Effects of charge compensation on red emission in CaYAl3O7:Eu3+ phosphor

Monovalent ions Li+, Na+, and K+, as charge compensators, are introduced into CaYAl3O7: M(M =Eu3+, Ce3+) in this letter. Their crystal phases and photoluminescence properties of different alkali metal ions doped in CaYAl3O7 are investigated. In addition, the influence of charge compensation ion Li+which has a more obvious role in improving luminescence intensity on CaYAl3O7: Eu3+phosphor is intentionally discussed in detail and a possible mechanism of charge compensation is given. The enhancement of red emission centered at 618 nm belonging to Eu3+is achieved by adding alkali metal ion Li+under 393-nm excitation.     

Na+离子掺杂Gd2O3:Sm3+纳米晶的发光增强

采用柠檬酸作燃烧剂,在柠檬酸-硝酸盐体系下制备了Gd2O3:Sm3+和Gd2O3:Sm3+,Na+纳米晶.用X射线衍射仪、透射电子显微镜、荧光光谱仪等对样品的结构、形貌和光致发光性能进行了分析.结果表明:所得纳米样品为纯立方相,晶粒尺寸约为30 nm.在室温下,用275 nm激发光激发各样品时,可观测到Sm3+离子的较强发光,其主发射峰位分别位于561.5,603.5,651.5 nm,分别对应着Sm3+离子的4G5/2→6H5/2,4G5/2→6H7/2和7G5/2→6H9/2的电子跃迁,其中以4G5/2→6H7/2跃迁的光谱强度最强.实验表明:Na+离子的掺入使得Sm3+离子的光发射强度显著增强.对引起样品荧光强度变化的原因进行了分析.     

Cathodoluminescence properties of Tb3+-doped Na3YSi2O7 phosphors

Tb³⁺-doped Na₃YSi₂O₇ phosphors were prepared by the sol–gel method and then characterized by X-ray diffraction (XRD), field-emission scanning electron microscopy, and cathodoluminescence spectroscopy. The XRD results reveal that the Tb³⁺ ions have been introduced as dopants into the Na₃YSi₂O₇ host lattice. Under low-voltage electron beam excitation, the phosphors exhibit the characteristic emissions of Tb³⁺ (⁵ D _3,4→⁷ F _J , J=3–6 transitions). The luminescence color of the phosphors can be tuned from greenish-blue to bluish-green and to green by controlling the Tb³⁺ concentration within the 0.0005–0.15 (x value). The optimum Tb³⁺ doping concentration is 10 mol%, and the “dead voltage” is approximately 1.35 kV. All results indicate that the sample is a phosphor candidate for field-emission displays.     

Synthesis and luminescence properties of Na2Ba2Si2O7:Eu2+ phosphor

Green-emitting phosphor Na₂Ba₂Si₂O₇:Eu²⁺ has been synthesized by a conventional high-temperature solid-state reaction. The phase structure and luminescence properties are characterized by the X-ray powder diffraction, diffuse reflectance spectra, photoluminescence excitation and emission spectra, temperature-dependent emission spectra, respectively. It can be efficiently excited in the wavelength range of 325–400 nm and consists of a strong broad green band centered at about 501 nm, which is ascribed to 4f⁶6s⁰5d¹ → 4f⁷6s²5d⁰ transition of Eu²⁺. The critical quenching concentration of Eu²⁺ in the Na₂Ba₂Si₂O₇ host is about 0.8 mol % and corresponding quenching behavior is ascribed to be electric dipole–dipole interaction. Furthermore, the phosphor has good thermal stability property, and the activation energy for thermal quenching is calculated as 0.34 eV.     

Effect of charge compensation on emission spectrum of Ca2SiO4:Dy3+ phosphor

The Ca2SiO4:Dy3+ phosphor was synthesized by the high temperature solid-state reaction method in air.The emission spectrum of Ca2SiO4:Dy3+ phosphor shows several bands at 486, 575, and 665 nm under the 365-nm excitation. The effects of Li+, Na+, and K+ on the emission spectrum of Ca2SiO4:Dy3a+ phosphor were studied. The results show that the emission spectrum intensity is greatly influenced by Li+, Na+,and K+. The charge compensation concentration corresponding to the maximum emission intensity is different with different charge compensations.     

SrAl_2B_2O_7:Dy~(3+)材料的制备及其发光性能

采用高温固相法制备了SrAl2B2O7:Dy3+发光材料.在350nm紫外光激发下,测得SrAl2B2O7:Dy3+材料的发射光谱为一个多峰宽谱,主峰分别为480,573和678nm;分别和Dy3+的4F9/2→6H15/2,4F9/2→6H13/2,4F9/2→6H11/2的跃迁发射相对应;监测573nm的发射峰,得到材料的激发光谱为一个多峰宽谱,主峰分别为295,325,350,365,400nm.研究了Dy3+掺杂浓度对SrAl2B2O7:Dy3+材料发射光谱的影响,随着Dy3+掺杂浓度的增大,SrAl2B2O7:Dy3+材料的Iy/Ib逐渐增大,根据Judd-Ofelt理论解释了其原因.随着Dy3+掺杂浓度的增大,Dy3+的4F9/2→6H13/2跃迁产生的573nm发射峰强度先增大,在4%时达到最大值,之后减小,其自身的浓度猝灭机理为电偶极-电偶极相互作用.不同的电荷补偿剂Li+,Na+,K+的引入均使发光强度得到提高,尤其以Li+最佳,发光强度提高了大约33%.     

Jahn-Teller effect on Sm3+ ions in fluctuating-valence compounds

The dynamic and static Jahn-Teller effects are observed in ESR on rare-earth ions, specifically, on Sm³⁺ ions in the fluctuating-valence material SmB₆. Pis’ma Zh. éksp. Teor. Fiz. 66, No. 10, 645–648 (25 November 1997)     

Jahn-Teller effect on Sm3+ ions in SmB6

Electron spin resonance on samarium ions with stabilized valence Sm³⁺ is investigated in the fluctuating-valence semiconductor SmB₆, both pure and doped with the rare-earth ions Eu²⁺, Er³⁺, and Gd₃₊. The dynamic and static Jahn-Teller effects have been observed for the first time on rare-earth ions. The relation between the Jahn-Teller effect in a fluctuating-valence semiconductor and the excitonic nature of the ground state of such a semiconductor is discussed. Zh. éksp. Teor. Fiz. 115, 1860–1871 (May 1999)     

The luminescence properties of Dy3+-activated SrB4O7 under VUV excitation

Dy³⁺-doped SrB₄O₇ phosphors were synthesized by solid-state reaction. The luminescence properties of white-light SrB₄O₇:Dy³⁺ under vacuum ultraviolet (VUV) excitation were firstly investigated. According to strong absorption around 147 nm in excitation spectra, energy can easily be transferred to the energy levels of Dy³⁺ from host absorption, and hence luminescence of SrB₄O₇:Dy³⁺ under VUV excitation was effective, and it has the potential of being applied to a white lamp-house for mercury-free lamp.     

The synthesis and afterglow luminescence properties of a novel red afterglow phosphor: ZrO2:Sm3+,Sn4+

A novel ZrO₂:Sm³⁺,Sn⁴⁺ phosphor is synthesized by solid state reaction. The ZrO₂:Sm³⁺ does not show afterglow. But, after doping Sn⁴⁺, intense red afterglow luminescence is firstly observed in ZrO₂:Sm³⁺,Sn⁴⁺ and it can last more than 1000 s at maximum. The afterglow decay curves of ZrO₂:Sm³⁺,Sn⁴⁺ are fitted by three exponential components and the decay process consists of initial fast, intermediate and slow decay. The thermoluminescence indicates that the Sn⁴⁺ ions induce suitable traps with the depth of 0.436 eV and result in efficient afterglow luminescence of ZrO₂:Sm³⁺,Sn⁴⁺. The thermoluminescence filling and fading experiments further confirm the important role of the proper shallow traps induced by doping Sn⁴⁺ on the afterglow of ZrO₂:Sm³⁺,Sn⁴⁺.     

Luminescent properties of Eu2+and Dy3+ ions in Ba4Al2O7 phosphor for solid state lighting

In this paper we report the combustion synthesis of rare earth (RE=Eu, Dy) doped Ba₄Al₂O₇ phosphors. Prepared phosphors were characterized by X-ray powder diffraction (XRD), scanning electron microscope (SEM), Fourier transform infrared spectroscopy (FTIR), CIE color co-ordinates and their photoluminescence (PL) properties were also investigated. In case of Ba₄Al₂O₇: Eu²⁺, the emission spectra show unique band centered at 495 nm, which corresponds to the 4f⁶5d¹→4f⁷ transition of Eu²⁺, and PL emission spectra of Dy³⁺ ion under 348 nm excitation give two bands centered at 478 nm (blue) and 575 nm (yellow), which originate from the transitions of ⁴F_9/2→⁶H_15/2 and ⁴F_9/2→⁶H_13/2 of Dy³⁺, respectively. The results indicate that the Eu²⁺ and Dy³⁺ activated Ba₄Al₂O₇ phosphor could find application in solid state lighting.     

Thermal annealing behavior of luminescence of Gd3+-doped PbWO4 single crystal in air atmosphere

The results of photoluminescence measurements on as-grown PbWO₄:Gd³⁺ show that Gd³⁺ acts as a sensitizer of luminescence in the PbWO₄ lattice. Effects of sequential annealing in air atmosphere on luminescence of PbWO₄:Gd³⁺ were investigated by means of X-ray excited luminescence and photoluminescence. The annealing experiments indicate that the essence of the annealing in air atmosphere is the exchange of oxygen components between PbWO₄:Gd³⁺ crystal and the environment to improve the defects in the lattice. Annealing at a temperature of about 640 °C could further enhance the luminescence of PbWO₄ and depress it at a higher temperature. However, PbWO₄:Y³⁺ and PbWO₄:La³⁺ crystals do not show any luminescence enhancement in the same annealing process. A tentative mechanism of luminescence enhancement due to annealing is suggested. PACS 74.62.Dh; 81.40.Tv; 78.55.-m; 82.80.Pv; 78.70.En     

The luminescence properties of Eu2+ doped Na2CaMg(PO4)2 phosphor

The blue-emitting phosphors of Eu²⁺-doped Na₂CaMg(PO₄)₂ were prepared by high-temperature solid-state reaction. The crystal phase formation was confirmed by X-ray powder diffraction measurement. The luminescence properties were investigated by photoluminescence excitation and emission spectra. The phosphor exhibited the blue luminescence due to the 4f⁶5d¹→4f⁷ transition of Eu²⁺ ions under the excitation of near UV light. The influence of temperature on the luminescence intensities and decay lifetimes of Eu²⁺ was investigated. An unusual increase of the decay lifetimes of the 4f⁶5d emission of Eu²⁺ ion is observed in Na₂CaMg(PO₄)₂ from 10 K to room temperature. The thermal stability of the luminescence of Eu²⁺-doped Na₂CaMg(PO₄)₂ was discussed.     

Size-dependent luminescence in Y2Si2O7 nanoparticles doped with Ce3+ ions

Powders and thin films of nanocrystalline yttrium disilicate (Y₂Si₂O₇) doped with Ce³⁺ have been prepared by a sol–gel method. Structure and morphology of the synthesised samples have been determined and spectroscopic properties compared. The triclinic α-Y₂Si₂O₇ form (space group P 1-) for the powders annealed between 1000°C and 1200°C has been found. A total conversion into a thortveitite-type monoclinic β-Y₂Si₂O₇ polymorph after annealing of powder samples at 1400°C (space group C2/m) has been observed. In the case of films even at 1300°C the basically pure triclinic α-Y₂Si₂O₇ phase was observed with luminescent spectroscopy. The influence of grain size, controlled by thermal treatment, on the structure and luminescence properties of the fabricated materials are presented and discussed.     

Preparation of Sm3+–Eu3+ coactivating red-emitting phosphors and improvement of their luminescent properties by charge compensation

By charge compensating, a series of red-emitting phosphors Ca_0.54Sr_0.16Ca_0.54Sr_0.31Eu_0.08Sm_0.02(MoO₄)_0.6(WO₄)_0.4 were synthesized. Two approaches to charge compensation were used: (a) 2Ca²⁺/Sr²⁺→Eu ³⁺/Sm³⁺+M ⁺, where M⁺ is a monovalent cation like Li⁺, Na⁺ or K⁺; (b) Ca²⁺/Sr²⁺→Eu ³⁺/Sm³⁺+N ^?, where N⁺ is a monovalent anion like F^?, Cl^?, Br^?, or I^?. One red LED was made by combining the phosphor and 390–405 nm emitting LED chip under 20 mA forward-bias current, the color purity, chromaticity coordinates and the luminous intensity of which were 99.5%, x=0.66, y=0.33, 5600 mcd, respectively.