Synthesis and luminescent properties of LaPO4:Eu microspheres

LaPO₄:Eu³⁺ microspheres were synthesized, using LaCl₃, EuCl₃ and (NH₄)₂HPO₄ as starting materials. The morphology, formation mechanism, and luminescent property of samples were systemically studied. X-ray diffraction (XRD) and infrared spectroscopy (IR) show that LaPO₄:Eu³⁺ microspheres have a pure monoclinic phase. Cetyltrimethyl ammonium bromide (CTAB) usually forms spherical micelles above a critical micelle concentration, which plays an important role in the formation of LaPO₄:Eu³⁺ microspheres. The excitation spectrum of LaPO₄:Eu³⁺ microspheres consists of several sharp lines due to the direct excitation of the Eu³⁺ cations from the ground state to higher levels of the 4f-manifold. The emission intensity of microspheres is higher than irregular particles because of the lowlier surface area. The lifetimes of Eu³⁺ ions in the LaPO₄:Eu³⁺ microspheres are determined to be 2.41 ms.     

A new yellowish green luminescent material SrMoO4:Tb

A novel yellowish green phosphor tervalent terbium (Tb³⁺) doped strontium molybdate (SrMoO₄) was synthesized by conventional solid-state reaction method and its crystal structure and luminescent properties are investigated in this paper. The X-ray diffraction patterns (XRD) showed that the phosphor sintered at 750 °C for 3 h was a pure SrMoO₄ phase. The excitation spectrum consisted of two bands and the two excitation peaks located at 375 nm and 488 nm respectively. The emission spectrum was composed of four narrow bands, in which the strongest emission was located at 548 nm. The particle size analysis indicated that the median particle size D₅₀ = 2.89 μm and range of particle size distribution was narrow. These results showed that the SrMoO₄:Tb³⁺ phosphor was a promising yellowish green phosphor for ultraviolet light emitting diode (UVLED) and blue LED based white LED. The appropriate concentration of Tb³⁺ was 5 mol% for the highest emission intensity at 548 nm. Natrium ion (Na⁺) was found to be a promising charge compensator for SrMoO₄:Tb³⁺ phosphor.     

Synthesis and Luminescence of BiPO4:Tb3+ Nanowires by a Hydrothermal Process

We synthesized BiPO₄:Tb³⁺ nanowires by the hydrothermal process. The synthesized nanoparticles were measured using XRD, SEM, and luminescence spectrophotometry. The XRD patterns and SEM images indicate that reaction time induces phase changes but has no obvious influence on size and morphology. All samples show characteristic excitation and emission bands of Tb³⁺ ions. The BiPO₄:Tb³⁺ samples reacted for 3.5 h showed the highest emission intensity, which was induced by the pure monoclinic phase.     

Photoluminescence properties of Y2O3:Tb and YBO3:Tb green phosphors synthesized by hydrothermal method

In this work, two Tb³⁺ activated green phosphors: Y₂O₃:Tb³⁺ and YBO₃:Tb³⁺ were prepared by hydrothermal method. Photoluminescence properties of both phosphors were studied in details. Both phosphors exhibit similar luminescent characteristics symbolized by the dominant green emission at 545 nm. Concentration quenching occurs at the Tb³⁺ concentration of 1.60 atomic% and 2.57 atomic% for Y₂O₃:Tb³⁺ and YBO₃:Tb³⁺, respectively. Luminescence decay properties were characterized to better understand the mechanism of concentration quenching. Based on the calculation, the concentration quenching in both phosphors was caused by the dipole–dipole interaction between Tb³⁺ ions.     

White light generation in Al2O3:Ce:Tb:Mn films deposited by ultrasonic spray pyrolysis

Aluminium oxide (Al₂O₃) films doped with CeCl₃, TbCl₃ and MnCl₂ were deposited at 300 °C with the ultrasonic spray pyrolysis technique. The films were analysed using the X-ray diffraction technique and they exhibited a very broad band without any indication of crystallinity, typical of amorphous materials. Sensitization of Tb³⁺ and Mn²⁺ ions by Ce³⁺ ions gives rise to blue, green and red simultaneous emission when the film activated by such ions is excited with UV radiation. The overall efficiency of such energy transfer results to be about 85% upon excitation at 312 nm. Energy transfer from Ce³⁺ to Tb³⁺ ions through an electric dipole-quadrupole interaction mechanism appears to be more probable than the electric dipole-dipole one. A strong white light emission for the Al₂O₃:Ce³⁺(1.3 at.%):Tb³⁺(0.2 at.%):Mn²⁺(0.3 at.%) film under UV excitation is observed. The high efficiency of energy transfer from Ce³⁺ to Tb³⁺ and Mn²⁺ ions, resulting in cold white light emission (x = 0.30 and y = 0.32 chromaticity coordinates) makes the Ce³⁺, Tb³⁺ and Mn²⁺ triply doped Al₂O₃ film an interesting material for the design of efficient UV pumped phosphors for white light generation.     

A novel green luminescent material AlPO4:Tb

A novel green phosphor Tb³⁺ doped AlPO₄ was synthesized by conventional solid-state reaction method. The phosphor showed prominent luminescence in green due to the ⁵D₄-⁷F₅ transition of Tb³⁺. Structural characterization of the luminescent material was carried out with X-ray powder diffraction (XRD) analysis. The XRD measurements indicated that there are no crystalline phases other than AlPO₄. Luminescence properties were analyzed by measuring the excitation and photoluminescence spectra. Photoluminescence measurements indicated that the phosphor exhibited bright green emission at about 542 nm under UV excitation. It is shown that the 3 mol% of doping concentration of Tb³⁺ ions in AlPO₄:Tb³⁺ phosphor is optimum. The measured chromaticity for the phosphors AlPO₄:Tb³⁺ under UV excitation is (0.32, 0.53).     

Enhanced G4 emission in NaLaF4: Pr, Yb and charge transfer in NaLaF4: Ce, Yb studied by fourier transform luminescence spectroscopy

A high resolution luminescence study of NaLaF₄: 1%Pr³⁺, 5%Yb³⁺ and NaLaF₄: 1%Ce³⁺, 5%Yb³⁺ in the UV to NIR spectral range using a InGaAs detector and a fourier transform interferometer is reported. Although the Pr³⁺(³P₀ → ¹G₄), Yb³⁺(²F_7/2 → ²F_5/2) energy transfer step takes place, significant Pr³⁺¹G₄ emission around 993, 1330 and 1850 nm is observed. No experimental proof for the second energy transfer step in the down-conversion process between Pr³⁺ and Yb³⁺ can be given. In the case of NaLaF₄: Ce³⁺, Yb³⁺ it is concluded that the observed Yb³⁺ emission upon Ce³⁺ 5d excitation is the result of a charge transfer process instead of down-conversion.     

Photoluminescence and radioluminescence of pure and Ce activated Na3Gd(PO4)2

The spectroscopic properties of Na₃Gd(PO₄)₂ and Na₃Gd(PO₄)₂:Ce³⁺ phosphors in the VUV-UV spectral range were investigated. Five excitation bands of Ce³⁺ ions at Gd³⁺ sites are observed at wavelengths of 205, 246, 260, 292, and 321 nm. Doublet Ce³⁺ 5d → 4f emission bands are observed at 341 and 365 nm with a decay constant τ_1/e around 26 ns. The X-ray excited luminescence of Na₃Gd_0.99Ce_0.01(PO₄)₂ at room temperature shows a photon yield of ∼17,000 photons/MeV of absorbed X-ray energy.     

The influence of the Pr 4f5d configuration on the S0 emission efficiency and lifetime in LaPO4

The photoluminescence and excitation spectra of Pr³⁺ activated LaPO₄ has been investigated in the 1.6-300 K temperature region. At room temperature, the luminescence of LaPO₄:Pr³⁺ is composed of the interconfigurational 4f¹5d¹ → 4f² emission transitions. However, in the 1.6-60 K temperature range, the emission spectrum also consists of the intraconfigurational emission transitions that emanate from the ¹S₀ state. A radiative lifetime of 145 ns is measured for the Pr³⁺¹S₀ → ¹I₆ emission transition in LaPO₄. This is one of the shortest radiative lifetime observed for this transition in a solid. The energy position of the Pr³⁺¹S₀ state in LaPO₄ is established by high-resolution emission spectrum at 46 375 ± 5 cm⁻¹. A detailed analysis of the thermal quenching of the ¹S₀ lifetime and emission intensity is presented. It is proposed that the lowest energy state of the relaxed 4f¹5d¹ configuration is situated energetically below that of the ¹S₀ state.     

Scintillation properties of Ce-doped LuLiF4 and LuScBO3

The crystals of 1 mol% Ce-doped LuLiF₄ (Ce:LLF) grown by the micro-pulling down (μ-PD) method and 1 mol% Ce-doped LuScBO₃ (Ce:LSBO) grown by the conventional Czochralski (Cz) method were examined for their scintillation properties. Ce:LLF and Ce:LSBO demonstrated ∼80% transparency at wavelengths longer than 300 and 400 nm, respectively. When excited by ²⁴¹Am α-ray to obtain radioactive luminescence spectra, Ce³⁺ 5d-4f emission peaks were detected at around 320 nm for Ce:LLF and at around 380 nm for Ce:LSBO. In Ce:LSBO, the host luminescence was also observed at 260 nm. By recording pulse height spectra under γ-ray irradiation, the absolute light yield of Ce:LLF and Ce:LSBO was measured to be 3600±400 and 4200±400 ph/MeV, respectively. Decay time kinetics was also investigated using a pulse X-ray equipped streak camera system. The main component of Ce:LLF was ∼320 ns and that of Ce:LSBO was ∼31 ns. In addition, the light yield non-proportionality and energy resolution against the γ-ray energy were evaluated.     

Novel blue-emitting phosphor NaMg4(PO4)3:Eu, Ce with energy transfer

A blue-emitting phosphor of NaMg₄(PO₄)₃:Eu²⁺, Ce³⁺ was prepared by a combustion-assisted synthesis method. The phase formation was confirmed by X-ray powder diffraction measurement. Photoluminescence excitation spectrum measurements show that the phosphor can be excited by near UV light from 230 to 400 nm and presents a dominant luminescence band centered at 424 nm due to the 4f⁶5d¹ → 4f⁷ transition of Eu²⁺ ions at room temperature. Effective energy transfer occurs in Ce³⁺/Eu²⁺ co-doped NaMg₄(PO₄)₃ due to large spectral overlap between the emission of Ce³⁺ and excitation of Eu²⁺. Co-doping of Ce³⁺ enhances the emission intensity of Eu²⁺ greatly by transferring its excitation energy to Eu²⁺, and Ce³⁺ plays a role as a sensitizer. Ce³⁺-Eu²⁺ co-doped NaMg₄(PO₄)₃ powders can possibly be applied as blue phosphors in the fields of lighting and display.     

Improved luminescence from Y2Sn2O7:Tb nanoparticles co-doped with Sb ions

Very small nanoparticles (size 3-5 nm) of Y₂Sn₂O₇, Y₂Sn₂O₇:Tb³⁺ and Sb³⁺ co-doped Y₂Sn₂O₇:Tb³⁺ were prepared at a relatively low temperature of 700 °C. Y₂Sn₂O₇ host is characterised by an emission around 436 nm, which is arising from the oxygen vacancies present in the lattice. Tb³⁺ emission improves significantly when Sb³⁺ ions are co-doped with Y₂Sn₂O₇:Tb³⁺ nanoparticles. Incorporation of Sb³⁺ ions at the Y³⁺ site of Y₂Sn₂O₇ lattice and associated lattice distortion around Tb³⁺/Y³⁺ ions brought about by the difference in the stable coordination number of Sb³⁺ and Y³⁺ ions are responsible for the improved Tb³⁺ emission from the co-doped samples.     

Sol-gel synthesis of yellow-emitting La4Ca(SiO4)3O:Ce phosphors for white-light emitting diodes

Ce³⁺ doped La₄Ca(SiO₄)₃O phosphors with silicate oxyapatite structure were synthesized by the sol-gel process. The X-ray diffraction (XRD) patterns showed that a pure phase was formed when sintering temperature was higher than 1300°C. The optical properties of La₄Ca(SiO₄)₃O:Ce³⁺ phosphors with varying sintering temperature and concentration were investigated by examining their excitation and emission spectroscopy. The phosphors exhibited a broad emission band centered at 550nm which could be attributed to the 5d-4f transition of Ce³⁺ and a stronger excitation peak around 467nm as well as several shoulder bands, nicely matching with the widely applied blue LED chips. Higher emission intensity was observed when firing temperature above 1300°C, due to increasing crystallinity of the powders. When Ce³⁺ concentration was equal to 5 at%, the sample exhibited the optimum excitation and emission efficiency. The results indicate that La₄Ca(SiO₄)₃O:Ce³⁺ is a promising candidate in the application of blue chip excited white light emitting diodes (LEDs).     

Spectroscopic characterization and optical waveguide fabrication in Ce, Tb and Ce/Tb doped zinc–sodium–aluminosilicate glasses

A spectroscopy investigation of Ce³⁺ and Tb³⁺ ions in sodium–zinc–aluminosilicate glasses is performed using the photoluminescence technique. Blue–white light, with x = 0.24 and y = 0.24 CIE chromaticity coordinates, is obtained for the Tb³⁺ singly-doped glass excited at 351 nm. When the sodium–zinc–aluminosilicate glass is co-doped with Ce³⁺ and Tb³⁺ a non-radiative energy transfer from Ce³⁺ to Tb³⁺ ions is observed upon 320 nm excitation. From an analysis of the cerium emission decay curve, the Ce³⁺ → Tb³⁺ energy transfer microscopic parameter and efficiency are obtained. Different concentrations of Ce³⁺ and Tb³⁺ ions in the glass host gives rise to blue and blue–green emissions, with different CIE coordinates. Optical waveguides were produced in the samples by Ag⁺–Na⁺ ion-exchange, and their characterization is presented.     

Luminescence enhancement of CaZnGe2O6:Tb afterglow phosphors synthesized using ZnO nanopowders

CaZnGe₂O₆:Tb³⁺ afterglow phosphors were prepared by solid state reaction using organic coated ZnO nanopowders and their photoluminescence, X-ray luminescence and afterglow properties were investigated. The CaZnGe₂O₆:Tb³⁺ samples emit a green luminescence at 548 nm attributed to the ⁵D₄-⁷F₅ transition of Tb³⁺. It was observed that the replacement of bulk ZnO by ZnO nanopowder in the sample synthesis increases the luminescence intensity. By adjusting the mass ratio of bulk ZnO to nanopowder ZnO, the photoluminescence intensity, X-ray luminescence intensity, and afterglow efficiency are improved. The optimized sample made with a 0.71 ratio of nano ZnO to bulk ZnO has a factor of four enhancement in X-ray luminescence, photoluminescence and afterglow intensities in comparison with the sample made with 100% bulk ZnO.     

Luminescence properties of Dy-doped Li2SrSiO4 for NUV-excited white LEDs

A series of single-phase full color phosphors, Dy³⁺-doped Li₂SrSiO₄ was synthesized by a solid-state reaction method. The phase of the as-prepared powders was measured by X-ray diffraction pattern (XRD) and the chemical composition was characterized using energy dispersive spectroscopy (EDS). The luminescent properties of Li₂SrSiO₄:Dy³⁺ were systematically investigated by concentration quenching, decay behavior and thermal stability measurements. The results suggested that the emission intensity of the Li₂SrSiO₄:Dy³⁺ was much stronger than that of Li₂SrSiO₄:Eu²⁺. It was worth to mention that Li₂SrSiO₄:Dy³⁺ phosphor possessed excellent thermal stability for use in light-emitting diodes (LEDs) and the emission intensity measured at 300 °C was only decreased 8% comparing with that measured at room temperature. Furthermore, the Commission International del’Eclairage (CIE) chromaticity coordinates of Li₂SrSiO₄:Dy³⁺ moved toward the ideal white light coordinates (0.33, 0.33). All results demonstrated that Li₂SrSiO₄:Dy³⁺ might be a potential phosphor for NUV-based white light-emitting diodes.     

Long wavelength Ce emission in Y6Si3O9N4 phosphors for white-emitting diodes

Y₆Si₃O₉N₄:Ce³⁺ phosphor was prepared by a solid-state reaction in reductive atmosphere. X-ray powder diffraction (XRD) analysis confirmed the formation of Y₆Si₃O₉N₄:Ce³⁺. Scanning electron microscopy (SEM) observation indicated that the microstructure of the phosphor consisted of irregular fine grains with an average size of about 5 μm. Photoluminescence (PL) measurements showed that the phosphor can be efficiently excited by near ultraviolet (UV) or blue light excitation, and exhibited bright green emission peaked at about 525 nm. Compared with Ce³⁺-doped Y₄Si₂O₇N₂ phosphors, Ce³⁺-doped Y₆Si₃O₉N₄ phosphors showed longer wavelengths of both excitation and emission. The Y₆Si₃O₉N₄:Ce³⁺ is a potential green-emitting phosphor for white LEDs.     

Factors for determining photoluminescence properties of YBO3:Ce phosphor prepared by hydrothermal method

YBO₃:Ce³⁺ blue-emitting phosphors were prepared from boric acid and nitrates of yttrium and cerium(III) by hydrothermal method. An excess amount of boric acid, prolonged aging, high temperature, and a high pH value promote the formation of crystalline YBO₃. The higher crystallinity results in the higher photoluminescence (PL) intensity corresponding to the 5d-4f transition of Ce³⁺ under the irradiation of near-UV light. The PL intensity also depends on the pH value of precursor suspension and the nominal Ce³⁺ concentration, where the sample prepared at pH = 8 and Ce/(Y + Ce) = 0.25-0.5 at% shows the maximum PL intensity. In addition, the hydrothermally prepared sample shows the characteristic photobleaching behavior under the continuous irradiation of near-UV light. These results suggest that the crystallinity of the host YBO₃ crystal and the homogeneity of substituted Ce³⁺ ions play significant roles in the PL properties.     

Photoluminescence of Tb/Ce co-doped aluminum oxynitride powders

Aluminum oxynitride(AlON) phosphors co-doped by Tb³⁺ and Ce³⁺ were synthesized by nitridation of the precursor which was co-precipitated from Al(NO₃)₃ solution and nanosized carbon black at 1750 °C for 2 "hrs" in flowing nitrogen atmosphere. The obtained AlON based powders were composed of polycrystalline spinel typed particles with sizes in the range of 1-3 μm. Under an excitation of 275 nm, it was found that co-doping of Ce³⁺ could drastically enhance the luminescence of AlON:Tb³⁺ powder by energy transfer. The product with 0.5 mol% Ce³⁺ and 0.67 mol% Tb³⁺ exhibited a strong broad green emission at 540 nm. The critical quenching concentration of Tb³⁺ in AlON:0.5 mol% Ce³⁺/xmol% Tb³⁺ phosphor was determined to be 0.67 mol%. It was supposed that the mechanism of concentration quenching of Tb³⁺ in AlON:0.5 mol% Ce³⁺ xmol% Tb³⁺ phosphor was dipole-dipole interaction.     

High and low spin energy states of the Tb 4f5d configuration in BaF2

In this paper we present results of detailed spectroscopic studies of Tb³⁺ luminescence from BaF₂:0.075 mol% Tb performed at Superlumi station of Hasylab, DESY, Hamburg and at Institute of Physics, N. Copernicus University, Torun, Poland (IF UMK Torun).We have measured UV/VUV excitation spectra of the dominant blue Tb³⁺ luminescence and emission spectra under excitation into various bands found from the excitation spectra. The excitation spectra are dominated by the two well known broad bands due to the parity and spin-allowed (SA) 4f⁸ → 4f⁷5d transitions. The higher energy triple t-band and unresolved single e-band at lower energies are widely separated (10 Dq about 16,500 cm⁻¹) reflecting the single d-electron energy in the high symmetry cubic crystal field with a relatively low contribution from the low symmetry component.In addition to these bands we have also detected a number of weaker bands at lower energy sides of both dominant SA bands. While the structured band with components at 252.8, 252.3, 250.4 and 248.4 nm clearly corresponds to the SF (spin-forbidden) band found earlier in LiYF₄:Tb, the bands at 183, 178 and 172 nm have been never, to the best of our knowledge, reported before. We present arguments that these new bands are the SF counterparts of the triple SA t-band at about 158 nm. The d-f exchange energies for d(e) and d(t) electrons are different at 7779 and 8245 cm⁻¹, respectively.Although the energy levels corresponding to the identified high and low spin (HS and LS) states of the 4f⁷5d configuration are, in BaF₂, well separated, there are no SA nor SF transitions generating d-f emission in BaF₂:Tb. This is because the numerous 4f⁸ energy levels intercept the excitation energy from 4f⁷5d levels leading to the well known blue and green Tb³⁺ 4f⁸ emissions.