Absorption and emission spectral analysis of Pr<Superscript>3+</Superscript>: tellurite glasses

This paper reports on the results concerning optical absorption and fluorescence properties of 60TeO₂–25ZnO–10BaO–4.5La₂O₃–0.5Pr₂O₃ (Pr³⁺: TZBL) glass. Both electronic (α_e) and vibrational (α_v) band edge cut-off wavelengths of the host glass (TZBL) have been evaluated from the measurement of its UV–Vis and IR transmission spectra. The glass studied has shown 80% transmittance throughout its optical window from 0.366 μm (α_e = 3.39 eV) to 6.30 μm (α_v = 0.197 eV). The FT-IR transmission spectra of Pr³⁺ doped and also reference tellurite glasses have demonstrated the presence of TeO₄ and TeO₃₊₁ or TeO₃ structural units. The thermal properties of this glass have been investigated from the study of DTA profile. The recorded optical absorption spectra of Pr³⁺: TZBL glass have shown eight absorption bands from 300 nm to 2,500 nm. The fluorescence emission has been observed mainly from ³P₁, ³P₀ and ¹D₂ states to the lower lying states and which are assigned to the transitions of ³P₀→ ³H_4,5,6; ³P₀→ ³F_2,3,4; ³P₁→³H₅ & ¹D₂→³H_4,5 upon excitations at three excitation states of ³P_0,1,2. From the time resolved spectra, it is found that ³P₀ level decays faster than ¹D₂ level. The fluorescence decay kinetics of ³P₀ and ¹D₂ levels have been measured and the lifetimes are found to be 21 and 39 μs, respectively.     

Structural,optical and non-linear investigation of Eu<Superscript>3+</Superscript>: Al(NO<Subscript>3</Subscript>)<Subscript>3</Subscript>-SiO<Subscript>2</Subscript> sol-gel glass

Optical absorption and fluorescence spectra of Eu³⁺ ions in Al(NO₃)₃-SiO₂ sol-gel glass have been investigated using the Judd- Ofelt theory. JO intensity parameters (ω _λ ) and subsequent radiative properties for⁵ D ₀ ↔⁷ F _1,2,4,6 transitions are determined. The lifetime (τ_r) of⁵ D ₀ state is computed and along with JO parameters are compared with their corresponding values in other glasses prepared by conventional technique. A structural analysis, using IR and XRD spectra and non- linear parametrization of the silica gel glass is carried out. The study reveals the glass to be a very good third order non- linear amorphous optical material.     

Photochemical behaviors during the photosensitization of colloidal TiO<Subscript>2</Subscript> particles by a newly synthesized multidentate squaraine

A new squaraine dye Bis(4-N,N-dicarboxymethyl-2-hydroxyphenyl)squaraine (SQ) which could be used as organic photovoltaic materials, was synthesized, and its molecular structure was fully characterized by elemental analysis, IR, ¹H NMR and MS. SQ exhibits strong absorption band over 600–700 nm. Addition of TiO₂ colloids to the ethanol solution of SQ resulted in the increase of optical density, quenching of fluorescence and shortened fluorescence lifetime. The apparent association constant between the sensitizer and semiconductor as measured from the fluorescence quenching data, was 2427 M⁻¹. Fluorescence lifetime measurements gave the rate constant for the electron injection process from the excited singlet of SQ to the conduction band of TiO₂ nanoparticles as 2.55 × 10 ⁸ s⁻¹. In addition, SQ doped SiO₂ gel glass slices were prepared and characterized by absorption and emission spectra.     

Preparation and characterization of Eu<Superscript>3+</Superscript> activated CaSiO<Subscript>3</Subscript>, (CaA)SiO<Subscript>3</Subscript> [A = Ba or Sr] phosphors

Eu³⁺ activated CaSiO₃, (Ca, Ba) SiO₃ and (Ca, Sr) SiO₃ have been prepared by sol-gel technique. Residual solvent and organic contents in the gel were removed by firing at 100°C for 3–4 h at 300 and 600°C for 2 h. Small exothermic shoulder around 850 to 875°C, as observed in DTA curve, corresponds to crystallization temperature of the doped calcium silicate. Influence of firing temperature on the luminescence of Eu³⁺ shows the maximum emission intensity in gel fired at 850°C. Photoluminescence emission peak is observed at 614 nm due to⁵D₀ →⁷F₂ transition of Eu³⁺ ion in (Ca, Ba) SiO₃ and (Ca, Sr) SiO₃ phosphors, when excited by 254 nm. The (Ca, Ba) SiO₃ material is proposed as an efficient red phosphor.     

Spectral analysis of Cu<Superscript>2+</Superscript> and Mn<Superscript>2+</Superscript> ions doped borofluorophosphate glasses

We report here on the development and spectral analysis of Cu²⁺ (0.5 mol%) and Mn²⁺ (0.5 mol%) ions doped in two new series of glasses. The visible absorption spectra of Cu²⁺ and Mn²⁺ glasses have shown broad absorption bands at 820 nm and 495 nm, respectively. For Cu²⁺ BFP glasses, excitation at 380 nm, a blue emission at 441 nm and also a weak emission at 418 nm ions have been observed. For Mn²⁺ ions doped BFP glasses, excitation at 410 nm and a red shift at 605 nm emission have been observed.     

Synthesis and luminescence properties of Eu<Superscript>2+</Superscript>-doped Li<Subscript>2</Subscript>SrSiO<Subscript>4</Subscript>

We have studied the luminescence spectra of Li₂Sr_{1 − x} Eu _x SiO₄ (x = 0.0001–0.01) solid solutions prepared by solid-state reactions and a sol-gel process in a reducing atmosphere. The spectra show a broad band in the range 500–700 nm, centered at 578 nm, which is due to the 4f ⁶5d → 4f ⁷ transition. The luminescence excitation spectrum shows, in addition to bands due to Eu²⁺ 4f ⁷ → 4f ⁶5d transitions, a strong band centered at 174 nm, attributable to absorption in the SiO₄⁴⁻ group.     

Growth of Nd<Superscript>3+</Superscript> doped LiNbO<Subscript>3</Subscript> crystals using Bridgman method and its spectral properties

The growth of Nd³⁺ doped lithium niobate crystals using Bridgman method has been reported in this paper. By means of the optimum conditions such as proper feed materials, sealed platinum crucibles, growth rate of 1–1·5 mm/h and temperature gradient of 30–35°C/cm across the solid-liquid interface under the furnace temperature of 1300°C, single crystals containing Nd³⁺ ion with 0·54 mol% concentration were obtained. X-ray diffraction and ICP-AES were used to characterize the crystals and its composition. The absorption, emission and fluorescence lifetime are also measured. Based on the Judd-Ofelt theory, we obtained the optical parameters of the crystal such as the luminescent quantum efficiency, the radioactive lifetimes, the branching ratios and the emission cross-section.     

Effects of samarium dopant on photocatalytic activity of TiO<Subscript>2</Subscript> nanocrystallite for methylene blue degradation

Sm³⁺-doped TiO₂ nanocrystalline was synthesized by a sol–gel auto-combustion method and characterized by X-ray diffraction, Brunauer-Emmett-Teller method (BET), UV–vis diffuse reflectance spectroscopy (DRS), and also photoluminescence (PL) emission spectroscopy. The photocatalytic activity of Sm³⁺–TiO₂ catalyst was evaluated by measuring degradation rates of methylene blue (MB) under either UV or visible light. The results showed that doping with the samarium ions significantly enhanced the photocatalytic activity for MB degradation under UV or visible light irradiation. This was ascribed to the fact that a small amount of samarium dopant simultaneously increased MB adsorption capacity and separation efficiency of electron-hole pairs. The results of DRS showed that Sm³⁺-doped TiO₂ had significant absorption between 400 nm and 500 nm, which increased with the increase of samarium ion content. The adsorption experimental demonstrated that Sm³⁺–TiO₂ had a higher MB adsorption capacity than undoped TiO₂ and adsorption capacity of MB increased with the increase of samarium ion content. It is found that the stronger the PL intensity, the higher the photocatalytic activity. This could be explained by the points that PL spectra mainly resulted from surface oxygen vacancies and defects during the process of PL, while surface oxygen vacancies and defects could be favorable in capturing the photoinduced electrons during the process of photocatalytic reactions, so that the recombination of photoinduced electrons and holes could be effectively inhibited.     

X-ray diffraction,optical absorption and emission studies on Er<Superscript>3+</Superscript>- and Er<Superscript>3+</Superscript>/Yb<Superscript>3+</Superscript>-doped Li<Subscript>3</Subscript>NbO<Subscript>4</Subscript> powder

Er³⁺(/Yb³⁺)-doped Li₃NbO₄ powder were prepared by thermally sintering mixtures of Er₂O₃ (0.5, 1.0 mol%), Yb₂O₃ (0, 0.5, 1.0 mol%), Li₂CO₃ (48–49 mol%) and Nb₂O₅ (50 mol%) at 1125, 1150 and 1450 °C over the durations of 8–22 h. The crystalline phases contained in these samples were determined by using X-ray diffraction and discussed in comparison with a vapor-transport-equilibration-treated (VTE-treated) Er(2.0 mol%):LiNbO₃ single crystal and ErNbO₄ powder previously reported. The results show that the X-ray patterns of the rare-earth-doped samples reveal little difference each other, but large differences with those of the VTE crystal and ErNbO₄ powder. The doped rare-earth ions Er³⁺ (and Yb³⁺) present in the powder as the ErNbO₄ (and YbNbO₄) phase(s). The possibility that the highly Er-doped LiNbO₃ crystal contains Li₃NbO₄ precipitates is small. Optical absorption and emission studies show that the only Er-doped Li₃NbO₄ powder shows similar absorption and emission characteristics with the pure ErNbO₄. The codopant Yb³⁺ ion enhances the 980-nm-upconversion emissions of Er³⁺ ions, results in remarkable spectral alterations at 0.98 μm region, and causes the alterations of relative absorbance and relative emission intensity of individual peaks or bands at 1.5 μm region. On the other hand, the Yb-codoping hardly affects the Er³⁺ energy structure and the lifetime of Er³⁺ ion at 1.5 μm. The measured lifetimes at 1.5 μm of Er³⁺ ions in the singly Er³⁺- and doubly Er³⁺/Yb³⁺-doped mixtures have a nearly same value of ∼ 1.5 ms. For the pure ErNbO₄ powder, the lifetime is prolonged to ∼2 ms perhaps due to radiation trapping effect.     

Synthesis of Er<Superscript>3+</Superscript> and Er<Superscript>3+</Superscript> : Yb<Subscript>3+</Subscript> doped sol-gel derived silica glass and studies on their optical properties

Er₃₊ and Er₃₊ : Yb₃₊ doped optical quality, crack and bubble free glasses for possible use in making laser material have been prepared successfully through sol-gel route. The thermal and optical, including UV-visible absorption, FTIR etc characterizations were undertaken on the samples. The absorption characteristics of Er₃₊ doped samples clearly revealed the absorption due to Er₃₊ ions. On the other hand Yb₃₊ : Er₃₊ doped samples showed enhanced absorption due to² F _7/2 →² F _5/2 transition. The absorption and emission cross-section for² F _7/2 ↔² F _5/2 of Yb³⁺ were estimated. FTIR absorption spectra have clearly shown the reduction of the absorption peak intensity with heat treatment in the range 3700–2900 cm⁻¹. The 960 cm^-1 band also showed progressive decrease in the absorption band peak intensity with heat treatment. The result of the investigations with essential discussions and conclusions have been reported in this paper.     

The influence of ions’ substitution on the optical properties of A<Subscript>2</Subscript>MX<Subscript>4</Subscript> crystals

In this article, results based on the research of optical properties of A₂MX₄ type crystals (A—organic cation, M—metal, X—halogen) composed of different chemical elements are presented. These crystals were grown by the evaporation method from water solutions of AX and MX₂ compounds in an appropriate molar ratio. The conducted X-ray investigations show a different crystal structures, ranging from tetragonal to triclinic ones. Also, the structure of the ion complex for Cu²⁺ crystals varied. The investigation showed both CuCl₄²⁻ tetrahedral and CuCl₄ · 2H₂O²⁻ octahedral deformed complexes in investigated crystals. Additionally, the optical spectra of the samples were measured in the range of 250–850 nm. Based on the crystal field theory, it was shown that the shape of absorption spectra and colour of the crystals depend on the distortion of these complexes.     

Combusion synthesis,structural and photo-physical characteristics of Eu<Superscript>2+</Superscript> and Dy<Superscript>3+</Superscript> co-doped SrAl<Subscript>2</Subscript>O<Subscript>4</Subscript> phosphor nanopowders

In this research, we reported the synthesis of Eu²⁺ and Dy³⁺ co-doped SrAl₂O₄ phosphor nanopowders with high brightness and long afterglow by urea-nitrate solution combustion synthesis (SCS) at 600 °C, followed by heating the resultant combustion ash at 1,200 °C in a weak reductive atmosphere (5% H₂ + 95% N₂). The broad-band UV-excited luminescence of the SrAl₂O₄: Eu²⁺, Dy³⁺ nanopowders was observed at λ _max = 517 nm due to transitions from the 4f⁶5d¹ to the 4f⁷ configuration of the emission center (Eu²⁺ ions). The excitation spectra consist of 240- and 254 nm broad peaks. Finally, it was found that the optimum ratio of urea is 2.5 times higher than theoretical quantities for the best emission condition of SrAl₂O₄: Eu²⁺, Dy³⁺ phosphor nanopowders.     

Studies of Fe-doped SiO<Superscript>2</Superscript>/TiO<Superscript>2</Superscript> composite nanoparticles prepared by sol-gel-hydrothermal method

Fe-doped SiO²/TiO² composite nanoparticles were directly prepared by sol-gel-hydrothermal process, and characterized by X-ray diffraction (XRD), transmission electron microscope (TEM), thermal gravimetry (TG), X-Ray photoelectron spectroscopy (XPS), and UV-Vis diffuse reflectance spectra (DRS). It was found that the Fe^{3 +} was well dispersed in solid solution of SiO²/TiO² composite nanoparticles that was about 10 nm with spherical morphology and rich silica layer external surface. It could effectively offer broadband shield for both UVB (290–320 nm) and UVA (320–400 nm). The results of Photodecomposition of methylene blue showed that the photoactivity of Fe-doped SiO²/TiO² composite was minimized due to the addition of iron ion.     

Synthesis and characterization of sol-gel derived ZnS : Mn2+ nanocrystallites embedded in a silica matrix

Synthesis and characterization of undoped and Mn²⁺ doped ZnS nanocrystallites (radius 2–3 nm) embedded in a partially densified silica gel matrix are presented. Optical transmittance, photoluminescence (PL), ellipsometric and electron spin resonance measurements revealed manifestation of quantum size effect. PL spectra recorded at room temperature revealed broad blue emission signal centred at ∼ 420 nm and Mn²⁺ related yellow-orange band centred at ∼ 590 nm while ESR indicated that Mn in ZnS was present as dispersed impurity rather than Mn cluster.     

Role of tin as a reducing agent in iron containing heat absorbing soda-magnesia-lime-silica glass

The role of tin as a reducing agent in a 18Na₂O·2MgOO·8CaOO·72SiO₂ glass containing a definite amount of total, ΣFe = [Fe²⁺] + [Fe³⁺], was investigated with different concentrations of total tin, ΣSn = [Sn²⁺] + [Sn⁴⁺], by absorption spectra of iron ions in the optical range 300–1200 nm recorded on a JASCO-7800 spectrophotometer. The single broad absorption band for Fe²⁺ ion was marked at 1055 nm in the near infrared region and a narrow weak band for Fe³⁺ ion at its λ_max at around 380 nm was observed in the silicate glass. The proportion of ferrous iron was found to increase in the glass in the beginning with the addition of tin up to 0 788% Σ Sn and then it approached a maxima with 1182% Σ Sn. Further addition of tin was found to be futile for the constant iron concentration of 0–875% for achieving higher [Fe²⁺]/[Fe³⁺] ratio for maximum heat absorption due to Fe²⁺ ion in the glass. The mechanism of the process was discussed on the basis of Sn²⁺/Sn⁴⁺ and Fe²⁺/Fe³⁺ mutual redox interaction in the molten glass at 1400°C. The suitable limit of tin was suggested to be 0.788 ≤x ≤ 1.182% by wt for 0.875% of total iron for getting maximum ferrous ion in the glass.     

Spectroscopic studies and evanescent optical fibre wave sensing of Cu<Superscript>2+</Superscript> based on activated mesostructured silica matrix

This paper report on the synthesis and test of eriochrome cyanine R (ECR) doped mesostructured silica films as Cu²⁺ sensing without prior removal of the surfactant. ECR activated mesostructured silica (via sol-gel technique) coated optical fibre core were used to Cu²⁺ sensing by evanescent wave method. The sol was prepared via acidic hydrolysis-condensation of tetraethoxysilane (TEOS) in the presence of cetyltrimethylammonium bromide (CTAB:C₁₆H₃₃NCH₃Br) as the structure-directing agent. Spectrophotometric investigations using doped sol-gel thin films dip-coated on glass slides were reported. Heat treatment temperature effect (optimum temperature 150°C), absorption dependence on the pH of the aqueous phase (pH = 8 seems to be the optimal absorption pH), sensitivity, reversibility and response range (0.05 mmol/l) were reported.     

Cu ion in-diffusion in congruent LiNbO3 single crystals

Congruent LiNbO₃ (LN) crystals were grown by Czochralski technique. Thermal in-diffusion of transition metal ion Cu²⁺ into crystal wafers was performed at various temperatures. The absorption peaks in transmission spectra indicates the Cu²⁺ ion diffusion in LN crystal wafer. A broad absorption band centered at 948 nm was observed in the absorption spectra due to the vibronic transition associated with Cu²⁺ centers. The significant red shift in absorption edges indicates the decrease in Li/Nb ratio in Cu in-diffused crystal wafers. Powder XRD of pure and Cu in-diffused LN samples show no structural change during thermal diffusion.     

Synthesis and luminescent characterization of YAl<Subscript>3</Subscript>(BO<Subscript>3</Subscript>)<Subscript>4</Subscript>:Tb<Superscript>3+</Superscript> phosphors

YAl₃(BO₃)₄:Tb³⁺ phosphors were fabricated by the sol–gel method. The phosphor showed prominent luminescence in green due to the magnetic dipole transition of ⁵D₄–⁷F₅. Structural characterization of the luminescent material was carried out with X-ray powder diffraction (XRD) analysis. Luminescence properties were analyzed by measuring the excitation and photoluminescence spectra. Photoluminescence measurements indicated that the phosphor exhibited bright green emission at about 541 nm under UV excitation. It is shown that the 11% of doping concentration of Tb³⁺ ions in YAl₃(BO₃)₄:Tb³⁺ phosphors is optimum.     

Infrared spectroscopic study of water in mesoporous silica under supercritical conditions

The structure of water under high temperature–pressure conditions in mesospace was investigated by measuring the infrared spectra of water in mesoporous silica. Absorption peaks attributed to OH-stretching vibration of water in mesoporous silica were detected at lower wavenumbers as compared with bulk water, and the absorption peak positions were dependent on pore diameter. For small pore diameters (3–20 nm), absorption peak positions of water were detected at lower wavenumbers (ca. 3,300 cm⁻¹) at 400 °C, while for larger pore diameters (30–50 nm) the peaks were detected at higher wavenumbers (ca. 3,500 cm⁻¹). We attribute these features to the effects of mesoporous silica surface structure on the structural and vibrational modes of water. Furthermore, absorption peak positions changed significantly at different pore sizes (20 and 30 nm), indicating that the structure of water in small pores approaches a more ice-like structure. Based on our experimental results, the structured water layer in mesoporous silica is estimated to be at least 10 nm thick, which is thicker than that previously documented in molecular dynamic simulation studies where the thickness of structured water was found to be two or three layers from the surface.     

Synthesis and photoluminescence properties of Eu<Superscript>3+</Superscript>-activated SrZnO<Subscript>2</Subscript>

Synthesis, X-ray diffraction, and photoluminescence (PL) investigations of SrZnO₂ doped with Eu³⁺ were carried out in order to characterize the material. The emission spectra showed a broad band emission at 525 nm attributed to oxygen defect centers in the host matrix, along with peaks corresponding to the ⁵D₀ → ⁷F _j (j = 1, 2) transitions of Eu ion under 250 nm excitation. PL decay time studies were done to confirm these investigations. Time-resolved emission spectrometric (TRES) study was carried out to extract the emission spectra of the Eu ion which was buried under the broad band emission. After giving suitable delay times and by choosing a proper time gate, transitions due to ⁵D₀ → ⁷F _j (j = 0, 1, 2, 3, and 4) could be observed. Judd–Ofelt intensity parameters and other radiative properties for the system were evaluated from this emission spectrum and decay time data by adopting standard procedure. The color coordinates of the system were also evaluated and plotted on a standard CIE index diagram. The observations showed that the SrZnO₂:Eu³⁺material has near white light emission (also considering the emission from host) whereas, the extracted emission spectrum due to only Eu ions has a near red emission.