Luminescence and Scintillation Characterization of Cs2NaGdBr6: Ce3+ Single Crystal

Luminescence and scintillation properties of newly discovered bromo-elpasolites Cs₂NaGdBr₆: Ce³⁺ (CNGB: Ce³⁺) are presented. Single crystals of CNGB: Ce³⁺ with dimensions up to Ø7×10 mm³ are successfully grown by the Bridgman technique. X-ray excited luminescence measurements of the grown samples showed a broad emission band in the wavelength range from 365 to 470 nm. It offered an energy resolution of 5.1% (FWHM) at 662 keV for 10% Ce sample. The light output of the investigated samples increases along with cerium concentration. A maximum light yield of ～36,800 ph/MeV is measured for the 10% Ce sample crystal. Under γ-ray excitation, CNGB: Ce³⁺ crystals showed three exponential decay time components. The scintillation mechanism in the sample crystal is presented.     

Luminescence spectroscopy of Ce3+-doped ABaPO4 (A=Li, Na, K) phosphors

Ce³⁺ doped ABaPO₄ (A=Li, Na, K) phosphors were prepared by conventional high temperature solid-state reaction. The phosphors were investigated by XRD, photoluminescence excitation and emission spectra, and luminescence decay curves. The five 5d levels corresponding to the 4f¹→4f⁰5d¹ transition of Ce³⁺ ions were identified. The spectroscopic parameters, e.g., the 5d barycenter, the crystal-field splitting, and the Stokes shift, were discussed. LiBaPO₄:Ce³⁺ phosphor could be efficiently excited by the near-UV lights (330–420 nm) and showed a broad emission band in the range of 430–620 nm with the maximum wavelength at 468 nm. In contrast, Ce³⁺-doped NaBaPO₄ and KBaPO₄ showed only excitation bands in a limited UV region (230–370 nm) and have blue emission at 385 nm and 416 nm, respectively. The temperature quenching of luminescence and the chromaticity coordinates were reported. The luminescence properties were discussed by analyzing the crystal structure and the local surroundings of Ce³⁺ ions on the Ba²⁺ sites.     

Luminescence properties of Ce3+ doped gadolinium-calcium-silicaborate glass scintillator

In this work, the Ce³⁺ doped gadolinium-calcium-silicaborate glass scintillators of the composition ratio 25Gd₂O₃:10CaO:10SiO₂:(55−x)B₂O₃:xCeF₃, have been fabricated by using the melt-quenching technique. The doping concentration of the Ce³⁺ was varied from 0.05 mol% to 2.5 mol%. The 4f-5d transition of the Ce³⁺ allowed scintillation with a fast decay time. The absorption spectrum, X-ray induced emission spectrum, photo luminescence spectrum, laser luminescence spectrum and decay time of the scintillators were measured for studying the luminescence properties. From the X-ray induced emission spectrum result, we checked the trend between doping concentration and light yield. The laser induced luminescence spectrum was measured while changing the temperature from 300 K to 10 K. We also measured the decay time by using the laser excitation of the 0.15 mol% Ce³⁺ doped glass scintillator.     

Photoluminescence properties of Ca9Lu(PO4)7:Ce3+, Mn2+ prepared by conventional solid-state reaction

A new red-emitting phosphor Ca₉Lu(PO₄)₇:Ce³⁺, Mn²⁺ has been synthesized by solid-state reaction, and its luminescence properties have been investigated. The broad red emission peaked at 645 nm of Mn²⁺ is greatly enhanced by the sensitizer Ce³⁺ due to efficient energy transfer from Ce³⁺ to Mn²⁺. The energy transfer was demonstrated to belong to a resonant type via a dipole–quadrupole mechanism. The critical distance for Ce³⁺→Mn²⁺ energy transfer was calculated to be 15.04 Å by concentration quenching method. Preliminary results indicate that the phosphor might be a promising red phosphor for UV-based white LEDs.     

Improving the dielectric constant of Al2O3 by cerium substitution for high-k MIM applications

Process compatible high-k dielectric thin films are one of the key solutions to develop high performance metal–insulator–metal (MIM) structures for future microelectronic devices. Engineered cerium–aluminate (Ce_xAl_2–xO₃) thin films were deposited on titanium nitride metal electrodes by electron-beam co-evaporation of ceria and alumina in a molecular beam deposition chamber. X-ray photoelectron spectroscopy clearly reveals that Ce cations can be stabilized in the 3+ valence state in Ce_xAl_2–xO₃ up to x = 0.7 by accommodation in the alumina host matrix. Higher Ce content was observed to result in cerium dioxide segregation in cerium aluminate matrix, probably due to the chemical tendency of Ce cations to exist rather in the 4+ than in the 3+ state. Electrical characterization of the X-ray amorphous Ce_0.7Al_1.3O₃ films reveals a dielectric constant value of about 11 and leakage current lower than 10^?4 A/cm². No parasitic low-k interface formation between the high-k Ce_0.7Al_1.3O₃ film and the TiN metal electrode is detected.     

Luminescence of calcium orthoborate doped by Ce3+ ions

The luminescence properties of calcium orthoborate Ca₃(BO₃)₂ doped with cerium are studied upon x-ray (～30 keV) and VUV (3.5–15 eV) synchrotron excitation. The emission bands peaked at 392 and 420 nm are attributed to interconfigurational transitions of Ce³⁺ ions. The short-wavelength emission band at 340 nm is caused by radiative decay of exciton-like states. The fundamental absorption edge of Ca₃(BO₃)₂ is found to be near 7.1 eV. Based on thermoluminescence data and other information, the behavior of defects in Ca₃(BO₃)₂:Ce³⁺ is studied.     

Luminescence and energy transfer in phosphor LiAl5O8: Ce3+, Dy3+

Ce³⁺ and Dy³⁺-doped LiAl₅O₈ were synthesized in the present study. The luminescence properties of Ce³⁺ and Dy³⁺, and the energy transfer from Ce³⁺ to Dy³⁺ were investigated. The Ce³⁺ species in LiAl₅O₈ emit one broad band that peaks at 351 nm under the excitation of ultraviolet light, which is attributed to the 5d–4f transitions of Ce³⁺. The luminescence of Dy³⁺ in singly doped LiAl₅O₈ can not be detected due to its low oscillator strength. However, Dy³⁺ emit intense blue (477 nm) and yellow (569 nm) light after the introduction of Ce³⁺. This phenomenon demonstrates that there exists effective energy transfer from Ce³⁺ to Dy³⁺, which occurs because the emission spectrum of Ce³⁺ perfectly overlays the excitation spectrum of Dy³⁺. The energy transfer from Ce³⁺ to Dy³⁺ is performed through dipole–dipole interactions. The experimental results show that LiAl₅O₈ co-doped with Ce³⁺ and Dy³⁺ can be a potential two-band (blue and yellow) phosphor.     

Mechanisms for Ce3+ excitation at energies below the zero-phonon line in YAG crystals and nanocrystals

Excitation of YAG:Ce³⁺ crystals and nanocrystals was performed at λ_exc=473–584 nm over a wide temperature range. It was observed that the luminescence of both nano- and single-crystal YAG:Ce samples is efficiently excited with photon energies well below the Ce³⁺ absorption band and at least 1650 cm^?1 below the ZPL of the 4f¹(²F_5/2)?4f⁰5d¹ transition, located at 489 nm. The studies of Ce³⁺ fluorescence spectra as a function of temperature and excitation wavelength and of their temporal evolution point to the role of phonon-assisted nonradiative energy transfer between different groups of Ce³⁺ centers in the excitation mechanism.     

Luminescence spectral properties of Sm-and (Ce, Sm)-containing silica gel glasses

The spectroscopic behavior of Sm³⁺ ions is investigated in monoactivated and coactivated (with cerium) glasses obtained by the direct sol-gel-glass transition. It is shown that the majority of the Sm³⁺ ions form optical centers of the same type, whose luminescence spectral characteristics depend weakly on the concentration of the activator and the technique used to introduce it. Complex centers, including Sm³⁺ and Ce⁴⁺ ions bound by bridge oxygen, are also formed in the coactivated glass during the pore nucleation stage. The Sm³⁺ ions in these centers are characterized on the average by higher local symmetry, the efficient enhancement of luminescence by photoreduced (Ce⁴⁺)⁻ ions, and its extinction by Ce-containing clusters. Fiz. Tverd. Tela (St. Petersburg) 40, 458–465 (March 1998)     

Electronic excitations and luminescence of SrAlF5 crystals doped with Ce3+ ions

This paper reports the results of a time-resolved photoluminescence and energy transfer processes study in Ce³⁺ doped SrAlF₅ single crystals. Several Ce³⁺ centers emitting near 4 eV due to 5d-4f transitions of Ce³⁺ ions substituting for Sr²⁺ in non-equivalent lattice sites were identified. The lifetime of these transitions is in the range of 25–35 ns under intra-center excitation in the energy region of 4–7 eV at T = 10 K. An effective energy transfer from lattice defects to dopant ions was revealed in the – 7–11 eV energy range. Both direct and indirect excitation channels are efficient at room temperature. Excitons bound to dopants are revealed at T = 10 K under excitation in the fundamental absorption region above 11 eV, as well as radiative decay of self-trapped excitons resulting in luminescence near 3 eV.     

Luminescence study of cerium-doped La2Hf2O7: Effects due to trivalent and tetravalent cerium and oxygen vacancies

X-ray excited emission spectra, photoluminescence excitation and emission spectra, optical reflectivity spectra, and pulsed X-ray and optical excited luminescence decay measurements are reported for cerium-doped La₂Hf₂O₇ powders prepared by solid state synthesis. A broad luminescence associated with oxygen vacancies is observed in the region 350–750 nm with a peak around 460 nm. The photoluminescence spectra and the number of oxygen vacancies vary for samples annealed in oxidizing or reducing atmospheres and with the temperature of the synthesis process. Increasing the cerium concentration reduces the oxygen-vacancy-related emission due to the presence of Ce⁴⁺. First principles calculations predict that Ce⁴⁺ can substitute in Hf sites; this is confirmed from the optical reflectivity spectrum of cerium-doped La₂Hf₂O₇. Photoluminescence excitation and emission spectra characteristic of Ce⁴⁺ charge transfer transitions and possibly Ce³⁺ are also observed. Although trivalent cerium may be present, no emission observed from cerium-doped La₂Hf₂O₇ can be attributed to Ce³⁺ in La sites.     

Spectroscopic properties of Ce doped silica annealed at different temperatures

Ce³⁺-doped silica was synthesized by sol-gel technique. The absorption band at 252 nm of Ce³⁺-doped silica is close to the main absorption band of Ce(NO₃)₃ solution. Three different luminescence bands were observed in the samples annealed at temperatures from 100 to 1200 °C, and the intensity of these luminescence bands changed with the alteration of the heat-treating temperatures. In addition to two well-known main luminescence bands of 4f-5d transition of Ce³⁺ with the wavelength at 357 and 450 nm, a rarely reported luminescent band with the wavelength at 344 nm was also observed, which was attributed to some kind of oxygen-related defects of silica.     

Efficiently visible and 2 μm infrared emission in K2YbF5: Ce3+/Ho3+ microcrystals

Ho³⁺/Ce³⁺ co-doped K₂YbF₅ microcrystals were synthesized by solvent-thermal method. Under excitation of 980 nm laser diode, effectively visible and 2 μm-infrared luminescence of Ho³⁺ ion were obtained in the microcrystals. By changing Ce³⁺-ion doping concentration, the luminescence properties of visible and 2 μm emission were effectively regulated. At low Ce³⁺-ion doping level, the red and green upconversion emission obviously increases and decreases respectively with the increase of Ce³⁺-ion amount in the samples, meanwhile the intensity of 2 μm fluorescence changes very little. At high Ce³⁺-ion doping level, the intensities of the red and green emission both decrease with the increase of Ce³⁺-ion concentration, while the 2 μm emission intensity increases obviously. In the sample doped with 16% Ce³⁺ ion, the intensity of 2 μm emission is about 4.5 times that of the sample without Ce³⁺ ion, and the corresponding quantum efficiency is about 78.3%. The result is attributed to the influence of the different cross relaxation between Ho³⁺ and Ce³⁺ ion in luminescence process at low and high Ce³⁺-ion doping concentration. The corresponding luminescence mechanism and energy transfer process were discussed in detail.     

Violet-blue-shift of emission and enhanced luminescent properties of Ca3(PO4)2:Ce3+ phosphor induced by substitution of Gd3+ ions

Ca₃(PO₄)₂:1mol%Ce³⁺/xGd³⁺ (where x = 0.5, 1.0, 3.0 and 5.0 mol%) phosphors were synthesized by the conventional combustion synthesis method. The X-ray diffraction patterns showed their rhombohedral structure with space group of R3c. The optical properties including reflectance, excitation and emission were investigated. The band gaps of the phosphors were calculated from diffuse reflectance spectra data using the Kubelka–Munk function. The photoluminescence (PL) excitation spectra exhibited the broadband 4f–5d transition of Ce³⁺ ions centered at ~265 nm. The PL emission properties of the Ca₃(PO₄)₂:Ce³⁺/Gd³⁺ phosphors were studied as a function of the Gd³⁺ ion concentration. The Ca₃(PO₄)₂:Ce³⁺/Gd³⁺ phosphor had a wide emission band ranging from 320 to 400 nm, and peaking at 365 nm. This emission is ascribed to the transition from the higher 5d band to ²F_7/2, ²F_5/2 states of the Ce³⁺ ion. The 365 nm peak shifted to longer wavelengths with increasing concentration of the Gd³⁺ ion. The CIE chromaticity diagram of Ca₃(PO₄)₂:Ce³⁺/Gd³⁺ phosphor showed tunable emission colour from violet to violet-blue, suggesting that this phosphor can act as a source of violet-blue colour for application in information displays, phototherapy and photoluminescent liquid crystal displays.     

Potential tunable white-emitting phosphor LiSr4(BO3)3:Ce3+, Eu2+ for ultraviolet light-emitting diodes

A novel Ce³⁺/Eu²⁺ co-activated LiSr₄(BO₃)₃ phosphor has been synthesized by traditional solid-state reaction. The samples could display varied color emission from blue towards white and ultimately to yellow under the excitation of ultraviolet (UV) light with the appropriate adjustment of the relative proportion of Ce³⁺/Eu²⁺. The resonance-type energy transfer mechanism from Ce³⁺ to Eu²⁺ in LiSr₄(BO₃)₃:Ce³⁺, Eu²⁺ phosphors is dominant by electric dipole–dipole interaction, and the critical distance is calculated to be about 29.14 Å by the spectra overlap method. White light was observed from LiSr₄(BO₃)₃:mCe³⁺, nEu²⁺ phosphors with chromaticity coordinates (0.34, 0.30) upon 350 nm excitation. The LiSr₄(BO₃)₃:Ce³⁺, Eu²⁺ phosphor has potential applications as an UV radiation-converting phosphor for white light-emitting diodes.     

Optical study of Ce ion in gamma-irradiated binary barium-borate glasses

Absorption spectra measurements of cerium-doped binary system from barium-borate glasses have been measured. The effects of dopant concentration of CeO₂ and Al₂O₃ in the concentration range 0.54-2.9 and 4.8-9.2 mol%, respectively, and exposed to different irradiation doses have been measured in the range 1-7 eV and the result have been interpreted in terms of structural concepts. The radiation-induced broad band at 2.25-1.88 eV in the base glass is observed to be suppressed by the presence of cerium due to the transformation of Ce⁴⁺ to Ce³⁺. The released electrons are then used to annihilate positive holes responsible for this band. The resolution of the observed absorption spectra show two to seven induced bands depending on the glass composition. Absorption spectra of the irradiated binary glass system are found to be controlled by the cerium concentration. From the absorption edge studies, the values of optical band gap E_opt and Urbach energy ΔE have been evaluated. The oxidoreduction (redox) reaction Ce³⁺/Ce⁴⁺ is assumed to be related to the glass basicity and the possible complex-ion formation. The oxygen ion activity (O²⁻) is believed to be related to the basicity and to the possible oxygen ion formation in the glass melt, and the redox equilibrium is shifted toward the reduced state.     

Investigations on acceptor (Pr3+) and donor (Nb5+) doped cerium oxide for the suitability of solid oxide fuel cell electrolytes

Nanocrystalline acceptor (Pr³⁺) and donor (Nb⁵⁺) doped cerium oxide are synthesized by sol-gel method via hydrolysis process and evaluated for the suitability of applying as an electrolyte for the intermediate temperature solid oxide fuel cells. Phase purity and crystallite size of the synthesized materials are ascertained by powder X-ray diffraction studies. Introduction of Pr³⁺ ions in the cerium lattice exhibited a lower crystallite size than the Nb⁵⁺, which exposes the probability to attain high oxide ion conductivity of Pr³⁺ doped cerium oxide. Fourier transform infrared and Raman spectra confirm the functional groups and formation of Pr³⁺ and Nb⁵⁺ ions in the cerium lattice. Absorbance spectra exhibit the charge-transfer transition from O²⁻ (2p) to Ce⁴⁺ (4f) orbital in cerium oxide. Pr³⁺ and Nb⁵⁺ ions doped cerium lattice create the oxygen vacancies and favor the formation of Ce³⁺ from Ce⁴⁺. Valence band transition of Ce³⁺ ions from the 5d to 4f levels are examined by photoluminescence studies. The morphological features of Ce-Pr-O and Ce-Nb-O are investigated by scanning and transmission electron microscopy. Electrochemical impedance spectroscopy is used to analyze the conductivity properties of solid electrolytes. Ce-Pr-O shows the high oxide ion conductivity of 0.1 S/cm at 600 °C with an activation energy of 0.73 eV. Electrolytes with specific conductivities higher than 10⁻² S/cm at intermediate temperatures (∼400–600 °C) are required for solid oxide fuel cells to operate with less maintenance. Hence, Ce-Pr-O can be a suitable electrolyte material for intermediate temperature solid oxide fuel cells.

     

Electron paramagnetic resonance of Ce3+ ions in lead thiogallate single crystals

The results of electron paramagnetic resonance (EPR) studies of Ce³⁺ impurity ions in single crystals of lead thiogallate PbGa₂S₄ have been reported. The Ce³⁺ ions substitute for Pb²⁺ ions in the crystal lattice of PbGa₂S₄. A number of paramagnetic cerium centers in lead thiogallate have been observed. The spectra are described by the spin Hamiltonian of rhombic symmetry with the effective spin S = 1/2. The g factors of the main cerium centers have been determined. A large number of paramagnetic centers are due to both nonequivalent positions of lead and local charge compensation under the substitution Ce³⁺ ?? Pb²⁺.     

Luminescence and evaluation of trapping parameters in NaMgSO4Cl: X (X=Cu or Ce) phosphor

Thermoluminescence (TL) characteristics of recently developed high sensitive mixed halosulphate phosphors, NaMgSO₄Cl: Cu and NaMgSO₄Cl: Ce were studied in comparison with CaSO₄: Dy in order to assess the possibility of their use in personal monitoring and TLD phosphors at very low dose of 5 Gy. It was found that NaMgSO₄Cl: Cu is 5.59 times and NaMgSO₄Cl: Ce is 6.18 times more sensitive as compared to standard CaSO₄: Dy. UV photo-excited luminescence from Cu to Ce doped NaMgSO₄Cl halosulphate phosphors has been investigated. The intense emission of the spectrum is assigned to electronic transitions 3d⁹4s¹→3d¹⁰ in monovalent copper ion and 5d→4f in Ce³⁺ ions. Increase in PL peak intensity suggesting that Cu and Ce play an important role in PL emission in the present matrix. These phosphors were synthesized by the wet chemical method. XRD, photoluminescence (PL) and thermoluminescence (TL) characterization of phosphors has been reported in this paper. The preparation of an inexpensive and high sensitive NaMgSO₄Cl: Cu and NaMgSO₄Cl: Ce with TL glow peaks for different concentrations are observed between 160 and 195 °C and between 200 and 225 °C, respectively, exposed to gamma-rays of ⁶⁰Co for their thermoluminescence (TL) properties. The glow curves have been recorded at a heating rate of 2 K s^?1 and irradiated at a dose rate of 0.995 kGy h^?1 for 5 Gy. In present study the trapping parameters such as order of kinetics (b), activation energy (E) and frequency factors (s) have been calculated for the 195 and 200 °C glow peaks of NaMgSO₄Cl: Cu and NaMgSO₄Cl: Ce, respectively by using Chen's method. The paper discusses the luminescence of Cu⁺ and Ce³⁺ by simple method of incorporation in NaMgSO₄Cl host.     

Na2SrMg(PO4)2: Ce3+, Mn2+荧光粉的发光性质及其能量传递机理

采用高温固相法制备了Na₂SrMg(PO₄)₂: Ce³⁺, Mn²⁺ (NSMP: Ce³⁺, Mn²⁺) 荧光粉, 并对其发光性质及Ce³⁺ 对Mn²⁺ 的能量传递机理进行了研究. Ce³⁺ 和Mn²⁺ 在334 nm 和617 nm 的发射峰分别为Ce³⁺ 的5d→4f 跃迁和Mn²⁺ 的⁴T₁(⁴G)→⁶A₁(⁶S) 跃迁产生. Ce³⁺ 对Mn²⁺ 的发光有较强的敏化作用, 根据Dexter能量传递效率公式判断Na₂SrMg(PO₄)₂ 中Ce³⁺ 对Mn²⁺ 的能量传递属于电偶极-电四极相互作用引起的共振能量传递.