Luminescence Spectra of Poly(methylmethacrylate)/ZnS:Eu(III),Tb(III) Composites

Colloidal zinc sulfide solutions have been prepared by reacting zinc trifluoroacetate and thioacetamide in methyl methacrylate as a reaction medium, and europium and terbium salts have been added to the solution. Using methyl methacrylate block polymerization, we have synthesized PMMA/ZnS, PMMA/ZnS:Eu(III), PMMA/ZnS:Tb(III), and PMMA/ZnS:Eu(III),Tb(III) composites. The luminescence of the composites is due to charge recombination at energy levels of structural defects and impurities in ZnS and also to ⁵D₀ → ⁷F _j and ⁵D₄ → ⁷F _j electronic transitions of the Eu³⁺ and Tb³⁺ ions. It depends on the composition and structure of the composites, excitation wavelength, and other factors. The mutual effects of the ZnS and the Eu³⁺ and Tb³⁺ ions show up as changes in the position and relative intensity of luminescence bands in the spectra of the composites.     

Irradiation induced grain growth and surface emission enhancement of chemically tailored ZnS : Mn/PVOH nanoparticles by Cl<Superscript>+9</Superscript> ion impact

Manganese doped zinc sulfide nanoparticles are fabricated on polyvinyl alcohol dielectric matrix. They are bombarded with energetic chlorine ions (100 MeV). The size of the crystallites is found to increase with ion fluence due to melting led grain growth under ion irradiation. The increased size as a result of grain growth has been observed both in the optical absorption spectra in terms of redshift and in electron microscopic images. The photoluminescence (PL) study was carried out by band to band excitation (λ_ex = 220 nm) upon ZnS : Mn, which results into two emission peaks corresponding to surface states and Mn⁺² emission, respectively. The ion fluence for irradiation experiment so chosen were 1 × 10¹¹, 5 × 10¹¹, 5 × 10¹² and 10¹³ Cl/cm².     

Microstructures and photo-catalytic properties of B3+ and F− co-doped TiO2 films

The nano-crystalline B³⁺ and F^? co-doped titanium dioxide films were successfully prepared by the improved sol–gel process. The as-prepared specimens were characterised using X-ray diffraction (XRD), high-resolution field emission scanning electron microscopy (FE-SEM), the Brunauer–Emmett–Teller (BET) surface area, X-ray photo-electron spectroscopy, photoluminescence spectra and UV–Vis diffuse reflectance spectroscopy. The photo-catalytic activities of the films were evaluated by degradation of an organic dye in aqueous solution. The results of XRD, FE-SEM and BET analysis indicated that the TiO₂ films were composed of nano-particles. B³⁺ and F^? co-doping could obviously not only suppress the formation of brookite phase but also inhibit the transformation of anatase to rutile at high temperature. Diffuse reflectance measurements showed that co-doping could clearly extend the absorbance spectra of TiO₂ into visible region. Compared with pure TiO₂, B³⁺ doped or F^? doped TiO₂ film, the B³⁺ and F^? co-doped TiO₂ film exhibited excellent photo-catalytic activity. It is believed that the surface microstructure of the films and the doping methods of the two ions are responsible for improving the photo-catalytic activity.     

Synthesis and photoluminescent properties of doped ZnS nanocrystals capped by poly(vinylpyrrolidone)

Zinc sulfide semiconductor nanocrystals doped with selected transition metal ions (Mn²⁺, Cu²⁺, and Ni²⁺) have been synthesized via a solution-based method utilizing low dopant concentrations (0–1%) and employing poly(vinylpyrrolidone) (PVP) as a capping agent. UV/Vis absorbance spectra for all of the synthesized nanocrystals show an exitonic peak at around 310 nm, indicating that the introduction of the dopant does not influence the particle size. Calculated particle sizes for undoped and doped nanocrystals are in the 4.3 nm size range. Photoluminescence spectra recorded for undoped ZnS nanocrystals, using an excitation wavelength of 310 nm, exhibit an emission peak centered at around 460 nm. When a dopant ion is included in the synthesis, peaks in the corresponding photoluminescence spectra are red-shifted. For Mn-doped nanocrystals, an intense peak centered at approximately 590 nm is found and is seen to increase in photoluminescence intensity with an increase in dopant concentration. In contrast, for Cu-doped and Ni-doped nanocrystals, weaker peaks centered at around 520 and 500 nm, respectively, are observed and are noticed to decrease in photoluminescence intensity with an increase in dopant concentration. These results clearly show that careful control of synthetic conditions must be employed in the synthesis of doped semiconductor nanocrystals in order to obtain materials with optimized properties.     

Hydrothermal synthesis of blue-emitting YPO<Subscript>4</Subscript>:Yb<Superscript>3+</Superscript> nanophosphor

The blue-emitting YPO₄ phosphors doped with Yb³⁺ were prepared by a simple hydrothermal method. All the products were characterized by XRD and TEM, which revealed that they were zircon structure with leaf-like morphology. According to the analysis of photoluminescence spectra, upon ultraviolet (275 nm) excitation, the Yb³⁺ doped YPO₄ phosphor showed an intense blue emission composed of two main bands at 420 and 620 nm assigned to charge transfer state (CTS) → ²F_5/2 and CTS → ²F_7/2, respectively. Moreover, the optimum doping concentration of Yb³⁺ in YPO₄ phosphor was 1%, which exhibited the maximum emission intensity. The possible physical mechanism of concentration quenching was discussed, and the critical transfer distance determined to be 23.889 Å. In particular, the color purity of the as-synthesized Yb³⁺ doped YPO₄ phosphor was as high as 83%, which made it an excellent candidate for blue-emitting materials.     

A new fluorescent film sensor for Pb(II) ions developed by simulating bio-mineralization process synthesizing of ZnS/CS nanocomposite

Chitosan/zinc sulfide (CS/ZnS) nano-composite films have been prepared by simulating bio-mineralization process. Factors affecting the hydrothermal stability and fluorescence properties of the films have been studied. Furthermore, the sensing properties of nano-composite films to lead ions have been systematically investigated. SEM and TEM observations showed that the size of ZnS particles is 70 nm, and the particles are evenly distributed within the CS films. The fluorescence emission of the nano-composite films indicates that the sizes of real fluorescing ZnS particles are less than 20 nm. This suggests that ZnS particles observed via SEM and TEM may be aggregates of smaller ZnS particles, and the smaller particles may be separated by the organics. The fluorescence emission (363 nm) of the nano-composite films is very sensitive to the presence of Pb ions. C_(Pb²⁺₎ increased from 0 to 664.2 mg L⁻¹ increases the emission dramatically. The emission is hardly affected by common ions in water, except for the iron ions. The films may be developed as excellent sensing films for Pb ions in water.     

Luminescence enhancement of Eu3+-doped poly(acrylic acid) using 1,10-phenanthroline as antenna ligand

This work reports on the photoluminescence enhancement of Eu³⁺-doped poly(acrylic acid) using 1,10-phenanthroline as antenna ligand. The polymeric material was synthesized by polymerization in aqueous solution of the monomer partially neutralized with Eu₂O₃, containing 1,10-phenanthroline, and using potassium persulfate as initiator. The monomer modification and the coordination of antenna ligand to the Eu³⁺ ions were confirmed by ¹H-NMR. The doped polymer was characterized by luminescence spectroscopy. The excitation spectra show clear evidence of the coordination between the Eu³⁺ ions and the 1,10-phenanthroline ligands in the polymer matrix. On the other hand, the emission spectra show an inhomogeneous broadening and, together with the relative intensity of the ⁵D₀ → ⁷F_1,2 transitions of Eu³⁺, indicate that the dopant ions are uniformly distributed in low symmetry coordination sites. Besides, an enhancement in the intensity of the Eu³⁺ characteristic red emission by 1,10-phenanthroline addition is observed, and it is due to the antenna effect of the ligand, which acts as a sensitizer of the Eu³⁺ ions. An estimation of the increasing luminescence efficiency is presented.     

Structural,optical, photocurrent and mechanism-induced photocatalytic properties of surface-modified ZnS thin films by chemical bath deposition

ZnS thin films were prepared by chemical bath codeposition using ZnSO₄–ZnCl₂ or Zn(CH₃COO)₂–ZnCl₂ as zinc ion sources. The presence of SO₄ ^2? favors the heterogeneous growth of ZnS thin film. The coexistence of two zinc salts impedes the formation of homogeneous precipitation and improves the growth rate of ZnS film. XRD and HRTEM results show that all the samples exhibit the cubic structure. EDS analysis shows that Zn/S atom ratios from the codeposition are closer to 1:1 than those deposited from a single zinc salt, and ZnS thin films of S3 and S7 are very uniform without stirring. FTIR reveals that –NH₂ group as a surface modifier is adsorbed on the surface of ZnS nanoparticles. Raman spectra further reveal that S3, S4 and S7 form the ZnS films, and ZnO phase is present in short or middle range of the S6 nanocrystal, indicating that different amounts of zinc salts affect the structure of ZnS films significantly after three 2.5 h deposition cycles. The grain sizes determined by FESEM are inversely proportional to RMS determined by AFM. The band gap values of ZnS thin films agree well with the results of HRTEM. The photocurrent responses of different samples are similar, indicating that different amounts of zinc salts have little effect on the photocurrent of ZnS films. The photocatalytic performance of S6 and S8 is much better than that of S1–S5. S6 decomposes 65 % of methyl orange within 3 h, and its K value is 4.78 × 10^?1 h^?1. The photocatalytic performance is induced by the growth mechanism, which determines the grain size of ZnS thin film. The tendency of grain sizes of ZnS films agrees well with that of photocatalytic performance, especially under the clusters by clusters deposition.     

Luminescent properties of Al2O3:Tb3+ powders embedded in polyethylene terephthalate films

The luminescent properties of Al₂O₃:Tb³⁺ powders embedded in polyethylene terephthalate (PET) films have been studied. Luminescent Al₂O₃:Tb³⁺ polycrystalline powders were synthesized by a simple evaporation method. The powder embedded films were obtained by the spray pyrolysis technique. The photoluminescence and cathodoluminescence emission spectra from these samples show, in both cases, luminescence peaks associated with transitions within the electronic energy levels of Tb³⁺ ions. The dominant peak is at 544 nm corresponding to the ⁵D₄ to ⁷F₅ transition. In the case of the powder embedded films, the CIE coordinates depend on the excitation wavelength because there is a blue emission contribution from the PET host. UV–Vis% transmission measurements on these films show that they are transparent (∼80% and 95% T).     

Fabrication and photoluminescence of thin films of lanthanide–polyoxometalates grafted on colloid silica sphere

In this paper, two lanthanide–polyoxometalates Na₉LnW₁₀O₃₆ (Ln=Eu, Dy, LnW₁₀) were grafted on 400 nm amine-functionalized spherical Stöber silica. The monolayer thin films of hybrid particles were fabricated on quartz by spin-coating method. The hybrid particles and thin films obtained were characterized by IR, UV–vis spectra, scanning electron microscopy, transmission electron microscope and luminescent spectra, respectively. The hybrid particles show strong luminescence which could be seen by naked eyes. The excitation spectra of hybrid particles and thin films show both abroad ligand to metal charge band and the excitation lines of rare earth ions. The transition ⁵D₀→⁷F₀ could be seen in the emission of hybrid EuW₁₀/SiO₂ spheres and thin films, which could not be found in spectrum of EuW₁₀ solid. It is noticed that the intensity ratio of red (⁵D₀→⁷F₂) to orange (⁵D₀→⁷F₁) of Eu³⁺ and the yellow to blue (⁴F_9/2→⁶H_13/2: ⁴F_9/2→⁶H_15/2) of Dy³⁺ in LnW₁₀/SiO₂ particles and thin films are quite different from those of LnW₁₀ solids. The different shapes and ratios between characteristic emissions of hybrid particles and thin films indicated the various symmetry of sites occupied by Ln³⁺ ions.     

Fabrication and characterization of the photoluminescent properties of Tb doped one-dimensional GdPO4 nanorods

In this letter, one-dimensional GdPO₄:Tb³⁺ nanostructures were successfully synthesized by an easy hydrothermal method at 120 °C and 150 °C. Their morphology and structure were characterized and their photoluminescent properties were investigated, including excitation and emission spectra as well as fluorescent dynamics. Results indicated that one-dimensional GdPO₄:Tb³⁺ nanorods formed at low temperature. The hydrothermal temperature did not affect their morphology and size. The crystal structure of GdPO₄:Tb³⁺ nanostructures belongs to monoclinic phase. According to excitation and emission spectra, the strong green emission of Tb³⁺ ions from ⁵D₄-⁷F₅ transitions and the energy transfer from Gd³⁺ to Tb³⁺ ions were observed.     

Rapid thermal annealing effects on atomic layer epitaxially grown Zns:Mn thin films

ZnS:Mn thin films were coated on transparent conducting layer indium tin oxide (ITO) 2×2 in. glass substrates by an atomic layer epitaxy process. Grazing-angle X-ray diffraction on thin films shows a phase-pure ZnS with a wurtzite structure oriented along the 002 direction. Photoluminescence and CL measurements were carried out on the films. The emission from ZnS:Mn thin films consists of two strong bands at 515 and 452 nm with an excitation band at 329 nm. For improved brightness, the samples were annealed in a rapid thermal annealing furnace under different gas atmospheres (N₂, O₂ and forming gas) so that the green emission was increased. The green emission is due to donar-acceptor combination. Promising results were obtained when the thin films were annealed in forming gas at 600°C for one minute. Scanning electron microscope micrographs showed that the particles are well crystallized, with a grain size of 0.3–0.5 μm. This paper reports the particle size and morphology on the luminescent characteristics of a Mn²⁺ center in ZnS thin films. Received: 16 April 1999 / Reviewed and accepted: 21 April 1999     

Luminescence performance of Eu<Superscript>3+</Superscript>-doped lead-free zinc phosphate glasses for red emission

In this study, the luminescence performance of zinc phosphate glasses containing Eu³⁺ ion with the chemical compositions (60–x)NH₄H₂PO₄-20ZnO-10BaF₂-10NaF–x Eu₂O₃ (where x = 0.2, 0.5, 1.0 and 1.5 mol%) has been studied. These glasses were characterized by several spectroscopic techniques at room temperature. All the glasses showed relatively broad fluorescence excitation and luminescence spectra. Luminescence spectra of these glasses exhibit characteristic emission of Eu³⁺ ion with an intense and most prominent red emission (614 nm), which is attributed to ⁵D₀ → ⁷F₂ transition. Judd-Ofelt (Ω₂, Ω₄) parameters have been evaluated from the luminescence intensity ratios of ⁵D₀ → ⁷F_J (where J = 2 and 4) to ⁵D₀ → ⁷F₁ transition. Using J-O parameters and excitation spectra, the radiative parameters are calculated for different Eu³⁺-doped glasses. Effect of γ-irradiation at fixed dose has been studied for all the Eu³⁺-doped glass matrices. The lifetimes of the excited level, ⁵D₀, have been measured experimentally through decay profiles. The colour chromaticity coordinates are calculated and represented in the chromaticity diagram for Eu³⁺-doped zinc phosphate glasses for all concentrations.     

Control of ZnO thin film surface by ZnS passivation to enhance photoluminescence

To enhance the optical property of zinc oxide (ZnO) thin film, zinc sulfide (ZnS) thin films were formed on the interfaces of ZnO thin film as a passivation and a substrate layer. ZnO and ZnS thin films were deposited by atomic layer deposition (ALD) using diethyl zinc, H₂O, and H₂S as precursors. Investigations by X-ray diffraction and transmission electron microscopy showed that ZnS/ZnO/ZnS multi-layer thin films with clear boundaries were achieved by ALD and that each film layer had its own polycrystalline phase. The intensity of the photoluminescence of the ZnO thin film was enhanced as the thickness of the ZnO thin film increased and as ZnS passivation was applied onto the ZnO thin film interfaces.     

Hydrothermal synthesis and optical properties of Eu doped NaREF4 (RE = Y, Gd), LnF3 (Ln = Y, La), and YF3·1.5NH3 micro/nanocrystals

5 mol% Eu³⁺ doped NaYF₄ (α-, β-), YF₃, YF₃·1.5NH₃, NaGdF₄, and LaF₃ micro/nanocrystals have been synthesized by a hydrothermal method. The final products are characterized by X-ray diffraction, field emission scanning electron microscopy, photoluminescence excitation and emission spectra, and luminescent dynamic decay curves. Due to its sensitivity to local symmetry, Eu³⁺ shows different optical properties in the above samples. It has stronger luminescent intensity in β-NaYF₄ than that in α-NaYF₄ while it exhibits different higher energy ⁵D_1,2 to lower ⁷F_J emissions as well as the asymmetric ratios and the splits of ⁵D₀ → ⁷F₁, ⁷F₄. YF₃, LaF₃, and β-NaGdF₄ have analogous optical intensities to those of β-NaYF₄. However, β-NaGdF₄ has the similar spectral profile to that of β-NaYF₄ while YF₃ and LaF₃ have the opposite cases in the ⁵D₀ → ⁷F₂, ⁷F₁ emissions. Further, Judd-Ofelt calculation has been used to analyze the experimental phenomena.     

Optical properties of water-soluble Co:ZnS semiconductor nanocrystals synthesized by a hydrothermal process

Water-soluble ZnS:Co²⁺ nanocrystals (NCs) were synthesized by a low temperature hydrothermal process using 3-mercaptopropionic acid (MPA) as capping agent and the influence of doping on the optical properties of ZnS:Co²⁺ NCs was investigated. It was found that the ZnS:Co²⁺ NCs are highly crystalline and show zinc blende structure with an average particle size of about 7 nm. The lattice constant of the ZnS:Co²⁺ NCs decreases slightly by the introduction of Co²⁺. The Co dopants were well doped into the ZnS:Co²⁺ NCs, as confirmed by X-ray photoelectron spectroscopy(XPS) and the ⁴A₂(F) → ⁴T₁(P) transition of Co²⁺ was detected from the UV-vis absorption spectra. The absorption edge of the ZnS:Co²⁺ NCs is blue-shifted as compared with that of bulk ZnS, indicating the quantum confinement effect. The PL intensity of the NCs shows the maximum value when the Fe-doping concentration is 0.5 at.%.     

Upconversion fluorescence in Sm3+-doped zinc phosphate glassy matrix

The mechanism governing the upconversion fluorescence from the ⁴G_5/2 level of Sm³⁺ ion has been investigated in zinc phosphate glass matrices under infrared (1.06?µm) laser excitation. This visible emission is centred at 590?nm and corresponds to the ⁴G_5/2?→?⁶H_7/2 transition. The dependence of the integrated intensity on the excitation power confirms that this emission is due to the three-photon absorption process and is in agreement with the existing theory. The intensity of the upconversion fluorescence has a cubic dependence on the excitation power. An absolute upconversion efficiency of about 10^?7 was obtained for the sample doped with 0.5?wt% Sm³⁺ ions. A quantitative estimate of the number of photons leaving the sample was also determined.     

Structural and luminescence characterization of Eu3+/ZnS nanoparticle-doped ZrO2/PEG composites

ZnS nanoparticles of varying concentrations were incorporated into Eu³⁺ doped ZrO₂/PEG composite system through non-hydrolytic sol–gel method. The presence of the nanoparticles was confirmed by XRD and TEM analyses. The elemental composition of the prepared sample was verified using EDX analysis. Different vibrational modes of the composite system were found out by FTIR spectra. Thermal stability of the as-prepared sample was measured using TGA and DTA analyses. The optical bandgap of the composite system was calculated from the absorption spectrum. The excitation spectrum shows the broad excitation bands of the sensitizer (ZnS) and Host (ZrO₂/PEG) as well as the characteristic excitation peaks of the activator (Eu³⁺). The emission spectra reveal that the characteristic emission of Eu³⁺ can be obtained using 392 nm as well as the excitation wavelength of the sensitizer (275 nm). The CIE chromaticity analysis shows a change in the emission colour of the co-doped samples from yellow to reddish orange corresponding to a change in the excitation wavelength from 392 to 275 nm. These results suggest the applicability of the as-synthesized composite system as a potential candidate in various optoelectronic devices.

     

Structure and photoluminescence properties of ZnS nanowires sheathed with SnO2 by atomic layer deposition

Influence of the thermal annealing atmosphere on the photoluminescence properties of ZnS-core/SnO₂-shell coaxial nanowires was investigated. ZnS nanowires were synthesized by a two-step process: the thermal evaporation of ZnS powders and the atomic layer deposition of SnO₂. Transmission electron microscopy and X-ray diffraction analyses reveal that two crystalline ZnS phases: one with a zinc blende structure and the other with an wurtzite structure coexist in the cores whereas the SnO₂ cores in the as-prepared coaxial nanowires are amorphous. The SnO₂ shells are found to be crystallized by thermal annealing. Photoluminescence (PL) measurements at room temperature show that the green emission of the ZnS/SnO₂ coaxial nanowires is enhanced in intensity by thermal annealing regardless of the annealing atmosphere. The PL emission is more significantly enhanced in intensity by annealing in a reducing atmosphere than in an oxidative atmosphere since Au_Zn ⁻ is more easily generated in the ZnS cores in the former atmosphere.     

Tuning photoluminescence of ZnS nanoparticles by silver

We report the results of investigation of the interaction of silver with presynthesized ZnS nanoparticles (NPs) that was stabilized by cetyl trimethyl ammonium bromide (CTAB). The photoluminescence properties of ZnS NPs were followed in the presence of Ag⁺ ions, Ag NPs and by the synthesis of Ag@ZnS core-shell nanoparticles. We observed that CTAB stabilized ZnS NPs emitted broadly in the region from 350–450 nm, when excited by 309 nm light. In the presence of Ag⁺ ions the emission peak intensity up to 400 nm was reduced, while two new and stronger peaks at 430 nm and 550 nm appeared. Similar results were obtained when Ag NPs solution was added to ZnS solution. However, when Ag@ZnS NPs were synthesized, the emission in the 350–450 nm region was much weaker in comparison to that at 540 nm, which itself appeared at a wavelength shorter than that of Ag⁺ ion added ZnS NPs. The observations have been explained by the presence of interstitial sulfur and Zn²⁺, especially near the surface of the nanocrystals and their interaction with various forms of silver. In addition, our observations suggest that Ag⁺ ions diffuse into the lattice of the preformed ZnS NPs just like the formation of Ag⁺ doped ZnS NPs and thus changes the emission characteristics. We also have pursued similar experiments with addition of Mn²⁺ ions to ZnS and observed similar results of emission characteristics of Mn²⁺ doped ZnS NPs. We expect that results would stimulate further research interests in the development of fluoremetric metal ion sensors based on interaction with quantum dots.