Scintillation and optical properties of Ce-doped YAGG transparent ceramics

We investigated photoluminescence(PL) and scintillation properties of Ce~(3+)-doped Y_3Al_2Ga_3O_(12)(Ce:YAGG) transparent ceramics synthesized by vacuum sintering with different Ce~(3+) concentrations(mol.%) from 0.3% to 1%(0.3%Ce:YAGG, 0.5%Ce:YAGG, 0.8%Ce:YAGG and 1%Ce:YAGG). The samples were synthesized by the vacuum sintering technique. The obtained samples showed a very strong and broad PL emission by the 5d1-4f transition of Ce~(3+) in the wavelength range from 470 to 600 nm. The PL decay profiles were approximated by a single exponential decay function with the time constants of around 33–39 ns. Furthermore, the scintillation spectra induced by X-rays showed similar features with those observed in PL. The scintillation decay time profiles followed a second-order exponential decay function. The fast component group(ranged 35–42 ns) were dominantly contributed by the 5d_1-4f transition of Ce~(3+). The pulse height spectra utilizing the latter emissions showed a clear photoabsorption peak. Among those samples tested, 0.5%Ce:YAGG sample showed the highest scintillation light yield of 21,400 ph/MeV under ~(137)Cs γ-ray irradiation.     

Luminescent properties of Ce~(3+)/Tb~(3+) co-doped glass ceramics containing YPO_4 nanocrystals for W-LEDs

Ce~(3+)/Tb~(3+) co-doped transparent glass ceramics containing YPO_4 nanocrystals were prepared using high temperature melting method,and their structural and luminous properties were investigated.XRD analysis and TEM images confirmed the existence of YPO_4 nanocrystals in glass ceramics.The transmission spectra proved that the glass ceramics specimens still maintained a high transparency.Then the excitation and emission spectra of the Ce~(3+) and Tb~(3+) single-doped and co-doped glass and glass ceramics were discussed,which proved that the glass ceramics had better luminescent properties.Under the near ultraviolet(331 nm)excitation,the broadband emission located at 385 nm was observed which was ascribed to 5d→~2F_(5/2) and ~2F_(7/2) transition of Ce~(3+) ions.Several characteristic sharp peaks centered at 489,543,578 and 620 nm originated from the ~5D_4 to ~7F_J(J=6,5,4,3)of Tb~(3+) ions.The decay time of Tb~(3+) ions at 543 nm and the relevant energy levels of Ce~(3+) ions and Tb~(3+) ions illustrated the transfer process from Ce~(3+) ions to Tb~(3+) ions.The best CIE chromaticity coordinate of the glass ceramics specimen was calculated as(x=0.3201,y=0.3749),which was close to the NTSC standard values for white(x=0.333,y=0.333).All the results suggested that the YPO~4-based Ce~(3+)/Tb~(3+) co-doped glass ceramics could act as potential luminescent materials for white light-emitting diodes.     

Structural and optical properties of Dy~(3+):YAlO_3 phosphors for yellow light-emitting diode applications

The spectroscopic properties of a series of Dy~(3+) single-doped and Dy~(3+)/Nd~(3+),Dy~(3+)/Tb~(3+),and Dy~(3+)/Tm~(3+)co-doped YAlO_3(yttrium aluminum perovskite,YAP) phosphors were investigated and compared through the measurements of optical absorption,emission spectra,and fluorescence decay curves.For the Dy~(3+) ion single-doped samples,the intensity of each absorption band increases with an increment in Dy~(3+) ion doping concentration,and the identified strong absorption peak at 447 nm indicates that Dy~(3+):YAP phosphors are suitable to be pumped by a blue laser diode(LD).For all co-doped samples,absorption peaks of Dy~(3+) ion along with some of the absorption bands of Nd~(3+),Tb~(3+),and Tm~(3+) ions are observed.Under 351 and 447 nm excitation,a prominent emission peak at 572 nm was obtained in all the samples,corresponding to Dy~(3+):~4 F_(9/2)→~6 H_(13/2) transition.Here,2 at% Dy~(3+):YAP phosphor exhibits the highest yellow emission intensity under 447 nm pumping.Among the three kinds of Dy~(3+) co-doped phosphors,Dy~(3+)/Tb~(3+):YAP phosphor possesses the dominant yellow emission.The fluorescence decay curves show exponential behaviour and are fitted well.The Commission International de L'Eclairage(CIE)chromaticity coordinates were calculated following the respective emission spectra,and it is found that all the coordinates locate in the yellow region.The energy transfer(ET) processes were investigated and the concentration quenching mechanism was discussed.The obtained results suggest that Dy~(3+)-activated YAP phosphors are good candidates for yellow LED applications.     

Optical studies of Y_3(Al,Ga)_5O_(12):Ce~(3+),Cr~(3+),Nd~(3+) nano-phosphors obtained by the Pechini method

The Y3(AI,Ga)_5O_(12):Ce~(3+),Cr~(3+),Nd~(3+)(YAGG) nano-phosphors with homogeneous particle-size distribution,low aggregation and average crystalline size of about 65 nm were obtained using a modified Pechini method.Only slight aggregation of the crystallites occurs after post-annealing at 1100℃.The intense Ce~(3+)bands in the excitation spectra of the Ce~(3+),Cr~(3+),Nd~(3+)co-doped materials monitoring the Cr~(3+) emission at 690 nm indicate energy transfer from Ce~(3+) to Cr~(3+).Weak Nd~(3+) lines are observed,as well.In addition,the emission of Nd~(3+)at 1060 nm with excitation of Ce~(3+) and Cr~(3+) confirms the Ce~(3+)/Cr~(3+)to Nd~(3+)energy transfer.The short average luminescence decay times for the Ce~(3+) emission indicate the Ce~(3+)/Cr~(3+)to Nd~(3+)energy transfer.Eventually,the Y_3(AI,Ga)_5O_(12):Ce~(3+),Cr~(3+),Nd~(3+) nano-phosphors exhibit persistent luminescence originating from the 4f~3→4f~3 transitions of Nd~(3+) which matches well to the first biological window to be used in bioimaging applications.     

Efficient near-infrared quantum cutting in Tb~(3+),Yb~(3+) codoped LuPO_4 phosphors

Tb~(3+) and Yb~(3+) codoped LuPO_4 phosphors were prepared by the reverse-strike co-precipitation method.The obtained LuPO_4:Tb~(3+),Yb~(3+) phosphors were characterized by X-ray diffraction(XRD),photoluminescence(PL) spectra and decay kinetics to understand the near-infrared quantum cutting(QC) phenomena.The XRD results showed that all the phosphors exhibited good crystallinity and had a pure tetragonal phase of LuPO_4.The experimental results showed that the strong green emission around 545 nm from Tb~(3+)(~5D_4→~7F_5) and near-infrared(NIR) emission at 1003 nm from Yb~(3+)(~2F_(5/2)→~2F_(7/2)) of LuPO_4:Tb~(3+),Yb~(3+)phosphors were observed under 489 nm excitation,respectively.The Yb~(3+) concentration dependence on luminescent properties and lifetimes of both the visible and NIR emissions were also investigated.The quenching concentration of Yb~(3+) ions approached as high as 10 mol.%.The excellent luminescence properties of the LuPO_4:Tb~(3+),Yb~(3+) indicated its potential application in improving the energy conversion efficiency of the silicon based solar cells by converting one blue photon to two NIR ones.     

Photoluminescence properties of YAG:Ce~(3+),Pr~(3+) nano-sized phosphors synthesized by a modified co-precipitation method

Monophasic Ce~(3+) and Pr~(3+) co-doped yttrium aluminum garnet(YAG:Ce~(3+),Pr~(3+)) nanoparticles with good dispersity and uniform grain sizes in the range of 50–80 nm were prepared by a two-step route, which consisted of a modified co-precipitation preparation of mixed metal hydroxide hydrate intermediates at low temperature of about 40 oC and a subsequent calcination conversion of the synthesized intermediates to crystalline nanoparticle products at about 1000 oC. The influences of both the lanthanide ion(Ce~(3+) and Pr~(3+)) doping concentration and different doping(Ce~(3+)/Pr~(3+)) ratio on the photoluminescence intensity were systematically investigated. The synthesized (Ce_(0.6)Pr_(0.4))_(0.04)Y_(2.96)Al_5O_(12) nanoparticles were near spherical nanoclusters with good dispersity and uniform sizes in the range of 50–80 nm for about 85% of the particles. The strongest photoluminescence intensity was observed for the (Ce_(0.6)Pr_(0.4))_(0.04)Y_(2.96)Al_5O_(12) nanoparticle products.     

Phase relations,microstructure, and valence transition studies on CaZr_(1-x)Ce_xTi_2O_7(0.0≤x≤1.0) system

In this study, Ce-doped zirconolite was synthesized through high-temperature solid-state reaction at 1250 ℃ in air for 96 h. The crystal phase.microstructure and valence transition were studied by X-ray diffraction(XRD), scanning electron microscopy(SEM), and X-ray photoelectron spectroscopy(XPS).Phase relations of CaZr_(1-x)Ce_xTi_2O_7 systems were determined by XRD analyses and Rietveld refinements.Four different phases are identified, namely zirconolite, perovskite, pyrochlore, and cerianite. The phase transformation(2M-zirconolite → 4M-zirconolite → Ce-pyrochlore) is caused by cations rearrangement as cerium content increases. The solubility limit of cerium ions in CaZr_(1-x)Ce_xTi_2O_7 system is estimated to be approximately 0.80. Under sintering air atmosphere, partial reduction of Ce~(4+) in Ce~(3+) is detected in Ce 3d XPS spectra, and the ratio of Ce~(3+) and Ce~(4+) significantly decreases as cerium content increases.     

Spectroscopic analysis of trivalent Nd~(3+)/Yb~(3+) ions codoped in PZS host glasses as a new laser material at 1.06 μm

This paper reports on the spectral results of Nd~(3+)/Yb~(3+) ions codoped 50P_2O_5-30ZnO-20SrO(PZS, in mol.%) glasses which were prepared by a melting technique. The glass transition temperature and spectroscopic properties of these glasses were estimated. From the absorption spectra, Judd-Ofelt(J-O) intensity parameters(Wk), were calculated. Using J-O intensity parameters, several radiative properties such as spontaneous transition probabilities(AR), radiative branching ratios(bR) and radiative lifetimes(tR) were determined for the exciting levels of the Nd~(3+) ions. The large value of the stimulated integrated cross-section and the lifetimes of Nd~(3+) level revealed the potential of the present glasses as a candidate for generating laser emission at 1.06 μ m as continuous wave laser action and exploited for optical device fabrication. A broad emission band from 950 to 1100 nm was detected when the Nd~(3+)/Yb~(3+) was co-doped in PZS glasses excited by 805 nm lighting diode(LD). The energy transfer process from Nd~(3+)→Yb~(3+) in co-doped phosphate glasses was described in this paper.     

Effect of BaF2 addition on luminescence properties of Er3+/Yb3+ co-doped phosphate glasses

Er~(3+)/Yb~(3+) co-doped phosphate glasses(P_2O_5-Al_2O_3-BaO-BaF_2-K_2O-Er_2O_3-Yb_2O_3) with varying BaF_2 content,were prepared by a conventional melt quenching technique and their spectroscopic properties were examined through the Raman, absorption, emission and decay measurements. Raman spectra(350-1400 cm~(-1)) of the Er~(3+)/Yb~(3+) co-doped phosphate glasses with varying BaF_2 content, were recorded upon laser excitation at 785 nm. Near infrared luminescence spectra were measured in the1400-1600 nm region under 970 nm diode laser excitation and characteristic band was observed at1533 nm corresponding to ~4Ⅰ_(13/2)→~4Ⅰ_(15/2) transition of Er~(3+) ion. The decay curves for the ~4Ⅰ_(13/2) level of Er~(3+)ion, were measured and the lifetime is found to decrease from 7.94 to 7.70 ms when BaF_2 content increases from 0 to 8 mol% and then increases up to 7.83 ms with further increase in BaF_2 content(12 mol%). The emission cross-section.lifetime and figure of merit for the ~4Ⅰ_(13/2)→~4Ⅰ_(15/2) transition of Er~(3+) ion were evaluated and compared to the other host matrices. The upconversion luminescence was measured and intense red emission was observed for all the studied samples.     

Optical and luminescence characteristics of Eu3+-doped B2O3:SiO2:Y2O3:CaO glasses for visible red laser and scintillation material applications

Europium(Eu~(3+)) doped glasses of chemical compositions(55-x)B_2O_3:10 SiO_2:25 Y_2O_3:10CaO:xEu_2O_3,where x denotes mol% and ranges 0≤ x ≤ 2.5, were synthesized by adopting conventional melt quenching technique, Physical properties like density, molar volume, polaron radius, inter-ionic distance and field strength of the glass samples were investigated to assess the impact of Eu_2O_3. Optical and luminescence properties of the glasses were characterized with optical absorption, photoluminescence,X-ray induced emission spectra, temperature dependence emission spectra and decay times. Judd-Ofelt(JO) intensity parameters(Ω_λ) of the glasses were evaluated based on the absorption spectrum of 0.5 mol%. JO parameters, calculated from absorption spectra with thermal corrections on oscillator strength, were used to evaluate radiative properties such as radiative transition probability(A_R),branching ratio(β_R), stimulated cross section emission(σ) and radiative lifetime(τ_R) for ~5D_0→~7 F_J(J = 0,1,2,3 and 4) transitions. The decay rate of ~5D_0 fluorescent level for all the glass samples was single exponential. Lifetimes of the ~5D_0 level were decreased with increasing concentrations of Eu~(3+)ions from 0.05 mol% to 2.5 mol% which might be due to energy transfer through cross-relaxation in the glasses. The chromaticity coordinates(x, y) were similar for all BSYCaEu glasses and were located at the red region of CIE 1931 color chromaticity diagram. Hence, these results confirm that the Eu~(3+) doped BSYCaEu glasses could be useful for visible red lasers and glass scintillation applications.     

Study of Complexes Formed by Adrenaline with Nd~(3+),Gd~(3+) and Tm~(3+)

The solution reaction mechanisms,composition,donor atoms,properties of coordinate link and stability ofthe complexes on the systems of adrenaline with Na~(3+),Gd~(3+)and Tm~(3+)have been studied by pH-potentiometrictitration and electronic spectroscopy.Adrenaline perturbs the f-f electronic transition of Nd~(3+)and Tm~(3+)sothat the absorption spectra of their complexes are shifted toward longer wavelengths.The absorption spectra ofthe complexes formed by the three f-block element ions with adrenaline are shifted toward shorter wavelengthswith the increase of PH in Δγ=350～650 nm     

Luminescence properties of phosphate phosphors Ba3Gd1−x(PO4)3:xSm3+

A series of reddish orange phosphors Ba_3Gd_(1-x)(PO_4)_3:xSm~(3+)(x = 0.02.0.04,...,0.12) were prepared by the high-temperature solid-state reaction. X-ray powder diffraction(XRD) and diffuse reflectance and photoluminescence spectra were utilized to characterize the structure and spectral properties of the phosphors. The phosphors have strong absorption in the near-UV region. CIE chromaticity coordinates of the phosphors are located in the reddish orange region since the strongest emission band is around 598 nm and related to the ~4 G_(5/2)→~6 H_(7/2) transition of Sm~(3+). Optimal concentration of Sm~(3+) in the phosphors is about 6.0 at%. The quantum yield of the Ba_3Gd_(0.94)(PO_4)_3:0,06 Sm~(3+) under excitation at 403 nm is about 52.07%. Temperature dependent photoluminescence spectra of the Ba_3Gd_(0.94)(PO_4)_3:0.06 Sm~(3+) were measured and the phosphor exhibits high thermal stability of emission. All the results show that the Ba_3Gd(PO_4)_3:Sm~(3+) phosphor may be a potential red phosphor for near-UV based white LEDs.     

Silver nanoparticles enhanced near-infrared luminescence of Er~(3+)/Yb~(3+) co-doped multicomponent phosphate glasses

A new way to improve the 1.53 μm emission in Er~(3+)/Yb~(3+) co-doped multicomponent phosphate glass was demonstrated by introducing silver nanoparticles(NPs) in rare-earth doped glass.The existence of Ag NPs was confirmed by absorption spectra and transmission electron microscopy(TEM) measurements.The homogeneous distribution of silver NPs could be observed by the TEM images.UV-Vis-NIR absorption spectra revealed that the surface plasmon band was centered at about 420 nm.The photoluminescence spectra of glass samples were used to investigate the effect of silver NPs on the fluorescence properties of Er~(3+).Efficient 1.53 μm emission was obtained in prepared samples when pumped at 980 nm laser diode(LD).The 1.53 μm emission intensity could be enhanced 87% by doping 2 mol.% AgC l due to the increased localized field effect in the vicinity of NPs and the possible energy transfer from silver NPs to Er~(3+) ions.Our present work may point out one way to enhance the gain coefficient of Er~(3+)/Yb~(3+) co-doped glass fiber.     

UC/DC luminescence of Ho~(3+) doped pyrochlore structured La_(2(1–x))Yb_(2x)TiO_5 phosphor synthesized by sol-gel method

Ho~(3+) doped La_(2(1–x))Yb_(2x)TiO_5 samples were prepared by sol-gel method. Pyrochlore structured powders were obtained under the annealing of the as-prepared samples at 1100 °C for 3 h in the air. All the samples were characterized by X-ray diffraction(XRD), scanning electron microscopy(SEM) and photoluminescent spectroscopy. When x=0, we obtained La_2TiO_5 phosphors. Monitored at 546 nm, the excitation spectrum of Ho~(3+) activated La_2TiO_5 phosphors consisted of a broad band originating from the charge-transfer band(CTB) between Ho~(3+) ions and the nearest neighboring O~(2–) ions at 250–280 nm and four sharp bands associated to f-f transitions of Ho~(3+) ions at 350–500 nm. Under the blue light excitation at 461 nm, Ho~(3+) ion in La_2TiO_5 emitted an intense green emission band at 546 nm due to the transition of ~5S_2, ~5F_4→~5I_8. Two intense bands were observed at 490 nm(blue, ~5F_3→I_8) and 663 nm(red, ~5F_5→~5I_8) in the up-conversion(UC) spectrum under 980 nm NIR laser excitation in La_2TiO_5 phosphors activated with Ho~(3+) alone, whereas they were much different from the down-conversion(DC) luminescent samples. When x=7.5 mol.%–17.5 mol.%, the UC emission spectra of them dominated at 546 nm(green, ~5S_2, ~5F_4→~5I_8) and enhanced significantly with the dose of Yb~(3+) ion. The decay curve also confirmed that the transitions of ~5F_4→~5I_8 and ~5S_2→~5I_8 were merged into one emission band at 546 nm.     

Upconversion photoluminescence properties of SrY_2O_4:Er~(3+),Yb~(3+) under 1550 and 980 nm excitation

Er~(3+)/Yb~(3+) co-doped SrY_2O_4 phosphors with high color purity and brightness were successfully synthesized via a solid-state reaction method.Luminescence spectrum studies showed that the main red peaks and the minor green peaks of upconversion emissions were located at approximately 634–681 nm and 543–570 nm,respectively,corresponding to the transitions of ~4F_(9/2)→~4I_(15/2) and ~4S_(3/2)→~4I_(15/2) of Er~(3+) ions.Under the excitation of 980 and 1550 nm lasers,the spectra of all of the samples exhibited similar peak positions but different intensities.When excited by the 980 nm laser,the intensity ratio of red to green emission increased with increasing Yb~(3+) doping concentration and decreased with increasing excitation power.In the case of 1550 nm excitation,the intensity ratio of red to green emission increased with increasing Yb~(3+) doping concentration and excitation power,thereby,improving the color purity of the red emission.The intensity of red emission was considerably stronger under 1550 nm excitation than that under 980 nm excitation.Therefore,the color of the proposed phosphors could be efficiently tuned by tailoring both the Yb~(3+) doping concentration and excitation power.     

Investigation on 1.07 μm laser emission in Nd~（3＋）-doped sodium fluoroborate glasses

Spectroscopic and fluorescence properties of Nd 3+ ions in sodium fluoroborate(SFB) glasses were prepared and characterized through optical absorption,emission and decay measurements.The energy level analysis was carried out using free-ion Hamiltonian model.Experimental oscillator strengths were determined by measuring the area encompassed by the absorption peaks recorded for 1.0 mol.% Nd 3+-doped glasses.The Judd-Ofelt parameters(2,4,6) were used to evaluate the laser characteristic parameters such as radiative transition probability(A R),radiative decay time(τ R),fluorescence branching ratio(β R) and stimulated emission cross-section(σ e) for the 4 F 3/2 metastable state.The fluorescence spectra for different concentrations of Nd 3+ ions were recorded by exciting the samples at 514.5 nm Ar + ion laser.     

Synthesis of luminescent KY_3F_(10) nanopowder multi-doped with lanthanide ions by a co-precipitation method

A series of KY_3F_(10) nanophosphors doped with Gd~(3+), Ce~(3+) and Eu~(3+) ions were obtained with the use of a co-precipitation method. The resulting products were white precipitates, consisting of spherical particles with diameter about 150–200 nm, which was confirmed using transmission electron microscopy(TEM) technique. Powder X-ray diffraction(XRD) and energy dispersive X-ray analysis(EDX) measurements confirmed appropriate structures of the nanoparticles obtained. Spectroscopic properties of the products were examined on the basis of the measured excitation/emission spectra and luminescence decay curves. The synthesized samples showed orange-red luminescence, characteristic for Eu~(3+) ions. The reaction process was performed in required alkaline pH adjusted with the use of ethylenediaminetetraacetic acid(EDTA) and potassium hydroxide. The samples containing large amounts of Gd~(3+) dopant ions exhibited a tendency to form products with different morphologies.     

Effect of dopant concentration on the spectra characteristic in Zr~(4+) doped Yb:Nd:LiNbO_3 crystals

A series of Yb:Nd:LiNbO_3 crystals tridoped with various concentrations of Zr~(4+)(1 mol.%, 2 mol.% and 4 mol.%) were grown by the Czochralski technique from the congruent melt. The X-ray powder diffraction, UV-Vis-NIR absorption spectra and IR transmittance spectra were measured to analyze the crystal composition and defect structure. The Zr~(4+), Yb~(3+) and Nd~(3+) ions in LiNbO_3 crystal had two effects: volume compensation effect and ion valence state compensation effect. The Zr O2 doping threshold concentration was nearly 2.0 mol.%. The fluorescence emissions of Nd~(3+) ions and Yb~(3+) ions were observed under 808 nm excitation. The intensity of fluorescence emissions enhanced with the increasing of the Zr~(4+) doping concentrations. The Zr:Yb:Nd:LiNbO_3 crystals with 4 mol.% doping concentration of Zr~(4+) ion revealed strong emission around 1 μm, which is of great significance for laser materials.     

Growth,structural, spectral and high-power continuous-wave laser operation of Yb_(0.11)Gd_(0.89)COB crystal

A Yb_(0.11)Gd_(0.89)Ca_4O(BO_3)_3 crystal with new composition was grown by the Czochralski method. The crystal structure was measured and analyzed. The unit-cell parameters of the Yb_(0.11)Gd_(0.89)COB were calculated to be a=0.8089(7) nm, b=1.5987(6) nm, c=0.3545(8) nm, β=101.22o. The absorption and fluorescence spectra were measured. The maximum absorption cross-section of Yb_(0.11)Gd_(0.89) COB crystal was 0.79×10~(–20)cm~2, which occurred at 976 nm with Y polarization. The emission cross-section at 1027 nm was calculated to be 0.33×10~(–20) cm~2. The radiative lifetime trad was calculated to be 2.74 ms. The Stark energy-level diagram of Yb~(3+)in the Yb_(0.11)Gd_(0.89)COB crystal field at room temperature was determined. The ground-state energy level ~2F_(7/2) splitting was calculated to be as large as 1004 cm~(–1) and the zero-line energy was 10246 cm~(–1). A maximum output power of 9.35 W was achieved in continuous-wave(CW) mode, with the slope efficiency being 42.1%. Chemical etching experiment revealed that the dominating imperfections in the studied Yb_(0.11)Gd_(0.89) COB crystal were dislocations and sub-grain boundaries. The existence of crystal defects could cause light scattering, and degrade laser output efficiency. The influence of crystal defects on laser properties was discussed.     

Structure and Dielectric Study of Ce3 NbO7＋δ

The structure, phase composition, and migration of oxygen ion in Ce3 NbO7＋δ were reported on the basis of lone-pair substitution concept. X-ray diffraction study revealed that Ce3 NbO7＋δ sample was comprised of Ce3 NbO7＋δ phase and CeNbO4.25 phase. In the dielectric study of Ce3 NbO7＋δ sample, two dielectric loss peaks were observed both in temperature spectra and frequency spectra. Both peaks were shifted towards higher temperature with increase in frequency in temperature spectra and towards higher frequency with increase in temperature in frequency spectra, indicating the relaxation essence of these two peaks. It was suggested that the short distance diffusions of oxygen ions in both Ce3 NbO7＋δ phase and CeNbO4.25 phase gave rise to the two dielectric relaxation peaks.