Growth and luminescent properties of Lu2SiO5 and Lu2SiO5:Ce single crystalline films

Single crystalline films (SCF) of Lu₂SiO₅ (LSO) and Lu₂SiO₅:Ce (LSO:Ce) silicates with thickness of 2.5-15 μm were crystallized by liquid phase epitaxy method onto undoped LSO substrates from melt-solution based on PbO-B₂O₃ flux. The scintillation and luminescence properties of LSO:Ce SCF were compared with the properties of LSO:Ce single crystal. The peculiarities of luminescence properties of LSO:Ce SCF in comparison with crystal analog can be due to different distribution of Ce³⁺ over the Lu1 and Lu2 positions of LSO host and are further influenced by Pb²⁺ flux-originated contamination.     

Effect of coactivation with Dy<Superscript>3+</Superscript> and Yb<Superscript>3+</Superscript> ions on the efficiency of energy storage in Lu<Subscript>2</Subscript>SiO<Subscript>5</Subscript>:Ce<Superscript>3+</Superscript> crystals

Cerium-activated lutetium oxyorthosilicate Lu₂SiO₅:Ce³⁺ (LSO:Ce) and coactivated LSO:Ce,Dy and LSO:Ce,Yb crystals have been synthesized by the sol-gel technique. It is shown that the introduction of coactivator (Yb and Dy) ions influences the energy storage in LSO:Ce, thus making it possible to control the afterglow and thermoluminescence in these crystals. The observed effect is related to the electron properties of coactivator ions (donor against acceptor), which determine the recharge of electron traps in LSO crystals.     

Influence of yttrium content on the CeLu1 and CeLu2 luminescence characteristics in (Lu1−xYx)2SiO5:Ce single crystals

This work deals with luminescence and scintillation characteristics of highly efficient cerium-doped scintillators, lutetium–yttrium orthosilicate (Lu_2(1−x)Y_2xSiO₅:Ce³⁺, x = 0−1). The radioluminescence, photoluminescence excitation (PLE) and emission (PL) spectra of the Ce_Lu1, Ce_Lu2 centers in LSO, LYSO and YSO are measured and discussed between 80 and 400 K with respect to the Ce_Lu1 and Ce_Lu2 features assignment and separation. The influence of yttrium concentration in Lu_2(1−x)Y_2xSiO₅:Ce³⁺ on Ce_Lu1, Ce_Lu2 luminescence characteristics is demonstrated. Temperature dependence shows that with increasing yttrium content the onset of the Ce_Lu1 and Ce_Lu2 decay time decrease and Ce_Lu1, Ce_Lu2 delayed recombination integrals increase shift to higher temperatures. The 5d₁ thermally induced excited-state ionization of both Ce_Lu1 and Ce_Lu2 centers is confirmed and studied by purely optical methods.     

Luminescent properties of Al2O3:Ce single crystalline films under synchrotron radiation excitation

The paper is dedicated to study the luminescent and scintillation properties of the Al₂O₃:Ce single crystalline films (SCF) grown by LPE method onto saphire substrates from PbO based flux. The structural quality of SCF samples was investigated by XRD method. For characterization of luminescent properties of Al₂O₃:Ce SCFs the cathodoluminescence spectra, scintillation light yield (LY) and decay kinetics under excitation by α-particles of Pu²³⁹ source were used. We have found that the scintillation LY of Al₂O₃:Ce SCF samples is relatively large and can reach up to 50% of the value realized in the reference YAG:Ce SCF. Using the synchrotron radiation excitation in the 3.7–25 eV range at 10 K we have also determined the basic parameters of the Ce³⁺ luminescence in Al₂O₃ host.     

掺铈硅酸镥(Lu2SiO5:Ce)晶体的生长与闪烁性能

用Czochralsky方法和铱坩埚感应加热技术生长出了尺寸为φ35mm×40mm的掺铈硅酸镥(LSO:Ce)闪烁晶体.透射光谱表明,由于铈离子的掺入,使晶体的吸收边由纯LSO晶体的195nm红移至380nm.LSO:Ce晶体的紫外激发波长按强度递减的顺序依次为380、333、319和216nm,其光发射为带状谱,波长覆盖范围从390nm至560nm.X射线激发的发射谱具有典型的双峰特征,峰值波长为393nm和.426nm.这些特征与Ce³⁺离子基态能级⁴f₁因自旋-轨道耦合而产生的两个分裂能级和Ce⁺离子在LSO晶体中占据两个不同的结晶学格位有关.     

Luminescent properties of Sr2Al2SiO7:Ce3+,Eu2+ phosphors for near UV-excited white light-emitting diodes

The Sr₂Al₂SiO₇:Eu²⁺, Ce³⁺ phosphors were synthesized by a high temperature solid-state reaction. Effective energy transfer occurs in Ce³⁺ and Eu²⁺ co-doped Sr₂Al₂SiO₇ due to large spectral overlap between the emission of Ce³⁺ and excitation of Eu²⁺ ions. Co-doping of Ce³⁺ enhances the emission intensity of Eu²⁺ greatly by transferring its excitation energy to Eu²⁺ ions. The critical distance has been estimated to be about 1.83 nm by spectral overlap method. Furthermore, the developed phosphors can generate lights from blue to green region under the excitation of UV radiation by appropriately tuning the activator content. The Sr₂Al₂SiO₇:Eu²⁺,Ce³⁺ phosphors are promising phosphors for warm-white-light-emitting diode because of its effective excitation in the near ultraviolet range.     

An investigation of X-ray luminosity versus crystalline powder granularity

At the High-Throughput Discovery of Scintillator Materials Facility at Lawrence Berkeley National Laboratory, scintillators are synthesized by solid-state reaction or melt mixing, forming crystalline powders. These powders are formed in various granularity and the crystal grain size affects the apparent luminosity of the scintillator. To accurately predict a “full-size” scintillator's crystal luminosity, the crystal luminosity as a function of crystal granularity size has to be known. In this study, we examine Bi₄Ge₃O₁₂ (BGO), Lu₂SiO₅:Ce³⁺ (LSO), YAlO₃:Ce³⁺(YAP:Ce), and CsBa₂I₅:Eu²⁺ (CBI) luminosities as a function of crystalline grain size. The highest luminosities were measured for 600- to 1000-μm crystal grain sizes for BGO and LSO, for 310- to 600-μm crystal grain sizes for CBI, and for crystal grains larger than 165 μm for YAP:Ce. Crystal grains that were larger than 1 mm had a lower packing fraction, and smaller grains were affected by internal scattering. We measured a 34% decrease in luminosity for BGO when decreasing from the 600- to 1000-μm crystal grain size range down to the 20- to 36-μm range. The corresponding luminosity decrease for LSO was 44% for the same grain size decrease. YAP:Ce exhibited a luminosity decrease of 47% when the grain size decreased from the 165- to 310-μm crystal grains to the 20- to 36-μm range, and CBI exhibited a luminosity decrease of 98% when the grain size decreased from the 310- to 600-μm crystal grain range to the 36- to 50-μm range. We were able to very accurately estimate full-size crystal luminosities from crystalline grains that are larger than 90 μm.     

Incorporation of Si–O induced valence state variation of cerium ion and phase evolution in YAG:Ce phosphors for white light emitting diodes

The role of Si⁴⁺ in the valence state of Ce and phase control in YAG:Ce phosphors was investigated upon incorporation of Si–O in the form of SiO₂. By varying the amount of SiO₂ addition, the valence state of tetravalent and trivalent Ce ions was identified distinctly by X-ray photoelectron spectroscopy and the phase purity of YAG host phase was examined by X-ray diffraction patterns. The self-reduction phenomena from Ce⁴⁺ to Ce³⁺ in YAG:Ce samples was observed to be featured in a typical 5d → 4f yellow-green transition of Ce³⁺ ion upon firing in air, driven by charge compensation for imbalance substitution of Ce⁴⁺ for Y³⁺. The addition of SiO₂ promotes further reduction of Ce⁴⁺ to Ce³⁺ in an amount up to 7.0 wt%, owing to spontaneous charge compensation, and suppresses the formation of YAP (yttrium aluminate perovskite, YAlO₃) and YAM (yttrium aluminate monoclinic, Y₄Al₂O₉). The results reveal the role of SiO₂ addition in a proper amount to be able to achieve desired luminous center of Ce³⁺ and phase-pure YAG for a series of YAG hosted luminescence materials such as blue-excitable YAG phosphor or laser-pumped YAG-based transparent ceramics or glass ceramics for lighting and display purposes.     

Effect of annealing on the spectroscopy performance of YVO4:Ce3+ single crystals

In this study, 1.0 at.% YVO₄:Ce³⁺ single crystals were grown in the protective atmosphere by using the Czochralski method. The crystals were annealed in Ar and H₂ atmospheres at different temperatures. The absorption and fluorescence spectra of the samples before and after annealing were measured. Results showed that the luminescent efficiency of the crystals was significantly enhanced after annealing in H₂ than after annealing in Ar. This phenomenon can be attributed to the existence of some Ce⁴⁺ ions in the crystal lattice. These Ce⁴⁺ ions can be effectively reduced to Ce³⁺ via annealing in H₂. With a fixed annealing time in H₂, the luminescent intensity significantly increased with increasing annealing temperature. The possibility of the crystal as white light material was also discussed according to the luminescence properties.     

Synthesis and structure of cerium-substituted hydroxyapatite

The aim of this study was to explore the effect of cerium ions on the formation and structure of hydroxyapatite (HAP). All particles, prepared by hydrothermal method, were synthesized at varied X_Ce = Ce/(Ca + Ce) (from 0 to 10%) with the atomic ratio (Ce + Ca)/P fixed at 1.67. Their morphology, composition and crystal structure were characterized by TEM, EPMA, XRD and FTIR. The results showed that in this composition range the apatite structure is maintained, Ce^{3 +} ions could enter the crystal lattice of apatite and substitute Ca^{2 +} ions. The doping of Ce^{3 +} ions resulted in the decrease of the crystallite size with increase in X_Ce. The HAP particles without doping were short rods having a diameter from 10 to 20 nm and a length from 30 to 50 nm. They grew into long needles upon increasing X_Ce.     

Luminescence response and CL degradation of combustion synthesized spherical SiO2:Ce nanophosphor

This study was aimed to systematically investigate the luminescence response of SiO₂:Ce³⁺ nanophosphors with different excitation sources. The powders were synthesized by using an urea assisted combustion method. SiO₂:Ce_1m% samples were also annealed at 1000 °C for 1 h in a charcoal environment to reduce incidental Ce⁴⁺ to partial Ce³⁺ ions. High resolution transmission electron microscopy (HRTEM) images of the as synthesized and annealed powder samples confirmed that the particles were spherical and in the size range of 3-8 nm in diameter. X-ray diffraction (XRD) and electron dispersion spectroscopy (EDS) results showed that the SiO₂ was crystalline and pure. Diffused reflectance, photoluminescence (PL) and cathodoluminescence (CL) results of the SiO₂:Ce³⁺ samples were obtained and compared with each other. The CL degradation and the surface reactions on the surface of the SiO₂:Ce³⁺ were studied with X-ray photoelectron spectroscopy (XPS) and Auger electron spectroscopy (AES). A clear improvement in the chemical stability of the SiO₂:Ce³⁺ annealed at 1000 °C were obtained.     

Growth and optical properties of (Yb3−xYx)Al5O12:Ce single crystals

To improve the infrared emission of Yb³⁺ ions doped in the garnet host Y₃Al₅O₁₂ (YAG) single crystal through the energy transfer from Ce³⁺ to Yb³⁺ ions, the 〈1 1 1〉-oriented YAG:Ce³⁺, YAG:Yb³⁺, YAG:(Ce³⁺, Yb³⁺) and Yb₃Al₅O₁₂:Ce³⁺ (YbAG:Ce³⁺) single crystals were grown using the Czochralski Method, respectively. The excitation and emission spectra of these garnet single crystals were characterized. In YAG:Ce³⁺ crystal, the yellow emission of Ce³⁺ ions present, but it was completely extinguished in YAG:(Ce³⁺, Yb³⁺) crystal and YbAG:Ce³⁺ crystal. However, the characteristic absorption bands of Ce³⁺ still existed in the excitation spectrum of Yb³⁺ ions, which showed that the energy absorbed by Ce³⁺ ions can be transferred to Yb³⁺ ions for its infrared emission.     

Luminescence enhancement of Tb3+ in Sr3SiO5:Eu2+ phosphor

Sr₃SiO₅ phosphors co-doped with Eu²⁺ and Tb³⁺ were prepared by a conventional solid-state reaction method. The prepared Sr₃SiO₅:Eu²⁺,Tb³⁺,Li⁺ phosphors had characteristic luminescent spectra excited under near-UV excitation in which both the broadband spectrum assigned to Eu²⁺ and the line spectrum assigned to Tb³⁺ are observed, although Tb³⁺ is inactive with this photon energy in general. For Eu²⁺–Tb³⁺ codoped Sr₃SiO₅, energy transfer process takes place and the mechanism is ascribed to the overlap between the shorter Eu²⁺ luminescence band from the Sr₃SiO₅ crystal structure with two Sr sites and ₅D⁴ energy level of Tb³⁺ ion. Due to the energy transfer, PL intensity of Eu²⁺ emission increased about 26 %. We suggest that this enhancement mechanism could shed light on the potential applications in white light-emitting diodes excited by near-UV light. In addition, the emission peak position near the orange region indicates that our system is a step towards a new class of wavelength sources for artificial lighting with improved PL intensity and lower energy consumption.     

Green emission enhancement of Ba2SiO4:Eu2+ phosphor via Gd co-doping and charge compensation

A series of new green-emitting Ba_2?x?2ySiO₄:xEu²⁺, yGd³⁺, yR⁺ (R = Li, Na or K) phosphors were synthesized by the solid-reaction method. X-ray diffraction (XRD) and fluorescence spectrophotometer are utilized to characterize the crystal structure and luminescence properties of the as-synthesized phosphors, respectively. The XRD patterns reveal that the doping of Gd³⁺, Eu²⁺ and R⁺ ions have no significant influence on the Ba₂SiO₄ phase. The green emission of Eu²⁺ ion associated with 4f⁶5d¹ → 4f⁷ can be obtained by 396 nm UV excitation source, which match well with the emission wavelength of UV-LEDs chip (380–420 nm). Moreover, the effect of charge compensator ions (Li⁺, Na⁺ or K⁺) on the luminescence intensity of (Ba, Gd)₂SiO₄:Eu²⁺ phosphors were also investigated. When introducing the Li⁺ ions into the (Ba, Gd)₂SiO₄ host lattices, the as-prepared phosphors show the strongest emission. The emission intensity of Ba_1.95SiO₄:0.04Eu²⁺, 0.005Gd³⁺, 0.005Li⁺ is about 1.39 times than that of Ba_1.96SiO₄:0.04Eu²⁺. Furthermore, the mechanism of energy transfer and concentration quenching of Ba_1.982?xSiO₄:xEu²⁺, 0.009Gd³⁺, 0.009Li⁺ phosphors are also discussed.     

The synthesis and optical property of solid-state-prepared YAG:Ce phosphor by a spray-drying method

Ce³⁺-activated yttrium aluminum garnet (Y₃Al₅O₁₂:Ce, YAG:Ce) powder as luminescent phosphor was synthesized by the solid-state reaction method. The phase identification, microstructure and photoluminescent properties of the products were investigated by X-ray powder diffraction (XRD), scanning electron microscopy (SEM), absorption spectrum and photoluminescence (PL) analysis. Spherical phosphor particle is considered better than irregular-shaped particle to improve PL property and application, so this phosphor was granulated into a sphere-like shape by a spray-drying device. After calcinating at 1500 °C for 0, 4, and 8 h, the product was identified as YAG and CeO₂ phases. The CeO₂ phase content is decreased by increasing the calcination time or decreasing the Ce³⁺ doping content. The product showed higher emission intensity resulted from more Ce³⁺ content and larger grain size. The product with CeO₂ was found to have lower emission intensity. This paper presents the crystal structures of Rietveld refinement results of powder XRD data.     

Novel porous perovskite composite CeO2@LaMnO3/3DOM SiO2 as an effective catalyst for activation of PMS toward oxidation of urotropine

Perovskites with stable crystal structure and excellent catalytic performance have attracted extensive attention in peroxomonosulfate (PMS) activation, however, severe agglomeration has always been the main obstacle limiting the catalytic activity of them, so novel perovskite catalysts are urgently needed. In this study, three-dimensional ordered macroporous silica (3DOM SiO₂) was prepared by colloidal crystal template method, then CeO₂@LaMnO₃/3DOM SiO₂ was prepared by sol-gel method combined with impregnation method and used to activate PMS for urotropine (URO) degradation. CeO₂@LaMnO₃/3DOM SiO₂ activated PMS system exhibited high URO removal efficiency and quick kinetic, as 99.98 % URO was degraded even within 30 min. The catalyst has a wide pH range and still has high catalytic activity in the presence of organic matter and inorganic ions. The three components in CeO₂@LaMnO₃/3DOM SiO₂ showed a synergetic effect. CeO₂ and LaMnO₃ were uniformly loaded on 3DOM SiO₂, which effectively avoided agglomeration. The specific surface area of CeO₂@LaMnO₃/3DOM SiO₂ was 11.88 times that of LaMnO₃ prepared by sol-gel method. There are two redox cycles of Ce³⁺/Ce⁴⁺ and Mn²⁺/Mn³⁺/Mn⁴⁺ in CeO₂ and LaMnO₃, respectively, which synergistically realize the activation of PMS. Both quenching experiments and electron paramagnetic resonance (EPR) analysis revealed that that SO₄^?, OH and ¹O₂ jointly achieved the degradation of URO. In summary, CeO₂@LaMnO₃/3DOM SiO₂ would be a promising candidate for practical wastewater treatment.     

Strong blue, green and red light emission at elevated temperatures from Y2SiO5 doped by the rare-earth ions

The temperature dependence of the photoluminescence (PL) of the rare-earth ion activated Y₂SiO₅ was investigated from room temperature to 573 K. Ion activators such as Eu³⁺, Ce³⁺, Sm³⁺, Tb³⁺ and some of their combinations were studied in this study. The most efficient blue, green and red phosphors at elevated temperature were found by doping the (Ce³⁺ + Tb³⁺), Tb³⁺ and Eu³⁺ respectively, in this material system. Meanwhile, the relationship between the structure and the temperature dependence of the PL in Re _x Y_2–x SiO₅ was also discussed.     

Ce<Superscript>3+</Superscript> and Eu<Superscript>2+</Superscript> luminescence in calcium and strontium aluminates

Compound CaAl₄O₇ (CA4), SrAl₄O₇ (SA4), CaAl₁₂O₁₉ (CA12) and SrAl₁₂O₁₉ (SA12) have been synthesized by using single step combustion method. The phosphors have been characterized by XRD, SEM and PL techniques. Both CA4 and SA4 possess monoclinic crystal structure whereas CA12 and SA12 possess hexagonal structure. Effects of crystal symmetry on the emission spectrum have been studied by doping the samples with Ce³⁺ and Eu²⁺ ions. The luminescence properties of Ce³⁺ and Eu²⁺ in these hosts is discussed on the basis of their covalent character and the crystal field splitting of the d-orbital of dopant ions. The spectroscopic properties, crystal field splitting, centroid shift, red shift and stokes shift have been studied. Spectroscopic properties of Eu²⁺ ions have been accurately predicted from those of Ce³⁺ ions in the same host. Most importantly experimental results were matched excellently with the calculated results. The preferential substitution of Ce³⁺ and Eu²⁺ at different Ca²⁺, Sr²⁺ crystallographic sites have been discussed. The dependence of emission wavelengths of Ce³⁺ and Eu²⁺ on the local symmetry of different crystallographic sites was also studied by using Van Uitert’s empirical relation. Differences in the emission spectrum of these samples have been observed despite their similar crystal structures and space group. Possible reasons have been discussed.     

The development of Ce3+-activated (Gd,Lu)3Al5O12 garnet solid solutions as efficient yellow-emitting phosphors

Abstract

Ce³⁺-activated Gd₃Al₅O₁₂ garnet, effectively stabilized by Lu³⁺ doping, has been developed for new yellow-emitting phosphors. The powder processing of [(Gd_1?xLu_x)_1?yCe_y]₃Al₅O₁₂ solid solutions was achieved through precursor synthesis via carbonate precipitation, followed by annealing. The resultant (Gd,Lu)AG:Ce³⁺ phosphor particles exhibit typical yellow emission at ～570 nm (5d–4f transition of Ce³⁺) upon blue-light excitation at ～457 nm (the ²F_5/2–5d transition of Ce³⁺). The quenching concentration of Ce³⁺ was determined to be ～1.0 at% (y = 0.01) and the quenching mechanism was suggested to be driven by exchange interactions. The best luminescent [(Gd_0.9Lu_0.1)_0.99Ce_0.01]AG phosphor is comparative to the well-known YAG:Ce³⁺ in emission intensity but has a substantially red-shifted emission band that is desired for warm-white lighting. The effects of processing temperature (1000–1500 °C) on the spectroscopic properties of the phosphors, especially those of Lu³⁺/Ce³⁺, were thoroughly investigated and discussed from the centroid position and crystal field splitting of the Ce³⁺ 5d energy levels.     

Comparative study of the luminescence of Al2O3:Ti and Al2O3 crystals under VUV synchrotron radiation excitation

The comparative study of the luminescent properties of Al₂O₃:Ti crystal in comparison with those for undoped Al₂O₃ crystal counterpart is performed under synchrotron radiation excitation with an energy of 3.7–25 eV. Apart from the main emission band peaked at 725 nm related to the ²E → ²T₂ radiative transitions of Ti³⁺ ions, the luminescence of excitons localized around Ti ions in the band peaked at 290 nm and the luminescence of F⁺–Ti and F–Ti centers in the bands peaked at 325 and 434 nm are also found in the emission spectra of Al₂O₃:Ti crystal. We show also that the luminescence of Ti³⁺ ions in Al₂O₃:Ti crystal can be effectively excited by the luminescence of excitons localized around Ti dopant as well as by the luminescence of F–Ti centers.