Vacuum ultraviolet spectroscopic properties of KSrPO4:Tb

KSrPO₄:Tb³⁺ phosphors were prepared by a solid-state method and their photoluminescence properties were investigated under vacuum ultraviolet excitation. In the excitation spectrum monitoring at 544 nm, the band in the region of 120-162 nm can be attributed to be the overlap of host absorption and charge transfer transition of O²⁻ → Tb³⁺, and the band ranging from 162 to 300 nm was assigned to the f-d transition of Tb³⁺. The photoluminescence spectrum shows that the phosphors exhibited a strong green emission around 544 nm corresponding to the ⁵D₄ → ⁷F₅ transition of Tb³⁺ under the excitation of 147 nm. Optimal emission intensity was obtained when x = 7% in KSr_1-xPO₄:xTb³⁺ and the luminescent chromaticity coordinates were calculated to be (x = 0.317, y = 0.522) for KSr_0.93PO₄:7%Tb³⁺.     

Luminescence properties of Ca10K(PO4)7:RE (RE = Ce, Tb, Dy, Tm and Sm) under vacuum ultraviolet excitation

A series of RE³⁺ (RE = Ce, Tb, Dy, Tm and Sm) activated Ca₁₀K(PO₄)₇ were synthesized by conventional state reaction and their photoluminescence properties under vacuum ultraviolet excitation were investigated. The PO₄³⁻ absorption lies within the range from 125 to 180 nm in all the excitation spectra of Ca₁₀K(PO₄)₇:RE³⁺. The first f-d transition of Ce³⁺ is observed at 316 nm, and the Ce³⁺ emission is located at about 350 nm. Both the first spin-allowed and spin-forbidden f-d transitions of Tb³⁺ are situated at 232 and 263 nm, respectively. The emission spectrum of Ca₁₀K(PO₄)₇:Tb³⁺ exhibits typical Tb³⁺ emissions with the predominant peak at 544 nm. The O²⁻-Dy³⁺ charge transition band was calculated and identified around 173 nm, the CIE chromaticity coordinates of Dy³⁺ were calculated to be 0.364 and 0.392. The Ca₁₀K(PO₄)₇:Tm³⁺ demonstrates the strongest excitation at about 182 nm assigned to O²⁻-Tm³⁺, and gives the predominant emission at 453 nm. The ⁴G_5/2-⁶H_7/2 transition of Sm³⁺ at 601 nm is the most intensive in the emission spectrum.     

LaPO4:Eu, LaPO4:Ce, and LaPO4:Ce,Tb nanocrystals: Oleic acid assisted solvothermal synthesis, characterization, and luminescent properties

LaPO₄:Ln³⁺ (Ln = Eu, Ce, Tb) nanocrystals were successfully synthesized via a facile solvothermal process in the presence of oleic acid. The as-prepared crystals were well characterized by X-ray diffraction (XRD), transmission electron microscopy (TEM), X-ray photoelectron spectra (XPS), Fourier transform infrared spectroscopy (FT-IR), optical spectra as well as the kinetic decay times, respectively. In the synthesis process, oleic acid as a surfactant has played a crucial role in confining the growth and size of the LaPO₄:Ln³⁺ phosphors. All the samples are well crystallized and assigned to the monoclinic monazite-type structure of the LaPO₄ phase. The prepared LaPO₄:Ln³⁺ phosphors present a narrow distribution with an average particle size of about 15 nm. Upon excitation by ultraviolet radiation, the LaPO₄:Eu³⁺ phosphors show the characteristic ⁵D₀-⁷F_1-3 emission lines of Eu³⁺, while the LaPO₄:Ce³⁺,Tb³⁺ exhibits the characteristic ⁵D₀-⁷F_3-6 emission lines of Tb³⁺. It is believed that these rare earth ion doped (Eu³⁺ ion or Ce³⁺ and Tb³⁺ ions co-doped) monoclinic monazite-type LaPO₄ nanocrystals could find potential application as future advanced optical materials.     

Synthesis and luminescent properties of Ln3+ (Ln3+ = Eu3+, Dy3+) -doped Bi2ZnB2O7 phosphors

The new phosphors Bi2ZnB2O7:Ln3+ (Ln3+ =Eu3+,Dy3+) were synthesized by solid-state reaction technique.The obtained phosphors were investigated by means of X-ray powder diffraction (XRD),photoluminescence excitation and emission spectra with the aim of enhancing the fundamental knowledge about the luminescent properties of Eu3+ and Dy3+ ions in the Bi2ZnB2O7 host lattice.XRD analysis shows that all these compounds are of a single phase of Bi2ZnB2O7.The excitation and emission spectra of Bi2ZnB2O7:Ln3+ (Ln3+ =Eu3+,Dy3+) at room temperature show the typical 4f-4f transitions of Eu3+ and Dy3+,respectively.The hypersensitive transitions of 5D0→7F2 (Eu3+) and 4F9/2→ 6H13/2 (Dy3+) are relatively higher than those of the insensitive transitions in Bi2ZnB2O7.It is conceivable that the Bi2ZnB2O7 structure provides asymmetry sites for activators (Eu3+,Dy3+).The optimum concentrations of Eu3+ and Dy3+ ions in Bi2ZnB2O7 phosphors are both x =0.05.     

Sol-gel preparation and characterization of uniform core-shell structured LaInO3:Sm/Tb@SiO2 phosphors

The core-shell structured LaInO₃:Ln³⁺@SiO₂ (Ln³⁺ = Sm³⁺, Tb³⁺) phosphors were realized by coating LaInO₃:Ln³⁺ phosphors on the surface of silica microspheres via a modified Pechini sol-gel process. The phase, structure, morphology, and fluorescent properties of the materials were well characterized by means of X-ray diffraction (XRD), field emission scanning electron microscopy (FE-SEM), transmission electron microscopy (TEM), Fourier transform IR spectroscopy (FT-IR), photoluminescence (PL) spectra, cathodoluminescence (CL) spectra, and the kinetic decays, respectively. The results reveal that the obtained core-shell structured phosphors consist of amorphous silica core and crystalline LaInO₃:Ln³⁺ shell, which keep the uniform spherical morphology of pure silica spheres with narrow size distribution. Upon excitation by ultraviolet (UV) irradiation or electron beam, the phosphors show the characteristic emission lines of Sm³⁺ (⁴G_5/2-⁶H_5/2,7/2,9/2, orange) in LaInO₃:Sm³⁺@SiO₂ and characteristic emissions of Tb³⁺ (⁵D₄-⁷F_6,5,4,3, green) in LaInO₃:Tb³⁺@SiO₂, respectively. This kind of phosphors may have potential applications in field emission displays (FEDs) based on their uniform shape, low-cost synthetic route, and diverse luminescent properties.     

VUV photoluminescence of (Gd,Zn)PO4:Tb3+ phosphors synthesized by ultrasonic spray pyrolysis

High-quality (Gd_0.955−xZn_0.045)PO₄:xTb³⁺ (0.06≤x≤0.15) green phosphors were synthesized by ultrasonic spray pyrolysis. With an increase of Tb³⁺ content, the emission intensities caused by the ⁵D₄→^{7 F} _J (J = 3, 4, 5, and 6) and ⁵D₃→⁷F_J (J = 4, 5, and 6) transitions of Tb³⁺ increased and decreased, respectively, allowing a purer green emission. The emission intensity of (Gd_0.805Zn_0.045)PO₄:0.15Tb³⁺ at 544 nm was 53.0% stronger than that of (Gd_0.895Zn_0.045)PO₄:0.06Tb³⁺. The emission intensity and the green color purity were remarkably improved by increasing Tb³⁺ content in (Gd_0.955−xZn_0.045)PO₄:xTb³⁺.     

Enhanced photoluminescence of GdPO4:Tb under VUV excitation by controlling ZnO content and annealing temperature

High-quality Zn-free and added GdPO₄:Tb³ green phosphors, i.e., fine size as well as smooth and spherical morphologies, were synthesized by ultrasonic spray pyrolysis. The influence of Zn²⁺ content and annealing temperature on the photoluminescence properties of the GdPO₄:Tb³ phosphors annealed at 800-1100 °C was investigated. The addition of Zn²⁺ for Gd³⁺ was highly effective for improving the photoluminescence properties of GdPO₄:Tb³. The Zn added GdPO₄:Tb³ phosphors with Zn/Gd = 0.045/0.805 showed the strongest emission of the prepared phosphors. The emission intensity at 544 nm for the GdPO₄:Tb³ phosphors with Zn/Gd = 0.045/0.805 annealed at 900 °C was 496% stronger than that at 800 °C.     

Citric based sol-gel synthesis and luminescence characteristics of CaLa2ZnO5:Euphosphors for blue LED excited white LEDs

A novel class of orange-red phosphors namely CaLa₂ZnO₅ (CLZ) doped with Eu³⁺ ions were prepared by adopting citrate based sol-gel method. Those were thoroughly characterized by means of XRD, SEM, Tg-DTA, photoluminescent (PL) spectral profiles. PL studies reveal that its emission intensity strongly depends on sintering temperature as well as the dopant ion (Eu³⁺) concentration. Eu³⁺ ion doped CaLa₂ZnO₅ phosphor has a strong excitation at 468 nm, which correspond to the popular emission line from a GaN based blue light-emitting diode (LED) chip. The influence of the preparation method on the luminescence property was studied by comparing the emission performance of phosphors prepared by sol-gel and solid-state reaction methods along with a commercial red phosphor Y₂O₂S:Eu³⁺. Thus, the intense red emission (⁵D₀ → ⁷F₂) of the Eu³⁺ doped CLZ phosphors under blue excitation suggests them to be a potential candidate for the production of white light by blue LEDs.     

Synthesis and luminescence properties of Bi-doped YVO4 phosphors

YVO₄:Bi³⁺ phosphors have been prepared by a convenient high-temperature solid-state method. X-ray diffraction (XRD), scanning electron microscopy (SEM) and photoluminescence (PL) technologies are used to study the luminescence properties of YVO₄:Bi³⁺ phosphors. The emission and excitation spectra of Bi³⁺ in the YVO₄ lattice have been investigated at room temperature. The excitation band peaks at 330 nm in a region among 250-400 nm, and the emission spectrum exhibits an intense yellowish-white broad emission centered at about 543 nm covering from 400 nm to 800 nm. The full width at half maximum (FWHM) is about 144 nm. The color coordinates of the as-synthesized YVO₄:Bi³⁺ phosphors are in a range of x = 0.358-0.374, y = 0.482-0.496. The dependence of the luminescence intensity on Bi³⁺ concentrations and heat treatment condition has also been discussed. In addition, we found that a little amount of flux NH₄Cl could enhance the Bi³⁺ luminescence intensity.     

Synthesis, characterization and magnetic properties of complex oxides Ln2Mn2/3Re4/3O7 (Ln = Er, Y) and Y2Zn2/3Re4/3O7

Complex oxides Ln₂Mn_2/3Re_4/3O₇ (Ln = Y, Er) and Y₂Zn_2/3Re_4/3O₇ with a zirkelite structure and hexagonal unit cells (space group P3₁21, z = 6) have been obtained. Static and dynamic magnetic susceptibility measurements show that these oxides possess spin-glass behavior at low temperatures. Valence combinations of d-metals in the oxides are Mn²⁺(Zn²⁺)–Re⁵⁺. It is supposed that the examined specimens Ln₂Mn_2/3Re_4/3O₇ (Ln = Y, Er) contain the second magnetic phase of an unknown composition.     

Effect of Yb concentration on the structures and upconversion luminescence properties of Y2O3:Er ultrafine phosphors

Y₂O₃:Er³⁺ ultrafine phosphors with a varying Yb³⁺ ion concentration were prepared by a urea homogeneous precipitation method. The results of XRD show that all the samples are of a pure cubic structure and the average crystallite sizes can be calculated as 45, 34, and 28 nm for Y₂O₃:Er³⁺ ultrafine phosphors with Yb³⁺ ion concentrations of 0, 10%, and 20%, respectively. The lattice constant and cell volume of the ultrafine phosphors decrease with enhancing Yb³⁺ ion concentration. The upconversion luminescence spectra of all the samples were studied under 980 nm laser excitation. The strong green and red upconversion emission were observed, and attributed to the ²H_11/2 → ⁴I_15/2, ⁴S_3/2 → ⁴I_15/2 and ⁴F_9/2 → ⁴I_15/2 transitions of Er³⁺, respectively. The intensity of red emission increases with increasing Yb³⁺ ion concentration. The effect of Yb³⁺ ion concentration on the structures and upconversion luminescence mechanism were discussed.     

Hydrothermal synthesis and photoluminescence of Ce and Tb doped La2Sn2O7 nanocrystals

Phase-pure Ce-/Tb-doped and co-doped lanthanum stannates (La₂Sn₂O₇) nanocrystals were synthesized by a co-precipitation process combined with hydrothermal techniques without any further heat treatment. The crystal structure, particle size, morphologies, and photoluminescence properties of the as-synthesized products were investigated by X-ray powder diffraction (XRD), transmission electron microscopy (TEM), and photoluminescence spectroscopy (PL). The as-prepared samples were single-phase cubic pyrochlore-type nanocrystals with a typical size of 10-20 nm. PL spectra showed a dominating green-emitting line around 544 nm attributing to ⁵D₄-⁷F₅ magnetic dipole transition for Tb³⁺ doped and Ce³⁺/Tb³⁺ co-doped La₂Sn₂O₇ nanocrystals. Meanwhile, the concentration quenching phenomenon was observed in both La_2−xTb_xSn₂O₇ and La_1.82−xCe_xTb_0.18Sn₂O₇ nanocrystals. Furthermore, an interesting enhancement of the energy transfer induced green emission was observed in the as-synthesized La_1.82−xCe_xTb_0.18Sn₂O₇ nanocrystals.     

Hydrothermal synthesis of YBO3:Tb microflowers and their luminescence properties

Three-dimensional flowerlike YBO₃:Tb³⁺ phosphors have been successfully prepared by an efficient surfactant-free hydrothermal process directly without further sintering treatment. X-ray diffraction (XRD), scanning electron microscopy (SEM), transmission electron microscopy (TEM), energy-dispersive X-ray (EDS) spectrometry, selected area electron diffraction (SAED), photoluminescence (PL) spectra were used to characterize the samples. The as-obtained samples present flowerlike agglomerates composed of nanoflakes with thickness of 20 nm and high crystallinity in spite of the moderate reaction temperature of 180 °C. The reaction mechanism has been considered as a dissolution/precipitation mechanism; the self-assembly evolution process has been proposed on homocentric layer-by-layer growth style. The different luminescent intensity with different molar ratio of Y-Tb [Y:Tb = 8:2; 7:3; 6:4; 5:5; 4:6], YBO₃:Tb³⁺ phosphors exhibit different light (white, red, green) under ultraviolet excitation, which might find potential applications in the fields such as light display systems and optoelectronic devices.     

Spectroscopic properties of Yb in NaYbP2O7 diphosphate single crystals

Yb³⁺ absorption and fluorescent emissions were investigated for NaYbP₂O₇ diphosphate single crystals. The interpretation of electronic energy level positions has been done by using the comparison of absorption and emission spectra with those of vibronic sideband energy positions from Raman and IR absorption spectroscopies. The Yb³⁺ energy levels scheme in this host was drawn. The decay time for infrared Yb³⁺ (⁵F_5/2 excited state) fluorescence was in the range of 1–2 ms. The interest feature is leading to broad emission band at room temperature from 940 nm to 1100 nm, which seems of high interest for ultra-short laser pulse production.     

Synthesis, photoluminescence, thermoluminescence and dosimetry properties of novel phosphor KSr4(BO3)3:Ce

Polycrystalline powder sample of KSr₄(BO₃)₃ was synthesized by high-temperature solid-state reaction. The influence of different rare earth dopants, i.e. Tb³⁺, Tm³⁺ and Ce³⁺, on thermoluminescence (TL) of KSr₄(BO₃)₃ phosphor was discussed. The TL, photoluminescence (PL) and some dosimetric properties of Ce³⁺-activated KSr₄(BO₃)₃ phosphor were studied. The effect of the concentration of Ce³⁺ on TL intensity was investigated and the result showed that the optimum Ce³⁺ concentration was 0.2 mol%. The TL kinetic parameters of KSr₄(BO₃)₃:0.002 Ce³⁺ phosphor were calculated by computer glow curve deconvolution (CGCD) method. Characteristic emission peaking at about 407 and 383 nm due to the 4f⁰5d¹ → ²F_{(5/2, 7/2)} transitions of Ce³⁺ ion were observed both in PL and three-dimensional (3D) TL spectra. The dose–response of KSr₄(BO₃)₃:0.002 Ce³⁺ to γ-ray was linear in the range from 1 to 1000 mGy. In addition, the decay of the TL intensity of KSr₄(BO₃)₃:0.002 Ce³⁺ was also investigated.     

Growth of Mn, Co and Ni-doped near-stoichiometric LiNbO3 by Bridgman method using K2O flux

The near-stoichiometric LiNbO₃ (SLN) single crystals doped Mn²⁺, Co²⁺ and Ni²⁺ in 0.5 mol% concentration in the raw compositions were grown by the Bridgman method under the conditions of taking K₂O as flux, a high temperature gradient (90–100 °C/cm) for solid–liquid interface. The XRD, absorption spectra, excitation spectra and emission spectra have been carried out. From the absorption edges of Mn²⁺, Co²⁺ and Ni²⁺-doped SLN crystals, the molar ratio of [Li⁺]/[Nb⁵⁺] are estimated to be about 0.977. The absorption spectra of Mn²⁺:SLN have shown a broad absorption band centered at 571 nm (⁶A_1g(⁶S) → ⁴T_1g(⁴G)), three absorption peaks at 520, 549 and 612 nm (overlapping of the ⁴T₁(F)–⁴A₂(F), ⁴T₁(F)–⁴T₁(P)), and a wide absorption band at 1400 nm (⁴T₁(F) → ⁴T₂(F)) of Co²⁺:SLN, Ni²⁺:SLN, and five absorption peaks at 381 nm (³A_2g(F) → ³T_1g(P)), 733 nm (³A_2g(F) → ³T_1g(F)), 1280 nm (³A_2g(F) → ³T_2g(F)), 430 nm (³A_2g(F) → ¹T_2g(D)), and 840 nm (³A_2g(F) → ¹E(D)) of Ni²⁺:SLN were observed. A red emission at 612 nm (⁴T_1g(⁴G) → ⁶A_1g(⁶S)) for Mn²⁺:SLN, a red emission at 775 nm (⁴T₁(P) → ⁴T₁(F)) for Co²⁺:SLN, and a green emission at 577 nm (¹T_2g(D) → ³A_2g(F)) and a red emission at 820 nm (¹T_2g(D) → ³T_2g(F)) for Ni²⁺:SLN were observed under excited by 416, 520 and 550 nm lights, respectively. The concentration distribution of Mn²⁺, Co²⁺and Ni²⁺ ion in SLN crystals was investigated primarily from the absorption and emission spectra for various parts. The effective distribution coefficient for Mn²⁺ was less than 1. While, for Co²⁺ and Ni²⁺ were more than 1.     

Photoluminescence and time-resolved luminescence spectroscopy of novel NaBa4(BO3)3:Tb phosphor

This paper reports the photoluminescence (PL) properties of Tb³⁺ in NaBa₄(BO₃)₃, as well as the time-resolved luminescence properties. The PL excitation spectrum exhibits intense f → f transition absorption; the PL emission spectrum shows the strongest ⁵D₄ → ⁷F₅ emission at 540 nm. The relative intensity of ⁵D₃ emission is much weaker than that of ⁵D₄ emission even in the samples with lower Tb³⁺ concentration. The ⁵D₃ → ⁵D₄ cross-relaxation produces a marked increase in the ⁵D₃ decay rate with increasing Tb³⁺ concentrations and introduces a non-exponential component into the initial part of the decay. The dipole-dipole interaction is found to be responsible for the cross-relaxation. The decay curves of ⁵D₄ → ⁷F₅ transition exhibit an initial rise phenomenon. The two exponential fitting indicates that the initial slow rise is attributed to the ⁵D₃ → ⁵D₄ cross-relaxation process.     

Synthesis and phosphorescence properties of Mn, La and Ho in MgAl2Si2O8

Mn⁴⁺, La³⁺ and Ho³⁺ doped MgAl₂Si₂O₈-based phosphors were first synthesized by solid state reaction. They were characterized by thermogravimetry (TG), differential thermal analysis (DTA), X-ray powder diffraction (XRD), photoluminescence (PL) and scanning electron microscopy (SEM). The phosphors were obtained at about 1300 °C. They showed broad red and fuchsia-pink emission bands in the range of 610-715 nm and had a different maximum intensity when activated by UV illumination. Such a fuchsia-pink emission can be attributed to the intrinsic d-d transitions of Mn⁴⁺.     

Subsolidus phase relations of the SrO–Ta2O5–CuO system at 900 °C in air

The subsolidus phase relations of the SrO–Ta₂O₅–CuO system were investigated in air. The samples were equilibrated at 900 °C. The ternary oxide Sr₃Ta₂CuO₉ compound is stable under these conditions. This phase presents a solid solution range, its actual composition being Sr₃Ta_2−xCu_1+xO_9+δ with 0.0 ≤ x ≤ 0.2. Up to about 5 at.% Cu can be incorporated in the Sr_3−xTa_1+xO_5.5+δ phase. Similarities with the SrO–Nb₂O₅–CuO system are discussed.     

Luminescence and energy transfer of Mn and Tb in Y3Al5O12 phosphors

Mn²⁺ is an excellent luminescent ion with variable color from green, yellow to red in different hosts and has been widely utilized in recent years. The luminescent intensity of Mn²⁺ in many hosts is so low that the correlative application is restricted. In the present paper, two methods, i.e. employing a charge compensator and introducing a sensitizer, were adopted to enhance the luminescence of Mn²⁺ in Y₃Al₅O₁₂ (YAG). By employing Si⁴⁺ as a charge compensator, the doping content of Mn²⁺ (x) in Y₃Mn_xAl_5−2xSi_xO₁₂ can be lifted up to 0.4. Mn²⁺ in YAG emits orange light in a broad band. The peak wavelength shifts from 586 to 593 nm with the increasing x. The luminescent intensity of Mn²⁺ reaches its maximum when x = 0.1. Co-doping Tb³⁺ into Mn²⁺ doped YAG, the sensitization effect of Tb³⁺ on Mn²⁺ was observed clearly. The resonance energy transfer from Tb³⁺ to Mn²⁺ occurs because there is a well overlapping between emission spectrum of Tb³⁺ and excitation spectrum of Mn²⁺. A reasonable explanation for the sensitization effect of Tb³⁺ on the luminescence of Mn²⁺ was brought forward.