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.     

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.     

A novel red-emitting phosphors K2Ba (MoO4)2: Eu, Sm and improvement of luminescent properties for light emitting diodes

The novel red-emitting phosphors K₂Ba(MoO₄)₂: Eu³⁺, Sm³⁺ were prepared by solid-state reaction and their crystal structures, photo luminescent characteristics were investigated. The results show that all samples can be excited efficiently by UV (397 nm) and blue (466 nm) light, which are coupled well with the characteristic emission from UVLED and blue LED, respectively. A small amount of Sm³⁺, acting as a sensitizer, increased the energy absorption around 400 nm. In the Eu³⁺-Sm³⁺ co-doped system, both Eu³⁺ and Sm³⁺ f-f transition absorptions are observed in the excitation spectra, the intensities of the main emission line (⁵D₀ → ⁷F₂ transition of Eu³⁺ at 616 nm) are strengthened because of the energy transition from Sm³⁺ to Eu³⁺. The doping concentration of Eu³⁺-Sm³⁺ was optimized. The approach to charge compensation was used: Ba²⁺ → Eu³⁺/Sm³⁺ + X⁻ (X = F, Cl, and Br), and the influence of charge compensation on the luminescent intensity of phosphors is investigated.     

Color-conversion and photoluminescence properties of Ba2MgW(Mo)O6:Eu phosphor

Compounds B₂AXO₆:Eu (B = Ba, Sr; A = Ca; and X = W, Mo) have recently been investigated and suggested to be color-conversion phosphor for WLED devices. In this work, we investigated the photoluminescence properties of the analogues Ba₂MgXO₆:Eu (X = W and Mo) and the energy transfer from W(Mo)O₆ groups to Eu³⁺ ions within the phosphors. The phase structure, UV-vis diffuse reflectance spectrum, photoluminescence properties and decay of Ba₂MgW_(1−x)Mo_xO₆:Eu were studied as a function of the W/Mo ratio. It was found that these phosphors showed excellent color-conversion capability from near-UV to orange-red light. The color-conversion process was considered to be performed by energy transferring from MoO₆ groups to doped Eu³⁺ ions. The MoO₆ → Eu³⁺ energy transfer efficiency could be greatly enhanced by partial substitution of Mo by W. The structure and photoluminescence properties of Ba₂AW_0.5Mo_0.5O₆:Eu (A = Ca and Mg, respectively) compounds were also investigated to reveal the effect of the Eu³⁺ ion coordination environment on its photoluminescence properties.     

Luminescent properties of Na3Gd1−xEux(PO4)2 and energy transfer in these phosphors

A series of Eu³⁺ activated Na₃Gd_1−xEu_x(PO₄)₂ (0 ≤ x ≤ 1) phosphors were synthesized by solid-state reaction method. The structures and photo-luminescent properties of these phosphors were investigated at room temperature. The results of XRD patterns indicate that these phosphors are isotypic to the orthorhombic Na₃Gd(PO₄)₂. The excitation spectra indicate that these phosphors can be effectively excited by near UV (370-410 nm) light. The intensities of magnetic dipole transition ⁵D₀ → ⁷F₁ and forced electric dipole transition ⁵D₀ → ⁷F₂ are comparable, and the energy ratio (⁵D₀ → ⁷F₁/⁵D₀ → ⁷F₂) is 1.1. The emission spectra exhibit strong reddish orange performance (CIE chromaticity coordinates: x = 0.62, y = 0.38), which is due to the ⁵D₀ → ⁷F_J transitions of Eu³⁺ ions. The correlation between the structure and the photo-luminescent properties of the phosphors was studied. The energy transfer and concentration quenching of the phosphors were discussed. Na₃Gd_1−xEu_x(PO₄)₂ has a potential application for white light-emitting diodes.     

Spectroscopic properties of Eu(III) complexes with 2,6-lutidine N-oxide and its bromo-methoxy derivative; of Eu(LNO)6, Eu(LNO)5L, EuCl3(BrMLNO)3 and Eu(LNO)8 type

Luminescence, luminescence excitation and electronic absorption spectra of europium salts of isomeric lutidine N-oxide derivatives were studied at 293 and 77 K. The role of radiative and non-radiative processes in emission intensity is discussed. The absorption transitions to the ³F_J, ⁵D_J, ⁵L_J and ⁵G_J levels and emissions from the ⁵D₀ and ⁵D₂ levels were detected. The role of CT transition inside the ligand and its influence on the LMCT transition is analysed. The co-ordinating function of the lutidine N-oxide group is discussed using IR spectroscopy.     

Preparation and luminescent properties of Eu doped Sr3La(PO4)3 phosphor

Eu²⁺-doped Sr₃La(PO₄)₃ phosphors were synthesized by solid-state reaction method. Their luminescent properties were investigated. The phosphor could be excited by ultraviolet light effectively. The emission spectra exhibit two emission peaks located at 418 nm and 500 nm, respectively. These two peaks originated from two different luminescent centers, respectively. One is nine-coordinated Eu(I) center, other is six-coordinated Eu(II) center. It was found that the doping concentration of Eu²⁺ ions affected the shape of emission spectra. As the doping concentration increasing, Eu²⁺ ions are more likely to form Eu(I) luminescent centers and emit purple light.     

Multiwavelength excited novel red-emitting phosphor Eu-activated Li2Zn2(MoO4)3

Eu³⁺-activated Li₂Zn₂(MoO₄)₃ multiwavelength excited red-emitting phosphors were synthesized via a solid state reaction. The structure and photoluminescence characteristics were investigated by X-ray powder diffraction and fluorescent spectrophotometry, respectively. The excitation spectrum included a strong broadband ranging from 250 to 350 nm and some sharp peaks at 363, 384, 395, 465, and 533 nm, which matchs the radiations of near-UV or blue light-emitting diodes chip well. Upon excitation either of near-UV or blue even green light, the intense red emission with 615 nm peak can be observed, which is ascribed to the ⁵D₀-⁷F₂ transition of Eu³⁺ ions. The chromaticity coordinates (x = 0.65, y = 0.34) of the as-obtained phosphor is very close to the National Television Standard Committee standard values (x = 0.67, y = 0.33). All these characteristics suggest that Eu³⁺-doped Li₂Zn₂(MoO₄)₃ wavelength-conversion material to be suitable candidate red component for phosphor-converted white light-emitting diodes.     

Spectroscopic analysis of Nd:Ca3Gd2(BO3)4 crystal and laser operating at 1.06 μm

Laser crystal Ca₃Gd₂(BO₃)₄ of high quality activated with Nd³⁺ has been grown successfully by Czochralski technique. The product was characterized by means of X-ray diffraction (XRD) powder investigation. The absorption spectra along a-, b- and c-axes were measured and investigated according to the Judd-Ofelt theory. The fluorescence properties were pursued and the factors influencing the fluorescence quantum efficiency were indicated. Xe lamp-pumped pulsed laser results were also obtained and the highest output power was up to 62 mJ.     

Luminescent properties of UV excitable blue emitting phosphors MSr4(BO3)3:Ce (M = Li and Na)

A series of Ce³⁺ doped novel borate phosphors MSr₄(BO₃)₃ (M = Li or Na) were successfully synthesized by traditional solid-state reaction. The crystal structures and the phase purities of samples were characterized by powder X-ray diffraction. The optimal concentrations of dopant Ce³⁺ ions in compound MSr₄(BO₃)₃ (M = Li or Na) were determined through the measurements of photoluminescence spectra of phosphors. Ce³⁺ doped phosphors MSr₄(BO₃)₃ (M = Li or Na) show strong broad band absorption in UV spectral region and bright blue emission under the excitation of 345 nm light. In addition, the temperature dependences of emission spectra of M_1+xSr_4−2xCe_x(BO₃)₃ (M = Li or Na) phosphors with optimal composition x = 0.05 for Li and x = 0.09 for Na excited under 355 nm pulse laser were also investigated. The experimental results indicate that the M_1+xSr_4−2xCe_x(BO₃)₃ (M = Li or Na) phosphors are promising blue emitting phosphors pumped by UV light.     

Effects of sucrose concentration on morphology and luminescence performance of Gd2O3:Eu nanocrystals

Red Gd₂O₃:Eu nanophosphors were prepared by novel sucrose-assisted combustion method. The sucrose hydrolysis and complexing procedures were discussed by the Fourier transform infrared spectroscopy (FTIR) analysis. The effect of sucrose-to-metal ratio (S:M) on morphology and luminescence intensity of Gd₂O₃:Eu nanocrystals were investigated. And the optimum ratio was found to be S:M = 7:1, as confirmed by the results of scanning electron microscope (SEM), transmission electron microscope (TEM) and photoluminescence (PL) measurements. The highest photoluminescence emission from the particles obtained at S:M = 7:1 was about 85% of the commercial red phosphors.     

Simultaneous tuning for excitation and emission of N doped Sr2SiO4:Eu for white light LEDs

Tunable color point and efficient excitation are two important challenges for improving white light LEDs. In this paper, red-shift in the emission spectra of Sr₂SiO₄:Eu has been achieved, and the excitation band has been tuned to fit the blue LED chips simultaneously by doping N into the host. XRD results showed that the unit cell volume markedly increased after nitridation. Moreover, nitridation resulted in the increase in weight loss, which can be attributed to the substitute of Si-O bonds by Si-N bonds. The effect of nitridation on the luminescence properties was well discussed.     

Preparation and luminescent characteristics of Sr3RE2(BO3)4:Dy (RE = Y, La, Gd) phosphors for white LED

Dysprosium-activated Sr₃RE₂(BO₃)₄ (RE = Y, La, Gd) phosphors were synthesized by a high temperature solid-state reaction method. The phase uniformity of the phosphors was characterized by X-ray powder diffraction (XRD) and the luminescence characteristics were investigated. The excitation spectra at 575 nm emission show strong spectral bands in the region of 300-500 nm. The emission spectra of the phosphors with 365 nm excitation show three bands centered at 484 nm, 575 nm and 680 nm, which originate from the transitions of ⁴F_9/2 → ⁶H_15/2, ⁴F_9/2 → ⁶H_13/2 and ⁴F_9/2 → ⁶H_11/2 of Dy³⁺, respectively. The effect of Dy³⁺ concentration on the emission intensity of the phosphors was investigated. The fluorescence decay curves for ⁴F_9/2 → ⁶H_13/2 excited at 365 nm and monitored at λ_em of 575 nm were measured. The decay times decreased slowly with increasing Dy³⁺ doping concentration due to a trap capturing to resonance fluorescence transfer of the activated ions and due to the exchange interactions between activated ion pairs. In order to determine the type of interaction between activated ions, the concentration dependence curves (lg(I/x) versus lg x) of Sr₃RE₂(BO₃)₄:Dy³⁺ (RE = Y, La, Gd) were plotted. The concentration quenching mechanism of the ⁴F_9/2 → ⁶H_13/2 (575 nm) transition of Dy³⁺ is the d-d interaction. All results indicate these phosphors are promising white-color luminescent materials.     

Synthesis, characterization, shape-preserved transformation, and optical properties of La(OH)3, La2O2CO3, and La2O3 nanorods

A simple method to directly synthesize stable and crystalline pure phase La(OH)₃ nanorods, with a diameter of around 15 nm and lengths in the range of 120-200 nm, was developed using cationic surfactant (cetyltrimethylammonium bromide, CTAB). The obtained La(OH)₃ nanorods can be successfully converted to La₂O₂CO₃ and La₂O₃ nanorods via calcination under appropriate conditions. Analytical methods such as X-ray diffraction (XRD) spectra, Fourier transformed infrared (FTIR) spectrum, differential scanning calorimetry and thermogravimetric analysis (DSC-TGA), transmission electron microscopy (TEM), and high-resolution TEM (HRTEM) were employed to characterize the morphology and microstructure of the final products. The results reveal that La(OH)₃ nanorods were shape-preserved and transformed to La₂O₂CO₃ nanorods at 400 °C for 2 h and to La₂O₃ nanorods at 800 °C for 2 h, respectively. TEM images indicate that the as-obtained La₂O₂CO₃ and La₂O₃ entirely consist of uniform nanorods in high yield with diameters of about 15 nm and 23 nm, lengths of 200-300 nm and 300-500 nm, respectively. The formation mechanism of the La(OH)₃, La₂O₂CO₃ and La₂O₃ nanorods was investigated. Room-temperature photoluminescence (RTPL) properties were investigated under the excitation of 275 nm. The ⁵D₃ → ⁷F_j (j = 2-6) emission peaks at the wavelength below 500 nm were found in the RTPL spectra.     

Preparation and luminescence characterization of new carbonate (Y2(CO3)3·nH2O:Eu) phosphors via the hydrothermal route

A new Eu³⁺-activated Y₂(CO₃)₃·nH₂O phosphor was successfully prepared via the hydrothermal process using urea as a reaction agent. Y₂(CO₃)₃·nH₂O:Eu³⁺ phosphors displayed an intense red emission at 615 nm due to the ⁵D₀ → ⁷F₂ transition of Eu³⁺ ions under 254 nm excitation. The intensity of this emission was significantly increased with a rise in the hydrothermal temperatures. The study of photoluminescence properties demonstrated that Y³⁺ ions were replaced by Eu³⁺ ions in the host lattice at the 9-coordination sites. With an increase in heating temperatures, the morphology of Y₂(CO₃)₃·nH₂O:Eu³⁺ powders changed from a spherical to a rod-like shape. Calcination at elevated temperatures resulted in thermal decomposition of Y₂(CO₃)₃·nH₂O:Eu³⁺ to form Y₂O₃:Eu³⁺. The formed Y₂O₃:Eu³⁺ powder exhibited a rod-like morphology with an intense red emission.     

Blue excited photoluminescence of Pr doped CaBi2Ta2O9 based ferroelectrics

Pr³⁺ doped CaBi₂Ta₂O₉ based bismuth layered-structure oxides were synthesized by a simple solid state reaction method. The photoluminescence properties of the samples were investigated by excitation and emission spectra. Photoluminescence excitation spectra show that the samples have broad blue excitation band located at 430-510 nm, which covers the emission wavelength of commercial blue light-emitting diode (LED) chips. Upon the excitation of 450 nm light, a novel red emission centered at 621 nm of Pr doped CaBi₂Ta₂O₉ makes it useful in the white LEDs. In addition, it was also found that the photoluminescence can been improved by partial substituting Sr for Ca. These Pr³⁺ doped CaBi₂Ta₂O₉ based ferroelectrics could possibly be used as a multifunctional material for a wide range of applications, such as integrated electro-optical devices.     

Luminescence based on energy transfer in xerogels doped with Ln2−xTbx(WO4)3

This paper presents preparation, optical absorption and photoluminescence properties of luminescent materials consisting of Ln_2−xTb_x(WO₄)₃ [where Ln = Gd(III) or La(III)] incorporated into silica xerogel. Photoluminescence behaviour of the salt in the rigid matrix was studied by the luminescence spectroscopy. The excitation spectra of the system Ln_2−xTb_x(WO₄)₃ show an intense broad band with a maximum placed at about 240 nm. This band is attributed to ligand–metal charge transfer (LMCT) inside the tungstate group. On the other hand, Tb³⁺ ion exhibits its characteristic emission in the material. Owing to energy transfer from the excited tungstate groups to the Tb³⁺ ions the emission intensity is improved. The energy transfer from WO₄²⁻ group to Tb(III) ion is particularly effective for such dopants as Gd_0.4Tb_1.6(WO₄)₃ or La_0.8Tb_1.2(WO₄)₃ incorporated into SiO₂ xerogel. Concentration of the emission quenchers such as water molecules and OH groups was reduced by thermal treatment. The high emission intensity and easy preparation of these systems make them potential candidates for application as luminescent materials.     

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.