Enhanced photoluminescence of Gd0.94(P1−xVx)O4:Eu0.06 red-emitting (0 ≤ x ≤ 1.0) phosphors

High-quality Gd_0.94(P_1−xV_x)O₄:Eu_0.06 (0 ≤ x ≤ 1.0) powders having small size, spherical morphology, smooth surface, and nonaggregation are synthesized by the ultrasonic spray pyrolysis. The complex host composition, Gd_0.94(P_1−xV_x)O₄:Eu_0.06 (x ≥ 0.5), shows a single phase with the tetragonal xenotime structure. The introduction of V⁵⁺ ions in the P⁵⁺ lattice yields the deviation from the centrosymmetry of Eu³⁺ ions. By increasing the V⁵⁺ content, the emission intensity corresponding to the ⁵D₀ → ⁷F₁ transition decreases. On the other hand, the emission intensity corresponding to the ⁵D₀ → ⁷F₂ transition increases up to x = 0.5, and then decreases upon further increasing the V⁵⁺ content. The emission intensity, peaking at 620 nm, of complex composition Gd_0.94(P_0.5V_0.5)O₄:Eu_0.06 is approximately five and two times stronger than that of the Gd_0.94PO₄:Eu_0.06 and Gd_0.94VO₄:Eu_0.06, respectively. It is believed that the introduction of the complex composition Gd_0.94(P_1−xV_x)O₄:Eu_0.06 is highly effective for improving the emission properties.     

Enhancement of green emission for Al-doped YBO3:Tb

High-quality Y_1−x−yAl_xTb_yBO₃ (0 ≤ x ≤ 0.1, 0.04 ≤ y ≤ 0.16) phosphor powders with fine size, spherical and regular morphology, and non-agglomeration were successfully prepared by ultrasonic spray pyrolysis. The blue emission from the ⁵D₃→⁷F_J (J = 4, 5, and 6) transition for the Y_0.94−xAl_xTb_0.06BO₃ phosphor was quenched. The optimal concentration of Tb³⁺ was reduced by doping Al³⁺ into the Y_1−yTb_yBO₃ phosphor, i.e., y = 0.1 and 0.12 for Y_0.975−yAl_0.025Tb_yBO₃ and Y_1−yTb_yBO₃, respectively. The Al³⁺ doping was highly effective for improving the photoluminescence characteristics. The photoluminescence emission intensity of the Al³⁺-doped Y_0.915Al_0.025Tb_0.06BO₃ phosphor at 543 nm was about three times stronger than that of the Al³⁺-free Y_0.94Tb_0.06BO₃ phosphor.     

UV and VUV characteristics of (YGd)2O3:Eu phosphor particles prepared by spray pyrolysis from polymeric precursors

Red-emitting (YGd)₂O₃:Eu phosphor particles, with high luminescence efficiency under vacuum ultraviolet (VUV) and ultraviolet (UV) excitation, were prepared by a large-scale spray pyrolysis process. To control the morphology of phosphor particles under severe preparation conditions, spray solution with polymeric precursors were introduced in spray pyrolysis. The prepared (YGd)₂O₃:Eu phosphor particles had spherical shape and filled morphology even after post-treatment irrespective of Gd/Y ratio. In the case of solution with polymeric precursors, long polymeric chains formed by esterification reaction in a hot tubular reactor; the droplets turned into viscous gel, which retarded the precipitation of nitrate salts and promoted the volume precipitation of droplets. The brightness of (YGd)₂O₃:Eu phosphor particles increased with increasing gadolinium content, and the Gd₂O₃:Eu phosphor had the highest luminescence intensity under UV and VUV excitation. The maximum peak intensity of Gd₂O₃:Eu phosphor particles under UV and VUV were 118 and 110% of the commercial Y₂O₃:Eu phosphor particles, respectively.     

Rapid synthesis of spherical-shaped green-emitting MgGa2O4:Mn phosphor via spray pyrolysis

Simple, one-step synthesis of spherical-shaped powder phosphors with aqueous precursors via a spray pyrolysis method is reported. Green-emitting MgGa₂O₄:Mn²⁺ phosphor with a controlled shape was successfully obtained by spraying under a reductive atmosphere (N₂ + H₂ carrier gas) without high-temperature post-heat treatment. In addition, the corresponding powder phosphors were well dispersed and showed a clean surface morphology compared to an existing cumbersome process using high-temperature post-annealing. The new method may help to prevent surface residual non-radiative defect sites. The result of highly luminescent and spherical morphology, non-aggregated powder phosphor by this procedure holds promise for a cost-effective and rapid synthesis process for conventional inorganic phosphors.     

Visible quantum cutting via downconversion in a novel green-emitting K2Gd(WO4)(PO4):Tb phosphor

A novel phosphor K₂Gd(WO₄)(PO₄):Tb was prepared via a solid-state reaction. The crystal structure of K₂Gd(WO₄)(PO₄) as a new host matrix for luminescence was defined to be the orthorhombic system with space group Ibca (73). Visible quantum cutting under Tb³⁺ 4f⁸–4f⁷5d¹ excitation and host excitation in K₂Gd(WO₄)(PO₄):Tb³⁺ via a downconversion was identified. In order to rationalize the quantum cutting effect, the proper mechanism was proposed. According to calculations, the quantum efficiency was up to 183.2% and 176.4% under excitation at 235 nm and 150 nm, respectively. When compared with Zn₂SiO₄:Mn²⁺ (P1-G1S), KGWP:0.5Tb³⁺ is slightly less bright over 450–650 nm but has a shorter decay time.     

The UV and VUV luminescence properties of the phosphor Mg2GeO4:Tb

A novel green phosphor Mg₂GeO₄:Tb³⁺ with pure phase was prepared by the solid state reaction. The luminescence properties were investigated in detail. The diffusion reflection spectra of the undoped and Tb³⁺ doped Mg₂GeO₄ phosphors were recorded, the result reveals that there is an absorption band superposition of the host material and Tb³⁺ ion. The study on the excitation and diffusion spectra shows that there is an effective energy transfer from the host material to Tb³⁺ ion. Under 277 and 172 nm excitation, the phosphor presents predominant green emission at 543 and 547 nm respectively. The excitation intensity at 172 nm is about 1.8 times of that at 272 nm. The promising luminescence properties make it a candidate for application in Plasma Display Panel.     

Upconversion in Er-doped Gd2O3 nanocrystals prepared by propellant synthesis and flame spray pyrolysis

In this study, monoclinic luminescent Gd₂O₃ nanocrystals doped with different concentrations of Er³⁺ (0.1, 1, and 10 mol%) were produced by propellant synthesis and flame spray pyrolysis (FSP). A comparison of their optical and morphological properties is reported. Following 980 nm excitation, an increase of the emission intensity from the ²H_11/2, ⁴S_3/2 → ⁴I_15/2 and ⁴F_9/2 → ⁴I_15/2 transitions was observed with increasing Er³⁺ concentration in the Gd₂O₃ nanocrystalline samples prepared via both techniques. However, the overall upconversion emission intensity was greater for the samples obtained by FSP. Furthermore, as the Er³⁺ concentration was increased, the intensity of the red (⁴F_9/2 → ⁴I_15/2) emission was observed to increase more rapidly in comparison to the green (²H_11/2, ⁴S_3/2 → ⁴I_15/2) emission resulting in an overall enhancement of the red component in the upconversion emission. Although both synthetic routes yield average crystallite sizes in the nanoscale, the TEM and SEM images confirm a more homogeneous morphology and lower particle aggregation for the nanocrystals produced by FSP.     

The effect of simultaneous addition of Gd and Al on the photoluminescence characteristics of (Y0.94−x−yAlxGdyEu0.06)BO3 phosphors

The (Y_0.94−x−yAl_xGd_yEu_0.06)BO₃ (0 ≤ x ≤ 0.04 and 0 ≤ y ≤0.4) phosphors were single-phase with a hexagonal vaterite crystal structure. The (Y_0.94−x−yAl_xGd_yEu_0.06)BO₃ phosphor powders showed smooth, regular, and spherical morphology. The emission intensity of the Al- and Gd-co-doped (Y_0.74−xAl_xGd_0.2Eu_0.06)BO₃ and (Y_0.925−yAl_0.015Gd_yEu_0.06)BO₃ phosphors was much higher than that of Al-free (Y_0.74Gd_0.2Eu_0.06)BO₃ and Gd-free (Y_0.925Al_0.015Eu_0.06)BO₃ phosphors, respectively. This means that the simultaneous addition of Gd and Al to yttrium borates was desirable for improving their photoluminescent properties.     

Photoluminescence and low-voltage cathodoluminescence characteristics of blue phosphor, ZnGa2O4:M (M = Na, Ag)

Photoluminescence and low-voltage cathodoluminescence characteristics of ZnGa₂O₄ phosphor doped with monovalent ions has been studied. Monovalent ions such as Na⁺ and Ag⁺ are incorporated into ZnGa₂O₄ lattices in order to increase the concentration of oxygen vacancies in the spinel lattice. By doping low concentrations of monovalent ions (Na⁺, Ag⁺) into ZnGa₂O₄, the self-activated blue luminescence originated from oxygen vacancies is enhanced. Also, the blue luminescence intensity is enhanced more along with a good color purity by annealing ZnGa₂O₄:Na⁺ in a reducing atmosphere, which is due to increasing the concentration of oxygen vacancies even more. The luminescence band at the UV region (λ_max=360 nm) does not become the major luminescence band by introducing Na⁺ ion into the ZnGa₂O₄ lattice, while the UV luminescence band becomes the major one by annealing the undoped ZnGa₂O₄ in a reducing atmosphere.     

Low temperature synthesis and optical properties of CaTiO3 nanoparticles from Ca(NO3)2·4H2O and TiO2 nanocrystals

Choosing low-melting-point Ca(NO₃)₂·4H₂O and high-reactive-activity TiO₂ nanocrystals as the raw materials, a simple and cost-effective route was developed for the synthesis of CaTiO₃ nanoparticles at 600 °C, which is much lower than that (about 1350 °C) used in the conventional solid state reaction methods. X-ray diffraction, energy dispersive X-ray spectroscopy and field emission scanning electron microscopy revealed the formation of orthorhombic phase CaTiO₃ nanoparticles with oxygen-deficiency at the surface. UV-vis absorption spectrum of the as-obtained CaTiO₃ nanoparticles displayed an absorption peak centered at around 325 nm (3.8 eV), together with a tail at lower energy side. Room temperature photoluminescence spectrum of the as-obtained CaTiO₃ nanoparticles upon laser excitation at 325 nm demonstrated a strong and broad visible light emission ranging from about 527 to 568 nm, which may be originated from the surface states and defect levels.     

Properties of Gd2O3:Eu, Tb nanopowders obtained by sol-gel process

A significant practical application for nanostructured materials is X-ray medical imagery, because it is necessary to use dense materials in order to enable absorption of high energy photons. An important requirement of these materials is UV-vis range emission produced by X-ray excitation, which can be influenced by the particle size. Europium doped gadolinium oxide is a well known red phosphor. Moreover, nanophosphors of Gd₂O₃ codoped with Tb³⁺, Eu³⁺ increase their light yield by energy transfer between Tb³⁺ and Eu³⁺. In this study, Gd₂O₃ nanopowders codoped with Eu³⁺ and Tb³⁺ (2.5 at.% Eu³⁺, and 0.005 and 0.01 at.% Tb³⁺) were obtained via a sol-gel process using gadolinium pentanedionate as precursor and europium and terbium nitrates as doping sources. In this paper, we report the influence of annealing temperature on the structure, morphology and luminescent properties of Gd₂O₃:Eu³⁺, Tb³⁺ by means of TGA, XRD, TEM and X-ray emission measurements.     

Investigation of Na3GdP2O8:Tb as a potential green-emitting phosphor for plasma display panels

The photoluminescent properties of a series of Tb³⁺-doped Na₃GdP₂O₈ phosphors excitable by vacuum ultraviolet and ultraviolet light are reported. The host related absorption, f-f and f-d transitions of Gd³⁺ and Tb³⁺, and charge transfer of O²⁻ → Gd³⁺ and O²⁻ → Tb³⁺ are assigned. Under 147 nm light excitation, Na₃GdP₂O₈:Tb³⁺ phosphors show efficient green emissions with a dominant peak at 545 nm. The optimal sample Na₃Gd_0.4Tb_0.6P₂O₈ shows a shorter decay time and a comparable brightness when compared with the commercial Zn₂SiO₄:Mn²⁺ green phosphor. These results demonstrate that it is a potential candidate for plasma display panels application.     

Structural investigation and improvement of photoluminescence properties in Ba(ZrxTi1−x)O3 powders synthesized by the solid state reaction method

In this paper, Ba(Zr_xTi_1−x)O₃ powders with different (x) compositions were synthesized by the solid state reaction method and their structure and improvement of photoluminescence (PL) properties with the Ti substitution by Zr were discussed. The structural investigation of these powders was performed by means of X-ray diffraction (XRD) and Fourier transform Raman (FT-Raman) spectroscopy. Their optical properties were monitored by ultraviolet–visible (UV–vis) absorption spectroscopy and PL measurements. XRD patterns indicated that the powders with x = 0 and 0.1 have a tetragonal structure while compositions with x ≥ 0.2 exhibit cubic structure. FT-Raman spectra revealed that the replacement of Ti by Zr significantly reduced the intensity of the Raman active modes. This behavior is related to the increase of undistorted [ZrO₆] clusters in the global matrix at short range and decrease in local concentration of distorted octahedral [TiO₆] clusters. UV–vis absorption spectra shown the presence of intermediary energy levels between the valence band (VB) and the conduction band (BC). These intermediary electronic levels are mainly related to 2p orbitals of O atoms, 4d orbitals of Zr atoms and 3d orbitals of Ti atoms between the VB and CB. A significant improvement in PL properties of Ba(Zr_xTi_1−x)O₃ powders was observed with an increase of undistorted [ZrO₆] clusters in the lattice. Finally, we propose possible wideband models based on intermediary energy deep and shallow levels to explain the PL behavior at room temperature.     

Near-ultraviolet excitable Ca4Y6(SiO4)6O: Ce,Tb white phosphors for light-emitting diodes

The present investigation aims to demonstrate the potentiality of Tb³⁺ and Ce³⁺ co-doped Ca₄Y₆(SiO₄)₆O phosphors. By incorporation of Ce³⁺ into Ca₄Y₆(SiO₄)₆O: Tb³⁺, the excitation band was extended from short-ultraviolet to near-ultraviolet region. The energy transfer from Ce³⁺ to Tb³⁺ in Ca₄Y₆(SiO₄)₆O host was investigated and demonstrated to be a resonant type via a dipole–dipole mechanism with the critical distance of 10.2 Å. When excited by 352 nm, Ca₄Y₆(SiO₄)₆O: Ce³⁺, Tb³⁺ exhibited a brighter and broader violet-blue emission (421 nm) from the Ce³⁺ and an intense green emission (542 nm) from the Tb³⁺. Combining the two emissions whose intensities were adjusted by changing the doping levels of the co-activator, an optimized white light with chromaticity coordinates of (0.278, 0.353) is generated in Ca₄Y₆(SiO₄)₆O: 2% Ce³⁺, 8% Tb³⁺, and this phosphor could be potentially used in near-ultraviolet light-emitting diodes.     

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.     

Structural, electrical and optical characteristics of SnO2:Sb thin films by ultrasonic spray pyrolysis

Antimony-doped tin oxide (SnO₂:Sb) thin films were fabricated by an ultrasonic spray pyrolysis method. The effect of antimony doping on the structural, electrical and optical properties of tin oxide thin films were investigated. Tin(II) chloride dehydrate (SnCl₂·2H₂O) and antimony(III) chloride (SbCl₃) were used as a host and a dopant precursor. X-ray diffraction analysis showed that the non-doped SnO₂ thin film had a preferred (211) orientation, but as the Sb-doping concentration increased, a preferred (200) orientation was observed. Scanning electron microscopy studies indicated that the polyhedron-like grains observed for the non-doped SnO₂ thin films became rounder and decreased in size with the Sb-doping concentration. The lowest resistivity (about 8.4 × 10^− 4 Ω·cm) was obtained for the 3 at.% Sb-doped films. Antimony-doping led to an increase in the carrier concentration and a decrease in Hall mobility. The transmittance level in the near infrared region was lowered with the Sb-doping concentration.     

Self-activated afterglow luminescence of un-doped Ca2ZrSi4O12 material and explorations of new afterglow phosphors in a rare earth element-doped Ca2ZrSi4O12 system

Un-doped Ca₂ZrSi₄O₁₂ material is prepared using a solid state reaction and it emits intense green afterglow luminescence peaking at 490 nm. The afterglow luminescence can be recorded for about 4800 s (0.32 mcd m⁻²). The thermoluminescence revealed that at least four types of traps existed in the Ca₂ZrSi₄O₁₂ material and the depths of these traps were calculated. The contributions of these traps on the afterglow luminescence were also investigated in detail. Accordingly, a possible afterglow mechanism of Ca₂ZrSi₄O₁₂ was proposed. Moreover, Ca₂ZrSi₄O₁₂ was also doped by rare earth or metal ions for developmental purpose and we arrived at some useful conclusions according to the experimental results.     

Structural and magnetic characterization of LiMn1.825Cr0.175O4 spinel obtained by ultrasonic spray pyrolysis

Quaternary spinel oxide LiMn_1.825Cr_0.175O₄ powder was synthesized by using an ultrasonic spray pyrolysis method, without additional annealing. The crystal structure of the as-prepared powder was revealed by X-ray powder diffraction and identified as a single spinel phase with Fd3m space group. The powders had a spherical morphology with extremely smooth surface appearance and densely congested interior structure. Transmission electron microscopy confirmed that the particle consisted by the cohesion of the primary particles. Magnetic measurements performed in DC field in both zero-field-cooled and field-cooled regimes, as well as AC susceptibility experiments, show that system undergoes spin-glass transition at the freezing temperature T_f = 20 K. The value of the effective magnetic moment μ_eff = 4.34 μ_B obtained from the Curie-Weiss fit in the high temperature region confirms the substitution of Mn³⁺ ions with Cr³⁺ ions.     

Hydrothermal synthesis and photoluminescence of SrWO4:Tb novel green phosphor

Tb³⁺-doped SrWO₄ phosphors with a scheelite structure have been prepared by hydrothermal reaction. X-ray powder diffraction, field-emission scanning electron microscopy, photoluminescence excitation and emission spectra and decay curve were used to characterize the resulting samples. Scanning electron microscopy image showed that the obtained SrWO₄:Tb³⁺ phosphors appeared to be nearly spherical and their sizes ranged from 1 to 3 μm. Photoluminescence spectra indicated the phosphors emitted strong green light centered at 545 nm under ultraviolet light excitation. Because 12 at.% SWO₄:Tb³⁺ phosphor exhibits intensive green emission under 254 nm excitation in comparison with the commercial green fluorescent lamp phosphor (LaPO₄:Ce,Tb), the excellent luminescence properties make it a new promising green phosphor for fluorescent lamps application.     

Hydrothermal synthesis and photoluminescence properties of Gd2Zr2O7:Tb phosphors

This paper presents hydrothermal synthesis, characterization, and photoluminescence (PL) properties of novel green-emitting phosphors, Gd₂Zr₂O₇:Tb³⁺. Their crystal structure, morphology and photoluminescence properties were investigated by X-ray powder diffraction (XRD), field emission scanning electron microscopy (FE-SEM), Transmission electron microscopy (TEM) and fluorescence spectrophotometer. The results revealed that one-dimensional Gd₂Zr₂O₇:Tb³⁺ nanorods with diameter of about 30 nm and length of 150-300 nm were formed, and the products exhibited a fluorite-type structure. PL study revealed that Gd₂Zr₂O₇:Tb³⁺ phosphors presented dominant green emission luminescence, which was attributed to the transitions from ⁵D₄ excited states to ⁷F_J (J = 3-6) ground states of Tb³⁺. The luminescence intensity of Gd₂Zr₂O₇:Tb³⁺ with different Tb³⁺ concentration was also investigated and reported, and an obvious concentration quenching was observed when Tb³⁺ ion concentration was 5 at.%.