Near-infrared quantum cutting platform in transparent oxyfluoride glass–ceramics for solar sells

This study investigated the photoluminescent properties of Er³⁺/Yb³⁺ and Ce³⁺/Er³⁺/Yb³⁺ -doped oxyfluoride glass–ceramics. The transparent oxyfluoride glass–ceramics were prepared by high temperature melting method and subsequent heat treatment. Effect of heat treatment schedules on crystallization behavior and microstructure were analyzed by differential scanning caborimetry, X-ray diffraction, infrared spectrum and scanning electron microscopy. The structure of fluoride nanocrystals indicates that the main phase in the oxyfluoride glass ceramics is CaF₂ nanocrystal sized at 25 nm at the optimal crystallization temperature 600 °C for 8 h. The Ce³⁺/Er³⁺/Yb³⁺ tri-doped oxyfluoride glass–ceramics shows wider absorption bands comparing with Er³⁺/Yb³⁺ co-doped oxyfluoride glass–ceramics. The effective energy transfer processes from Ce³⁺ to Yb³⁺, Er³⁺ to Yb³⁺ and Ce³⁺ to Er³⁺ all can take place simultaneously. The idea of using Ce³⁺ together with Er³⁺ and Yb³⁺ ions could enhance the ultraviolet visible light absorption and the 960–1040 nm near infrared emission. Results of this study demonstrate that the tri-activator Ce³⁺/Er³⁺/Yb³⁺ materials are promising for practical application to enhance the energy efficiency of crystalline Si solar cells via spectrum modification.     

Facile synthesis of cubic fluorite nano-Ce1−xZrxO2 via hydrothermal crystallization method

Nano-Ce_1?xZr_xO₂ (x = 0.15, 0.25, 0.5) were synthesized via co-precipitation using NH₄OH as precipitant and hydrothermal crystallization. The XRD results confirmed that the cubic fluorite nano-Ce_1?xZr_xO₂ can form in NH₄OH solution (pH > 10) at 150 °C for 12 h, and well crystallized 20–50 nm nano-Ce_1?xZr_xO₂ were obtained at 200 °C for 22 h. The crystal growth of Ce_1?xZr_xO₂ was suppressed under higher OH^? concentration and crystallite size decreased with increasing concentration of NH₄OH. Ce3d XP spectra showed that the main valence state of the cerium on Ce_1?xZr_xO₂ surface is +4, and substituting Ce⁴⁺ with Zr⁴⁺ has no obvious influence on Ce³⁺/Ce⁴⁺ ratio.     

Microwave-induced combustion synthesis and electrical conductivity of Ce1−xGdxO2−1/2x ceramics

Ce_1−xGd_xO_2−1/2x nanopowder were successfully synthesized by microwave-induced combustion process. For the preparation, cerium nitrate, gadolinium nitrate hexahydrate, and urea were used for the microwave-induced combustion process. The process took only 30 min to obtain Ce_1−xGd_xO_2−1/2x powders. The exo-endo temperature, phase identification, and morphology of resultant powders were investigated by TG/DTA, XRD, and SEM. The as-received Ce_1−xGd_xO_2−1/2x powders showed that the average particle size ranged from 18 to 50 nm, crystallite dimension varied from 11 to 20 nm, and the specific surface area was distribution from 16 to 46 m²/g. As for Ce_1−xGd_xO_2−1/2x ceramics sintered at 1450 °C for 3 h, the bulk density of Ce_1−xGd_xO_2−1/2x ceramics were over 91% of the theoretical density, the maximum electrical conductivity, σ_700 °C = 0.017 S/cm with minimum activation energy, E_a = 0.869 eV was found at Ce_0.80Gd_0.20O_1.90 ceramic.     

High permittivity and low dielectric loss of Na0.5Bi0.5−xLaxCu3Ti4O12 ceramics

The phase structure, microstructure and dielectric properties of Na_0.5Bi_0.5?xLa_xCu₃Ti₄O₁₂ (NBLCTO) ceramics were investigated. La³⁺ substitution had a great influence on the phase structure and dielectric properties. The results showed that the pure phase could be more easily obtained when substituting La³⁺ for Bi³⁺. Under the same processing condition (970 °C for 7.5 h) and measuring condition (10 kHz around room temperature), NBLCTO ceramics with x = 0.10 possessed the highest permittivity (1.02 × 10⁴) and lowest dielectric loss (0.022). The obtained NBLCTO ceramics with x = 0.10 also had good frequency stability and good temperature stability (?1.87% to +3.27%) from ?60 °C to 120 °C at both 1 and 10 kHz. Complex impedance results revealed that the grain resistance R_g was 7.18 Ω cm and the grain boundary resistance R_gb was 1.19 × 10⁶ Ω cm.     

Photoluminescence,photo-stimulated luminescence and thermoluminescence properties of CaB2O4 crystals activated with Ce3+

Photoluminescence (PL), photo-stimulated luminescence (PSL), and thermoluminescence (TL) properties of a Ce-doped CaB₂O₄ crystal were studied. The Ce-doped crystal was prepared by the simple solidification method using a Pt crucible under nitrogen atmosphere. A PL emission band in the 350–370 nm wavelength range was obtained under excitation at 325 nm owing to the 5d (t_2g)–4f (²F_5/2, ²F_7/2)-allowed transition of the Ce³⁺ emission center. The fluorescence quantum efficiency and the decay time of Ce³⁺ were estimated to be about 70% and 29 ns, respectively. The 5d–4f emission band of Ce³⁺ also appeared in the 350–370 nm wavelength range in the TL and PSL spectra. Good linear TL and PSL responses were observed in the 1–1000 mGy and 1–10,000 mGy X-ray dose range, respectively.     

VUV–UV luminescence of Ce3+, Tb3+, Eu3+, and Dy3+ doped GdOCl

The vacuum ultraviolet spectroscopic properties of GdOCl:Re³⁺ (Re³⁺ = Ce³⁺, Tb³⁺, Eu³⁺, and Dy³⁺) are investigated in detail for the first time. The host absorption band is determined to be around 179 nm, and the f–d transition bands as well as the charge transfer bands are assigned. Upon 179 nm excitation, Re³⁺ (Re³⁺ = Ce³⁺, Tb³⁺, Eu³⁺, Dy³⁺) ions shown their characteristic emissions. Energy transfers from Gd³⁺ to Re³⁺ ion were observed. A broad band ranging from 350 to 400 nm corresponding to the d–f transition of Ce³⁺ is observed. Eu³⁺ has typical red emission with the strongest peak at 620 nm; Tb³⁺ shows characteristic transition of ⁵D_3,4 → ⁷F_j, and its spin-forbidden and spin-allowed f–d transitions in VUV region are calculated with Dorenbos’ equations, these calculated values agree well with the experimental results. Dy³⁺ presents yellow emission (⁴F_9/2 → ⁶H_13/2) with the strongest peak at 573 nm.     

Luminescence and scintillation properties of Ce-doped Cs2ZnCl4 crystals

In this study, we have synthesized scintillation materials based on Ce-doped Cs₂ZnCl₄ crystals. The light yield was enhanced by up to 20% by doping Cs₂ZnCl₄ with Ce³⁺ ions. In the scintillation time profiles, fast components exhibited decay time constants on the order of nanoseconds, which was ascribed to Auger-free luminescence (AFL). The light yield of the AFL component decreased at 10 mol% Ce³⁺ concentration, which is mainly attributed to the reabsorption of AFL photons inside the crystals by Ce³⁺ ions, as seen in the scintillation spectra. Long components had decay time constants of approximately 30 ns. In addition, at 10 mol% Ce³⁺ concentration, a prominent band appeared at approximately 500 nm in the scintillation spectrum, which was not observed in the photoluminescence spectra. The long components in the scintillation time profiles and the 500 nm band in the scintillation spectra were tentatively attributed to self-trapped excitons perturbed by Ce³⁺ ions.     

Yellow-emitting (Ca2Lu1−xCex)(ScMg)Si3O12 phosphor and its application for white LEDs

Luminescence properties of the yellow-emitting (Ca₂Lu_1?xCe_x)(ScMg)Si₃O₁₂ (CLSM:xCe³⁺ x = 0.01–0.15) phosphor are investigated for various Ce³⁺ concentrations. Different Ce³⁺ emission sites and energy transfers between them are observed, resulting in a red shift of the emission spectra from 530 to 575 nm with increasing x from 0.01 to 0.15. Combining with blue (460 nm) InGaN LEDs, CLSM:Ce³⁺ shows excellent performances for phosphor-converted white LEDs with higher color rendering index R_a of 87.4–87.9 and lower color temperature T_C of 5034–5814 K, especially for warm pcWLEDs with a high color rendering (R_a > 80) and a low color temperature (T_C < 4000 K). Thermal quenching behaviors depending on Ce³⁺ concentrations and temperatures are discussed.     

The 1.53 μm spectroscopic properties of Er3+/Ce3+/Yb3+ tri-doped tellurite glasses containing silver nanoparticles

The metallic silver nanoparticles (NPs) was introduced into the Er³⁺/Ce³⁺/Yb³⁺ tri-doped tellurite glasses with composition TeO₂–ZnO–La₂O₃ to improve the 1.53 μm band fluorescence. The UV/Vis/NIR absorption spectra, 1.53 μm band fluorescence spectra, fluorescence lifetimes, X-ray diffraction (XRD) curves, differential scanning calorimeter (DSC) curves and transmission electron microscopy (TEM) image of tri-doped tellurite glasses were measured, together with the Judd–Ofelt intensity parameters, emission cross-sections, absorption cross-sections and radiative quantum efficiencies were calculated to investigate the effects of silver NPs on the 1.53 μm band spectroscopic properties of Er³⁺ ions, structural nature and thermal stability of glass hosts. It is shown that Er³⁺/Ce³⁺/Yb³⁺ tri-doped tellurite glasses can emit intense 1.53 μm band fluorescence through the combined energy transfer (ET) processes from Yb³⁺ to Er³⁺ ions and Er³⁺ to Ce³⁺ ions under the 980 nm excitation. At the same time, the introduction of an appropriate amount of silver NPs can further improve the 1.53 μm band fluorescence owing to the enhanced local electric field effect induced by localized surface Plasmon resonance (LSPR) of silver NPs and the possible energy transfer from silver NPs to Er³⁺ ions, and an improvement by about 120% of fluorescence intensity is found in the studied Er³⁺/Ce³⁺/Yb³⁺ tri-doped tellurite glass containing 0.5 mol% amount of silver NPs with average diameter of ∼15 nm. The energy transfer mechanisms from Yb³⁺ to Er³⁺ ions and Er³⁺ to Ce³⁺ ions were also quantitatively investigated by calculating energy transfer microparameters and phonon contribution ratios. Furthermore, the thermal stability of glass host increases slightly with the introduction of silver NPs while the glass structure maintains the amorphous nature. The results indicate that the prepared Er³⁺/Ce³⁺/Yb³⁺ tri-doped tellurite glass with an appropriate amount of silver NPs is an excellent gain medium applied for 1.53 μm band EDFA pumped with a 980 nm laser diode (LD).     

Characterization and electromagnetic properties of Ni1−xCuxFe2O4 nanoparticle ferrites synthesized by using egg white

Polycrystalline ferrite nano-powders, Ni_1−xCu_xFe₂O₄ (where x = 0, 0.2, 0.4, 0.6 and 0.8) were synthesized by using egg white route at 520 °C for 6 h, then pre-sintered and sintered into ceramics under 800 °C for 3 h and 900 °C for 3 h, respectively. X-ray diffraction, laser particle size analyzer, TEM, vibrating sample magnetometer, SEM and precision impedance analyzer were carried out to investigate phase formation, microstructural and influence of Cu content on magnetic and electrical properties of Ni–Cu ferrite samples. The results of XRD revealed that all samples were got the principal phase and there was no extra second phase except x = 0.2, the lattice parameter was found to vary from 8.337 Å to 8.378 Å, and the crystalline size was from 55.19 nm to 60.75 nm. The effect of Cu concentration on saturation magnetization and coercive force were calculated from hysteresis loop, the maximum value of saturation magnetization was 39.46 emu/g. Electrical resistivity, dielectric constant, dielectric loss tangent and permeability were measured from 10 MHz to 110 MHz. Two main contributing factors decrease the electrical properties: the reduction of the fraction of the grain boundary and the electron hopping mechanism between Fe²⁺ and Fe³⁺ ions. All results indicated that the Cu content has a significant influence on the properties.     

Investigation on the luminescence of RE3+ (RE = Ce,Tb, Eu and Tm) in KMGd(PO4)2 (M = Ca,Sr) phosphates

The VUV excited luminescent properties of Ce³⁺, Tb³⁺, Eu³⁺ and Tm³⁺ in the matrices of KMGd(PO₄)₂ (M = Ca, Sr) were investigated. The bands at about 165 nm and 155 nm in the VUV excitation spectra are attributed to host lattice absorptions of the two matrices. For Ce³⁺-doped samples, the Ce³⁺ 5d levels can be identified. As for Tb³⁺-doped samples, typical 4f–5d absorption bands in the region of 175–250 nm were observed. For Eu³⁺ and Tm³⁺-doped samples, the O²⁻–Eu³⁺ and O²–Tm³⁺ CTBs are observed to be at about 229 nm and 177 nm, respectively. From the standpoints of color purity and luminescent efficiency, KCaGd(PO₄)₂:Tb³⁺ is an attractive candidate of green light PDP phosphor.     

Modified giant dielectric properties of samarium doped CaCu3Ti4O12 ceramics

Effects of Sm³⁺ substitution on the microstructure and dielectric properties of CaCu₃Ti₄O₁₂ ceramics were investigated. The grain size of CaCu₃Ti₄O₁₂ ceramics was greatly decreased by doping with Sm³⁺, resulting from the ability of Sm³⁺ to inhibit the grain growth rate. This result can cause a decrease in the dielectric constant (?′) and loss tangent (tan δ) of CaCu₃Ti₄O₁₂ ceramics. Interestingly, high dielectric permittivity (?′ ～ 10,863) and low loss tangent (tan δ ～ 0.043 at 20 °C and 1 kHz) were observed in the Ca_0.925Sm_0.05Cu₃Ti₄O₁₂ ceramic. Nonlinear electrical properties of CaCu₃Ti₄O₁₂ ceramics were modified by doping with Sm³⁺. The dielectric relaxation behavior of Sm-doped CaCu₃Ti₄O₁₂ ceramics can be well ascribed based on the internal barrier layer capacitor model of Schottky barriers at the grain boundaries.     

Photoluminescent properties of LiInO2 nanocrystals

Synthesis and luminescence properties of LiInO₂ nanocrystals by the sol–gel process were investigated. The products were characterized by X-ray diffraction (XRD), scanning electron microscopy (SEM), photoluminescence spectroscopy and absorption spectra. The well-crystallized tetragonal LiInO₂ can be obtained by heat treatment above 600 °C from XRD. The excitation wavelengths at about 246 nm were associated with charge transfer between In and O with In³⁺ ions in octahedral coordination. The PL spectra excited at 246 nm have a broad and strong emission band maximum at 391 nm, corresponding to the self-activated luminescence. The optical absorption spectra of the 600 °C sample exhibited the band gap energies of 3.7 eV.     

Synthesis and tunable luminescence of RbCaGd(PO4)2:Ce3+, Mn2+ phosphors

RbCaGd(PO₄)₂ doped with Ce³⁺, Mn²⁺ was synthesized by the sol-gel method. The crystal structure and crystallographic location of Ce³⁺ in RbCaGd(PO₄)₂ were identified by Rietveld refinement. Powder X-ray diffraction (XRD) revealed that the structure of RbCaGd(PO₄)₂:Ce³⁺ compounds is hexagonal structure which is similar to that of hexagonal LnPO₄ with the lattice constant of a = b = 7.005(57) Å, c = 6.352(05) Å, and V (cell volume) = 269.980 Å³. The photoluminescence behavior and emission mechanism were studied systematically by doping activators in the RbCaGd(PO₄)₂ host. The Mn²⁺ incorporated RbCaGd(PO₄)₂:Ce³⁺, Mn²⁺ compounds exhibited blue emission from the parity- and spin-allowed f-d transition of Ce³⁺ and orange-to-red emission from the forbidden ⁴T₁ → ⁶A₁ transition of Mn²⁺. The emission chromaticity coordinates of RbCaGd(PO₄)₂:0.10Ce³⁺, xMn²⁺ (x = 0.16, 0.25) are close to the white region due to an energy transfer process and the energy transfer mechanism from Ce³⁺ to Mn²⁺ in the RbCaGd(PO₄)₂ host was dominated by dipole-dipole interactions.     

Synthesis and photoluminescence study of La1.8Eu0.2O3 coating on nanometric α-Al2O3

In this work the La_1.8Eu_0.2O₃ coating on nanometric alpha-alumina, α-Al₂O₃@La_1.8Eu_0.2O₃, was prepared for the first time by a soft chemical method. The powder was heat-treated at 100, 400, 800 and 1200 °C for 2 h. X-ray powder diffraction patterns (XRD), transmission electronic microscopy (TEM), emission and excitation spectra, as well as Eu³⁺ lifetime were used to characterize the material and to follow the changes in structure as the heating temperature increases. The Eu³⁺ luminescence data revealed the characteristic transitions ⁵D₀ → ⁷F_J (J = 0, 1 and 3) of Eu³⁺ at around 580, 591 and 613 nm, respectively, when the powders were excited by 393 nm. The red color of the samples changed to yellow when the powder was annealed at 1200 °C. The decrease in the (⁵D₀ → ⁷F₂)/(⁵D₀ → ⁷F₁) ratio from around 5.0 for samples heated at lower temperatures to 3.1 for samples annealed at 1200 °C is consistent with a higher symmetry of the Eu³⁺ at higher temperature. The excitation spectra of the samples also confirms this change by the presence of a more intense and broad band at around 317 nm, instead of the presence of the characteristic peak at 393 nm, which corresponds to the ⁷F₀ → ⁵L₆ transition of the Eu³⁺. The lifetimes of the ⁵D₀ → ⁷F₂ transition of Eu³⁺ for the samples heat-treated at 100, 400, 800 and 1200 °C was evaluated as 0.57, 0.72, 0.43 and 0.31 ms, respectively.     

Coating and spark plasma sintering of nano-sized TiN on Y-α-sialon

TiN coating on Y-α-sialon was accomplished by depositing TiO₂ on their particle surfaces through controlled hydrolysis of TiCl₄ and Ti(O-i-C₃H₇)₄ and subsequent nitridation with NH₃ gas at 1000 °C. TiN particles covering Y-α-sialon were about 20 nm in size. Spark plasma sintering (SPS) of TiN/Y-α-sialon particles produced composite ceramics with continuous TiN networks at 1400 °C, but with TiN grains isolated in elongated β-sialon grains at 1600 °C. The relative density and Vickers hardness of TiN/sialon ceramics SPSed at 1400–1600 °C containing 25 vol.% TiN were measured. The electrical resistivity was in a wide range of 10⁻⁴ to 10⁰ Ω cm for the ceramics sintered at 1400 °C, but lowered to the order of magnitude of 10⁻¹ and 10⁵ Ω cm at higher temperatures ≥1500 °C. It was found that the complete transition to β-sialon increased the resistivity to 10³ to 10⁵ Ω cm, due to breaking up continuous TiN layers by elongated β-sialon grains.     

The effects of binding type on luminescence LED phosphor based on GGG/Ce3+

Luminescence and reflectance spectra of coatings based on gadolinium gallium garnet doped by cerium (GGG/Ce³⁺) with silicone resin or potassium liquid glass compound were analyzed depending on concentration. It was established that the maximum emissions of the coatings at 75 wt.% compound concentration have luminescence band at 570 nm and absorption band at 470 nm. Both bands were detected by absorption or emission of cerium ions in gadolinium gallium garnet. Ce³⁺ ion transition into Ce⁴⁺ ion was observed upon quantum absorption, and the reverse transition was observed upon quantum emission.     

Spectroscopic properties of Eu3+/Nd3+ co-doped phosphate glasses and opaque glass–ceramics

This paper reports the fabrication and characterization of Eu³⁺/Nd³⁺ co-doped phosphate (PNE) glasses and glass–ceramics as a function of Eu³⁺ concentration. The precursor glasses were prepared by the conventional melt quenching technique and the opaque glass–ceramics were obtained by heating the precursor glasses at 450 °C for 30 h. The structural and optical properties of the glass and glass–ceramics were analyzed by means of X-ray diffraction, Raman spectroscopy, UV–VIS–IR absorption spectroscopy, photoluminescence spectra and lifetimes. The amorphous and crystalline structures of the precursor glass and opaque glass–ceramic were confirmed by X-ray diffraction respectively. The Raman spectra showed that the maximum phonon energy decreased from 1317 cm⁻¹ to 1277 cm⁻¹ with the thermal treatment. The luminescence spectra of the glass and glass–ceramic samples were studied under 396 nm and 806 nm excitation. The emission intensity of the bands observed in opaque glass–ceramic is stronger than that of the precursor glass. The luminescence spectra show strong dependence on the Eu³⁺ ion concentration in the Nd³⁺ ion photoluminescence (PL) intensity, which suggest the presence of energy transfer (ET) and cross-relaxation (CR) processes. The lifetimes of the ⁴F_3/2 state of Nd³⁺ ion in Eu³⁺/Nd³⁺ co-doped phosphate glasses and glass–ceramics under 806 nm excitation were measured. It was observed that the lifetimes of the ⁴F_3/2 level of Nd³⁺ of both glasses and glass–ceramics decrease with the increasing Eu³⁺ concentration. However in the case of opaque glass–ceramics the lifetimes decrease only 16%.     

Mixture of fuels approach for the solution combustion synthesis of LaAlO3 nanopowders

A modified solution combustion approach was used in the preparation of nanosize LaAlO₃ (～23.6 nm) using mixture of citric acid and oxalic acid as fuels with corresponding metal nitrates. The synthesized and calcined powders were characterized by Fourier transform infra red spectrometry (FTIR), Differential thermal analysis-Thermogravimetry analysis (DTA–TGA), X-ray diffractometry (XRD) and Transmission electron microscopy (TEM). The FTIR spectra show the lower frequency bands at 656 and 442 cm^?1corresponds to metal–oxygen bonds (possible La–O and Al–O stretching frequencies) vibrations for the perovskite structure compound. DTA confirms the formation temperature of LaAlO₃ varies between 830–835 °C. XRD results show that mixture of fuels ratio is influential on the crystallite size of the resultant powders. The average particle size of LaAlO₃-1 as determined from TEM was about 41 nm, whereas for LaAlO₃-2 and LaAlO₃-3 samples, particles are seriously aggregated.     

Photoluminescent properties of nanostructured Y2O3:Eu3+ powders obtained through aerosol synthesis

Red emitting Y₂O₃:Eu³⁺ (5 and 10 at.%) submicronic particles were synthesized through ultrasonic spray pyrolysis method from the pure nitrate solutions at 900 °C. The employed synthesis conditions (gradual increase of temperature within triple zone reactor and extended residence time) assured formation of spherical, dense, non-agglomerated particles that are nanostructured (crystallite size ∼20 nm). The as-prepared powders were additionally thermally treated at temperatures up to 1200 °C. A bcc Ia-3 cubic phase presence and exceptional powder morphological features were maintained with heating and are followed with particle structural changes (crystallite growth up to 130 nm). Emission spectra were studied after excitation with 393 nm wavelength and together with the decay lifetimes for Eu³⁺ ion ⁵D₀ and ⁵D₁ levels revealed the effect of powder nanocrystalline nature on its luminescent properties. The emission spectra showed typical Eu^{3+ 5}D₀ → ⁷F_i (i = 0, 1, 2, 3, 4) transitions with dominant red emission at 611 nm, while the lifetime measurements revealed the quenching effect with the rise of dopant concentration and its more consistent distribution into host lattice due to the thermal treatment.