Luminescent and scintillation properties of the Pr3+ doped single crystalline films of Lu3Al5−xGaxO12 garnet

The Pr³⁺ d–f luminescence was investigated in the single crystalline films (SCF) of Lu₃Al_5−xGa_xO₁₂:Pr garnet solid solution at x = 1–3, grown by the liquid phase epitaxy (LPE) method from the melt-solution based on the PbO–B₂O₃ flux. The shape of CL spectra and decay kinetics of Pr³⁺ ions in Lu₃Al_5−xGa_xO₁₂ SCFs strongly depend on the total gallium concentration x and distribution of Ga³⁺ ions between the tetrahedral and octahedral position of the garnet host. The best scintillation properties of Lu₃Al_5−xGa_xO₁₂:Pr SCF are achieved at the nominal Ga content in melt-solution in the x = 2–2.5 range.     

Luminescence and ESR characteristics of γ-irradiated Lu3Al5O12:Ce single crystalline film scintillators

The influence of γ-irradiation with a dose of ～10⁴ Gy on the characteristics of LuAG:Ce single crystalline films (SCF) was investigated using ESR and time-resolved luminescence spectroscopy under excitation by synchrotron radiation with the energies ranging from 3.7 to 12 eV. The origin of γ-ray induced radiation defects in LuAG:Ce SCF is discussed.     

Growth and transport properties of CaFeAsF_(1-x) single crystals

Using self-flux method,we have successfully grown the parent phase of the single crystals of CaFeAsF1-x.The X-ray di?raction indicates good crystallinity.In-plane resistivity shows a bad metallic behavior with a sharp drop of resistivity at about T SDW=119K.This anomaly is associated with the possible spin density wave(SDW)order.Interestingly near T SDW,the resistivity exhibits a cusp-like feature,which may be understood as the strong coupling effect between the electrons and the antiferromagnetic(AF)spin fluctuations.A reduction of fluorine or application of a high pressure will suppress the SDW feature and induce superconductivity.Hall effect measurements reveal a positive Hall coefficient below T SDW indicating a dominant role of the hole-like charge carriers in the parent phase.Strong magnetoresistance has been observed below T SDW suggesting multiple conduction channels of the charge carriers.     

Growth of high quality Ce~(3 ):YAP and (Ce~(3 ) Nd~(3 )): YAP single crystals

The effect of melt pretreatment of Ce~(3 ): YAP and (Ce~(3 ) Nd~(3 )): YAP and their growth ambient gases on the quality of the crystals are described. Firstly, a superheating pretreatment of YAP melt is adopted in a nitrogen atmosphere containing a little oxygen to eliminate carbon; then the YAP melt is superheated in a reduction atmosphere to fully reduce Ce~(4 ) ions into Ce~(3 ) ions in the melt. Finally, in a growth atmosphere of pure nitrogen, high quality Ce~(3 ): YAP and (Ce~(3 ) Nd~(3 )): YAP single crystals with high Ce~(3 ) concentration with only few light scattering centers were grown.     

Luminescent properties and energy transfer processes in Ce–Tb doped single crystalline film screens of Lu-based silicate,perovskite and garnet compounds

The work is dedicated to the development of scintillating screens based on the single crystalline films (SCF) of Ce,Tb doped Lu-based silicates, perovskites and garnets grown by the liquid phase epitaxy method. We confirm in this work the presence of the Ce → Tb energy transfer in LSO and LuAP hosts. We also show that in Ce–Tb doped LuAG SCF, the effective Tb → Ce energy transfer is observed. This results in increasing the light yield of the luminescence of double doped LuAG:Ce,Tb SCF up to 25–30% with respect to single Ce doped (Y,Lu)AG SCF counterparts at optimal ratio of Ce/Tb ions.     

Structural and magnetic–luminescent properties of carbon-doped aluminum oxide

Physics of the Solid State - Three-phase (corundum + δ phase + amorphous phase) amorphous–nanocrystalline powders of pure and carbon-doped Al2O3 (x C = 1.07–6.6 wt %) have been...     

Enhanced luminescent properties and optical absorption of γ-irradiated KI: Ce, Tb crystals

This paper reports that KI doped with Ce³⁺ or double doped with Tb³⁺ and Ce³⁺ were prepared by the Bridgman-Stockbarger method and characterized by optical absorption photoluminescence (PL), thermoluminescence (TL), photostimulated emission (PSL) and TL emission. The optical absorption measurement indicates that F and V₁, V₂ centers are formed in the crystals during the γ irradiation process. It was attempted to incorporate a broad band of Ce³⁺ activator into the narrow band emission of Tb³⁺ in the KI host without the reduction of emission intensity. Ce³⁺-co-doped KI and Tb crystals showed a broad band emission due to the d-f transition of Ce³⁺ and a reduction in the intensity of emission peaks due to the ⁵D₃-⁷F_j (j=3,4,5,6) transition of Tb³⁺, when they were excited at 240 nm.These results supported that an effective energy transfer occurs from Tb³⁺ to Ce³⁺ in the KI host. Co-doping Ce³⁺ ions greatly intensified the excitation peak at 260 nm for the emission at 393 nm of Tb³⁺, which means that more lattice defects, involved in the energy absorption and transfer to Tb³⁺, are formed by the Ce³⁺ co-doping. The integrated light intensity is an order of magnitude higher as compared to the undoped samples for similar doses of irradiation and heating rates. The defects generated by irradiation were monitored by optical absorption and TSL Trap parameters for the TL process are calculated and presented.     

Characteristics of the crystalline and luminescence properties of a-plane GaN films grown on γ-LiAlO_2(302) substrates

A-plane GaN films are deposited on(302) γ-LiAlO 2 substrates by metalorganic chemical vapor deposition(MOCVD) . The X-ray diffraction(XRD) results indicate that the in-plane orientation relationship between GaN and LAO substrates is [010] LAO [0001] GaN and [203] LAO [1100] GaN with 0.03% and 2.85% lattice mismatch,respectively. Raman scattering results indicate that the strain in the films decreases along with the increase in the thickness of the films. In addition to the band edge emission at 3.42 eV,defects-related luminescence at 3.35 eV is observed in the photoluminescence(PL) spectra. The cathodoluminescence(CL) spectra indicate that the 3.35-eV emission is related to the V pits.     

Influence of annealing treatment on the luminescent properties of Ta:β-Ga_2O_3 single crystal

Ta~(5+)doped β-Ga_2O_3 single crystals were grown by using the optical floating zone method, and then annealed in the air and nitrogen gas at 1400℃ for 20 hours.The transmittance spectra, photoluminescence(PL), x-ray irradiation spectra, and PL decay profiles of the samples were measured at room temperature.The relevant results show that the optical transmittance of the samples annealed in the air or nitrogen gas was improved.By drawing the(ahv)~2–hv graph,it can be seen that the band gap decreased after being annealed in the air, but increased in nitrogen gas.The PL spectra and x-ray irradiation spectra show that the luminescent intensity of the sample annealed in the air increased substantially,while decreased for the sample annealed in nitrogen.The PL decay time of the Ta:β-Ga_2O_3 annealed in the air increased significantly compared with that of the Ta:β-Ga_2O_3 sample without annealing, but the tendency after annealing in nitrogen gas was opposite.     

Growth and optical properties of Cr~（3＋）-doped CdWO_4 single crystals

A high-quality Cr 3+:CdWO4 single crystal at a size of approximatelyΦ25×80 mm is grown using the Bridgman method with CdO,WO3,and Cr2O3 as raw materials and their molar ratio of 100:100:0.5.The temperature gradient of solid-liquid interface at growth is approximately 50?C/cm and the growth rate is 0.05 mm/h.The X-ray diffraction(XRD),absorption,excitation,and emission spectra of different parts of the as-grown and O2-annealed crystals are investigated.Two strong broad optical absorption bands of about 472 and 708 nm are observed,and they are associated with the transitions 4 A2→ 4 T1 and 4 A2→ 4 T2.The weak 4 T2→ 2 E transition(the R-line)at 632 nm is also observed.The crystal-field parameter Dq and the Racah parameters B and C are estimated to be 1 412.4,776.8,and 3 427.6 cm? 1,respectively,according to the absorption spectra and crystal-splitting theory.A broadband fluorescence at about 1 000 nm due to 4 T2→ 4 A2 transition is produced by exciting the samples at 675 nm.After being annealed in an O2 atmosphere,the crystals become more transparent,while the effective light absorption of Cr 3+ ions is evidently enhanced and the emission intensity is also strengthened due to the reduction of oxygen vacancies in the CdWO4 crystal after annealing.     

Growth and characteristics of Mn-doped PMN–PT single crystals

Large sized 0.71PMN–0.29PT single crystals with different Mn-doping content (pure, 1 at.%, 3 at.%) have been grown by a modified Bridgman method. The piezoelectric and dielectric properties of the as-grown crystals are measured. The phase transitions of the poled 0.71PMN–0.29PT with the orientation along 〈001〉 and 〈110〉 directions take place during the heating process. The phase transition of the pure crystals is more complicated than that of the Mn-doped crystals. Both the pure 〈001〉- and 〈110〉-oriented crystals have two dielectric abnormal peaks besides the Curie peak. With Mn-doping, the temperature for the first dielectric abnormal peak shifts to a higher value. The Mn-doping content affects the piezoelectric and dielectric properties of the crystal greatly. 1 at.% Mn-doped crystals possesses a larger coercive field and mechanical quality factor at the expense of a little lower piezoelectric response. The growth and characteristics of pure and Mn-doped 0.71PMN–0.29PT single crystals are reported and discussed in this paper.     

Structure and magneto-optical properties of (CoPt3)1−xNix alloy films

The effect of the Ni addition on the structure and magneto-optical (MO) properties is investigated with (CoPt₃)_1−xNi_x alloy films. The result shows that, lower T_c and higher H_c could be simultaneously obtained in the Ni range of 0.43–0.7. <111>> texture is not the only reason for perpendicular magnetic anisotropy in the present system. Although Ni addition reduces the Kerr rotation angle value in the blue-wave range, it slightly enhances the value in the red-wave range. The films investigated can be considered as suitable for perpendicular magnetic recording applications if the proper Ni addition range (0.43–0.5) is selected. Received: 2 June 1999 / Accepted: 27 October 1999 / Published online: 23 February 2000     

The VUV–vis luminescent properties of NaYFPO4: Dy3+ phosphor

Dy³⁺-doped monoclinic NaYFPO₄ phosphor has been synthesized by solid-state reaction technique. Its photoluminescence in the vacuum ultraviolet (VUV)-visible region was investigated. The most intensity broadband emission centered at about 171 nm was the host-related absorption. Another broadband at 153 nm could be related to the O₂→Dy³⁺ charge transfer band (CTB) absorption. The excitation peaks located at 178 nm and 256 nm were the spin-allowed (SA) and spin-forbidden (SF) f–d transitions of Dy³⁺, respectively. Some sharp lines in the range of 280–500 nm were due to the f–f transitions of Dy³⁺ within its 4f⁹ configuration. Under the VUV–vis excitation, the Dy³⁺-doped NaYFPO₄ phosphor showed the characteristic emissions of Dy³⁺ (⁴F_9/2→⁶H_15/2 transitions and ⁴F_9/2→⁶H_13/2 transitions) with a stronger blue emission peaking at about 485 nm. All the chromaticity coordinates of the sample were in the near cold-white region. It can be predicted that this phosphor can be applied in both mercury-free luminescence lamps and white LED.     

Growth and photoluminescence properties of inclined ZnO and ZnCoO thin films on SrTiO_3（110） substrates

ZnO thin film growth prefers different orientations on the etched and unetched SrTiO 3（STO）（110） substrates.Inclined ZnO and cobalt-doped ZnO（ZnCoO） thin films are grown on unetched STO（110） substrates using oxygen plasma assisted molecular beam epitaxy,with the c-axis 42 inclined from the normal STO（110） surface.The growth geometries are ZnCoO[100]//STO[110] and ZnCoO[111]//STO[001].The low temperature photoluminescence spectra of the inclined ZnO and ZnCoO films are dominated by D 0 X emissions associated with A 0 X emissions,and the characteristic emissions for the 2 E（2G）→ 4A2（4F） transition of Co 2＋ dopants and the relevant phonon-participated emissions are observed in the ZnCoO film,indicating the incorporation of Co 2＋ ions at the lattice positions of the Zn 2＋ ions.The c-axis inclined ZnCoO film shows ferromagnetic properties at room temperature.     

Effect of NaF on optical and structural properties of CdxZn1−xS nano crystalline films

This work investigates the effect of NaF on optical and structural properties of nano crystalline Cd_xZn_1?xS films. The Cd_xZn_1?xS films are prepared through chemical bath deposition (CBD) technique in aqueous alkaline bath and their subsequent condensation on substrates. The as-obtained samples are characterized by X-ray diffraction (XRD), scanning electron microscopy (SEM) and UV–VIS absorption spectroscopy. Micro structural features, obtained from XRD analysis confirm the formation of cubic phase of undoped as well as NaF doped Cd_xZn_1?xS nano particles while SEM observations depict non-uniform distribution of grains. These results show the average grain size of pure as well as NaF doped samples to range from 50 to 90 nm. Tauc's plots, extracted from absorption spectra exhibit absorption to be dominating mainly in blue-green region of visible spectrum. The room-temperature photoluminescence (PL) spectra of Cd_xZn_1?xS samples show a peak around 425 nm, which gets blue shifted for doped sample indicating improvement in PL properties on its addition.     

Photoconductive properties of some chemically deposited (Cd–Pb)s films

Films of (Cd–Pb)S have been prepared using chemical deposition in aqueous alkaline bath and their subsequent condensation on substrates. Important achievements in terms of electrical response, optical absorption and photoconductivity (PC) excitation spectra, SEM, XRD and photoluminescence (PL) studies are presented and discussed. From the photocurrent curves, the ratio I_PC (saturated photocurrent)/I_DC (dark current) was observed to be of the order of 10⁶ for the systems prepared with CdCl₂, and to be 10⁷ when doped with samarium nitrate. Values of trap depth E, lifetime and mobility are evaluated from the PC decay. Band-gaps are determined from the two spectra. Diffraction lines in XRD studies are associated to CdS and PbS, and according to SEM studies layered growth of the films takes place. PL of samarium doped (Cd–Pb)S films shows an emission peak in the green-yellow region under 365?nm excitation. The PL brightness decreases with temperature.     

Synthesis and scintillation properties of GdCl3:Ce3+ (Gd1−xCexCl3, x = 0.005–0.08)

Single crystals of GdCl₃ doped with different concentrations of Ce³⁺ have been grown using the Bridgman–Stockbarger technique and their luminescence and scintillation properties were investigated. The luminescence spectrum of GdCl₃:Ce³⁺ is complex and consists of two bands with maxima at 350 nm and 370 nm. The maximal light yield in GdCl₃:Ce³⁺ was observed at ～1 mol% of Ce³⁺ (more than 38 000 ph/MeV).     

Factors affecting the electro-optical and structural characteristics of nano crystalline Cu doped (Cd–Zn)S films

This work investigates the effects of the temperature, deposition time and annealing ambient on the electro-optical and structural properties of nano crystalline (Cd–Zn)S films prepared by chemical bath deposition (CBD). The deposited films being uniform and adherent to the glass substrates are amorphous in nature and the crystallinity as well as the grain size is found to increase on post-deposition annealing. The obtained specimens are thoroughly characterized before and after annealing paying particular attention to their structure, composition and morphology. Annealing in air reduces the extent of disorder in grain boundaries and energy band-gap. A correlation between the structural and optical properties is investigated in detail. The surface morphology and structural properties of the as-deposited and annealed (Cd–Zn)S thin films are studied using X-ray diffraction (XRD), scanning electron microscope (SEM) and optical transmission spectra. The optical transmission spectra are recorded within the range of 300–800 nm and 300–900 nm. The electroluminescent (EL) intensity is found to be maximum at a particular temperature, which decreases with further increase in temperature and peaks of photoluminescent (PL) and EL spectra are centered at 546 nm and 592 nm. The emission intensity also increases with increasing thickness of the film.