Ni2+ emission in SrF2

Luminescence measurements of X-irradiated SrF₂:Ni are reported. After X-irradiation two emission bands have been found. One of them peaked at 293 nm and has an excitation band at 267 nm. The other one at about 770 nm, which is much weaker, has an excitation band at 274 nm. Both emission bands are also observed under X-ray excitation. A comparison with some previous studies of the absorption and thermoluminescence properties of X-irradiated SrF₂:Ni indicates that the emission bands are due to two different kinds of Ni²⁺ centers. The proposed emission mechanisms are similar to those found in CaF₂:Ni.     

Luminescence in x-irradiated CaF2:Co

Photoluminescence of X-irradiated CaF₂:Co single crystals is reported. The emission spectrum shows four peaks at 505, 550, 640 and 685 nm, all of them with an excitation band at 275 nm. The same emission spectrum, plus a band at 280 nm, is found in X-ray excited luminescence measurements. Thermoluminescence of 80 K X-irradiated crystals gives a glow curve with five peaks at 100, 125, 145, 190 and 225 K. The spectral distribution of these glow peaks is similar to that of the X-ray excited luminescence. The 280 nm band is associated with electron—hole recombination. The other four bands are associated with electron transitions among excited states of Co²⁺ produced by recombination of holes and Co⁺-ions created by X-irradiation.     

Thermoluminescence of 3d-ions doped CaF2

Thermoluminescence measurements of 80 K X-irradiated CaF₂: Me (Me: Mn, Co, Ni) are reported. The spectral distributions of the glow peaks coincide with those of the X-ray excited luminescence. It has been previously attributed to Me²⁺ emission. The temperatures, activation energies and order of the kinetics for each peak are reported. They do not depend on the dopant and are the same as those given by other authors for the glow peaks in 80 K X-irradiated CaF₂: RE. The observed emission is attributed to the de-excitation of Me²⁺ formed in an excited state by recombination of released holes with Me⁺ formed during low temperature X-irradiation. A similar mechanism has been proposed to explain the TL measurements in CaF₂: RE.     

Vacuum ultraviolet 5d14f9-4f10 emission of Ho3+ ions in alkaline-earth fluorides

Time-resolved emission and excitation spectra as well as emission decay kinetics of CaF₂, SrF₂, BaF₂ doped with HoF₃ were investigated. Intensive emission bands near 168 nm, having long decay time, are caused by the spin-forbidden transitions from the 5d¹4f⁹ high-spin states to the ground ⁵I₈ states of Ho³⁺ ions. Weak spin allowed 5d¹4f⁹(low-spin)-4f¹⁰ emission band at 158 nm was observed only in CaF₂–Ho crystals. Spin allowed and spin-forbidden excitation bands were observed near 166 and 155 nm, respectively, in all studied crystals. Fast component of spin-forbidden emissions due to multiphonon relaxation to low-lying 4f¹⁰ Ho³⁺ level also was observed for all crystals.     

Site selective 4f5d spectroscopy of CaF2 : Pr

Spectroscopic investigations were performed on a single crystal of CaF₂ doped with 0.05% Pr³⁺. Three different Pr³⁺ sites with different luminescent properties were identified. The 4f² →4f¹5d¹ excitation spectrum of the first site has a sharp maximum at 221.3 nm. Excitation in the 4f5d bands of this site yields strong 4f5d emissions in the UV/VIS part of the spectrum and also weaker intraconfigurational 4f² emissions. By comparing the intraconfigurational 4f emissions and their decay times with data from the literature, these 4f5d bands are assigned to transitions on Pr³⁺ ions on a site with C_4V symmetry. The fd excitation spectrum of the second site has a zero phonon line at 223.3 nm. Upon selective excitation in this band, only 4f5d emission is observed. Probably, these 4f5d bands correspond to Pr³⁺ ions on a O_h site. The third set of 4f5d bands has a 4f5d onset at 208 nm. By comparison of the luminescence spectra of the intraconfigurational 4f² transitions with literature data, these transitions are assigned to Pr³⁺ on an L site. Excitation in these 4f5d band yields ¹S₀ emission followed by emission from the ³P₀ state. The present results clarify some contradictions reported in the literature.     

The charge states’ conversion of the activator ions in CaF2:Eu nanophosphors

According to stationary X-ray-excited luminescence spectra and thermally stimulated luminescence spectra of CaF₂:Eu nanophosphors, it was found that Eu³⁺?→?Eu²⁺ conversion can occur during thermal annealing of fine-grained (d?=?25?nm) nanoparticles in the 200–800°C range, which is accompanied by an increase in their size within 40–189?nm. An important role of the exciton mechanism of Eu²⁺ luminescence excitation was revealed according to the temperature dependence of X-ray-excited luminescence spectra of CaF₂:Eu nanoparticles of 114?nm size. The maximum of the X-ray-excited luminescence light output of CaF₂:Eu nanophosphors in the Eu²⁺ ions’ emission band was traced out at 400–500°C annealing temperature and at the size of nanoparticles of 114–180?nm. The subsequent growth of the annealing temperatures, particularly in the 800–1000°C range, causes the reduction of X-ray-excited luminescence light output because of the increment of lattice defects’ concentration due to a sharp increase in the size of nanoparticles and their agglomeration.     

Photoluminescence studies of γ-irradiated CaF2:Dy:Pb:Na single crystals

The optical absorption (OA) and photoluminescence (hereafter referred to as luminescence) studies were made on CaF₂:Dy:Pb:Na single crystals (Dy—0.005 at%, Pb—0.188 at% and Na—0.007 at%) before and after γ-irradiation. The unirradiated crystal exhibited a strong OA band around 6.36 eV attributed to the ‘A’ band absorption of Pb²⁺ ions. The γ-irradiated crystal exhibited OA bands around 2.06, 3.28, 3.75 (broad shoulder) and 2.48 eV. The first three bands could be tentatively attributed to M_Na centre when compared with that of the coloured CaF₂:Na. The origin of 2.48 eV band was not explicitly known. Luminescence emission and excitation of Pb²⁺ and Dy³⁺ ions were negligible in the unirradiated crystal. Irradiated crystal exhibited a strong excitation spectrum with overlapping bands, due to different colour centres, in the UV-vis region for the 2.15 eV emission characteristic of Dy³⁺ ion. When excited, the absorbed energy (may be a part) was transferred from a colour centre to nearby Dy³⁺ ions and Dy³⁺ characteristic emission was observed. Exciting the irradiated crystal around 3.28 eV yielded emission at 2.56, 2.15 and 1.76 eV. The first two emission bands were due to Dy³⁺ ions. The excitation spectrum for the 1.76 eV emission showed two prominent bands around 2.02 and 3.08 eV and hence the emission was attributed to the M_Na centre. The luminescence mechanism was described.     

Luminescence properties of novel NaBa4(BO3)3:Ce, Eu phosphors

Novel Eu³⁺, Ce³⁺ activated NaBa₄(BO₃)₃ phosphors were synthesized by solid-state reactions. The excitation spectrum of NaBa₄(BO₃)₃:Ce³⁺ consists of an intense band peaking at 350 nm and a weak band in the higher energy side, and the emission spectrum exhibits a blue band with a maximum at about 420 nm. The Eu³⁺ emission in NaBa₄(BO₃)₃ consists of the transitions from ⁵D₀ to ⁷F_J, and the excitation spectrum consists of broad excitation band peaking at 270 nm and some intense narrow lines. The optimum doped concentration, the critical distance of the concentration quenching, and the fluorescence lifetime have also been investigated.     

Luminescence of Pr3+-Activated fluorides

The strong dependence of the emission spectrum of YF₃:Pr³⁺ on excitation source (228.8 nm, 213.9 nm or cathode rays) is ascribed to two different types of Pr³⁺ sites: one with a relatively strong crystal field and the other with a relatively weak crystal field. The presence of the latter is connected with the conversion of one short-wave UV (? 215 nm) photon into two visible photons. Two-photon luminescence of Pr³⁺ was also found for α-NaYF₄ and LaF₃, but not for CaF₂ and BaF₂ due to the too strong crystal field in these lattices. The occurrence of two-photon Pr³⁺ luminescence is compared with the intensity of the IR-excited green emission of the corresponding Yb³⁺, Er³⁺-activated lattices. The intensity of the Pr³⁺ luminescence at shortwave UV excitation (213.9 nm) is rather weak. Luminescence of reasonable efficiency is, however, observed on excitation with cathode rays.     

白光LED用LiBaBO3:Eu2+材料发光特性研究

采用高温固相法制备了LiBaBO₃:Eu²⁺绿色发光材料.测量了Eu²⁺浓度为1mol%时样品的激发与发射光谱,其发射光谱为双峰宽谱,主峰分别为482和507nm,与理论计算值符合很好;监测482nm发射峰时,对应激发光谱的峰值为287和365nm,监测507nm发射峰时,对应的激发峰为365和405nm.研究了Eu²⁺浓度对材料发射光谱的影响,结果显示,随Eu²⁺浓度的增大,蓝、绿发射峰均发生了     

Absorption,luminescence, and electron paramagnetic resonance of molybdenum ions in CdWO4

A single crystal of cadmium tungstate (CdWO₄) containing approximately 200 ppm of molybdenum was grown by the Czochralski method and then characterized in a series of optical absorption, photoluminescence (PL), photoluminescence excitation (PLE), and electron paramagnetic resonance (EPR) experiments. The Mo⁶⁺ ions substitute for W⁶⁺ ions and serve as recombination sites for electrons and holes when the crystal is exposed to ionizing radiation. A charge-transfer absorption band for the Mo⁶⁺ ions was observed near 320 nm at 10 K. The PL experiments, performed at low temperature with 325 nm excitation, showed a Mo-associated emission peaking near 680 nm. A direct correlation of the 680 nm emission and the 320 nm absorption band was established by the PLE data. When these doped CdWO₄ crystals are exposed at low temperature either to light that is near or above the band gap or to X-rays, the Mo⁶⁺ ions can trap an electron and form stable Mo⁵⁺ ions. The EPR spectrum of the Mo⁵⁺ ions was observed at temperatures near 15 K, and a complete set of parameters describing the g matrix was obtained from an angular dependence study.     

Photoluminescence properties of Eu and Mn-activated BaMgP2O7 as a potential red phosphor for white-emission

A phosphate compound, BaMgP₂O₇ was co-doped with Eu²⁺ and Mn²⁺ for making a red-emitting phosphor. The phosphor was prepared by a solid-state reaction at high temperature. The photoluminescence properties were investigated under ultraviolet (UV) ray excitation. From a powder X-ray diffraction (XRD) analysis, the formation of single-phased BaMgP₂O₇ with a monoclinic structure was confirmed. In the photoluminescence spectra, the BaMgP₂O₇:Eu,Mn phosphor emits two distinctive colors: a blue band centered at 409 nm originating from Eu²⁺ and a red band at 615 nm caused by Mn²⁺. Also, efficient energy transfer from Eu²⁺ to Mn²⁺ in the BaMgP₂O₇:Eu,Mn system was verified by observing that the excitation spectra of BaMgP₂O₇:Eu,Mn emitted at 409 and 615 nm by Eu²⁺ emission and Mn²⁺ emission, respectively, are almost the same as that of BaMgP₂O₇:Eu monitored at 409 nm. The optimum concentration of Eu²⁺ ions in BaMgP₂O₇:0.015Eu excited at 309 nm wavelength is 1.5 mol%. With an increase of Mn²⁺ content up to 17.5 mol%, a systematic decline in the intensity of the excitation spectrum by Eu²⁺ and a gradual growth in the intensity of emission band by Mn²⁺ were observed. Accordingly, the optimum concentration of Mn²⁺ in BaMgP₂O₇:0.015Eu,Mn is 17.5 mol%. The maximum spectral overlap between emission of Eu²⁺ and excitation of Mn²⁺ is achieved in a composition of BaMgP₂O₇:0.015Eu,0.175Mn, resulting in considerable red-emission at 615 nm.     

Ca2SiO4:Dy3+材料的制备及其发光特性

采用高温固相法制备了Ca₂SiO₄:Dy³⁺发光材料.在365nm紫外光激发下,测得Ca₂SiO₄:Dy³⁺材料的发射光谱为一多峰宽谱,主峰分别位于486nm,575nm和665nm处;监测575nm发射峰,测得材料的激发光谱为一多峰宽谱,主峰分别位于331nm,361nm,371nm,397nm,435nm,461nm和478nm处.研究了Dy³⁺掺杂浓度对Ca₂SiO₄:Dy³⁺材料发射光谱及发光强度的影响,结果显示,随Dy³⁺浓度的增大,黄、蓝发射峰强度比(Y/B)逐渐增大,利用Judd-Ofelt理论解释了其原因;随Dy³⁺浓度的增大,Ca₂SiO₄:Dy³⁺材料发光强度先增大,在Dy³⁺浓度为4 mol%时到达峰值,而后减小,根据Dexter理论其浓度猝灭机理为电偶极-电偶极相互作用.研究了电荷补偿剂Li⁺,Na⁺和K⁺对Ca₂SiO₄:Dy³⁺材料发射光谱的影响,结果显示,不同电荷补偿剂下,随电荷补偿剂掺杂浓度的增大,Ca₂SiO₄:Dy³⁺材料发射光谱强度的演化趋势相同,即Ca₂SiO₄:Dy³⁺材料发射峰强度先增大后减小,但不同电荷补偿剂下,材料发射峰强度最大处对应的补偿剂浓度不同,对应Li⁺,Na⁺和K⁺时,浓度分别为4mol%,4mol%和3mol%. 关键词： 白光LED 2SiO₄:Dy³⁺')" href="#">Ca₂SiO₄:Dy³⁺ 发光特性 电荷补偿     

Luminescence channels of manganese-doped spinel

Two independent luminescence channels are observed from manganese-doped spinel Mn:MgAl₂O₄. The luminescence around 520 nm is assigned to transition from the lowest electronic excited state ⁴T₁ to the ground state ⁶A₁ of Mn²⁺ (3d)⁵ ion by analyzing the excitation spectrum and electron spin resonance measurement. The emission at 650 nm is triggered by the band edge excitation and is assigned similarly to the charge-transfer process associated with the manganese ion.     

Absorption and emission spectroscopic characterisation of F<Subscript>3</Subscript><Superscript>-</Superscript> colour centers in a LiF crystal

For a LiF crystal containing F₃ (R₁, R₂), F₂, F₃ ⁺, F₄ (N₁, N₂), F₃ ^-, and F₂ ^- colour centers the absorption and emission spectroscopic behaviour of the F₃ ^- centers is studied. The absorption cross-section spectrum and the number density of F₃ ^- centers are extracted from saturable absorption and transmission measurements. Additionally fluorescence quantum distribution measurements and fluorescence lifetime measurements are carried out to determine the stimulated emission cross-section spectrum and the fluorescence quantum yield of the F₃ ^- centers. Fluorescence excitation spectroscopy reveals the presence of an absorption band with its absorption peak around 700 nm (called R ₁ band) in addition to the ground-state to first excited-state F₃ ^- center absorption band centered at 800 nm (called R ₂). PACS 61.72.Ji; 78.40.Ha; 78.55.Fv     

Synthesis and luminescent properties of oleic acid (OA)-modified CaF2: Eu nanocrystals

The OA-modified CaF₂: Eu nanocrystals that can be well dispersed in chloroform to form a clear solution were synthesized and characterized. The nanocrystals have a roughly spherical shape with particle diameter of about 10 nm. Possible mechanism was proposed to explain the growth process. Upon the excitation at 395 nm, the room-temperature emission spectrum of the nanocrystals in chloroform presents the characteristic transitions ⁵D₀→⁷F_J of Eu³⁺ ions, with ⁵D₀→⁷F₂ (610 nm) transition as the most prominent group. The luminescence decay of Eu³⁺ ions in CaF₂ nanocrystals was also investigated and two luminescence lifetimes of 737 μs (11.2%) and 2.08 ms (88.8%) were obtained.     

Optical absorption and emission from irradiated RbMgF3:Eu2+ and KMgF3:Eu2+

The optical properties of irradiated RbMgF₃:Eu²⁺ and KMgF₃:Eu²⁺ have been investigated. Previous research has shown that Eu²⁺ ions in unirradiated RbMgF₃ give rise to broad band absorption around 250 nm and sharp intense line emission at 360 nm. When this material is irradiated little or no change occurs in the 250 nm absorption, but the lifetime of the Eu²⁺ 360 nm transition is reduced. In addition, new emission is observed at 680 nm. In the case of irradiated KMgF₃:Eu²⁺ two new emission bands are observed at 600 and 800 nm. All of these transitions have short lifetimes and are not due to Eu³⁺ ions.     

Luminescent properties of RE-activated CaAl2B2O7 (RE=Tb, Ce) in VUV-visible region

RE³⁺-activated α- and β-CaAl₂B₂O₇ (RE=Tb, Ce) were synthesized with the method of high-temperature solid-state reaction. Their VUV excitation and VUV-excited emission spectra are measured and discussed in the present article. The charge transfer band of Tb³⁺ and Ce³⁺ is respectively calculated to be at 151±2 and 159±3 nm. All the samples show an activator-independent excitation peak at about 175 nm and an emission peak at 350-360 nm ascribed to the host absorption and emission band, respectively.     

The luminescence and structural characteristics of Eu- doped NaSrB5O9 phosphor

A red-emitting phosphor NaSrB₅O₉:Eu³⁺ was synthesized by employing a solid-state reaction (SSR) method. The structures of the phosphors were analyzed by X-ray diffraction (XRD), Fourier-transform infrared (FTIR) and Raman studies. The band at ~282 nm in the excitation spectra indicated the charge transfer band (CTB) of B-O in the host, whereas the CTB of Eu-O was observed at ~275 nm for the NaSrB₅O₉:Eu³⁺ (Eu³⁺=1 at.%) phosphor, which was supported by diffuse reflectance spectroscopy (DRS) measurements. The photoluminescence (PL) measurements exhibited a strong red emission band centered at about 616 nm (⁵D₀→⁷F₂) under an excitation wavelength of 394 nm (⁷F₀→⁵L₆). Upon host excitation at 282 nm, the pristine NaSrB₅O₉ exhibited a broad UV emission centered at ~362 nm. The energy transfer from host to Eu³⁺ ions was confirmed from luminescence spectra, excited with a 355 nm Nd:YAG laser. In addition, the asymmetric ratios indicate a higher local symmetry around the Eu³⁺ ion in the host. The calculated CIE (Commission International de l′Eclairage) coordinates displayed excellent color purity efficiencies (around 99.7%) compared to other luminescent materials.     

Blue emission in Ti-sapphire laser crystals

The time resolved emission spectrum of the blue band of Ti:sapphire laser crystal has been investigated as a function of temperature (range 10–290 K) and UV (266 nm) laser excitation intensity. Two blue emission bands, centred at 420 nm and 460 nm, have been detected. The 420 nm band is attributed to Ti⁴⁺ centres whereas the 460 nm one is proposed to be due to Ti³⁺ ions. The evolution of the emission spectrum vs the UV excitation intensity has shown that the concentration of Ti⁴⁺ centres is increased under UV irradiation at the cost of the centres responsible for the 460 nm band.