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A systematic investigation into the photoluminescence and afterglow mechanisms of trivalent Dy ion doped CaAl2O4.

Dy

Undoped SrSO4 nanoplates were synthesized via the composite hydroxide-mediated approach. The products were characterized by means of X-ray diffractometry, scanning electron microscopy, X-ray energy-dispersive spectroscopy, X-ray photoelectron spectroscopy, photoluminescence (PL) spectroscopy, electron spin resonance technique, afterglow spectroscopy, and thermoluminescence dosimetry. The steady-state PL spectrum of undoped SrSO4 nanoplates can be deconvoluted into two distinct Gaussian bands centered at 2.97 eV (417.2 nm) and 2.56 eV (484.4 nm), respectively. The nature of the defect emissions is confirmed through the emission-wavelength-dependent PL decays as well as the excitation-wavelength-dependent PL decays. A cyan-colored afterglow from undoped SrSO4 nanoplates can be observed with naked eyes in the dark, and the afterglow spectrum of the undoped SrSO4 nanoplates exhibits a peak at about 492 nm (2.52 eV). The duration of the afterglow is measured to be 16 s. The thermoluminescence glow curve of the undoped SrSO4 nanoplates shows a peak at about 40.1 °C. The trapping parameters are determined with the peak shape method, the calculated value of the trap depth is 0.918 eV, and the frequency factor is 1.2 × 1014 s-1. Using density functional calculations, the band structures and densities of states of oxygen-deficient SrSO4 and strontium-deficient SrSO4 are presented. The mechanisms of the cyan-colored afterglow are discussed for undoped SrSO4, and the oxygen vacancies in SrSO4 are proposed to be the luminescence center of the afterglow.

Dy3+ and Mn4+ codoped SrAl2O4 (SrAl2O4:Dy3+,Mn4+) phosphors were obtained by diffusing Mn4+ ions into Dy3+-doped SrAl2O4 via the constant-source diffusion technique. The influences of diffusion temperature and diffusion time on the emissions of SrAl2O4:Dy3+,Mn4+ were investigated. It was found that: (i) efficient red emission peaking at 651 nm can be readily achieved for SrAl2O4:Dy3+ by simply diffusing Mn4+ into SrAl2O4:Dy3+ at 800 °C and above; (ii) the red emission of Mn4+ becomes dominant over the characteristic emissions of Dy3+ when the diffusion temperature is 900 °C or higher; and (iii) the intensity of the red emission of SrAl2O4:Dy3+,Mn4+ is far more sensitive to diffusion temperature than to diffusion time. Our results have demonstrated that full-color tunable emissions can be realized for SrAl2O4:Dy3+, Mn4+ by tuning the parameters of diffusion temperature and diffusion time, which opens up a space for realizing easy color control of Dy3+-doped inorganic materials.

本文從行政爭訟案例發想其問題意識，即公立國中小教師申請介聘，經原服務學校及介聘委員會通過，卻遭介聘學校教評會以該教師有《教師法》第14條第1項各款為由審核未通過，引發的介聘制度及相關法律問題進行探討。本文透過法規研究、制度研究以及個案（案例）研究等途徑，輔以文獻分析及案例分析為研究方法，結果發現，現行公立國中小介聘制度須經過二校教評會審議，可能造成審議結果意見相左而導致申請介聘教師權利受損，況且以介聘程序連結不適任教師之處理，恐有違反不當連結之嫌。本文認為要避免此一情況，經介聘委員會決議通過後，應授權由受聘學校校長直接聘用，無須再由介聘學校教評會審查，以化解二校教評會意見相左之困境。 Rooted in the administrative litigation cases, this paper discusses teacher transfer system and relevant legal questions resulted from disagreeing review results in teacher transfers. Notable events have occurred in which teacher transfer among schools applied by the elementary and secondary teachers have been approved by the original school and its teacher transfer committee but disapproved by teacher evaluation committee of the teacher transfer schools with the reason of the teacher violating the regulations of Item 1, Article 14 of “Teacher’s Law”. According to the research findings, the current teacher transfer system in public elementary and secondary schools must be reviewed by the teacher evaluation committee of both schools and the teacher’s right to apply for teacher transfer may be damaged due to the difference in the review results and opinions. Besides, the link to unqualified teachers used by the treatment of the teacher transfer procedure may cause improper link. This paper suggests that to avoid this situation, the principal of the employing school should be authorized to directly employ this teacher after the teacher transfer is approved by the teacher transfer committee meeting.

It is significant to render visible-light photocatalytic activity to undoped ZnO nanostructures via intrinsic defect engineering. In this work, undoped ZnO nanocrystals were derived via co-precipitation synthesis. The resulting ZnO nanocrystals were characterized by means of X-ray diffraction, scanning electron microscopy, photoluminescence spectroscopy, and ultraviolet-visible absorption spectroscopy, respectively. The visible-light photocatalytic activity of the products were characterized by monitoring the decomposition of methyl orange in water under visible-light illumination of a 300 W halogen lamp. It is found that undoped ZnO nanocrystals exhibit visible-light photocatalytic activity with their first-order rate constant up to 4.6 &times, 10&minus, 3 min&minus, 1. Density functional calculations show that oxygen vacancies create deep energy levels at EV + 0.76 eV in the bandgap of ZnO. In conjunction with the density functional calculations, the photocatalytic degradation of methyl orange under visible-light irradiation provides direct evidence that oxygen vacancies in ZnO nanocrystals yield the visible-light photocatalytic activity. Our results demonstrate that visible-light photocatalytic activity can be endowed to undoped ZnO nanocrystals by manipulating the intrinsic defects in ZnO. Intrinsic defect-modulated ZnO photocatalysts thus represent a powerful configuration for further development toward visible-light responsive photocatalysis.

Nanocomposites of zinc oxide (ZnO) nanocrystals and liquid crystal N-(4-methoxybenzylidene)-4 -ethoxybenzenamine (MB2BA) were prepared by ultrasonic dispersing technology. The MB2BA/ZnO nanocomposi...

Zinc oxide (ZnO) nanohoneycombs were grown on the titanium dioxide (TiO2) layers of the photoanodes for dye sensitized solar cells (DSSC) via hydrothermal method at 93 °C for 5 h and then at 50 °C for 16 h. The photovoltaic performance of TiO2 based DSSCs with ZnO nanohoneycombs decorated photoanodes was investigated. Under the illumination of an air mass 1.5 solar simulator, the short-circuit current density of TiO2 based DSSCs with the decoration of ZnO nanohoneycombs was 21.48 mA/cm2, which was higher than that of TiO2 based DSSCs without the decoration of nanohoneycombs (7.65 mA/cm2). The high specific surface area in ZnO nanohoneycombs enhances the power conversion efficiency (η) of the DSSCs. It is found that the η of the TiO2 based DSSCs is 5.85% in the presence of ZnO nanohoneycomb decoration but only 4.12% in the absence of ZnO nanohoneycomb decoration. The enhanced photovoltaic performance of DSSCs with ZnO nanohoneycombs decorated TiO2 photoanodes can be ascribed to the high specific surface area of ZnO nanohoneycombs and more efficient pathways for electron transportation from the electrolyte to the electrode.

Eu2+ and Eu3+ co-doped SrSO4 microcrystals were synthesized by employing Eu3+ as the sole doping source in the precipitation synthesis. As the annealing temperature increases from 200 to 1000 °C, it is found that the broad photoluminescence (PL) band of Eu2+ peaking at 378 nm is dramatically enhanced in intensity as the cost of the narrowband emissions of Eu3+ at 584, 591 and 612 nm, respectively. Moreover, Two broad PL bands, one of which is centered at 500 nm while the other is centered at 625 nm, are recorded upon post annealing. On the basis of density functional calculations, post annealing introduced oxygen vacancy is proposed to play critical roles in tuning the PL of Eu2+ and Eu3+ co-doped SrSO4. On one hand, the oxygen vacancy is responsible for the enhanced emission of Eu2+ at 378 nm by reducing Eu3+ to Eu2+. On the other hand, the oxygen vacancy acts as electron trap and luminescence center in SrSO4 with the result of the broad PL band centered at 500 nm. Our results have demonstrated that the PL of Eu2+ and Eu3+ co-doped SrSO4 microcrystals can be tuned by simply varying the post annealing temperature.

Triclinic ZnMoO 4 nanowires are synthesized by vapor deposition in air. The morphology, crystal structure, optical absorption and photoluminescence (PL) of the obtained ZnMoO 4 nanowires are characterized by means of scanning electron microscopy, X-ray diffraction, diffuse UV–vis reflectance spectroscopy and PL spectrophotometry, respectively. The synthesized ZnMoO 4 nanowires are about 4.3 µm in length and 50 nm in diameter, exhibiting a high aspect ratio of 86. Under the 325 nm laser excitation, ZnMoO 4 nanowires exhibit a broad green PL band centered at around 560 nm. Our results have demonstrated that vapor deposition in air is an easy and cost-effective method to produce large quantities of single-crystalline ZnMoO 4 nanowires. All we need is the precursor of ZnMoO 4 and an air-filled box furnace.

ZnWO4 nanoplates with highly exposed {0 1 ¯ 1} facets were synthesized via a hydrothermal technique. The phase, morphology, and optical characteristics of ZnWO4 nanoplates were characterized with scanning electron microscopy, transmission electron microscopy, X–ray diffraction, diffuse ultraviolet–visible light (UV–Vis) reflectance spectroscopy, photoluminescence (PL) spectrophotometry, and PL lifetime spectroscopy. Optical characterizations, along with the density functional calculations, confirm that the strong blue PL band of ZnWO4 nanoplates originates from the intrinsic defects in ZnWO4 nanoplates. Furthermore, photocatalytic tests show that ZnWO4 nanoplates exhibit strong photo-oxidative capability of complete mineralization of the organic pollutant (methyl orange) in water, whereas ZnWO4 nanoparticles can only cleave the organic molecules into fragments. The superior photo-oxidative capability of ZnWO4 nanoplates can be attributed to the specific chemical bonding and stereochemistry on the exposed facets. This work demonstrates that crystal facet engineering is an efficient strategy to endow ZnWO4 with strong photo-oxidative capability.

At the doping level of 1 mol%, Tb3+ doped CaAl2O4 (Tb–doped CaAl2O4) nanocrystals were synthesized via the sol–gel combustion technique. Green afterglow was recorded for the as–prepared Tb–doped CaAl2O4. The effects of subsequent annealing on the green afterglow of Tb–doped CaAl2O4 were investigated by means of X–ray diffractometry, scanning electron microscopy, transmission electron microscopy, photoluminescence spectroscopy, afterglow spectroscopy, and thermoluminescence dosimetry, respectively. Both the intensity and duration of the afterglow of Tb–doped CaAl2O4 are found to decrease with the increase in the annealing temperature when annealing temperature is lower than 600 °C. Afterglow of Tb–doped CaAl2O4 is completely quenched as annealing temperature is over 700 °C. In combination with annealing temperature dependent photoluminescence and thermoluminescence of Tb–doped CaAl2O4, our results indicate that the degradation of the afterglow can be linked to the oxidation of Tb3+ into Tb4+ at high annealing temperatures.

Significant prolongation in the green afterglow of SrAl2O4:Dy3+ was achieved by adding 10 mol% H3BO3 into the starting material. The surface morphology, crystalline structure, chemical composition, photoluminescence, afterglow and decay characteristics of the phosphor were characterized by scanning electron microscopy, X-ray diffractometry, energy-dispersive X-ray spectroscopy, transmission electron microscopy, photoluminescence and photoexcitation spectroscopy, respectively. It was found that the afterglow time constant of the green afterglow from SrAl2O4:Dy3+ phosphor could be enhanced over 100 folds from 53 to 5538 s after the addition of 10 mol% H3BO3 flux. No traces of Eu were found in the phosphors within the 1 μg/g detection limit of the inductively coupled plasma atomic emission spectrometry. By employing meta generalized gradient approximation to describe the exchange–correlation functional, the band structures of SrAl2O4:Dy3+ were calculated within the framework of density functional theory. The ground state of Dy3+ ions and the defect levels of V O • • , V S r ″ and V A l ″ ′ were quantitatively determined in the band gap of SrAl2O4. A possible afterglow mechanism was proposed to shed fresh light on the green afterglow of SrAl2O4:Dy3+. The significant prolongation in the afterglow of SrAl2O4:Dy3+ can be attributed to the H3BO3 flux introduced V A l ″ ′ in the host lattice.

By increasing the temperature of hydrothermal reactions from 70 to 100°C, vertically aligned ZnO nanorods were grown on the TiO2 thin film in the photoanode of dye-sensitized solar cells (DSSCs) as the blocking layer to reduce the electron back recombinations at the TiO2/electrolyte interfaces. The length effects of ZnO nanorods on the photovoltaic performances of TiO2 based DSSCs were investigated by means of scanning electron microscope, X-ray diffractometer, photoluminescence spectrophotometer, and the photocurrent-voltage measurement. Under the illumination of 100 mW/cm2, the power conversion efficiency of DSSC with ZnO nanorods decorated TiO2 thin film as its photoanode can be increased nearly fourfold from 0.27% to 1.30% as the length of ZnO nanorods increases from 300 to 1600 nm. The enhanced efficiency of DSSC with ZnO nanorods decorated TiO2 thin film as the photoanode can be attributed to the larger surface area and the lower defect density in longer ZnO nanorods, which are in favor of more dye adsorption and more efficient transport in the photoanode.

晚近愈來愈多的司法裁判顯示，教師因違反聘約而遭學校停聘、解聘或不續聘，其中包括未經核准在外兼課、兼職、未能限期升等、未通過教師評鑑，以及未於規定年限取得博士學位⋯⋯等類型。《教師法》第14條第1項第14款規定：「違反聘約情節重大」構成停聘、解聘及不續聘之法律效果，上述事實雖可能「違反聘約」，但是否即屬「情節重大」不無疑問。本文首先歸納整理「違反聘約情節重大」之裁判類型；其次，就違反聘約情節重大得否由當事人於聘約中約定，以及違反聘約是否即屬情節重大等疑義，進行學說與實務之探討；再者，主管機關對違反聘約情節重大之核准權，究應採高密度之監督或低密度之審查一併進行檢討；最後，檢視司法裁判對於教師工作權保障之價值取捨並提出本文考察之心得。 A growing number of judicial cases have revealed that the violation of employment contracts by teachers could lead to dismissal or nonrenewal of contracts, which could result from unapproved side jobs, unsuccessful faculty promotion, failed faculty evaluation, or the inability to obtain a doctoral degree within the deadline. Although in Chapter III of the Teachers’ Act, Article 14-1 stipulates that teachers seriously violating employment contracts could be suspended, dismissed, or non-renewed, it still remains debatable whether the abovementioned are to be regarded as “serious violation”. To look into this issue, this paper first summarizes the adjudication of serious employment contract violation, and then explains the major actions constituting serious employment contract violation theoretically and practically. Further, the issue regarding whether the educational administrative authorities in validating the condition of “serious violation of employment contract” should be exercised by high-density super vision or by law-density screening is also reviewed. Based on the discussion, this paper then examines the value of judicial adjudication on university autonomy and protection of teachers’ right to work and finally proposes recommendations.

Tb-doped ZnO hexagonal pyramids with the doping level of 0.1 mol.% were synthesized by thermal decomposing the mixture of zinc nitrate and terbium nitrate at 500°C in an air-filled furnace. The crystal structures and photoluminescent properties of Tb-doped ZnO hexagonal pyramids were analyzed with a scanning electron microscope, x-ray diffractometer, fluorescence spectrophotometer and photoluminescence excitation spectrophotometer. Four characteristic emission peaks of Tb3+ ions were recorded over the broad green luminescent band of ZnO, at 488 nm, 544 nm, 584 nm and 620 nm for Tb-doped ZnO hexagonal pyramids. The characteristic emissions of the rare-earth dopant in Tb-doped ZnO were found to be unstable when stored in air. The 544-nm emission of dopant Tb in ZnO lost 12%, 37%, 78%, and 100% of its original intensity after stored in air for 2 months, 4 months, 6 months, and 8 months, respectively. With the help of calculated band structures, our results suggest that the instability of the characteristic emissions of dopant Tb in ZnO can be attributed to the possible expulsion of Tb out of the ZnO host.

Trivalent terbium-doped strontium aluminate (SrAl2O4:Tb3+) nanoparticles were synthesized via the sol–gel combustion technique, and the green photoluminescence (PL) and afterglow were evaluated to clarify the afterglow mechanism of SrAl2O4:Tb3+. The green PL of SrAl2O4:Tb3+ with characteristic emissions at 488, 543, 586, and 622 nm indicated that Tb dopant acts as the luminescent center of the PL. Contrarily, the green afterglow of SrAl2O4:Tb3+ was a broadband spectrum with its peak centered at around 520 nm, but no traces of Eu were found in SrAl2O4:Tb3+ phosphors within the detection limit of 1 μg/g. The band structures and density of states of SrAl2O4:Tb3+ were calculated within the framework of density functional theory. Both the ground state of Tb3+ dopant and the trap levels of oxygen vacancy were quantitatively determined in the band gap of SrAl2O4. Our results suggest that the deep electron trap of oxygen vacancy in the host acts as the luminescent center of the green afterglow from SrAl2O4:Tb3+. A possible afterglow mechanism is proposed to shed fresh light on the green afterglow of SrAl2O4:Tb3+.

Dy3+ doped barium aluminate (BaAl2O4:Dy3+) phosphors were prepared via the sol–gel combustion route at the ignition temperature of 600 °C. The phosphors were characterized with X-ray diffractometry, scanning electron microscopy, transmission electron microscopy, photoluminescence spectroscopy, Fourier transform infrared spectroscopy and X-ray photoelectron spectroscopy. Regardless of the absence of Eu2+ luminescent centers, broadband blue–green afterglow with its peak at about 490 nm was recorded in the BaAl2O4:Dy3+ phosphors. The decay profile of the blue–green afterglow can be best fitted into a two-component exponential function with the two lifetime decay constants to be 8.81 and 45.25 s, respectively. The observation of blue–green afterglow from BaAl2O4:Dy3+ in the absence of Eu2+ provides unique opportunity in unveiling the afterglow mechanisms of rare-earth doped alkaline-metal aluminates. Possible mechanisms on the blue–green afterglow in BaAl2O4:Dy3+ phosphors are discussed in terms of the Dy3+ ions introduced trap centers as well as luminescent centers in the crystal lattice.

Undoped CaAl2O4 nanocrystals were synthesized via sol–gel combustion technique, and the effects of subsequent thermal annealing on the photoluminescence (PL) and afterglow of undoped CaAl2O4 nanocrystals were investigated by means of X–ray diffractometry, PL spectroscopy and afterglow dosimetry, respectively. As the annealing temperature increases from 200 to 750 °C, the PL spectrum of undoped CaAl2O4 consists of one blue PL subband and one violet PL subband with their peak energies varying in the range of 2.67–2.86 eV and 3.12–3.31 eV, respectively. It is found that annealing CaAl2O4 can generate significant impacts on the PL and afterglow properties of undoped CaAl2O4. On one hand, the integrated PL intensity of undoped CaAl2O4 decreases with the annealing temperature. On the other hand, the blue afterglow intensity of undoped CaAl2O4 varies with the annealing temperature. More importantly, the duration of the blue afterglow can be extended seven times from 1.98 to 14.25 s when CaAl2O4 is annealed at 600 °C for 2 h. On the basis of density functional calculations, our work demonstrates that oxygen vacancies in CaAl2O4 are the luminescence center of the blue afterglow. In addition to providing valuable insight toward rational development of more efficient afterglow materials, these results are helpful for promoting our fundamental understanding of the afterglow mechanisms of Eu2+ doped CaAl2O4.

Eu3+ doped ZnWO4 phosphors were synthesized via the co-precipitation technique followed by subsequent thermal annealing in the range of 400–1000 °C. The phase, morphology, elemental composition, chemical states, optical absorption, and photoluminescence (PL) of the phosphors were characterized by X-ray diffraction, scanning electron microscopy, dispersive X-ray spectroscopy, X-ray photoelectron spectrometry, diffuse UV–vis reflectance spectroscopy, PL spectrophotometry, and PL lifetime spectroscopy, respectively. It is found that the PL from Eu3+ doped ZnWO4 is tunable through the control of the annealing temperature. Density functional calculations and optical absorption confirm that thermal annealing created intrinsic defects in ZnWO4 lattices play a pivotal role in the color tunable emissions of the Eu3+ doped ZnWO4 phosphors. These data have demonstrated that intrinsic defect engineering in ZnWO4 lattice is an alternative and effective strategy for tuning the emission color of Eu3+ doped ZnWO4. This work shows how to harness the intrinsic defects in ZnWO4 for the preparation of color tunable light-emitting phosphors.

Eu2+ and Eu3+ doubly doped ZnWO4 nanoplates with highly exposed {100} facets were synthesized via a facile hydrothermal route in the presence of surfactant cetyltrimethyl ammonium bromide. These ZnWO4 nanoplates were characterized using scanning electron microscopy, transmission electron microscopy, X-ray diffraction, X-ray photoelectron spectrometry, diffuse UV-vis reflectance spectroscopy, photoluminescence spectrophotometry, and photoluminescence lifetime spectroscopy to determine their morphological, structural, chemical, and optical characteristics. It is found that Eu-doped ZnWO4 nanoplates exhibit superior photo-oxidative capability to completely mineralize the methyl orange into CO2 and H2O, whereas undoped ZnWO4 nanoparticles can only cleave the organic molecules into fragments. The superior photocatalytic performance of Eu-doped ZnWO4 nanoplates can be attributed to the cooperative effects of crystal facet engineering and defect engineering. This is a valuable report on crystal facet engineering in combination with defect engineering for the development of highly efficient photocatalysts.

ZnO nanocrystals were synthesised via solution route and then thermally annealed in air in the temperature range of 60–900°C. The correlation between the hydroxyl groups on the surface of ZnO nanocrystals and the orange photoluminescence (PL) of ZnO nanocrystals was investigated. The crystal structure, surface chemistry and luminescent properties of thermally annealed ZnO nanocrystals were examined with X-ray diffractometer, Fourier transform infrared (FTIR) spectroscope, PL spectrophotometer, transmission electron microscope (TEM) and selected area electron diffraction technique, respectively. It is found that an orange PL band appeared in the PL spectrum at about 600 nm only when the annealing temperature was higher than 600°C. By contrast, the hydroxyl groups were always present on the solution-grown ZnO nanocrystals as the annealing temperature varied in the range of 60–900°C. Our results demonstrate that the orange PL band has no direct correlation with the hydroxyl groups on the surfaces of the ZnO ...

Trivalent Dy doped SrAl2O4 phosphors were synthesised via the sol–gel combustion route at 600°C. The dopant concentration-dependent photoluminescence (PL) and afterglows were investigated for the SrA12O4:Dy3+ phosphors by means of scanning electron microscope, X-ray diffractometer and PL spectrophotometer, respectively. Each PL spectrum of the SrA12O4:Dy3+ phosphors consists of a broad emission band originating from the host matrix SrA12O4 and two sharp band emissions of Dy3+ ions at 480 and 575 nm. The integrated PL intensity of the SrA12O4:Dy3+ phosphors increases with the concentration of Dy3+ as it increases from 0.125 to 3 mol%, and then drops as the concentration of Dy3+ increases further from 3 to 32 mol%. It is found that broadband green afterglow from the SrA12O4:Dy3+ phosphors heavily dependent on the concentration of Dy3+ ions, and that the longest afterglow was observed in the SrA12O4:Dy3+ phosphors when the concentration of Dy3+ was around 16 mol%. A model is constructed to interpret ...

Trivalent dysprosium doped strontium aluminates (SrA1 2 O 4 :Dy 3+ ) were synthesized by firing the sol–gel at 600, 700 and 800 °C. The morphology, crystal structure, photoluminescence and long afterglow of the synthesized SrAl 2 O 4 :Dy 3+ phosphors were characterized with scanning electron microscopy, X-ray diffraction, energy-dispersive X-ray spectroscopy and photoluminescence spectroscopy, respectively. It is found that SrA1 2 O 4 :Dy 3+ phosphors exhibit broadband afterglows with its peak at about 510 nm. As the sol–gel synthesis temperature increases from 600 to 800 °C, the green afterglow of the SrA1 2 O 4 :Dy 3+ phosphors becomes weaker in intensity and shorter in lifetime. The results are discussed in terms of thermally generated point defects in the host material.

Trivalent dysprosium doped strontium aluminate (SrA12O4:Dy3+) was synthesized via the sol–gel combustion method to realize green afterglow in the absence of Eu2+ luminescent centers. The morphology, crystal structure, photoluminescence and long afterglow of the SrAl2O4:Dy3+ were characterized with scanning electron microscopy, X-ray diffraction, energy-dispersive X-ray spectroscopy and photoluminescence spectroscopy, respectively. The bluish-green photoluminescence of SrAl2O4:Dy3+ consists of a broad emission band centered at about 520 nm and two characteristic emissions of Dy3+ ions centered at 480 and 575 nm, respectively. The green afterglow of SrAl2O4:Dy3+ is a broad emission band centered at around 520 nm, and the lifetime extracted from afterglow decay is found to be 53 s. The mechanism on the green afterglow from SrAl2O4:Dy3+ is discussed in terms of the possible defect levels in the host.

Synthesis of shape controlled and rare-earth doped ZnMoO4 nanostructures on a large scale with low costs is a present challenge in nanotechnology. The precursor of Eu3+ doped zinc molybdenum oxide hydrate (Zn5Mo2O11·5H2O) was synthesized at room temperature via the coprecipitation method. The influences of the sintering temperature on the microstructures and photoluminescence (PL) of the precursor were investigated by means of X-ray diffraction, scanning electron microscopy, thermal gravimetry, differential scanning calorimetry, energy dispersive X-ray spectroscopy, diffuse reflectance spectroscopy, and PL spectrophotometry. It is found that Eu3+ doped ZnMoO4 nanostructures can be derived by sintering the precursor at a relatively low temperature of about 400°C. Our results have demonstrated that Eu3+ doped ZnMoO4 nanostructures can be cost-effectively derived by sintering the precursor at a relatively low temperature.

Two-dimensional fern-like ZnO nanoleaves were synthesized by ultrasonicating zinc microcrystals in water. The morphology, crystal structure, optical property and photocatalytic activity of the fern-like ZnO nanoleaves were characterized with scanning electron microscopy, X-ray diffraction, transmission electron microscopy, photoluminescence spectroscopy and ultraviolet–visible spectroscopy, respectively. It is found that one fern-like ZnO nanoleaf is composed of one ZnO nanorod as the central trunk and a number of ZnO nanoplates as the side branches in opposite pairs along the central ZnO nanorod. The central ZnO nanorod in the fern-like nanoleaves is about 1 μm long while the side-branching ZnO nanoplates are about 100 nm long and 20 nm wide. Further analysis has revealed that ZnO nanocrystals are the building blocks of the central ZnO nanorod and the side-branching ZnO nanoplates. Under identical conditions, fern-like ZnO nanoleaves exhibit higher photocatalytic activity in photodegrading methyl orange in aqueous solution than spherical ZnO nanocrystals. The first-order photocatalytic rate constant of the fern-like ZnO nanoleaves is about four times as large as that of the ZnO nanoparticles. The branched architecture of the hierarchical nanoleaves is suggested be responsible for the enhanced photocatalytic activity of the fern-like ZnO nanoleaves.

Nanoclustered TiO2 networks were synthesized hydrothermally one-step in 0.45 M tetramethylammonium hydroxide (TMAOH) aqueous solution directly on pure polished Ti substrate for 12-hour growth. Polypyrrole (PPy) nanofilm was subsequently electropolymerized with galvanostatic photo-anodization on the nanostructured TiO2 sheet as the working electrode. Tafel polarization curve was employed to determine galvanostatic condition. Investigations of SEM, cyclic voltametry, potential-time growing curves, photo-response currents, UV-vis spectroscopy and Fourier Transform Infra-red (FTIR) spectroscopy revealed that photo-anodic polymerized pyrrole film could thoroughly change properties of nanoclustered TiO2 electrode. The networks of nanoclustered TiO2 was covered with homogeneous PPy nanofilm, the cyclic voltammetry revealed two reduction peaks, suggesting a compact and a porous layer of PPy. Moreover, PPy could enhance the photo-response by over 100 times compared with that of bare TiO2 nanonetworks. Optical absorbance visualized the full spectral absorptive feature of PPy, and FTIR further confirmed the vibrations of chemical bonds from PPy. This demonstrated that PPy infiltration in TiO2 nanonetworks could be successfully achieved via photo-anodic polymerization, and TiO2 nanonetworks/photo-anodic polymerized PPy are promising in applications of polymer-inorganic solar cell.

By heating zinc foil in an air-filled box furnace, one-dimensional ZnO nanorods, two-dimensional ZnO nanoplates and three-dimensional ZnO nanotetrapods were prepared by adjusting the temperature in the furnace in the ranges of 500–600, 650–750 and 800–900 °C, respectively. The morphologies, structures and emissions of the synthesized ZnO nanostructures were investigated by scanning electron microscopy, X-ray diffractometry, transmission electron microscopy, selected area electron diffraction and photoluminescence spectroscopy. Mechanisms on the control of the morphology and photoluminescence were discussed in terms of the crystal growth habits combined with the temperature-dependent diffusions of zinc and oxygen atoms in the ZnO lattices.

ZnO nanoparticles and one-dimensional vertically aligned ZnO nanorods were grown on the TiO 2 layers in the photoanodes via the hydrothermal method at 60 and 90 °C, respectively. The effect of ZnO decoration on the photovoltaic performance of TiO 2 based dye sensitized solar cells (DSSCs) was investigated. The morphologies, crystalline structures and optical properties of the synthesized ZnO nanoparticles and ZnO nanorods were characterized by field-emission scanning electron microscope, X-ray diffractometer and photoluminescence spectroscopy, respectively. The photocurrent–voltage curves of the fabricated DSSCs showed that the ZnO nanorods decorated DSSCs exhibited better photovoltaic performance than the ZnO nanoparticles decorated DSSCs. The improved performance of the ZnO nanorods decorated DSSCs can be ascribed to the fact that the vertically aligned ZnO nanorods provide high specific surface area for dye adsorption and the efficient pathway for electron transportation.

A low cost and effective working electrode with one dimensional ZnO nanorod grown on the porous TiO 2 film is used to improve the power conversion efficiency of dye sensitized solar cells. The one dimensional ZnO nanorod is introduced into the porous TiO 2 film by a simple and facile hydrothermal route, and the obtained composite film is characterized using the field-emission scan electron microscopy, X-ray diffractometer and photoluminescence spectroscopy. The photocurrent–voltage curves of fabricated dye sensitized solar cells are measured by a solar cell measurement system. Compared with the bare porous TiO 2 film based dye sensitized solar cell, it is found that the power conversion efficiency of dye sensitized solar cell with ZnO nanorod decorated TiO 2 porous film was improved by more than triple. It is mainly believed that the improved power conversion efficiency of dye sensitized solar cell is ascribed to the increased dye adsorption amount and formation of energy barrier between ZnO nanorod and porous TiO 2 film.

This paper reports on the intense blue afterglow from undoped CaAl2 O4 nanocrystals in an attempt to achieve a clear understanding of the afterglow mechanism of Eu2+ -doped CaAl2 O4 . Undoped CaAl2 O4 nanocrystals were obtained via solution combustion technique. Intense blue afterglow, which is quite similar to that of Eu2+ -doped CaAl2 O4 , is observed with naked eyes for undoped CaAl2 O4 regardless of no Eu2+ species in the phosphors. Based on density functional calculations, the electronic structures of oxygen-deficient CaAl2 O4 are given, and the mechanism of the blue afterglow from undoped CaAl2 O4 is discussed in terms of the oxygen vacancy introduced midgaps. The recorded blue afterglow from undoped CaAl2 O4 nanocrystals leads to significant progress in our fundamental understanding of the afterglow mechanisms of Eu2+ -doped CaAl2 O4 .

Li-doped ZnO nanorods with a diameter of 200 nm and a length of 1 μm were vertically grown on TiO2 photoanodes of dye-sensitized solar cells (DSSCs) via the hydrothermal route at 90 °C. The morphology, crystal structure and photoluminescence of Li-doped ZnO nanorods were examined. It is found that 10 mol% Li doping of the ZnO nanorods can dramatically improve the photovoltaic performance of ZnO nanorods decorated DSSCs. The efficiency of the DSSCs decorated with Li-doped ZnO nanorods reaches 2.50%, which is about fourfold higher than that of DSSCs decorated with undoped ZnO nanorods (0.54%). The improved efficiency of ZnO nanorods decorated DSSCs can be ascribed to the reduced resistivity in ZnO nanorods, which suppresses the electron recombination loss and enhances the open-circuit voltage and short-circuit current density.

Core–shelled Zn/ZnO microspheres were prepared by ultrasonic irradiation to investigate their photocatalytic activity for degrading methyl orange in waste water. The microstructural and optical properties of the core–shelled Zn/ZnO microspheres were investigated by means of a scanning electron microscope, a transmission electron microscope, an X-ray diffractometer and a photoluminescence spectrometer. The results indicated that the metallic Zn core was about 6 μm in diameter whereas the ZnO shell was about 200 nm in thickness. Owing to the metal–semiconductor junction formed at the Zn/ZnO interface, the core-shelled Zn/ZnO microspheres exhibited higher photocatalytic activity for degrading methyl orange in water when compared with that of ZnO nanoparticles. It suggests that the core–shelled Zn/ZnO microspheres are a promising photocatalyst for the degradation of organic pollutants in water.

ZnO/porous Si (PS) nanocomposite films were prepared with the sol–gel spin-coating method. The morphologies, crystal structures, chemical compositions, surface passivations and photoluminescence (PL) spectra of the ZnO/PS nanocomposite films were investigated. It is found that the PL of the ZnO/PS nanocomposites can be tuned from red to green–blue by increasing the concentration of zinc cations in the sol–gels from 7.5 to 240 mM. Post-thermal annealing of the ZnO/PS nanocomposite films at 600 °C can shift the PL further into violet–blue. The roles of SiO2 thin interfacial layer between the ZnO and the Si nanocrystals in the nanocomposites are discussed. Our work provides an affordable means of tuning the emission color of the ZnO/PS nanocomposites across the visible spectral region.

Zinc oxide (ZnO) was synthesized by solid-liquid reaction of raw Zn particles in water. The synthesized ZnO were characterized with X-ray diffraction (XRD), scanning electronic microscopy (SEM) and photoluminescence (PL) spectrophotometer. The XRD pattern confirmed that the formation of ZnO with wurtzite structure and ZnOOH crystals. The SEM study clearly exhibited a honeycomb-shaped structure of the Zn/ZnO/ZnOOH composites. Room-temperature PL spectra have been observed a very weak UV emission at 376 nm and a very strong yellow-green emission at 538 nm. Furthermore, a possible mechanism of the water-assisted conversion of ZnO from metallic Zn particles was discussed.

Controlling the photon propagation in materials by photonic crystals lies at the heart of quantum optics. The motivation of our work is to investigate the direct control of the photon confinement in the self-assembled two-dimensional SiO2 photonic crystals. Here we demonstrate the realization of transmitted light controls in the self-assembled two-dimensional SiO2 PCs. Our experimental results agree well with the theoretical calculations on the photonic band gaps in the spectral region of 400-1100 nm. These results present experimental evidence on the direct control of the photon confinement in the self-assembled two-dimensional SiO2 PCs.

Polystyrene encapsulated phosphors SrAl2O4:Eu2+,Dy3+ were prepared by dispersing the phosphors into the matrix of polystyrene. The phase, morphology and optical properties of the polystyrene encapsulated phosphors were characterized with X-ray diffractometry, scanning electron microscopy and photoluminescence (PL) spectroscopy, respectively. It has been observed that both the PL spectrum and the luminescent color of the polystyrene encapsulated phosphors can be dramatically modified although the phosphorescence of the polystyrene encapsulated phosphors is not affected. Tunable photoluminescent colors from green to deep-blue are expected for the polystyrene encapsulated phosphors by the control of the weight percentage of the phosphors in the composites.

In this presentation, we present the preparation and performance of ZnO gas sensors on glass substrates. The phase and microstructures of the prepared ZnO nanocrystals were characterized with the X-ray diffractometer and transmission electron microscope. The transient response characteristics of the ZnO based sensors were recorded at room temperatures in saturated ethanol gas. It has been observed that the ZnO sensors can be operated at room temperature.