Luminescence of Ce in some chloroaluminates

Chloroaluminate systems are important due to their use in the production of aluminum and sodium metals, in electro-deposition of aluminum alloys, extraction of aromatic hydrocarbons, etc. However, no data on luminescence in these compounds are available. Low melting points and instability due to the high volatility of AlCl₃ seem to be deterrents for carrying out such investigations. Synthesis and photoluminescence spectra of Ce³⁺ activated alkali chloroaluminates and some alkaline earth chloroaluminate phosphors are described for the first time in the present work. A simple wet chemical method is used for the preparation of the phosphor. Very intense emission was observed for LiCl·AlCl₃ and NaCl·AlCl₃. For the former, the emission attributable to d-f transitions is entirely in the UVA1 (ultraviolet A1) region. The intensity is comparable to that of a commercial phosphor. Ce³⁺ activated emission in the alkaline earth compounds CaCl₂·AlCl₃ and MgCl₂·2AlCl₃ was relatively much weaker.     

Luminescence of BaAl2O4:Mn,Ce phosphor

Powder samples of barium aluminate doped with Mn²⁺ and Ce³⁺ were prepared by solid-state reaction method and their photoluminescence and thermoluminescence properties were studied. Substitution of Ca/Sr in place of Ba resulted in enhanced emission from Ce³⁺ ions without changing the spectral profile. Cerium efficiently sensitized the manganese luminescence in barium aluminate. Photoluminescence and thermo luminescence observations have indicated the presence of V_k³⁺ defects in undoped barium aluminate. However, Barium aluminate (either undoped or doped with manganese) did not exhibit long afterglow.     

Luminescence and scintillation properties of YAG:Ce single crystal and optical ceramics

We use various techniques to study optical and scintillation properties of Ce-doped yttrium aluminum garnet, Y₃Al₅O₁₂ (YAG:Ce), in the form of a high-quality industrial single crystal. This was compared to optical ceramics prepared from YAG:Ce nanopowders. We present experimental data in the areas of optical absorption, radioluminescence, scintillation decay, photoelectron yield, thermally stimulated luminescence and radiation-induced absorption. The results point to an interesting feature—the absence of antisite (Y_Al, i.e. Y at the Al site) defects in optical ceramics. The scintillation decay of the ceramics is faster than that of the single crystal, but its photoelectron yield (measured with 1 μs integration time) is about 30-40% lower. Apart from the photoelectron yield value the YAG:Ce optical ceramic is fully comparable to a high quality industrial YAG:Ce single crystal and can become a competitive scintillator material.     

Luminescence of Ce in Ca0.65La0.35F2.35 host

The title compound was prepared by precipitation followed by thermal annealing at 1000 °C. Photoluminescence of Ce³⁺ was studied. In this host, Ce³⁺ exhibits PL that is totally different from that observed for the constituent fluorides. For 5 mol% Ce, blue emission was observed with a maximum at 449 nm corresponding to near UV excitation. It is suggested that these characteristics can be useful for obtaining a low cost, blue phosphor for the solid state lighting using near UV LED.     

Luminescence of Ce and Pr doped Sr2Mg(BO3)2 under VUV-UV and X-ray excitation

This report presents the luminescence properties of Ce³⁺ and Pr³⁺ activated Sr₂Mg(BO₃)₂ under VUV-UV and X-ray excitation. The five excitation bands of crystal field split 5d states are observed at about 46 729, 44 643, 41 667, 38 314 and 29 762 cm⁻¹ (i.e. 214, 224, 240, 261 and 336 nm) for Ce³⁺ in the host lattice. The doublet Ce³⁺ 5d→4f emission bands were found at about 25 840 and 24 096 cm⁻¹ (387 and 415 nm). The influence of doping concentration and temperature on the emission characteristics and the decay time of Ce³⁺ in Sr₂Mg(BO₃)₂ were investigated. For Pr³⁺ doped samples, the lowest 5d excitation band was observed at about 42017 cm⁻¹ (238 nm), a dominant band at around 35714 cm⁻¹ (280 nm) and two shoulder bands were seen in the emission spectra. The excitation and emission spectra of Ce³⁺ and Pr³⁺ were compared and discussed. The X-ray excited luminescence studies show that the light yields are ∼3200±230 and ∼1400±100 photons/MeV of absorbed X-ray energy for the samples Sr_1.86Ce_0.07Na_0.07Mg(BO₃)₂ and Sr_1.82Pr_0.09Na_0.09Mg(BO₃)₂ at RT, respectively.     

稀土硼酸盐玻璃中Ce3+的光谱性质和荧光衰减

合成Ｃｅ＾３＋掺杂的稀土硼酸盐玻璃,测试了材料的激发和发射光谱及荧光衰减曲线。紫外光激发下,玻璃中的Ｃｅ＾３＋发射强的蓝紫光,光谱的荧光寿命的分析结果表明,Ｃｅ＾３＋在这种稀土硼酸盐玻璃中形成两种性质不同的发光中心。     

Luminescence enhancement in (Nd+Ce) doped SiO2 : Al2O3 sol–gel glasses

An enhancement in NIR luminescence from Nd³⁺-doped Ce³⁺ co-doped SiO₂+Al₂O₃ sol–gel glasses has been observed. The lasing transition (⁴F_3/2→⁴I_11/2) at 1072 nm from the dual rare-earth Nd³⁺+Ce³⁺-doped glasses has shown an emission strength of about five times that of the single rare-earth ion Nd³⁺-doped glass. From the measurement of lifetimes of the transition at 1072 nm, the transfer rate (W_tr), critical distance (R₀) and energy transfer efficiency (η) of the neodymium glasses have been calculated.     

Luminescence spectroscopy of Eu in Ca3Sc2Si3O12

Ca₃Sc₂Si₃O₁₂ doped with 1 mol% Eu³⁺ and having a cubic garnet structure was prepared by a solid state reaction. The low temperature luminescence spectrum shows no measurable ⁵D₀→⁷F₀ band, in agreement with the location of the lanthanide dopant in a site of D₂ symmetry, i.e. with a Ca²⁺ substitution. On the other hand, the spectrum is clearly dominated by the ⁵D₀→⁷F₄ band, which is significantly stronger than that for the other transitions originating from the ⁵D₀ level. This unusual behavior is explained on the basis of a model describing the distortion of the EuO₈ coordination polyhedron from a cubic geometry to the actual D₂ one.     

High Pressure Spectroscopy of Ce Doped Yag Crystal

Electronic structure and optical properties of the Ce^3? in YAG has been investigated by standard spectroscopy (photoluminescence, absorption and excitation spectra) and high pressure spectroscopy. The bandshape of the emission spectrum for different pressures has been analyzed and influence of pressure on energy of the 5d¹ states and the electron-lattice coupling have been determined. The significant red shift of the peak of the emission band (the respective pressure coefficient has been equal to—12cm^?1/kbar) has been obtained. The shift has been understood by taking into account pressure induced increase of the 5d¹ level splitting and increase of the electron-lattice coupling strength.     

Heat-treatment-induced luminescence degradation in Tb-doped CePO4 nanorods

CePO₄:Tb nanorods were synthesized via a simple wet-chemical route. The as-synthesized CePO₄:Tb nanorods present high photoluminescence efficiency due to an efficient energy transfer form Ce³⁺ to Tb³⁺. However, heat treatment at 150 °C in air leads to a significant decrease of photoluminescence. X-ray photoelectron spectroscopy and excitation spectra revealed the oxidation of Ce³⁺ to Ce⁴⁺ in the heat-treatment process, which should be responsible for significant photoluminescence degradation due to the breakage of Ce³⁺→Tb³⁺ energy transfer. This conclusion is further supported by atmosphere and size effects of photoluminescence of CePO₄:Tb under the heat treatment.     

Infrared-excited bright green and red luminescence in La3Ga5.5Ta0.5O14 doped with erbium and ytterbium

Bright green (at 525 and 550 nm) and red (at 660 nm) luminescence in Er:Yb:La₃Ga_5.5Ta_0.5O₁₄ (LGT) powder synthesized by solid state reaction was obtained by pumping at 936 nm. Yb³⁺-Er³⁺ energy transfer processes accounting for population of the ²H2_11/2, ⁴S_3/2 and ⁴F_9/2 Er³⁺ levels are discussed. The dependence of ratio between the intensities of the green and red luminescence on pump intensity is analyzed. The rather high quantum efficiency (58%) of the (⁴S_3/2, ²H2_11/2) Er³⁺ emitting level recommends LGT doped with erbium and ytterbium for upconversion applications.     

Luminescence properties of Y3Al5O12:Ce nanoceramics

Comparative analysis of the luminescent properties of Y₃Al₅O₁₂:Ce (YAG:Ce) transparent optical ceramics (OС) with those of single crystal (SC) and single crystalline film (SCF) analogues has been performed under excitation by pulsed synchrotron radiation in the fundamental absorption range of YAG host. It has been shown that the properties of YAG:Ce OC are closer to the properties of the SCF counterpart, where Y_Al antisite defects are completely absent, rather than to the properties of SC of this garnet with large concentration of Y_Al antisite defects. At the same time, the luminescence spectra of YAG:Ce OC show weak emission bands in the 200-470 nm range related to Y_Al antisite defects and charged oxygen vacancies (F⁺ and F centers). YAG:Ce ОС also possesses significantly larger contribution of slow components in the Ce³⁺ luminescence decay under high-energy excitation in comparison with SC and SCF of this garnet due to the involvement of antisite defects, charged oxygen vacancies as well as boundaries of grains in the energy transfer processes from the host to the Ce³⁺ ions.     

5d-level energies of Ce and the crystalline environment. IV. Aluminates and “simple” oxides

Information on the energy of 5d-levels of Ce³⁺ ions in aluminates and “simple” oxides has been collected. The crystal field splitting of the 5d-levels is interpreted in terms of the type and size of anion polyhedron coordinating the Ce³⁺ ion. The centroid (barycenter) shift of the 5d-configuration is analyzed by a ligand polarization model providing values for the spectroscopic polarizability α_sp of the anion ligands. The data provide evidence that the centroid shift behaves independently from the crystal field splitting. By combining centroid shift and crystal field splitting, the “spectroscopic” redshift of the first electric dipole-allowed fd transition of Ce³⁺-doped in the compounds will be interpreted. The large crystal field splitting in garnet compounds and the small splitting in perovskite compounds will be discussed.     

Influence of temperature and electrolyte ions on the properties and spectrum of solvated electrons in irradiated hexamethylphosphortriamide

Abstract

Radiation-induced latchup in commercially available junction-isolated integrated microcircuits is reported. Four different types of construction of integrated microcircuits have been examined. They include quadruplediffused, diffused collector, epitaxial, and epitaxial with buried layer (gold-doped). It was found that pnpn switching could be obtained between isolated components on these devices. In fact, pnpn paths were quite common in all but the last type mentioned. The current gains of the parasitic transistors involved in these pnpn paths were measured and were, in most cases, shown to indicate that pnpn switching should occur. However, important exceptions were seen. Latchup between these isolated components could be induced by a pulse of ionizing radiation even with a reverse bias on the substrate of the microcircuits. As a result of this investigation, it is concluded that the pnpn mechanism, since it is so common, is a majorcause of latchup in junction-isolated integrated microcircuits.     

Photoluminescence properties of Tb in porous silicon

Terbium (Tb³⁺)/porous silicon (PS) nanocomposites have been formed by impregnation of PS layer in chloride solution of terbium. Complete and uniform penetration of Tb³⁺ into PS layer is confirmed by Rutherford backscattering spectrometry (RBS) study. Photoluminescence (PL) spectrum shows that Tb³⁺ ions emit highly in the green region, while the PL band of PS is quenched. The emission of Tb³⁺ ions depends strongly on the excitation energy and shows a high efficiency at 488 nm corresponding to the maximum absorption band in terbium. A systematic study of the PL versus annealing temperature was performed. It shows an important improvement of the PL intensity for 700°C temperature annealing.     

Luminescence spectroscopy of rare earth-doped oxychloride lead borate glasses

Ln-doped oxychloride lead borate glasses were studied using luminescence spectroscopy. Rare earth ions were limited to trivalent Pr³⁺, Tm³⁺, Eu³⁺ and Er³⁺. Luminescence spectra were registered, which correspond to ³P₀-³H₄ and ¹D₂-³H₄ transitions of Pr³⁺, ¹G₄-³H₅ and ¹G₄-³F₄ transitions of Tm³⁺, ⁵D₀-⁷F_J (J=0, 1, 2, 3, 4) transitions of Eu³⁺ and ⁴S_3/2,²H_11/2-⁴I_15/2 and ⁴I_13/2-⁴I_15/2 transitions of Er³⁺. Luminescence decays from the excited states of Ln³⁺ ions were analyzed in detail. The experimental results indicate that relatively high phonon energy of the host gives important contribution to the excited state relaxation of rare earth ions.     

Energy transfer in Y3Al5O12:Ce, Pr and CaMoO4:Sm, Eu phosphors

Non-radiative energy transfers (ET) from Ce³⁺ to Pr³⁺ in Y₃Al₅O₁₂:Ce³⁺, Pr³⁺ and from Sm³⁺ to Eu³⁺ in CaMoO₄:Sm³⁺, Eu³⁺ are studied based on photoluminescence spectroscopy and fluorescence decay patterns. The result indicates an electric dipole-dipole interaction that governs ET in the LED phosphors. For Ce³⁺ concentration of 0.01 in YAG:Ce³⁺, Pr³⁺, the rate constant and critical distance are evaluated to be 4.5×10⁻³⁶ cm⁶ s⁻¹ and 0.81 nm, respectively. An increase in the red emission line of Pr³⁺ relative to the yellow emission band of Ce³⁺, on increasing Ce³⁺ concentration is observed. This behavior is attributed to the increase of spectral overlap integrals between Ce³⁺ emission and Pr³⁺ excitation due to the fact that the yellow band shifts to the red spectral side with increasing Ce³⁺ concentration. In CaMoO₄:Sm³⁺, Eu³⁺, Sm³⁺-Eu³⁺ transfer occurs from ⁴G_5/2 of Sm³⁺ to ⁵D₀ of Eu³⁺. The rate constant of 8.5×10⁻⁴⁰ cm⁶ s⁻¹ and the critical transfer distance of 0.89 nm are evaluated.     

Luminescence of Mn ions in Tb3Al5O12 garnet

The paper is dedicated to investigation of the Mn²⁺ luminescence in Tb₃Al₅O₁₂ (TbAG) garnet, as well as the processes of excitation energy transfer between host cations (Tb³⁺ ions) and activators (Mn²⁺ and Mn²⁺-Ce³⁺ pair ions) in single crystalline films of TbAG:Mn and TbAG:Mn,Ce garnets which can be considered as promising luminescent materials for conversion of LED's radiation. Due to the effective energy transfer between TbAG host and activator, Mn²⁺ ions in TbAG possess the bright orange luminescence in the bands peaked at 595 nm with a lifetime of 0.64 ms which are caused by the ⁴T₁→⁶A₁ radiative transitions. The simultaneous process of energy transfer is realized in TbAG:Mn,Ce: (i) from Tb³⁺ to Mn²⁺ ions; (ii) from Tb³⁺ cations to Ce³⁺ ions and then partly to Mn²⁺ ions through Tb³⁺ ion sublattice and Ce-Mn dipole-dipole interaction.     

Photostimulated transformations of radiation color centers of SrCl2−Ce crystals

Spectra of x-ray radiation-induced absorption of SrCl₂−Ce crystals in the region of 340–830 nm under the effect of selective irradiation in the induced-absorption bands by both conventional and laser sources are investigated. It is established that irradiation of sufficient intensity causes irreversible photochemical transformations of PC, PC⁺, and Ce²⁺ color centers their destruction, and restoration of the transparency of the crystals. To whom correspondence should be addressed. I. Franko Lvov State University, 8, Kirill and Mefodii Str., Lvov, 290005, Ukraine. Translated from Zhurnal Prikladnoi Spektroskopii, Vol. 66, No. 5, pp. 666–668, September–October, 1999.     

Synthesis and luminescence properties of Eu, Ce and Tb-activated Sr3La2(BO3)4 under UV excitation

The spectroscopic properties in UV-excitable range for the phosphors of Sr₃La₂(BO₃)₄:RE³⁺ (RE³⁺=Eu³⁺, Ce³⁺, Tb³⁺) were investigated. The phosphors were synthesized by conventional solid-state reactions. The photoluminescence (PL) spectra and commission international de I'Eclairage (CIE) coordinates of Sr₃La₂(BO₃)₄:RE³⁺ were investigated. The f-d transitions of Eu³⁺, Ce³⁺ and Tb³⁺ in the host lattices are assumed and corroborated. The PL and PL excitation (PLE) spectra indicate that the main emission wavelength of Sr₃La₂(BO₃)₄:Eu³⁺ is 611 nm, and Sr₃La₂(BO₃)₄:Ce³⁺ shows dominating emission peak at 425 nm, while Sr₃La₂(BO₃)₄:Tb³⁺ displays green emission at 487, 542, 582 and 620 nm. These phosphors were prepared by simple solid-state reaction at 1000 °C. There are lower reactive temperature and more convenient than commercial phosphors. The Sr₃La₂(BO₃)₄:Tb³⁺ applied to cold cathode fluorescent lamp was found to emit green light and have a major peak wavelength at around 542 nm. These phosphors may provide a new kind of luminescent materials under ultraviolet excitation.