Received: 5 August 2002 / Accepted: 8 August 2002 / Published online: 17 December 2002
RID="*"
ID="*"Corresponding author. Fax: +34-91/564-5557, E-mail: j.gonzalo@io.cfmac.csic.es 相似文献
15.
H.S. Roh Y.C. Kang H.D. Park S.B. Park 《Applied Physics A: Materials Science & Processing》2003,76(2):241-245
Y2O3:Eu phosphor particles were prepared by large-scale spray pyrolysis. The morphological control of Y2O3:Eu particles in spray pyrolysis was attempted by adding polymeric precursors to the spray solution. The effect of composition
and amount of polymeric precursors on the morphology, crystallinity and photoluminescence characteristics of Y2O3:Eu particles was investigated. Particles prepared from a solution containing polyethylene glycol (PEG) with an average molecular
weight of 200 had a hollow structure, while those prepared from solutions containing adequate amounts of citric acid (CA)
and PEG had a spherical shape, filled morphology and clean surfaces after post-treatment at high temperature. Y2O3:Eu particles prepared from an aqueous solution with no polymeric precursors had a hollow structure and rough surfaces after
post-treatment. The phosphor particles prepared from solutions with inadequate amounts of CA and/or PEG also had hollow and/or
fragmented structures. The particles prepared from the solution containing 0.3 M CA and 0.3 M PEG had the highest photoluminescence
emission intensity, which was 56% higher than that of the particles prepared from aqueous solution without polymeric precursors.
Received: 22 March 2002 / Accepted: 26 March 2002 / Published online: 5 July 2002
RID="*"
ID="*"Corresponding author. Fax: +82-42/861-4245, E-mail: yckang@pado.krict.re.kr 相似文献
16.
W. Que Y. Zhou Y.L. Lam Y.C. Chan C.H. Kam 《Applied Physics A: Materials Science & Processing》2001,73(2):171-176
SiO2/TiO2/γ-glycidoxypropyltrimethoxysilane composite materials processed by the sol-gel technique were studied for optical waveguide
applications. Waveguide films with thickness more than 1.7 μm were prepared on a silicon substrate by a single-coating process
and low-temperature heat treatment from these high-titanium-content composite materials. Scanning electron microscopy (SEM),
atomic force microscopy (AFM), thermal gravimetric analysis (TGA), UV-visible spectroscopy (UV-VIS), Fourier-transform infrared
spectroscopy (FT-IR), and X-ray photoelectron spectroscopy (XPS) have been used to characterize the waveguide films. TGA curves
showed that organic compounds in the composite materials would decompose in the temperature range from 200 °C to 480 °C. SEM,
AFM and UV-VIS results showed that a dense, porous-free, and high transparency in the visible range waveguide film could be
obtained at a low heat-treatment temperature. It was also noted that the carbon content in the film with higher titanium content
heated at high temperature was evidenced by XPS. The waveguide propagation loss properties of the composite material films
were also investigated and showed a dependence on the titanium molar fraction.
Received: 13 June 2000 / Accepted: 21 June 2000 / Published online: 20 September 2000 相似文献
17.
S.S. Yi J.S. Bae B.K. Moon J.H. Jeong I.W. Kim H.L. Park 《Applied Physics A: Materials Science & Processing》2003,76(3):433-437
ZnGa2O4 thin-film phosphors have been grown on Si(100), Al2O3(0001) and MgO(100) substrates using pulsed laser deposition. The structural characterization was carried out on a series
of ZnGa2O4 films grown on various substrates under various substrate temperatures and oxygen pressures. The films grown on these substrates
not only have different crystallinity and surface morphology, but also different Zn/Ga composition ratio. The crystallinity
and photoluminescence (PL) of the ZnGa2O4 films are highly dependent on the deposition conditions, in particular the stoichiometry ratio of Zn/Ga and the kind of substrate.
The variation of Zn/Ga in the films also depends on not only the oxygen pressure but also the substrate temperature during
deposition. The PL properties of pulsed laser deposited ZnGa2O4 thin films have indicated that Al2O3(0001) and MgO(100) are promising substrates for the growth of high-quality ZnGa2O4 thin films and that the luminescence brightness depends on the substrate. The luminescence spectra show a broad band extending
from 350 to 600 nm and peaking at 460 nm.
Received: 11 July 2002 / Accepted: 31 July 2002 / Published online: 28 October 2002
RID="*"
ID="*"Corresponding author. Fax: +82-51-6206356, E-mail: jhjeong@pknu.ac.kr 相似文献
18.
J. Xu W. Li T. Ma Z. Li W. Lu K. Chen 《Applied Physics A: Materials Science & Processing》2000,71(6):651-655
Thin layers of hydrogenated amorphous carbon were prepared by using organic hydrocarbon source, xylene (C8H10), in plasma-enhanced chemical vapor deposition (PECVD) system. The microstructures were characterized by using Fourier-transform
infrared and Raman scattering spectra. The appearance of a sharp vibration signal in 1600 cm-1 strongly suggests the existence of sp2 carbon clusters with aromatic rings. With increasing the deposition rf power, the content of these aromatic structures is
increased in the films. In contrast to a broad single PL peak in methane (CH4)-baseda-C:H films, the PL band of xylene-based a-C:H films contains multiple peaks in blue-green light region, which is influenced
by rf power. We tentatively attributed it to the radiative recombination of electron-hole pairs through some luminescent centers
associated with aromatic structures.
Received: 26 April 2000 / Accepted: 9 May 2000 / Published online: 13 September 2000 相似文献
19.
The green emission intensity of ZnGa2O4:Ge4+, Li+, Mn2+ excited by the vacuum ultraviolet line of 147 nm reaches 70% of commercial green Zn2SiO4:Mn2+. The vacuum ultraviolet excitation spectra consist of four peaks. In a plasma display test bed filled with Ar and Ne plasma discharged by a radio-frequency generator of 13.6 MHz, ZnGa2O4:Ge4+, Li+, Mn2+ and commercial Zn2SiO4:Mn2+ phosphor screens show a linear increase in luminance with increasing self bias voltages. Increasing gas pressures cause the luminance to increase. Also, on increasing the self bias voltages and the gas pressures, the current densities of ZnGa2O4:Ge4+, Li+, Mn2+ phosphor screens are increased; this is the same behavior as that of the commercial phosphor. 相似文献
20.
The relationship between the macroscopic properties of PECVD silicon nitride and oxynitride layers and the characteristics of their networks 总被引:1,自引:0,他引:1
Silicon nitride and oxynitride films have been deposited on silicon wafers using plasma-enhanced chemical vapour deposition.
Various amounts of ammonia, silane and nitrous oxide gases were applied at fixed total gas flow and at the same deposition
temperature. The dependence of the macroscopic properties of the layers such as refractive index, internal stress and etch
rate on the reaction atmosphere during deposition has been demonstrated. The chemical structure of amorphous layers was studied
using infrared spectroscopy. The network was found to be characterised by SiNxOyHz tetrahedra, joined to each other by common corners. The characteristic vibrational bands due to species that join tetrahedral
units (N(-Si≡)3, ≡Si-N-Si≡, ≡Si-O-Si≡) and species that stop this interconnection (Si-H, N-H) were determined and discussed with reference
to the corresponding species available during deposition. The analysis resulted in the determination of the relationship between
the chemical structure of the network and the layer’s refractive index, internal stress and etch rate.
Received: 24 July 2000 / Accepted: 30 May 2001 / Published online: 30 August 2001 相似文献