X-ray Excited Luminescence Spectra Research Articles

Annealing effects on Czochralski grown Lu2Si2O7:Ce3+ crystals under different atmospheres

Cerium-doped lutetium pyrosilicate Lu2Si2O7:Ce3+ (LPS:Ce) single crystal samples grown via Czochralski method were annealed under air and H2 atmospheres from 350to1600°C. The x-ray excited luminescence spectra and UV as well as thermal stimulated luminescence spectra were measured. It was found that the luminescence efficiency after annealing in air at 1400°C was significantly enhanced compared to the unannealed samples. This phenomenon was suggested to be caused by the existence of some oxygen vacancies in the LPS:Ce crystals, and these oxygen vacancies can be effectively eliminated by means of annealing in air. Although the annealing will lead to the oxidization of cerium ions from Ce3+ ions to Ce4+, which is harmful to the luminescent efficiency, the annealing treatment does enhance the luminescent efficiency of LPS:Ce, without changing its luminescence mechanics.

Hydrothermal synthesis and luminescence of CaMO 4:RE 3+ ( M=W, Mo; RE=Eu, Tb) submicro-phosphors

Submicrometer crystalline CaMO 4:RE 3+ ( M=W, Mo; RE=Eu, Tb) phosphors with a sheelite structure have been synthesized via the hydrothermal process, which were characterized by X-ray powder diffraction (XRD), Fourier transform infrared spectroscopy (FT-IR), X-ray-excited luminescence (XEL), UV–vis diffuse reflectance spectra (UV–vis DRS) and scanning electron microscopy (SEM), respectively. The XRD patterns show that both CaWO 4 and CaMoO 4 have the same structure with space group I41/ a. The SEM images indicate that the optimal hydrothermal temperature is 120 °C for the particles that aggregate with the increase of temperature. The bands ranging from 380 to 510 nm in the XEL spectra of CaWO 4:Eu 3+ can be attributed to the charge transfer state from the excited 2 p orbits of O 2− to the empty orbits of the central W 6+ of the tungstate groups. The comparison between photoluminescent lifetimes and quantum efficiencies of the two phosphors was also investigated in detail.

A new promising scintillator Ba 3InB 9O 18

We report on the synthesis, crystal structure and scintillation property of a new compound Ba 3InB 9O 18. This compound crystallizes in space group P6 3/ m with unit cell of dimensions a=7.1359(3) Å, c=16.6151(8) Å and V=732.697 Å 3 with two Ba 3InB 9O 18 molecular formula. Its crystal structure is made up of planar B 3O 6 groups parallel to each other along the 〈0001〉 direction, regular InO 6 octahedra, irregular BaO 6 hexagons and BaO 9 polyhedra to form an analog structure of Ba 3YB 9O 18. DTA and TGA curves for Ba 3InB 9O 18 show that it is a chemically stable and congruent melting compound. Its X-ray excited luminescence spectra show an intense emission band in the range of 360–500 nm with a maximum at 400 nm. Light yield for Ba 3InB 9O 18 is about 75% as large as that for BGO under the same measurement conditions. There may exist a correlation between the scintillation properties and the crystal structural features of Ba 3InB 9O 18.

Crystal growth and characterization of rare earth iodides for scintillation detection

Abstract In this paper we report on the crystal growth and characterization of a new class of inorganic scintillators based on the rare earth iodides, in particular LuI 3 , YI 3 and GdI 3 , doped with trivalent cerium. Single crystals of LuI 3 :Ce 3+ , YI 3 :Ce 3+ and GdI 3 :Ce 3+ were grown by the vertical Bridgman technique in evacuated silica ampoules. In some cases, tantalum or graphite crucibles were used to minimize wetting of the ampoule. X-ray excited optical luminescence spectra of LuI 3 :Ce 3+ , YI 3 :Ce 3+ and GdI 3 :Ce 3+ exhibit a broad band due to Ce 3+ emission, peaking in the 500–550 nm region. LuI 3 :Ce 3+ , YI 3 :Ce 3+ and GdI 3 :Ce 3+ show high light yields up to 100,000 photons/MeV and fast principle decay time constants of

Effect of activator distribution on photo- and X-ray excited luminescence properties of ZnS:Cu,Cl phosphors

ZnS:Cu,Cl phosphors were prepared by conventional solid state reaction with the aid of NaCl–MgCl 2 flux. The copper activator was introduced into the phosphor precursors by three different methods: co-precipitated with ZnS (CP), wet-coated onto ZnS powders (WC), and simply mixed with ZnS in a mortar (SM). The samples were characterized by X-ray powder diffraction, photoluminescence spectra and X-ray excited luminescence spectra. The results show that both photo- and X-ray excited luminescence intensities of the as-prepared ZnS:Cu,Cl phosphors are in the decreasing order of CP > WC > SM. The different copper activator distribution in the phosphors resulting from the different methods was the main reason responsible for the different luminescence intensity, and uniform distribution is beneficial to the luminescence of the phosphors.

Growth and optical properties of YBa 3B 9O 18:Ce crystals

YBa 3B 9O 18:Ce scintillation crystals with a size up to 25×12×5 mm 3 were grown by the Czochralski method. The X-ray excited luminescence (XEL) spectrum of YBa 3B 9O 18:Ce 4+ crystal showed a strong emission at 400 nm similar to a pure YBa 3B 9O 18 crystal. A strong emission shifted to 385 nm and an additional emission at 325 nm was observed due to Ce 3+ after annealing the crystal in N 2. A new luminescence at 948 nm appeared under the excitation of a 532 nm laser. The refractive indices of the crystal measured by a prism method showed that the crystal is a negative uniaxial crystal. The birefringence is 0.12 in the visible light region, which is comparable to that of a β-BaB 2O 4 crystal. The refractive indices and transmittance both support that the crystal is strongly anisotropic. The large birefringence and luminescent properties make YBa 3B 9O 18:Ce an attractive optical crystal.

Getting to the Core of the Problem: Origin of the Luminescence from (Mg,Zn)O Heterostructured Nanowires

We have measured the time-resolved, X-ray excited optical luminescence spectra from two types of MgxZn(1-x)O core-shell, heterostructured nanowires: type I, with a small x, wurtzite core, encased in a larger x, wurtzite sheath; and type II, with a wurtzite core (x approximately 0), encased in a rock-salt sheath (x>0.62). By monitoring the X-ray energy dependence of the various luminescence peaks, we have determined the local environment of the sites where these peaks originate.

Growth and Luminescence Properties of NaIn(WO4)2 Crystal

Crystals of NaIn(WO4)2 that are 0.25 cm3 have been grown in two configurations by the top-seeded solution growth (TSSG) method. X-ray excited luminescence spectra of the grown crystals were studied at different temperatures. At room temperature, the light output of NaIn(WO4)2 was shown to be 65% of that of Bi4Ge3O12, while at liquid-nitrogen temperature it increases by 10-fold.

The optical and electrical properties in Nd3+ doped lead tungstate single crystals

The influence of Nd3+ doping with different concentration on the luminescence properties of PbWO4 single crystals were investigated by means of the thermo-luminescence, X-ray excited luminescence and photoluminescence spectra. Nd3+ doping has almost the same doping effects as that of La3+ doping in PbWO4. The doping mechanism of Nd3+ was briefly discussed. Dielectric loss spectroscopy and conductibility were measured when the PbWO4:Nd3+ single crystals were sequentially annealed in air atmosphere from 100 °C to 1000 °C. The heavily Nd3+-doped PbWO4 present a larger conductivity at the high temperature with low activation energy.

Preparation and luminescence property of Gd 2O 2S:Tb X-ray nano-phosphors using the complex precipitation method

The Gd 2O 2S:Tb X-ray nano-phosphors were prepared using the complex precipitation method combined with low temperature sulfurized method. The mixed solution of the ammonium water and ammonium hydrogen carbonate was employed as the complex precipitant. The samples were characterized by X-ray diffraction (XRD), transmission electron microscope (TEM), photoluminescence (PL) and X-ray excited luminescence (XL) spectra. The results show that the as-prepared samples can be sulfurized completely at 900 °C with flowing N 2 containing sulfur vapor, and show the pure Gd 2O 2S phases with the hexagonal structure. The obtained X-ray phosphor particles are quasi-spherical, disperse well. And the observed particle size of the sample calcined at 900 °C is 30–50 nm, while the one calcined at 1100 °C is about 50–70 nm. Therefore, both of them have successfully realized the nano-sized, which are beneficial to enhance the resolution of imaging system efficiently. When excited by the 254 nm UV light and X-ray, the Gd 2O 2S:Tb X-phosphors exhibit the same characteristic emission of Tb 3+, which arise from the transitions of 5D 3 and 5D 4 excited levels to 7F J ( J = 0–6) ground states. And the luminescence property of the nanocrystals and the process of energy transfer are studied in details.

Optical spectroscopy and luminescence quenching of [formula omitted

Optical spectroscopy of LuI 3 doped with Ce 3 + using ultraviolet and visible light excitation is reported. LuI 3 host excitation and emission and 4f–5d excitation and emission of Ce 3 + are observed. An empirical model based on crystal field splitting was used to estimate the energy of the highest 4f–5d excitation band. The crystal field splitting and centroid shift were compared to those of LuCl 3 : Ce 3 + and LuBr 3 : Ce 3 + . Temperature dependence of X-ray excited luminescence spectra shows thermal quenching, whereas that of the decay curve of Ce 3 + emission excited at the lowest 5d band of Ce 3 + does not indicate the presence of quenching of Ce 3 + emission for temperature below 625 K. The quenching in LuI 3 : Ce 3 + therefore occurs before the 5d Ce 3 + emission takes place.

Combustion Synthesis and Spectra Characteristic of Gd2O2S:Tb3+ and La2O2S:Eu3+ X-ray Phosphors

X-ray phosphors of Gd2O2S:Tb3+ and La2O2S:Eu3+ were synthesized by combustion reactions. The samples were characterized by x-ray diffraction (XRD), scanning electronic microscope (SEM), photoluminescence (PL), and x-ray excited luminescence (XEL) spectra. XRD results revealed pure oxy-sulfide phases when the sintering temperatures were no more than 500 °C, and the mean particle sizes were about 20 nm. While the sintering temperatures became higher, oxy-sulfate phases were present. SEM results illustrated a loose, porous agglomeration and a continuous three-dimensional network structure; PL spectra showed the characteristic emission of rare-earth activation ions. To our satisfaction, the PL intensities were nearly the same as some commercial x-ray phosphors. XEL spectra revealed the same characteristic emission, although their luminescence principles were different from those of the PL spectra. In addition, because absorption coefficients of these samples for x-ray and doped concentrations doped of activation ions were different, their light emission intensities and efficiencies also varied.

The temperature gradient technique (TGT) growth and optical properties of Yb-doped YAlO 3 single crystal

The dark-brown colored 5 at% Yb-doped YAlO 3 (Yb:YAP) single crystal was grown successfully by temperature gradient technique (TGT) for the first time. The TGT-grown Yb:YAP crystal with the perovskite structure and excellent crystallization perfection were confirmed by the X-ray diffractions techniques. The dark-brown color of TGT-Yb:YAP crystal turned into the colorless after annealing in the air at 1200 °C for 10 h. The absorption spectra, LD-excited infrared emission and X-ray excited luminescence spectra of the air-annealed Yb:YAP single crystal were investigated at the room temperature. The results indicate that the TGT-Yb:YAP single crystals can be used for the laser and scintillation applications.

A study of luminescence properties in the boron-doped lead tungstate

The present work is focused on the enhancement of luminescence in PbWO 4 by boron (B) ions doping. A series of boron-doped PbWO 4 polycrystals were synthesized by solid-state reaction in air atmosphere. The crystal structure of PbWO 4 was decided from powder X-ray diffraction data. The X-ray excited luminescence, UV excitation and emission spectra measurements were conducted on these samples under the same conditions to evaluate the doping effects of luminescence on PbWO 4. The B-doped PbWO 4 gave an enhanced broad emission band centered between 420 and 520 nm depending on different doping concentration. Another scintillating crystal, Bi 4Ge 3O 12, was also introduced to compare the effects of luminescence with B-doped PbWO 4. The doping mechanism of B ions in the PbWO 4 lattices was briefly discussed according to the present experimental results.

Influence of Nd co-doping on the Cr4+ content in PWO single crystal

The formation mechanism of Cr4+ in PbWO4 (PWO) crystals is studied by optical absorption and X-ray excited luminescence (XEL) spectra. It is found that the concentration of Cr4+ depends not only on the initial amount of Cr3+ but more importantly on the coaddition of Nd3+. This material may be used as a new passive Q-switched laser in view of its high absorption coefficient in the NIR region. For Cr-containing sample, Cr3+ primarily replaces Pb2+ and results in large relaxation of lattice. In order to keep the scheelite structure, some Cr3+ ions are oxidized into Cr4+ and occupy W6+ sites. In the codoping case, Nd3+ preferentially substitute for Pb2+ and Cr is forced into W6+ sites in the form of Cr4+ to keep charge neutrality and structural integrity. This view is strongly supported by FT-IR spectra. The origin of the decrease and even extinction of XEL is also discussed. (© 2004 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim)

Temperature gradient technique (TGT) growth and characterizations of large-sized Ce-doped YAG scintillation crystal

A good-quality Ce:YAG scintillation crystal with a diameter of 3 inches has been grown by temperature gradient technology (TGT) for the first time. The longitudinal distribution of cerium ions in the TGT-Ce:YAG crystal was measured by the ICP-AES method. The absorption spectrum in the range of 190–800 nm and the X-ray excited luminescence (XEL) of the as-grown Ce:YAG crystal were measured at the room temperature. The four typical absorption bands corresponding to internal 4f–5d transitions in Ce3+ ions, and the emission peak centered at 550 nm with the 2F5/2–2F7/2 ground state splitting were found in the absorption and XEL spectra. (© 2003 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim)

Spectroscopic properties of Yb 3+-doped PbWO 4 single crystal

Yb 3+-doped PbWO 4 single crystal was grown using modified vertical Bridgman method. X-ray diffraction (XRD) analysis, optical absorption spectra, X-ray excited luminescence (XEL), fluorescence of 2F 5/2→ 2F 7/2 and its lifetime at room temperature were investigated. PWO:Yb 3+ shows the broad absorption of Yb 3+ (850–1050 nm) and efficient emission (950–1100 nm). Annealing exerts a distinct influence on the PWO:Yb 3+ crystal, e.g. disappearance of color and annihilation of the absorption in the region around 450–750 nm, meanwhile the absorption of Yb 3+ ions was enhanced by the annealing treatment. A novel luminescence band on the X-ray excited luminescence spectra of PWO:Yb 3+ centered at about 500 nm was observed overlapped on that of PWO host.

A study of luminescence properties of (Gd3+, Dy3+, Nb5+)-doped lead tungstate single crystals

PbWO 4 single crystals doped with Gd 3+ , Dy 3+ , Nb 5+ ions were grown using the modified Bridgeman method. Optical transmission, X-ray excited luminescence spectra, excitation and emission spectra have been investigated. All the doped PbWO 4 crystals exhibit improved transmittance in the short wavelength region, while Nb 5+ doping makes the short wavelength cutoff sharper. Dy 3- and Nb 5- doping depresses the luminescence of PbWO 4 and the latter enhances the proportion of green component in spectra. In Dy:PbWO 4 , the WO 2- 4 group could absorbs excitation energy, and transfers part of the energy to the Dy 3- ions, followed by the strong luminescence of Dy 3- . Gd:PbWO 4 is an exception because Gd 3+ may be involved in the process of energy absorption and transfer the energy to the host. The luminescence of Gd:PbWO 4 has a similar intensity to that of pure PbWO 4 in the blue region, but the green component is decreased to some extent.

Energy transfer and annealing behavior of luminescence in Dy 3+-doped PbWO 4 single crystal

The Dy 3+: PWO single crystal was subsequently annealed in air atmosphere at a temperature of 500°C, 550°C, 600°C, 700°C, 800°C, 900°C, and 1000°C, respectively. X-ray excited luminescence spectra were measured before and after each step of annealing. Annealing experiments confirmed the energy transfer-taking place from PbWO 4 (PWO) host to Dy 3+ ions, followed by the enhancing characteristic emission of Dy 3+ ions. In the process of annealing, the luminescence of PWO host was significantly reduced while that of Dy 3+ was increased simultaneously. Annealing at a temperature below 700°C suppressed the blue luminescence of the PWO host and enhanced its green components, while the emission of Dy 3+ is increased to some extent. Further annealing at higher temperature strongly reduced the luminescence of the PWO host, while the emission of Dy 3+ was greatly increased. Interstitial oxygen O i could play an important role in the luminescence. Annealing could modify the luminescence of Dy 3+ ions in PWO, which may be useful in terms of some application purposes.

Influence of doping on the emission and scintillation characteristics of PbWO4 single crystals

X-ray excited luminescence spectra, wavelength-resolved thermoluminescence glow curves, ultraviolet and 22Na excited emission decays, and 60Co excited light yield were measured on a set of high purity (99.9999%) PbWO4:X (X=Lu3+, Y3+, Gd3+, Sc3+, Nb5+, Pb2+) samples grown in an equivalent way. Positive influence of trivalent doping (Lu, Gd, Y) was noted, which consists in suppressing the deeper trapping states in the PbWO4 structure. Such states are related to the radiative recombination processes in the green and red part of the spectra. The presence of the green emission centers also results in the increase of the slow recombination decay components in the microsecond time scale. High concentration of the dopant ions (670 atomic ppm for PbWO4:Nb) results in the creation of new nonradiative recombination sites, which suppress the recombination decay components and the light yield as well.