Photoluminescence and preparation of ZnNb2O6 doped with Eu and Tm nanocrystals for solar cell

Synthesis and luminescence properties of Eu³⁺ and Tm³⁺-doped ZnNb₂O₆ nanocrystals by the sol–gel process were investigated. The products were characterized by differential thermal analysis (DTA), scanning electron microscopy (SEM), and photoluminescence spectroscopy (PL). ZnNb₂O₆:Eu³⁺ shows bright red luminescence with maximum peak at 613 nm attributed to ⁵D₀ → ⁷F₂ transition. The major blue emission peak of ZnNb₂O₆:Tm³⁺ was at 483 nm, corresponding to the transitions ¹G₄ → ³H₆. The optimum concentration of Eu³⁺ and Tm³⁺ showing the maximum PL intensity was 4 mol% and 1 mol%, respectively.     

Effects of ZnNb2O6 addition on BaTiO3 ceramics for energy storage

BaTiO₃ ceramics were prepared using solid state reaction with addition of ZnNb₂O₆, to investigate the effects of ZnNb₂O₆ addition on structure and properties. The results show that the ZnNb₂O₆ addition lowers sintering temperature, decreases grain size, while introduces second phase (Ba₂Ti₅O₁₂) for x ≥ 7.26 wt%. The dielectric breakdown strength is enhanced with the increasing doping level of ZnNb₂O₆ and reaches a maximum value at x = 7.26 wt%, exhibiting a maximum energy storage capability.     

Synthesis and photoluminescence of In2O3 nanocrystals and submicron crystals from InCl3•4H2O and thiourea

Two routes have been proposed for the synthesis of In₂O₃ powders from InCl₃•4H₂O and thiourea. One route involved a two-step procedure (that is, firstly, In₂S₃ clusters constructed with mainly nanoflakes were synthesized by heating the mixture of InCl₃•4H₂O and thiourea in air from room temperature to 200 °C, coupled with a subsequent washing treatment; secondly, In₂O₃ was obtained by calcining the In₂S₃ clusters in air at 600 °C for 6 h), and the other route was a one-step procedure (that is, In₂O₃ was synthesized directly by calcining the mixture of InCl₃•4H₂O and thiourea in air at 600 °C for 6 h). The resultant products were characterized by X-ray diffraction, energy dispersive X-ray spectroscopy, scanning electronic microscope and room temperature photoluminescence (RT-PL) spectra. It was observed that the In₂O₃ nanocrystals obtained via the two-step procedure exhibited PL peaks at about 453 and 471 nm, corresponding to the defeat-related emission; while the In₂O₃ submicron polyhedral crystals obtained via the one-step procedure and In₂O₃ pyramids obtained by calcining the only InCl₃•4H₂O in air at 600 °C for 6 h displayed a PL band centered at around 338 nm, corresponding to the band edge emission.     

Optical properties of rare-earth doped epitaxial Sr0.5Ba0.5Nb2O6 thin films grown by pulsed laser deposition

Optical quality rare-earth (RE) (Nd³⁺, Eu³⁺, Gd³⁺ and Yb³⁺) doped Sr_0.5Ba_0.5Nb₂O₆ (SBN) epitaxial films of ~ 170 nm thick have been successfully grown on MgO (100) single crystal substrates using pulsed laser deposition technique. Strong residual stress in these films has been revealed by Raman spectroscopic studies. Two kinds of in-plane orientations with respect to the MgO substrate co-exist. All the film samples show high transparency in the visible wavelength. Their band-gap energies appear to be independent of the types of dopant. Photoluminescence (PL) spectra of RE-doped SBN ceramics show a strong and broad emission band at around 600 nm (2.07 eV). The peak position of this emission band changes slightly with different RE-dopants. Thin film samples, however, yield a broad PL band at around 385 nm (3.22 eV). This UV emission shows no observable shift in the peak position for different dopants. Apart from these broad emission bands, conspicuous emission lines from Eu³⁺ and Nd³⁺ ions are also noted. The origins of these PL spectra are discussed.     

Novel blue-emitting Sr3Ga2O5Cl2:Eu phosphor for UV-pumped white LEDs

A novel blue-emitting Sr₃Ga₂O₅Cl₂:Eu²⁺ phosphor has been synthesized by a two-step solid-state reaction. The luminescence properties have been investigated by photoluminescence (PL) spectra, and temperature-dependent PL spectra. It shows an efficient broad absorption band around 400 nm, which matches well with the commercial near-ultraviolet light-emitting chips, and an efficient blue emission. It shows a higher thermal quenching temperature than that of Sr₃Al₂O₅Cl₂:Eu²⁺ phosphor. Sr₃Ga₂O₅Cl₂:Eu²⁺ phosphor is a promising blue-emitting component for UV chip excited white light-emitting-diodes.     

Preparation and characterization of Co-doped ZnO-Al2O3-SiO2 glass-ceramics by the sol-gel method

Transparent glass-ceramics containing Co²⁺:ZnAl₂O₄ nanocrystals were obtained by the sol-gel process for the first time. The gels of composition 89SiO₂-5.9Al₂O₃-4.9ZnO-0.2CoO (ZAS) were prepared at room temperature, and heat-treated at different temperatures. The microstructure and optical properties of the heated samples were studied by using X-ray diffraction (XRD), transmission electron microscopy (TEM), infrared spectroscopy, and optical absorption spectra. Co²⁺:ZnAl₂O₄ nanocrystals were precipitated from ZAS system and dispersed in the SiO₂-based glass during heat-treatment in the temperature range 900-1100 °C. Co²⁺ ions were located in tetrahedral sites in ZnAl₂O₄ nanocrystals. The Co²⁺:ZnAl₂O₄ crystallite size was in the range of 4-15 nm.     

Hot-injection synthesis and characterization of quaternary Cu2ZnSnSe4 nanocrystals

Cu₂ZnSnSe₄ (CZTSe) is one of promising materials in the use of absorber layers of solar cells. It contains earth-abundant elements of zinc and tin, a near-optimal direct band gap of ∼ 1.5 eV, as well as a large absorption coefficient ∼ 10⁴ cm-1. The CZTSe nanocrystals in oleylamine (OLA) was successfully prepared via hot-injection method. The characterization of its structure, composition, morphology and absorption spectra were done using powder X-ray diffraction (XRD), energy-dispersive X-ray spectroscopy (EDS), transmission electron microscopy (TEM) and UV-vis absorption spectra. The results revealed that the monodispersed nanocrystals were single phase polycrystalline within the range of 15-20 nm. Optical measurements showed a direct band gap of 1.52 eV, which was optimal for low cost solar cells. The capping property of OLA was also demonstrated by examining Fourier Transform Infrared Spectroscopy (FTIR) feature peaks of CZTSe and OLA, respectively.     

Photoluminescence spectra of MnIn2S4

MnIn₂S₄ single crystals grown by the directional crystallization method were investigated by using the temperature and excitation power dependencies of photoluminescence (PL) spectra. PL spectra consist of one broad band resulting from donor-acceptor pair recombination. The analysis of the temperature quenching of the PL intensity yields one defect donor level with a thermal ionization energy of about 0.17 eV. The broad band of PL spectra indicates that radiative recombination is related to multiphonon optical processes. The energy of the involved phonon was found to be around 0.025 eV and the energy of the acceptor level is about 0.86 eV.     

Synthesis and structural characterization of Tm:Lu2O3 nanocrystals. An approach towards new laser ceramics

Nanocrystals of Tm³⁺ Thulium doped cubic sesquioxides, Tm:Lu₂O₃, with a maximum size around 30 nm have been synthesized by a modified Pechini sol-gel method. The calcination temperature for the synthesis is 1073 K. Electron microscopy was used to analyze the presence of aggregates, and the type of boundary between the nanocrystals. The linear coefficient of thermal expansion for these nanocrystals has been determined to be around 7.5 × 10⁻⁶ K⁻¹. The growth of the nanocrystals has been studied in terms of temperature and time. Nanocrystals start to grow at temperatures around 1267 K. Finally, the grain growth activation energy of this material has been evaluated to be 76 kJ/mol, indicating a diffusion growth mechanism. Linear thermal expansion of prepared nanocrystals is ≈7.5 × 10⁻⁶ K⁻¹.     

Oxygen vacancy in Al2O3: Photoluminescence study and first-principle simulation

Broad photoluminescence (PL) band at 2.97 eV excited in the band near 6.0 eV in amorphous chemical vapor deposition films is related to the neutral oxygen vacancy by analogy with crystalline Al₂O₃. The identification of this PL band was supported by the results of first-principle quantum chemical simulation, which showed 6.3 and 6.4 eV bands in the extinction spectra for α- and γ-Al₂O₃, respectively. Other PL bands are attributed to ionized single vacancies (F⁺-centers), divacancies (F₂) and, probably, interstitial Al.     

Synthesis of CdS-Au2S-Au hybrid dendritic nanostructures

The hybrid CdS-Au₂S-Au dendritic nanocrystals were synthesized in toluene solution at 70 °C. UV-vis and photoluminescence (PL) spectra recorded the optical properties of hybrid nanostructures, which showed an obvious blue shift relative to the absorption peak of CdS dendritic nanocrystals. The initial CdS dendritic nanocrystals exhibited band gap and trap state emission, both of which were quenched by Au parts. Analysis of the hybrid nanostructures by XRD shows the presence of appreciable amounts of Au₂S, indicating that the chemical process involving cation exchanges between Au⁺ ions and Cd²⁺ ions was found.     

Green hydrothermal synthesis and optical absorption properties of ZnO2 nanocrystals and ZnO nanorods

A green hydrothermal method was proposed for the controllable synthesis of ZnO₂ nanocrystals and ZnO nanorods, using the common and cost-effective 2ZnCO₃·3Zn(OH)₂ powder and 30 mass% H₂O₂ aqueous solution as the raw materials. The characterization results from X-ray diffraction, high resolution transmission electron microscopy, transmission electron microscopy and energy dispersive X-ray spectroscopy indicated that the products synthesized at 100-120 °C for 6 h or at 170 °C for 0 h were cubic phase ZnO₂ nanocrystals; while those synthesized at 170 °C for 3-6 h were hexagonal phase ZnO nanorods. The UV-vis absorption spectra showed that the as-synthesized ZnO₂ nanocrystals and ZnO nanorods had optical band gaps of about 4.1 and 3.3 eV, respectively.     

Photoluminescence properties of RE-activated Na3GdP2O8 (RE = Tb, Dy, Eu, Sm) under VUV excitation

RE³⁺-activated monoclinic Na₃GdP₂O₈ (RE³⁺ = Tb³⁺, Dy³⁺, Eu³⁺, Sm³⁺) phosphors have been synthesized by a solid-state reaction method. Their photoluminescence properties in the vacuum ultraviolet (VUV) region were investigated. By analyzing their excitation spectra, the host-related absorption band was determined to be around 166 nm. The f-d transition bands and the charge transfer bands for Na₃GdP₂O₈:RE³⁺ (RE³⁺ = Tb³⁺, Dy³⁺, Eu³⁺, Sm³⁺) were assigned and corroborated. For the sample Na₃GdP₂O₈:5%Tb³⁺, the strong bands at around 202 and 221 nm are assigned to the 4f-5d spin-allowed transitions and the weak band at 266 nm is related to the spin-forbidden transition of Tb³⁺. For Na₃GdP₂O₈:5%Dy³⁺, the broad band at 176 nm could be related to the f-d transitions of Dy³⁺ and the O²⁻ → Dy³⁺ charge transfer band (CTB) besides the host-related absorption. In the excitation spectrum of Eu³⁺ doped sample, the O²⁻ → Eu³⁺ CTB is observed to be at 245 nm. For the Sm³⁺ doped sample, the O²⁻ → Sm³⁺ CTB is not distinguished obviously and is overlapped with the host-related absorption band.     

Controlled synthesis of Mn3O4 and MnCO3 in a solvothermal system

Controlled synthesis of Mn₃O₄ nanocrystals and MnCO₃ aggregates was achieved by a facile solvothermal method using different divalent manganese source in the solvent of N,N-dimethylformamide (DMF) with/without the introduction of poly(vinylpyrrolidone) (PVP). PVP was used as a co-reducing reagent in the controlled formation of MnCO₃ crystal. The products were characterized by X-ray powder diffraction (XRD), transmission electron microscopy (TEM) and selected-area electron diffraction (SAED), Fourier transform infrared (FTIR) spectra, Raman spectrum and magnetic measurement. Higher process temperature and longer solvothermal time were favorable for the formation of MnCO₃ single phase using MnCl₂ as the manganese source. Mn₃O₄ nanocrystals were prepared at a relatively lower temperature. MnCO₃ aggregates consisted by small nanoparticles have a certain orientation, showing that the nanocrystals formed earlier through oriented aggregation. The size of Mn₃O₄ nanocrystals was 22.5 ± 7.3 nm and 7.3 ± 1.4 nm prepared using MnCl₂ and Mn(CH₃COO)₂, respectively, at 160 °C for 24 h. Raman spectra showed size-dependent characteristics. Smaller Mn₃O₄ nanoparticle resulted in a red-shift in Raman spectra. Magnetic property of the prepared Mn₃O₄ nanoparticle was influenced by the size distribution and crystallinity.     

Luminescent properties of Gd2Ti2O7: Eu phosphor films prepared by sol-gel process

Gd₂Ti₂O₇: Eu³⁺ thin film phosphors were fabricated by a sol-gel process. X-ray diffraction (XRD), atomic force microscopy (AFM) and photoluminescence (PL) spectra as well as lifetimes were used to characterize the resulting films. The results of XRD indicated that the films began to crystallize at 800 °C and the crystallinity increased with the elevation of annealing temperatures. Uniform and crack free phosphor films were obtained, which mainly consisted of grains with an average size of 70 nm. The doped Eu³⁺ showed orange-red emission in crystalline Gd₂Ti₂O₇ phosphor films due to an energy transfer from Gd₂Ti₂O₇ host to them. Both the lifetimes and PL intensity of the Eu³⁺ increased with increasing the annealing temperature from 800 to 1000 °C, and the optimum concentrations for Eu³⁺ were determined to be 9 at.%. of Gd³⁺ in Gd₂Ti₂O₇ film host.     

Optical properties of transparent Dy doped Ba2TiSi2O8 glass ceramic

The Ba₂TiSi₂O₈ is a well known piezoelectric, ferroelectric and non-linear crystal. Nanocrystals of Ba₂TiSi₂O₈ doped with 1.5 Dy³⁺ have been obtained by thermal treatment of a precursor glass and their optical properties have been studied. X-ray diffraction patterns and optical measurements have been carried out on the precursor glass and glass ceramic samples. The emission spectra corresponding to the Dy³⁺: ⁴F_9/2 → ⁶H_13/2 (575 nm), ⁴F_9/2 → ⁶H_11/2 (670 nm) and ⁴F_9/2 → ⁶H_9/2 (757 nm) transitions have been obtained under laser excitation at 473 nm. These measurements confirm the incorporation of the Dy³⁺ ions into the Ba₂TiSi₂O₈ nanocrystals which produces an enhancement of luminescence at 575 nm. At this wavelength has been demonstrated a maximum optical amplification around 1.9 cm⁻¹ (∼8.2 dB/cm).     

Synthesis and characterization of Mg2B2O5

Magnesium borate of the form Mg₂B₂O₅ has been prepared and its structural and thermal properties were studied using X-ray diffraction and differential thermal analysis. An investigation of the electrical and optical properties of Mg₂B₂O₅ system has been carried out. The electrical resistivity of the sample was measured in the temperature range of 170-400 K. The data analysis revealed an extrinsic nature of the conductivity with two impurity levels located at 0.13 and 0.71 eV in the temperature ranges of 170-230 K and 240-400 K, respectively. The optical transmission and reflection was recorded at 300 K in the incident photon energy range of 3.0-6.0 eV. The absorption coefficient data analysis revealed an indirect optical energy band gap of 4.73 eV. In addition, two impurity levels located at 3.43, and 4.49 eV were observed in the absorption spectra.     

Photoluminescence behaviors in ZnGa2O4 thin film phosphors deposited by a pulsed laser ablation

ZnGa₂O₄ thin film phosphors have been deposited using a pulsed laser deposition technique on Si (1 0 0) and Al₂O₃ (0 0 0 1) substrates at a substrate temperature of 550 °C with various oxygen pressures 100, 200 and 300 mTorr, and various substrate temperatures of 450, 550 and 650 °C with a fixed oxygen pressure of 100 mTorr. The films grown under different deposition conditions have been characterized using microstructural and luminescent measurements. Under the different substrate temperatures, ZnGa₂O₄ thin films show the different crystallinity and luminescent intensity. The crystallinity and photoluminescence (PL) of the ZnGa₂O₄ films are highly dependent on the deposition conditions, in particular, oxygen pressure, substrate temperature, a kind of substrates. The luminescent spectra show a broad band extending from 350 to 600 nm peaking at 460 nm. The PL brightness data obtained from the ZnGa₂O₄ films grown under optimized conditions have indicated that the sapphire is one of the most promised substrates for the growth of high quality ZnGa₂O₄ thin film phosphor.     

Ag2СdSnS4 single crystals as promising materials for optoelectronic

Single crystals of the quaternary single crystals Ag₂CdSnS₄ were grown for the first time using the horizontal gradient freeze technique. Optical spectral and photoelectric properties of obtained crystals were investigated. The band gap energy at 77 K according to the photoconductivity spectra is 1.94 eV. The energy levels of the major donor centers in the band gap were determined. The role of intrinsic defects in the observed dependences is analyzed. The energy levels of the major donor centers in the band gap were determined. A small photoconductivity maximum at low temperature is observed at wavelength λ_m = 640 nm (hν ∼ 1.94 eV); situated in the fundamental absorption band, which unambiguously corresponds to the intrinsic origin of photoconductivity. The increase of the extrinsic photoconductivity with the maximum at λ_m ∼ 800 nm with temperature leads to its domination above 240 K. The observed peculiarity can be explained by the photoexcitation of electrons from the valence band to the donor centers which are empty at high temperatures and with further thermal excitation to the conduction band.     

Vacuum ultraviolet excited photoluminescence properties of novel Na3Y9O3(BO3)8:Eu phosphor

The novel vacuum ultraviolet (VUV) excited Na₃Y₉O₃(BO₃)₈:Eu³⁺ red phosphor was synthesized and the photoluminescence (PL) properties were investigated. The phosphor showed strong VUV PL intensity, large quenching concentration (40 mol%) and good chromaticity (0.649, 0.351). The Eu³⁺-O²⁻ charge transition (CT) was observed to be at a higher energy (232 nm, 5.35 eV). The host absorption at 127-166 nm was broad and strong when monitoring the Eu³⁺ emission, which indicated that energy transfer from the host-lattice to the Eu³⁺ ions was efficient in Na₃Y₉O₃(BO₃)₈:Eu³⁺. These excellent VUV PL properties were revealed to be correlated with the unique isolated layer-type structure of Na₃Y₉O₃(BO₃)₈ host. The results showed that the Na₃Y₉O₃(BO₃)₈:Eu³⁺ would be a good candidate for VUV-excited red phosphor.