Selective formation of crystal polymorphs in Er3+-doped Bi2O3 thin films and their photoluminescence properties

The process conditions for selectively forming crystal polymorphs in Er³⁺-doped Bi₂O₃ films deposited on Si, SiO₂, and C-plane sapphire substrates were systematically investigated. Bi₂O₃:Er films were deposited at either room temperature or 300 °C and subsequently post annealed to promote crystallization. The critical factor controlling the crystal polymorphs was Er content. When the Er content was less than 1.5 at.%, only α-Bi₂O₃ phase nucleated upon post annealing. Deposition at 300 °C somewhat lowered the oxidization state, under which β-Bi₂O₃ structure appeared at lower temperatures and α-Bi₂O₃ structure appeared at higher temperatures. When the films were doped with over 2 at.% Er³⁺ ions, the excess Er₂O₃ stabilized the δ-Bi₂O₃ structure as the lowest temperature phase. The universal phase transition scheme with increasing annealing temperature was δ-Bi₂O₃ → β-Bi₂O₃ → α-Bi₂O₃. The δ → β transition proceeded through splitting each diffraction peak of δ-Bi₂O₃ into two components of β-Bi₂O₃, indicating a correlation between the structures of β-Bi₂O₃ and δ-Bi₂O₃. The γ-Bi₂O₃ phase appeared only in films on Si(100) substrates and after vacuum annealing, suggesting the formation of sillenite (Bi₁₂SiO₂₀). Deposition on C-plane sapphire by using H₂O as the oxygen source gas produced a highly (111)-oriented δ-Bi₂O₃ structure, whereas deposition with O₂ yielded a randomly oriented δ-Bi₂O₃ structure. At Er content exceeding 4 at.%, δ-Bi₂O₃ was the primary phase in the films on SiO₂. The photoluminescence (PL) activity of dopant Er³⁺ under excitation at a wavelength of 532 nm strongly depended on the crystal polymorphs. α-Bi₂O₃:Er exhibited intense and stable PL spectra consisting of eight Stark splitting lines. PL from γ-Bi₂O₃:Er exhibited much weaker two emission lines. δ-Bi₂O₃:Er and β-Bi₂O₃:Er films were not emission-active at all. However, δ-Bi₂O₃:Er film on SiO₂ with an Er content of 4 at.% exhibited an intense and broad emission at 1530 and 1560 nm.     

Elaboration and characterization of PVP-assisted NiO thin films for enhanced sensitivity toward H2 and NO2 gases

It is widely demonstrated that the synthesis conditions of sol-gel films have a great impact on their gas sensing properties. In this work, transparent PVP-assisted nickel oxide thin films with an average grain size of ~5?nm were synthesized using two distinctive deposition procedures combining the sol-gel method with the spin-coating technique then tested as optical gas sensors for the detection of hazardous pollutant gases. The first method is ascribed to a typical spin-coating deposition followed by a thermal annealing, and the second method consisted on a multistep coating annealing process. Structural and morphological studies showed enhanced crystallization rate and homogeneous surface morphology using a multistep deposition. The as prepared films exhibit a clear and reversible response toward H₂, CO and NO₂ gases and the multistep deposition process enhanced the sensitivity of about 113% and 194% toward 1% of H₂ and 0.1% of NO₂ respectively. The shrinkage of the band gap from 4.07 to 3.91?eV and the increased PL intensity indicate the presence of higher rate of charge density and intrinsic defect states that promoted the sensitivity of the film. Furthermore, improved response intensity was detected in the near UV region and higher stability with fast response was obtained for hydrogen gas.     

Effects of In2O3 nanoparticles doping on the photoluminescent properties of Eu2+/Eu3+ ions in silica glasses

Eu²⁺/Eu³⁺ ions doped silica glasses contained In₂O₃ nanoparticles (NPs) have been fabricated by using nanoporous silica glasses. Interestingly, efficient energy transfer from In₂O₃ NPs to Eu²⁺/Eu³⁺ ions enhanced the photoluminescence (PL) emission of Eu²⁺/Eu³⁺ ions, which derives from lattice defects in In₂O₃ NPs. Our work has not only demonstrated a facile way to fabricate NPs and rare earth ions co-doped silica glasses, but also extended the applications of semiconductor oxide NPs such as In₂O₃ NPs.     

Structural phase transition,electrical and photoluminescent properties of Pr3+-doped (1-x)Na0.5Bi0.5TiO3-xSrTiO3 lead-free ferroelectric thin films

Lead-free ferroelectric Pr³⁺-doped (1-x)Na_0.5Bi_0.5TiO₃-xSrTiO₃ (x?=?0–0.5) (hereafter abbreviated as Pr-NBT-xSTO) thin films were prepared on Pt/Ti/SiO₂/Si and fused silica substrates by a chemical solution deposition method combined with a rapid thermal annealing process at 700?°C, and their structural phase transition, dielectric, ferroelectric, and photoluminescent properties were investigated as a function of STO content. Raman analysis shows that with increasing STO content, the phase structures evolve from rhombohedral phase to coexistence of rhombohedral and tetragonal phases (i.e. morphotropic phase boundary), and then to tetragonal phase. The structural phase transition behavior has been well confirmed by temperature- and frequency- dependent dielectric measurements. Meanwhile, the variation in photoluminescence intensity of Pr³⁺ ions with different STO content in the NBT-xSTO thin films also indicates that there exists a clear structural phase transition when the film composition is close to the morphotropic phase boundary. Superior dielectric and ferroelectric properties are obtained in the Pr-NBT-0.24STO thin films due to the formation of morphotropic phase boundary. Our study suggests that Pr-NBT-xSTO thin films be promising multifunctional materials for optoelectronic device applications.     

Mn-doped titania thin films prepared by spin coating

TiO₂ thin films doped with ≤7 mol% Mn (metal basis) were deposited on F-doped SnO₂-coated (FTO) glass substrates by spin coating. The structural, morphological, and optical properties of the films were investigated by glancing angle X-ray diffraction (GAXRD), laser Raman microspectroscopy, field emission scanning electron microscopy (FESEM), and ultraviolet–visible spectroscopy (UV–VIS). Mn doping of TiO₂ (anatase) extended the optical absorption edge to longer wavelengths (lower photon energies) significantly lowering the band gap from 3.32 eV (undoped) to 2.90 (7 mol% Mn). The absorption edges of all films were sharp and the transparencies in the visible region were in the range 60–75%. All of the films were homogeneous, fully dense, and essentially crack-free.     

Influence of Gd2O3 on the microstructure and properties of transparent MgAl2O4: Cr3+ ceramic

In this work, MgAl₂O₄: Cr³⁺ transparent ceramics have been synthesized by the hot press sintering techniques, and the effect of the sintering aid Gd₂O₃ and its content on the densification, microstructure, and optical, photoluminescence was studied and discussed. The relative density reached 99.29% with 0.8 wt% Gd₂O₃ as a sintering aid, and the optical transmittance at 686 nm and 1446 nm were approximately 76%. As Gd₂O₃ content continued to increase, the grain size of the ceramics became smaller and uniform, accompanied by some pores with the size of ～1 μm. The ceramics with 4.0 wt% Gd₂O₃ showed a higher transmittance, of 82% at 1446 nm. Additionally, Gd₂O₃ was helpful for Cr³⁺ in the sites of octahedral symmetry, which increased the quantum yield. The quantum yield of MgAl₂O₄: Cr³⁺ with 0.8 wt% Gd₂O₃ was about 0.175, which was 36% higher than that of ceramic without Gd₂O₃. In short, the sintering aid Gd₂O₃ not only contributed to improving the densification, homogenizing the grain size, and heightening the optical transmittance but also enhanced the quantum yield of Cr³⁺.     

Electro-mechano-optical properties of the Er3+ modified Bi0.5Na0.4K0.1TiO3 versatile ceramics

A series of Bi_0.5-xEr_xNa_0.4K_0.1TiO₃ (BNKT-xEr) ceramics were designed and fabricated, the dopant effects on dielectric, piezoelectric and photoluminescence properties were studied. The results show that the piezoelectric property of BNKT can be enhanced by a trace amount of Er dopant, which is also reflected in the large linear electrostrain (S_uni = 0.29%, under 55 kV/cm) achieved in BNKT-0.0025 Er. On the other hand, higher Er content can produce excellent dielectric temperature stability, with △?/?_{150 °C} < ±15% over temperature range of 90～510 °C. Meanwhile, all BNKT-xEr ceramics exhibit good photoluminescence properties, which may open new applications of these multifunctional ceramics.     

Er3+替代Bi3+对Bi2(Zn1/3Nb2/3)2O7陶瓷烧结温度的影响

研究了Er3 替代Bi3 对Bi2(Zn1/3Nb2/3)2O7系介质材料结构和性能的影响,并借助X射线、扫描电镜、Agilent4284测试仪对其相结构和介电性能进行分析.研究结果表明:经Er3 替代的BZN陶瓷样品烧结温度升高(从960℃升高到1000℃);随着Er3 替代量的增加,Bi2(Zn1/3Nb2/3)2O7系介质材料的晶粒尺寸、介电常数、介电损耗都有所变化;当替代量x=0.1时,介电性能最佳,介电常数为78.7165,介电损耗为0.00134.     

Highly efficient photocatalytic activity and mechanism of novel Er3+ and Tb3+ co-doped BiOBr/ g-C3N5 towards sulfamethoxazole degradation

Bismuth oxyhalides (BiOX (X = Cl, Br, I) are considered to be an important p-type semiconductors in the photocatalysis applications. In particular, tetragonal BiOBr is considered as a stable photocatalyst due to its resilient absorption in the visible region with an band gap energy of 2.8 eV. In the meantime, lanthanide ions (with 3+ oxidation state) implies as conversion catalyst gained huge impact and remain a serious topic in materials chemistry. Here we synthesized upconversion photocatalyst mainly consists of BiOBr with the Er ³⁺ and Tb ³⁺ ions along with low band gap g-C₃N₅ for the improved photocatalytic performances. The synthesized Er³⁺/Tb³⁺@BiOBr-g-C₃N₅ heterojunction was systematically characterized by XRD, and FT-IR for the confirmation of the composite and their morphology were analysed with FESEM and HR-TEM analysis which revealed that the sheets of g-C₃N₅ were decorated by Er³⁺/Tb³⁺ loaded BiOBr microspheres. The XPS analysis confirmed the suitable oxidation state of all the individual elements existing in the composite. As the UV-DRS analysis showed that the band gap of the Er³⁺/Tb³⁺ BiOBr-gC₃N₅ heterojunction was narrowed to 2.64 eV. To evaluate the photocatalytic efficiency of the synthesized g-C₃N₅, Er³⁺/Tb³⁺@BiOBr and Er³⁺/Tb³⁺@BiOBr-gC₃N₅ heterojunction under the simulated visible light irradiation source towards the aqueous sulfamethoxazole degradation. The Er³⁺/Tb³⁺@BiOBr-gC₃N₅ heterojunction shows maximum degradation efficiency of 94.2% after 60 min of visible light irradiation whereas the pure g-C₃N₅ provided about 43.8% and Er³⁺/Tb³⁺@BiOBr implies 55.2% degradation efficiency. The plausible degradation mechanism of pollutant removal was proposed.     

Synthesis of nitrogen incorporated diamond-like carbon thin films using microwave surface-wave plasma CVD

Nitrogenated diamond-like (DLC:N) carbon thin films have been deposited by microwave surface wave plasma chemical vapor deposition on silicon and quartz substrates, using argon gas, camphor dissolved in ethyl alcohol composition and nitrogen as plasma source. The deposited DLC:N films were characterized for their chemical, optical, structural and electrical properties through X-ray photoelectron spectroscopy, UV/VIS/NIR spectroscopy, Raman spectroscopy, atomic force microscope and current–voltage characteristics. Optical band gap decreased (2.7 to 2.4 eV) with increasing Ar gas flow rate. The photovoltaic measurements of DLC:N / p-Si structure show that the open-circuit voltage (V_oc) of 168.8 mV and a short-circuit current density (J_sc) of 8.4 μA/cm² under light illumination (AM 1.5 100 mW/cm²). The energy conversion efficiency and fill factor were found to be 3.4 × 10^{− 4}% and 0.238 respectively.     

Structural and phase transformations and properties of thin films of the Bi2O3-Fe2O3-TiO2 system

Seven compositions of three-component sol-gel films obtained from solutions aged 1 and 93 days are described. The compositions of the films and their properties are investigated by the methods of electron and light microscopy and x-ray phase analysis.     

Iron doped thin TiO2 films synthesized with the RF PECVD method

Iron doped titanium dioxide coatings were synthesized with the help of RF plasma enhanced CVD technique. As a source of titanium, titanium chloride (IV) TiCl₄ was used while iron pentacarbonyl (0) Fe(CO)₅ served as iron supply. The coatings were diagnosed using Scanning Electron Microscopy (SEM) and Atomic Force Microscopy (AFM). Their elemental and chemical composition was studied with the help of X-ray energy dispersive spectroscopy (EDS) and Fourier transform infrared (FTIR) spectroscopy, respectively. For the determination of their optical properties, variable angle spectroscopic ellipsometry (VASE) and ultraviolet-visible (UV-Vis) spectroscopy techniques were used. Iron content in the range of 0.07–11.5 at% was found in the films. Apart from oxygen, titanium and iron, a presence of trace amounts of chlorine, very likely originating from the titanium precursor, was recorded. FTIR studies showed that iron was built-in in the structure of TiO₂ matrix. Surface roughness, assessed using SEM and AFM techniques, increases with an increasing content of this element. VASE measurements revealed an increase of the coatings refractive index with a growing iron concentration, with the extinction coefficient remaining low and independent of that parameter. Trace amounts of iron resulted in a lowering of an absorption threshold of the films as well as their optical gap, but the tendency was reversed for high concentrations of that element.     

The role of pressure on thin amorphous carbon films deposited using microwave surface wave plasma CVD

We report the effects of gas composition pressure (GCP) on the optical, structural and electrical properties of thin amorphous carbon (a-C) films grown on p-type silicon and quartz substrates by microwave surface wave plasma chemical vapor deposition (MW SWP CVD). The films, deposited at various GCPs ranging from 50 to 110 Pa, were studied by UV/VIS/NIR spectroscopy, atomic force microscopy, Raman spectroscopy, X-ray photoelectron spectroscopy and current–voltage characteristics. The optical band gap of the a-C film was tailored to a relatively high range, 2.3–2.6 eV by manipulating GCPs from 50 to 110 Pa. Also, spin density strongly depended on the band gap of the a-C films. Raman spectra showed qualitative structured changes due to sp³/sp² carbon bonding network. The surfaces of the films are found to be very smooth and uniform (RMS roughness < 0.5 nm). The photovoltaic measurements under light illumination (AM 1.5, 100 mW/cm²) show that short-circuit current density, open-circuit voltage, fill factor and photo-conversion efficiency of the film deposited at 50 Pa were 6.4 μA/cm², 126 mV, 0.164 and 1.4 × 10^− 4% respectively.     

Al3+ doping induced changes of structural,morphology, photoluminescence,optical and electrical properties of SnO2 thin films as alternative TCO for optoelectronic applications

Highly transparent and conductive pure (SnO₂) and aluminum doped tin oxide (Al:SnO₂) thin films were deposited on glass substrates by the sol-gel spin-coating method. The structural, morphological, optical and electrical properties of the prepared thin films at different doping rates have been studied. X-ray diffraction results revealed that all the films were polycrystalline in nature with a tetragonal rutile structure. SEM images of the analyzed films showed a homogeneous surface morphology, composed of nanocrystalline grains. The EDS results confirmed the presence of Sn and O elements in pure SnO₂ and Sn, O, Al in doped SnO₂ thin films. The optical results revealed a high transmittance greater than 85% in the visible and near infrared and a band gap varying between 3.82 and 3.89 eV. PL spectra at room temperature showed that the most dominant defects correspond to oxygen vacancies. A low resistivity of order varying between 10^?3 and 10^?4 Ω cm and a high figure of merits ranging between 10^?3 and 10^?2 Ω^?1 in the visible range were obtained. The best performances were obtained for samples containing 2 at. % Al, which could be used as an alternative TCO layer for future optoelectronic devices.     

Fabrication and characterization of Mn-doped CuO thin films by the SILAR method

Thin films of un-doped and Mn-doped CuO nanostructures have been deposited on glass substrates via the SILAR method. The morphological, compositional, structural and optical properties of the films have been investigated by scanning electron microscopy, energy dispersive spectroscopy, X-ray diffraction analysis and UV–vis spectrophotometry. The analyzed results indicate that the obtained films consist of plate-like nanostructures. From the EDS analysis it is seen that Mn-doping concentration affects the shapes of the nanostructures. XRD results show that all of the films have monoclinic structure. From the room temperature UV–vis analysis it is found that the optical band gap of the films increases with increasing Mn-doping concentrations.     

Tailoring of optical band gap and electrical conductivity in a-axis oriented Ni doped Chromium Oxide thin films

Ni doped Cr₂O₃ (NCO) films have attracted much attention due to their applications in the field of photovoltaics. This study reports the tailoring of structural, electrical and optical properties as a function of Ni doping in Chromium oxide (Cr₂O₃). NCO thin films were grown by Pulsed laser deposition (PLD) using 2nd harmonic Nd:YAG Laser on n-Si (100) with in-situ annealing of 450?°C. Structural analyses based on X-ray diffractometry (XRD) and Raman Spectroscopy showed the inconsistent variation in crystallinity and shift in $A_{1g}$ band in turn revealing the successful incorporation of Ni into Chromium oxide host lattice. In addition, electrical measurements also showed an inconsistent variation in resistivity ranging from 10² to 10⁴$\Omega ?\mathit{cm}$. The properties showed widening of band gap energy (E_g) from 3.41 to 3.60?eV as a function of Ni doping concentration with significantly decreased reflectance in the range of 500–600?nm thereby increasing the absorption, a pre-requisite for solar absorbers.     

Rietveld refinement,micro-structural,optical and thermal parameters of zirconium titanate composites

Pure titania and zirconium titanate composites have been synthesized using sol-gel technique and annealed at 650, 875 and 1100 °C for 4 h. Acetylacetone was used to control the rate of hydrolysis of precursors. The Rietveld refinement, micro-structural, optical and thermal parameters of prepared composites was investigated. Effect of annealing and concentration of Zr and Ti in composites on their crystal structure, morphology, PL emission wavelength and band gap have been studied. X-ray diffraction and Rietveld analysis exhibit that all prepared samples of composites have orthorhombic single phase of zirconium titanate with space group pbcn. The lower values of profile parameters such as R_p, R_wp, R_B, R_F, χ² indicated that the calculated diffraction pattern is in fair agreement with observed pattern. The increase in zirconia concentration decreases the degree of crystallization of ZrTiO₄. The photoluminescence spectra show the blue shifting of emission peak at 420 nm as the zirconia concentration increases. The optical band gap of zirconium titanate composites also blue shifted (3.24–3.64 eV) with decrease in crystallite size of composites.     

Characterization of Er in Porous Si

ABSTRACT: The fabrication of porous Si-based Er-doped light emitting devices is a very promising developing field for all-silicon light emitters. However, while luminescence of Er-doped porous silicon devices has been demonstrated, very little attention has been devoted to the doping process itself. We have undertaken a detailed study of this process examining the porous silicon matrix from several points of view, during and after the doping. In particular, we have found that the Er doping process shows a threshold level which, as evidenced by the cross correlation of the various techniques used, does depend on the sample thickness and on the doping parameters.     

Optimization of sensitizer concentration for upconversion photoluminescence of Yb3+/Er3+: La10W22O81 nanophosphor rods

Yb³⁺/Er³⁺codoped La₁₀W₂₂O₈₁ (LWO) nanophosphor rods have been successfully synthesized by a facile hydrothermal assisted solid state reaction method, and their upconversion photoluminescence properties were systematically studied. X-ray diffraction patterns revealed that the nanophosphors have an orthorhombic structure with space group Pbcn (60). A microflowers-like morphology with irregular hexagonal nanorods was observed using field emission scanning electron microscopy for the Yb³⁺(2 mol%)/Er³⁺(2 mol%):LWO nanophosphor. The shape and size of the nanophosphor and the elements along with their ionic states in the material were confirmed by TEM and XPS studies, respectively. A green upconversion emission was observed in the Er³⁺: LWO nanophosphors under 980 nm laser excitation. A significant improvement in upconversion emission has been observed in the Er³⁺: LWO nanophosphors by increasing the Er³⁺ ion concentration. A decrease in the upconversion emission occurred due to concentration quenching when the doping concentration of Er³⁺ ions was greater than 2 mol%. An optimized Er³⁺(2 mol%): LWO nanophosphor exhibited a strong near infrared emission at 1.53 μm by 980 nm excitation. The green upconversion emission of Er³⁺(2 mol%): LWO was remarkably enhanced by co-doping with Yb³⁺ ions under 980 nm excitation because of energy transfer from Yb³⁺ to Er³⁺. The naked eye observed this upconversion emission when co-doping with 2 mol% Yb³⁺. In order to obtain the high upconversion green emission, the optimized sensitizer concentration of Yb³⁺ ions was found to be 2 mol%. The upconversion emission trends were studied as a function of stimulating laser power for an optimized sample. Moreover, the NIR emission intensity has also been enhanced by co-doping with Yb³⁺ ions due to energy transfer from Yb³⁺ to Er³⁺. The energy transfer dynamics were systematically elucidated by energy level scheme. Colorimetric coordinates were determined for Er³⁺ and Yb³⁺/Er³⁺: LWO nanophosphors. The energy transfer mechanism was well explained and substantiated by several fluorescence dynamics of upconversion emission spectra and CIE coordinates. The results demonstrated that the co-doped Yb³⁺(2 mol%)/Er³⁺(2 mol%): LWO nanophosphor material is found to be a suitable candidate for the novel upconversion photonic devices.     

Thickness-dependent optimization of Er3+ light emission from silicon-rich silicon oxide thin films

This study investigates the influence of the film thickness on the silicon-excess-mediated sensitization of Erbium ions in Si-rich silica. The Er3+ photoluminescence at 1.5 μm, normalized to the film thickness, was found five times larger for films 1 μm-thick than that from 50-nm-thick films intended for electrically driven devices. The origin of this difference is shared by changes in the local density of optical states and depth-dependent interferences, and by limited formation of Si-based sensitizers in "thin" films, probably because of the prevailing high stress. More Si excess has significantly increased the emission from "thin" films, up to ten times. This paves the way to the realization of highly efficient electrically excited devices.