Ultraviolet to near-infrared spectral modification in Ce3+ and Yb3+ codoped phosphate glasses

The ultraviolet to near-infrared spectral modification in Ce³⁺ and Yb³⁺ codoped phosphate glasses was realized through the energy transfer from Ce³⁺ to Yb³⁺. The absorption spectra, fluorescence excitation and emission spectra, luminescence decay curves, and time-resolved emission spectra were measured and analyzed. The energy transfer efficiency and concentration quenching efficiency were calculated based on the decay curves of Ce³⁺ 340 nm emission and Yb³⁺ 976 nm emission. The calculated and experimental NIR emission intensities on the Yb³⁺ concentrations were compared and discussed.     

Study of the effects of Ga3+ co-doping on the Lu0.8Sc0.2BO3:Ce scintillation crystals

Transparent Lu_0.8Sc_0.2BO₃ crystals doped with 1 at%Ce³⁺ and co-doped with 1 at% and 3 at%Ga³⁺ were grown by the Czochralski method. We applied absorption spectrum, luminescence spectra under UV and X-ray excitation, fluorescence decay curve, three dimensional thermoluminescene and X-ray absorption near edge spectroscopy to study the effect of Ga³⁺ co-doping on the Lu_0.8Sc_0.2BO₃:Ce scintillation crystals. Experimental results indicated that no positive contribution of the Ga³⁺ ion doping on the scintillation efficiency was found. The causes for the deterioration of scintillation efficiency by co-doping Ga³⁺ were revealed. The decrease of practical cerium content and the Ce³⁺/Ce⁴⁺ ratio in crystals, and the increase of the trap concentrations, although the corresponding trap types still maintained the same, played a joint influence on the degrading of scintillation efficiency of Lu_0.8Sc_0.2BO₃:Ce crystals.     

Cathodoluminescent efficiency of Y3Al5O12 and YAlO3 single crystals in dependence on Ce3+ and other dopants concentration

The content of Ce³⁺ ions in the investigated single crystals grown under reducing conditions is limited by a low value of the distribution coefficient. This distribution coefficient decreases sharply with increasing concentration of Ce³⁺ ions in a melt. Cathodoluminescent efficiency rises with increasing Ce³⁺ concentration up to a certain state of saturation. At higher concentrations of Ce³⁺ ions emission from activator centres is dominant, while at lower concentrations defect centres play an important part. Iron acts as a strong quenching centre, especially in the YAlO₃ lattice. Nd, Ir, Fe, Ti, Cr centres exhibit a high quenching effect, too. A trace amount of Mo enhances cathodoluminescent efficiency.     

Cs2LiGdCl6 (Ce): New scintillation material

We investigated the scintillation properties of Cs₂LiGdCl₆:Ce³⁺ as a function of the Ce concentration. X-ray excited luminescence spectra of the scintillation material showed broad emission bands between 360 and 460 nm, with two overlapping peaks, due to the d→f transitions on Ce³⁺ ions. The samples provide good scintillation results. The energy resolution was found to be 5.0% (FWHM) at 662 keV for 10% Ce sample. Under γ-ray excitation, Cs₂LiGdCl₆:Ce³⁺ showed three exponential decay time components of about 130–200 ns decay time constant. The light output of the investigated samples was 20,000 photons/MeV for a 10% Ce concentration. The light output deviation from the linear response is within 7% between the energy range of 31 and 1333 keV. Overall, the scintillation properties confirm that Cs₂LiGdCl₆:Ce³⁺ single crystal is a promising candidate for medical imaging and radiation detection.     

The role of iron ions in YAG and YAP

Spectroscopic properties of YAG and YAP doped with Fe were compared. YAG :Fe crystals grown under reducing atmosphere showed strong colouration whereas similar colouration in YAP :Fe was found after oxygen treatment. Nd³⁺ luminescence was effectively quenched by Fe ions in YAP, whereas Ce³⁺ luminescence was quenched by Fe ions in both the materials.     

Changes in Optical Properties of Ce: YAG Crystals under Annealing and Irradiation Processing

Changes of optical properties of cerium doped YAG single crystals (0.05, 0.1, 0.2 at.% Ce, and 0.2 at.% Ce "+" 0.1at.% Mg) after thermal annealing at 1400°C in air or 1200°C in N₂+H₂ mixture and subsequent g or proton irradiation were investigated. For initial Ce³⁺ contents <0.05 at.% an increase and for Ce³⁺ contents >0,05 at.% a decrease of the final Ce³⁺ concentration was observed. Appropriate changes in luminescence of Ce: YAG crystals were observed as a consequence of dopant concentration changes. They were small after gamma-irradiation of Ce: YAG crystals with Ce³⁺ content >0,05at.% and reached about 100% after gamma-irradiation of crystals with Ce³⁺ content < 0.05 at.%.     

Colour Centre in Nd3+-doped Yttrium Aluminates

Spectroscopic and laser properties of YAG:Nd and YAP:Nd grown from the nonstoichiometric melts or those containing Mo and Fe impurity were compared. YAG:Nd grown from the melt with surplus of Y₂O₃ and annealed in H₂ at ∼ 1400 °C have an increased laser performance. Mo admixture in hydrogen annealed YAP:Nd laser crystals suppresses effectively the detrimental action of iron impurity.     

Growth and optical characteristics of Ce-doped and Ce : Na-codoped BaLiF3 single crystals

Ce-doped and Ce : Na-codoped BaLiF₃ single crystals were grown by the Czochralski technique under reactive atmosphere. Na⁺-ions, used as a charge-compensating impurity, compete with Ce³⁺-ions for Ba²⁺ sites in the host, reducing the Ce³⁺ incorporation and degrading the mechanical integrity of crystals. Ce-doped BaLiF₃ showed potential for UV tunable lasers.     

Photoacoustic Spectra of Pr3+, Nd3+, Gd3+ Acetate Complexes

The crystals of the complexes Pr(Ac)₃ · 4 H₂O, Nd(Ac)₃ · 4 H₂O, Gd(Ac)₃ · 4 H₂O were synthesized and their Pa spectra determined firstly. Their PA spectra and absorption are interpreted. The fluorescence properties of Pr³⁺, Nd³⁺, Gd³⁺ and the relaxation process models were studied by their PA spectra.     

Bridgman Growth and Characterization of LuAlO3—Ce3+ Scintillator Crystals

Chemical and structural effects in LuAlO₃-Ce³⁺ single crystals grown by the Bridgman method were studied using spectral emission, x-ray, etching and optical techniques. The Ce concentration distribution was found to exhibit the normal freeze behavior with partition coefficient of 0,17. The expansion of the unit cell volume due to incorporation of Ce was measured. Dislocation etch pits were revealed on (010), (100) and (001) crystal faces. Thermal expansion behavior of LuAlO₃ was studied along the major crystallographic axes in between the room temperature and 1000 °C. The scintillation performance of 5 × 5 × 10 mm³ samples was measured using a 662 keV gamma source with a shaping time of 1.2 μs. The light yield was increasing from 40% BGO to 70% BGO with increasing of the Ce³⁺ content from 0.13 at.% to 0.9 at.%.     

Novel luminescence behaviors of Ce3+/Tb3+ co-doped phosphate glasses

In the present work, Ce³⁺/Tb³⁺ co-doped 60P₂O₅-30BaO-10B₂O₃ phosphate glasses are prepared and their luminescence properties are presented. Under excitation at 303 nm, the Ce³⁺ ions singly doped sample show a novel red emission besides the UV one. The co-doped samples show enhanced Tb³⁺ ions emission with the increasing of Tb³⁺ ions concentration at the cost of Ce³⁺ emission. The mechanism of this luminescent behavior is discussed with respect to the relevant energy transfer process.     

Synthesis and Luminescence Characteristics of LiMgAlF6:Ln3+ (Ln = Ce,Eu, Tb)

By solid state reaction, LiMgAlF₆ and LiMgAlF₆: Ln³⁺ are synthetized with the ratio 120/100/110 of LiF/MgF₂/AlF₃, at 1008 K, in high-purity Ar stream. Their crystal structure which belongs to hexagonal system are determined by X-Ray-Diffraction (XRD). Luminescence characteristics of Ce³⁺, Eu³⁺, Tb³⁺ and sensitization of Ce³⁺ to Tb³⁺ in LiMgAlF₆ are studied. It is shown that the sensitization of Ce³⁺ to Tb³⁺ is efficient and a bright green emission is observed.     

Color centers and charge state change in Ce:YAG crystals grown by temperature gradient techniques

Color centers and impurity defects of Ce:YAG crystals grown in reduction atmosphere by temperature gradient techniques have been investigated by means of gamma irradiation and thermal treatments. Four absorption bands associated with color centers or impurity defects at 235, 255, 294 and 370 nm were observed in as-grown crystals. Changes in optical intensity of the 235 and 370 nm bands after gamma irradiation indicate that they are associated with F⁺-type color center. Charge state change processes of Fe³⁺ impurity and Ce³⁺ ions take place in the irradiation process. The variations of Ce³⁺ ions concentration clearly indicate that Ce⁴⁺ ions exist in Ce:YAG crystals and gamma irradiations could increase the concentration of Ce³⁺ ions. Annealing treatments and the changes in optical density suggest that a heterovalent impurity ion associated with the 294 nm band seems to be present in the crystals.     

Solarization mechanism of glass containing Ce3+ and As5+

The solarization mechanism in a glass containing both Ce³⁺ and As⁵⁺, 16Na₂O·11CaO·73SiO₂:0.15AsO_x·0.015CeO_x (in mol.%), is newly proposed by elucidating the valence and coordination structure of arsenic after the photochemical reaction, the mechanism being traditionally expressed as

$\text{2}\text{Ce}{}^{\mathrm{3+}}\text{+}\text{As}{}^{\mathrm{5+}}\text{→}\text{hv}\text{2}\text{Ce}{}^{\mathrm{4+}}\text{+}\text{As}{}^{\mathrm{3+}}$

ESR hyperfine quartets due to an As⁴⁺ ranging from 0.1 to 0.5 T built up on UV-irradiation and their line shape varied with the duration of the irradiation. The line shape analysis of the ESR spectra employing a computer simulation technique has led to the following conclusions; (1) As⁵⁺ is reduced to As⁴⁺ in the solarization process. (2) The geometry around the As⁴⁺ in the solarized glass is tetrahedral during the early stage and trigonal-pyramidal during the latter stage of the reaction.     

退火温度对Ce:YAlO3单晶体的影响研究

将生长完成的Ce:YAlO2单晶体在1680℃的高温氢气气氛下退火,晶体颜色、吸收光谱和荧光光谱相对于未退火的样品均发生了变化.本文对此现象进行了分析.研究结果表明,1680℃高温氢气退火后,Ce:YAP晶体中同时包含YAP相和YAG相.     

Modeling the redox equilibrium of the Ce4+/Ce3+ couple in silicate glass by voltammetry

Square-wave voltammetry was used to determine the characteristic potential of the Ce⁴⁺/Ce³⁺ couple in four glass formulations covering a wide range of silicate glass compositions suitable for nuclear waste containment. The temperature range investigated extended from 1178 K to 1523 K. As the Ce⁴⁺/Ce³⁺ peak potential is situated near the silicate oxidation wall, its position was determined more precisely by superimposing the theoretical peak on voltammetry diagram. The results were then used to develop a model relating the Ce⁴⁺/Ce³⁺ redox ratio to the oxygen fugacity, temperature and optical basicity. In its general expression, the relation accounts for the evolution predicted by the laws of thermodynamics, and is similar to the relations established for the Fe³⁺/Fe²⁺ redox couple by other authors.     

XPS characterization of YAlO3:Co single crystals

YAlO₃:Co (YAP:Co) single crystals have been obtained by the Czochralski method. The XPS spectra of YAP:Co annealed in reducing atmospheres: H₂, vacuum and vacuum plus H₂ are presented and discussed. As confirmed by magnetic measurements and the electron spectroscopy XPS the dopant concentration of Co is lower than a nominal one. The annealing processes removed colour centers due to relocation and some reduction of oxygen ions in the structure. The increased unit volume during the long annealing process may be caused by the change in some Co³⁺ ions into Co²⁺ ions. This explains the occurrence of the violet colour of the longtime annealed samples. The chemical shift analysis shows more ionic bond of Y–O than Al–O. (© 2007 WILEY‐VCH Verlag GmbH & Co. KGaA, Weinheim)     

Crystal growth and optical properties of LuYAG:Ce single crystal

Crystals of Ce³⁺-doped (Lu_xY_1?x)₃Al₅O₁₂ (LuYAG) have been grown and studied by X-ray powder diffraction, emission spectroscopy, excitation spectroscopy and X-ray excited fluorescence spectroscopy. The X-ray powder diffraction pattern revealed that the as-grown LuYAG:Ce crystal possessed the garnet structure. Compared with Ce³⁺-doped Y₃Al₅O₁₂ (YAG), the absorption bands associated with the 4f–5d transition shifted to shorter wavelengths, the emission band that originated from a transition from the lowest 5d level to the ²F ground state of the Ce³⁺ ions shifted to the blue, which was probably due to a larger Stokes shift of the emission, and the reduction of relative intensity of antisite defect emission in the X-ray excited fluorescence spectra revealed that introducing Lu ions into YAG could reduce the antisite defect.     

Energy transfer studies of Ce:Eu system in phosphate glasses

The preparation of sodium phosphate glasses singly and doubly doped with rare earth ions Ce³⁺ and Eu³⁺ by melt quench method is described. The spectroscopic characterizations of the samples are done using absorption, excitation and emission spectra. The nonradiative energy transfer between trivalent cerium and europium is achieved through the phosphate lattice and the results are incorporated. The main reason of quenching of Ce³⁺ ions and the mechanism of energy transfer is mainly electric dipole-dipole in nature for Ce³⁺:Eu³⁺ system.     

Concentration distribution of Nd3+ In Nd:Gd3Ga5O12 crystals studied by optical absorption method

Nd:Gd₃Ga₅O₁₂ crystals with different concentrations of Nd³⁺ were grown by Czochralski method, their absorption spectra were measured at room temperature. By using the optical absorption method, the effective distribution coefficient k_eff for Nd³⁺ in GGG was fitted to be 0.40±0.01, which is higher than that of Nd³⁺ in YAG. The 808nm absorption cross‐section was calculated to be 4.0±0.2×10^‐20cm^‐2. The lengthways and radial concentration distribution of Nd³⁺ in the crystals were also analyzed and discussed. (© 2005 WILEY‐VCH Verlag GmbH & Co. KGaA, Weinheim)