Luminescence properties of ZnMoO4:Tb3+ green phosphor prepared via co-precipitation

Tb³⁺-doped ZnMoO₄ green phosphor was synthesized by a co-precipitation method. The morphology and structure of the phosphor were characterized by Scanning electron microscopy (SEM) and X-ray diffraction (XRD). Photoluminescence (PL) spectra were also used to characterize the ZnMoO₄:Tb³⁺ samples. The results show that ZnMoO₄:Tb³⁺ phosphor has triclinic structure with diameters ranging from 1.0 to 2.0 μm. The obtained ZnMoO₄:Tb³⁺ phosphor emits green light emission centered at 541 nm corresponding to the ⁵D₄ → ⁷F₅ transition of Tb³⁺ when excited by 378 nm or 488 nm. The optimized concentration of Tb³⁺ is 15 mol.% for the highest emission intensity at 541 nm, and the concentration quenching occurs when the Tb³⁺ concentration is beyond 15 mol.%. The concentration quenching mechanism can be interpreted by the quadrupole–quadrupole interaction of Tb³⁺ ions. The present work suggests a convenient, cost-effective method for green phosphor, which may lead to potential applications in white light-emitting diodes (WLED).     

Microwave-assisted synthesis and characterization of LaPO4:Re (Re = Ce3+, Eu3+, Tb3+) nanorods

LaPO₄:Re (Re = Ce³⁺, Eu³⁺ and Tb³⁺) nanorods have been successfully synthesized on a large scale by a facile and rapid microwave heating method. The structure, morphology and physical properties of the as-prepared products were characterized by X-ray powder diffraction (XRD), transmission electron microscopy (TEM) and photoluminescence spectroscopy (PL). XRD patterns showed that the as-prepared products had hexagonal structure and high crystallinity and purity. TEM images showed that these LaPO₄:Re nanorods have a high yield and an obvious one-dimensional structure with diameter from 6 nm to 30 nm and length up to 400 nm. The luminescence spectra of the products indicated that different rare-earth ions had been successfully doped in LaPO₄ matrix via the microwave heating method and the actual doping amounts of Re ions were determined by the inductively coupled plasma (ICP).     

Hydrothermal synthesis and luminescence properties of hierarchical SrF2 and SrF2:Ln3+ (Ln = Er,Nd, Yb,Eu, Tb) micro/nanocomposite architectures

Highly uniform SrF₂ and SrF₂:Ln³⁺ (Ln = Er, Nd, Yb, Eu, Tb) hierarchical microspheres assembled by 2D nanoplates have been successfully synthesized by a facile and friendly hydrothermal route. X-ray powder diffraction (XRD), scanning electron microscopy (SEM), transmission electron microscopy (TEM), and photoluminescence (PL) spectra were used to characterize the samples. The experimental results indicate that reaction time and chelating reagent play a key role in forming the hierarchical microspheres. The formation mechanism was proposed based on the evolution of this morphology as a function of hydrothermal time. The near-infrared luminescence of lanthanide ions (Er, Nd, and Yb) doped SrF₂ microspheres were discussed in detail. In addition, the as-obtained SrF₂:Eu³⁺ sample exhibits orange-red emission centered at 590 nm under excitation at 393 nm, while the SrF₂:Tb³⁺ exhibits a strong green emission at 540 nm. The as-synthesized SrF₂:Ln³⁺ luminescent microspheres might find some potential applications in areas of photoluminescence, telecommunication and laser emission.     

Strong luminescence and efficient energy transfer in Eu3+/Tb3+-codoped ZnO nanocrystals

Single crystalline Eu³⁺/Tb³⁺-codoped ZnO nanocrystals have been synthesized by using a simple co-precipitation method. Successful doping is realized so that strong green and red luminescence can be efficiently excited by ultraviolet and near ultraviolet radiation, demonstrating an efficient energy transfer from ZnO host to rare earth ions. The energy transfer from the ZnO host to Tb³⁺ in ZnO: Tb³⁺ samples and ZnO host to Eu³⁺ in the ZnO: Eu³⁺ samples under UV excitation are investigated. It is found that the red ⁵D₀ → ⁷F₂ emission of Eu³⁺ ions decreases with increasing temperature but the green ⁵D₄ → ⁷F₅ emission of Tb³⁺ ions increases with increasing temperature, implying a different energy transfer processes in the two samples. Moreover, energy transfer from Tb³⁺ ions to Eu³⁺ ions in ZnO nanocrystals is also observed by analyzing luminescence spectra and the decay curves. By adjusting the doping concentration, the Eu³⁺/Tb³⁺-codoped ZnO phosphors emit green and red luminescence with chromaticity coordinates near white light region, high color purity and high intensity, indicating that they are promising light-conversion materials and have potential in field emission display devices and liquid crystal display backlights.     

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.     

Optical properties of sol–gel derived Sr2SiO4:Dy3+ – Photo and thermally stimulated luminescence

Trivalent dysprosium-doped strontium silicate (Sr₂SiO₄) phosphors were prepared by sol–gel synthesis using tetra ethyl orthosilicate (TEOS) as precursor. The synthesis temperature could be brought down to 600 °C for formation of a single phase sample. The material was characterized by X-ray diffraction (XRD), Scanning electron microscopy (SEM), photoluminescence (PL), and thermally stimulated luminescence (TSL). The luminescence study revealed strong ⁴F_9/2 → ⁶H_13/2 transition at 577 nm (yellow), strong ⁴F_9/2 → ⁶H_15/2 transition at 482 nm (blue) and weak ⁴F_9/2 → ⁶H_11/2 transition at 677 nm (red), when excited by 250 nm (Charge transfer band, CTB) or 352 nm (f–f band). The concentration of the dopant ion and the temperature of annealing were optimized for maximum PL intensity. The critical energy-transfer distance for the Dy³⁺ ions was evaluated based on which, the quenching mechanism was verified to be a multipole–multipole interaction. The thermally stimulated luminescence studies of Sr₂SiO₄:Dy³⁺ sample showed main TSL glow peak at 413 K. The trap parameters namely activation energy (E), order of kinetics (b), and frequency factor (s) for this peak were determined using glow curve shape method.     

Comparison between synthesis techniques to obtain ZnO nanorods and its effect on dye sensitized solar cells

This paper reports additive-free, reproducible, low-temperature solution-based process for the preparation of crystalline ZnO nanorods by homogeneous precipitation from zinc acetate. Also, ZnO nanorod structured dye sensitized solar cells using ruthenium dye (Z907) have been fabricated and characterized. The formation and growth of zinc oxide nanorods are successfully achieved. We analyzed three different synthesis method using solution phase, autoclave and microwave. The calcination effects on the morphology of ZnO nanorods are also investigated. Analysis of ZnO nanorods shows that calcination at lower temperature is resulted in a nanorod growth. Additive-free, well-aligned ZnO nanorods are obtained with the length of 330–558 nm and diameters of 14–36 nm. The XRD, SEM, and PL spectra have been provided for the characterization of ZnO nanorods. Microwave-assisted ZnO nanostructured dye sensitized solar cell devices yielded a short-circuit photocurrent density of 6.60 mA/cm², an open-circuit voltage of 600 mV, and a fill factor of 0.59, corresponding to an overall conversion efficiency of 2.35% under standard AM 1.5 sun light.     

Microstructure,luminescence and thermal stability properties of NaSrPO4:Tb3+ phosphors with various doping concentrations prepared using conventional solid-state sintering

This paper reports the microstructure, luminescence and thermal stability properties of the NaSr_1−xPO₄:xTb³⁺ powders (x = 0.008, 0.01, 0.02, 0.04 and 0.06) via the conventional solid-state sintering at 1200 °C for 5 h. The X-ray diffraction result verifies all diffraction peaks are pure phase of NaSrPO₄. The luminescence results show that the NaSrPO₄:xTb³⁺ powders mainly excited at 370 nm have a series of the emission-states, related to the typical 4f → 4f intra-configuration forbidden transitions of Tb³⁺, and a major emission peak of around 546 nm. The concentration quenching of the NaSr_1−xPO₄:xTb³⁺ phosphors is appeared at x = 0.02. The decay time values of the NaSr_1−xPO₄:xTb³⁺ phosphors for the ⁵D₄ state of the Tb³⁺ are around 3.30 ms to 3.60 ms. It is also found the chromaticity coordinate of NaSrPO₄:Tb³⁺ phosphor varies with the increase of the concentration of Tb³⁺ ions from blue to green. Moreover, the thermal stability of the NaSrPO₄:xTb³⁺ phosphors is slightly better than that of conventional YAG phosphors.     

Influence of Yttrium on optical,structural and photoluminescence properties of ZnO nanopowders by sol–gel method

Undoped and Yttrium doped ZnO nanopowders (Zn_1−xY_xO, 0 ⩽ x ⩽ 0.05) were prepared by sol–gel method and annealed at 500 °C for 4 h under air atmosphere. The prepared nanopowders were characterized by powder X-ray diffraction, energy dispersive X-ray spectra, UV–Visible spectrophotometer and Fourier transform infrared spectroscopy. The EDS analysis confirmed the presence of Y in the ZnO system. Both atomic and weight percentages were nearly equal to their nominal stoichiometry within the experimental error. XRD measurement revealed the prepared nanoparticles have different microstructures without changing a hexagonal wurtzite structure. The calculated average crystallite size decreased from 26.1 to 23.2 nm for x = 0–0.02 then reached 24.1 nm for x = 0.05. The change in lattice parameters was demonstrated by the crystal size, bond length, micro-strain and the quantum confinement effect. The observed blue shift of energy gap from 3.36 eV (Y = 0) to 3. 76 eV (Y = 0.05) (ΔE_g = 0.4 eV) revealed the substitution of Y³⁺ ions into ZnO lattice. The presence of functional groups and the chemical bonding are confirmed by FTIR spectra. The appreciable enhancement of PL intensity with slight blue shift in near band edge (NBE) emission from 396 to 387 nm and a red shift of green band (GB) emission from 513 to 527 nm with large reduction in intensity confirm the substitution of Y into the ZnO lattice. Y-doped ZnO is useful to tune the emission wavelength and hence is appreciable for the development of supersensitive UV detector.     

Polyvinylpyrrolidone (PVP)-assisted solvothermal synthesis of flower-like SrCO3:Tb3+ phosphors

Well-crystallized flower-like SrCO₃:Tb³⁺ phosphors have been synthesized by an inexpensive and friendly solvothermal process using polyvinylpyrrolidone (PVP, K30) as an additive without further annealing treatment. X-ray diffraction (XRD), Fourier transform-infrared spectroscopy (FT-IR), and field emission scanning electron microscopy (FESEM) as well as photoluminescence spectroscopy (PL) were used to characterize the resulting samples. The amount of PVP and the reaction time have strong effect on the morphology of the SrCO₃:Tb³⁺ particles. The results of XRD confirm the formation of a well-crystallized SrCO₃ phase with an orthorhombic structure. The possible formation mechanism for flower-like SrCO₃:Tb³⁺ phosphor is proposed. The SrCO₃:Tb³⁺ phosphors show the characteristic ⁵D₄–⁷F_J (J = 6, 5, 4, 3) emission lines with green emission ⁵D₄–⁷F₅ (544 nm) as the most prominent group under ultraviolet excitation.     

Effect of annealing on the magnetic properties of solution synthesized Zn1−xMnxO nanorods

Mn-doped ZnO nanorods with ～30 nm in diameter and ～200 nm in length were synthesized by a seed-mediated solution method. The structures, magnetic properties, as well as the annealing effect were characterized by transmission electron microscopy, electron energy loss spectroscopy, X-ray diffraction, X-ray photoelectron spectroscopy, Raman spectrum and physical properties measurement system. Magnetic properties measurement revealed that the Zn_0.97Mn_0.03O nanorods exhibited ferromagnetism with a saturation magnetization of 0.005 emu g^?1 and a coercivity of 110 Oe at 305 K. After annealing the samples at 900 °C for 2 h in air, the nanorods were transformed into nanoparticle aggregates. The coercivity and saturation magnetization increased obviously. Detailed analyses proved that a phase-separation process was happened at the high temperature. In this process, most of the particles preserved the wurtzite ZnO structure, while a few small ones evolved into spinel-structured particles. The increasing of the ferromagnetism of the annealed sample is attributed to the formation of secondary phase Zn_xMn_3?xO_4.     

Microstructure and photoluminescent properties of BaY2ZnO5:Tb3+ phosphors with addition of lithium carbonate

In this paper, Tb³⁺ activated BaY₂ZnO₅ phosphors with addition of lithium carbonates (0, 0.0125, 0.025, 0.05, 0.1, and 0.2 molar ratio) were synthesized using the solid-state reaction, and the morphology and photoluminescent properties are investigated. When BaY₂ZnO₅:Tb³⁺ phosphors to which lithium carbonates were added were sintered at 1250 °C for 12 h, X-ray powder diffraction analysis showed that the un-reacted Y₂O₃ raw material decreased and scanning electron microscopy showed that the grain growth is improved. From PL studies, the photoluminescent properties were decreased when Li⁺ ion was added, which might be resulted from the increase of the oxygen vacancy in BaY₂ZnO₅:Tb³⁺ phosphors. The green emission of the BaY₂ZnO₅:Tb³⁺, Li⁺ phosphors showed the CIE chromaticity coordinates in the range of x = 0.3361–0.3510 and y = 0.5202–0.5492.     

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.     

Tb3+/Yb3+ codoped silica–hafnia glass and glass–ceramic waveguides to improve the efficiency of photovoltaic solar cells

In this paper we present the investigation of the energy transfer efficiency between Tb³⁺ and Yb³⁺ ions in silica–hafnia waveguides. Cooperative energy transfer between these two ions allows to cut one 488 nm photon in two 980 nm photons and could have important applications in improving the performance of photovoltaic solar cells. Previous works revealed that for a given concentration of donors (Tb³⁺), increasing the number of acceptors (Yb³⁺) located near to the Tb³⁺ ion can increase the Tb–Yb transfer probability. However, when increasing the density of active ions, some detrimental effects due to cross-relaxation mechanisms become relevant. On the basis of this observation the sample doping was chosen keeping constant the molar ratio [Yb]/[Tb] = 4 and the total rare earths contents were [Tb + Yb]/[Si + Hf] = 5%, 7%, 9%. The choice of the matrix is another crucial point to obtain an efficient down conversion processes with rare earth ions. To this respect a 70SiO₂–30HfO₂ waveguide composition was chosen. The comparison between the glass and the glass–ceramic structures demonstrated that the latter is more efficient since it combines the good optical properties of glasses with the optimal spectroscopic properties of crystals activated by luminescent species. A maximum transfer efficiency of 55% was found for the highest rare earth doping concentration.     

Synthesis and photoluminescence of Y,Eu co-doped ZnO red phosphor

A red emitting ZnO·Y₂O₃:Eu phosphor has been prepared using pyrolysis technique at temperatures ≤1000 °C. When NH₄Cl was used as an ingredient, its luminescence efficiency was quite high indicating that Cl^? ions act as charge compensators since the introduction of Y³⁺ and Eu³⁺ cations in ZnO lattice demands the introduction of equal amount of excess anions. However, Na⁺ or Li⁺ quenches the luminescence efficiency of ZnO·Y₂O₃:Eu. Due to ZnO host absorption, the excitation peaks of ZnO·Y₂O₃:Eu phosphor near 260 nm and 394 nm are suppressed while the one at 468 nm is intense. This red emitting phosphor may find applications when monochromatic excitation such as lasers are involved. XRD data of (Zn_0.93Y_0.07)O_z:Eu³⁺,Cl^? shows the presence of the ZnO phase as well as the Y₂O₃ phase. It shows that Y₂O₃ forms a sublattice within ZnO host. This is supported by the PL data of (Zn_0.93Y_0.07)O_z:Eu³⁺,Cl^? which showed no significant change in the PL efficiency with increase in ZnO molar concentration.     

A facile low temperature hydrothermal route to CdSO4 nanotubes/rods

Cadmium sulphate nanotubes/rods have been synthesized by hydrothermal treatment using CdSO₄ powder as precursor and hexadecylamine (HDA) as surfactant at 180 °C for 7 days. The powder X-ray diffraction (PXRD) pattern reveals that the CdSO₄ nanotubes/rods are of orthorhombic phase. Fourier transform infrared (FTIR) spectrum shows characteristic bands due to the sulfate ion in 1114 cm^? 1 and 617 cm^? 1 region, besides bands due to the amine moiety. Transmission electron micrograph (TEM) images reveal the nanorods are of 10–15 nm in thickness and nanotubes of wall thickness 5–8 nm. UV–visible absorption spectrum of CdSO₄ nanotubes/rods shows the peak at 221 nm. Photoluminescence (PL) spectrum exhibits an intense UV band at 372 nm and weak green band at 484 nm.     

Cold white light generation through the simultaneous emission from Ce3+ and Tb3+ in sodium germanate glass

A spectroscopic investigation of sodium germanate glasses activated with Ce³⁺, Tb³⁺ and Ce³⁺/Tb³⁺ is carried out by analyzing their photoluminescence spectra and decay times. Non-radiative energy transfer from Ce³⁺ to Tb³⁺ is observed upon near-UV excitation at 310 nm (peak emission wavelength of AlGaN-based LEDs). The non-radiative nature of this energy transfer is inferred from the increase in the decay rate of the Ce³⁺ emission when the glass is co-doped with Tb³⁺. From an analysis of the Ce³⁺ emission decay time curve it is inferred that an electric dipole–quadrupole interaction might to be the dominant mechanism for the Tb³⁺ emission sensitized by Ce³⁺. Energy transfer from Ce³⁺ to Tb³⁺ leads to a simultaneous emission of these ions in the blue, green, yellow and red, resulting in white light with CIE1931 chromaticity coordinates, x = 0.30 and y = 0.32, which correspond to cold white light with a colour temperature of 7320 K and very small deviation from the Planckian black-body radiator locus (0.005).     

RE3+ (RE = Ce3+, Tb3+) doped BaGdF5 nanocrystals: Synthesis,optical and magnetic properties,and energy transfer

Through a citric acid assisted hydrothermal method, the RE³⁺ (RE³⁺ = Ce³⁺, Tb³⁺) doped cubic phase BaGdF₅ nanocrystals with a sphere-like morphology and an average size of 30 nm have been synthesized. The samples show paramagnetic properties at 300 K. The photoluminescence spectra of the obtained samples suggest that the existence of Ce³⁺ can dramatically enhance the emission intensity of Tb³⁺ due to an efficient energy transfer from Ce³⁺ to Tb³⁺. The energy transfer efficiency from Ce³⁺ to Tb³⁺, the critical energy transfer distance between Ce³⁺ and Tb³⁺, and the energy transfer mechanism of Ce³⁺–Tb³⁺ are discussed based on the experimental data and the theoretical analysis.     

Optical investigations on Tb3+ doped l-Histidine hydrochloride mono hydrate single crystals grown by low temperature solution techniques

The potential nonlinear optical material of Terbium (Tb³⁺) ion doped l-Histidine hydrochloride monohydrate (LHHC) single crystals were successfully grown. Tb³⁺:LHHC crystals of 7 mm × 5 mm × 3 mm and 59 mm length and 15 mm diameter have been grown by the slow solvent evaporation and Sankaranarayanan-Ramasamy (SR) techniques respectively. The grown crystals were characterized by single crystal X-ray diffraction analysis to confirm the crystalline structure and morphology. High resolution X-ray diffraction (HRXRD) studies revealed that the SR grown sample shows relatively good crystalline nature with 9″ full-width at half-maximum (FWHM) for the diffraction curve. Functional groups were identified by Fourier transform infra-red spectroscopy (FTIR). The optical transparency and band gaps of grown crystals were measured by UV–Vis spectroscopy. Thermogravimetric and differential thermal analysis (TG/DTA) studies reveal that the crystal was thermally stable up to 155 °C in SR grown crystal. Surface morphology of the growth plane was observed using scanning electron microscopy (SEM). The incorporation of Tb ion was estimated by EDAX. The frequency-dependent dielectric properties of the crystals were carried out for different temperatures. Vickers hardness study carried out on (1 0 0) face at room temperature shows increased hardness of the SR method grown crystal. Second harmonic generation efficiency of SEST and SR grown crystals are 3.2 and 3.5 times greater than that of pure KDP. The Photoluminescence (PL) studies of Tb³⁺ ions result from the radiative intra-configurational f-f transitions that occur from the ⁵D₄ excited state to the ⁷F_j (j = 6, 5, 4, 3) ground states. The decay curve of the ⁵D₄ level of emission was observed with a long life time of 319.2041 μs for the SR grown Tb³⁺:LHHC crystal.