Enhanced upconversion luminescence of transparent Eu3+-doped glass-ceramics containing nonlinear optical microcrystals

We report on near-infrared to visible upconversion luminescence in transparent Eu3+-doped SrO-TiO2-SiO2 glass-ceramics. X-ray diffraction analysis indicates that Sr2TiSi2O8 crystallites are precipitated in the glass after heat treatment at 850 degrees C for 2 h. The Eu3+-doped glass-ceramics show strongly enhanced upconversion luminescence and greatly improved damage threshold compared with the as-prepared glass. The mechanisms of the observed phenomena are discussed.     

Synthesis and luminescence properties of Er3+-doped Lu3Ga5O12 nanocrystals

The concentration-dependent luminescence properties of sol–gel-derived nanocrystalline Lu_3(1?x)Er_3xGa₅O₁₂ powders (where x=0.01, 0.05 and 0.1) have been studied. Laser-excited luminescence spectra, emission decays and upconversion luminescence of Er³⁺-doped Lu₃Ga₅O₁₂ nanocrystalline samples have been measured. The decay curve of the (²H_11/2,⁴S_3/2) emission exhibits a non-exponential behavior presumably due to cross-relaxation process. Moreover, near-infrared to visible upconversion luminescence has been observed in the green region for 1.0 mol% Er³⁺ ions in Lu₃Ga₅O₁₂ nanocrystals upon 815 nm excitation. The power dependence of the anti-Stokes luminescence suggests that upconversion is probably achieved through the sequential absorption of two photons. To the best of our knowledge, this is the first report on the preparation and optical properties of Er³⁺-doped Lu₃Ga₅O₁₂ in the form of nanocrystalline powders.     

纳米晶Gd2O3：Eu^3＋的制备及发光性能

采用低温燃烧合成法制备了Gd2O3：Eu^3＋纳米晶。用X射线衍射仪（XRD）、高分辨透射电子显微镜（HRTEM）和荧光光谱仪分别对样品的结构、形貌和发光性能进行了研究。结果表明，改变甘氨酸与稀土离子的比例（G／M）、退火温度可以制备出不同结构和晶粒尺寸的Gd2O3：Eu^3＋纳米晶。在退火温度为800℃，G／M等于0．83和1．0时，均得到了纯立方相的Gd2O3：Eu^3＋纳米晶，随着G／M的增加，Gd2O3：Eu^3＋从立方相逐渐向单斜相转变。粉末的晶粒尺寸随着退火温度的增高而增大，晶粒尺寸在10-30nm之间。立方相的Gd2O3：Eu^3＋纳米晶主发射峰位置在612nm（^5D^0→^7F2跃迁），激发光谱中电荷迁移态发生了红移。     

稀土Eu3+掺杂纳米TiO2-SiO2发光材料的制备和发光性质的研究

采用溶胶-凝胶法制备了稀土Eu3+掺杂于不同比例的纳米TiO2-SiO2复合体系,研究了基质中钛、硅摩尔配比对发光性能的影响.样品的FTIR谱图显示:纳米复合氧化物SiO2-TiO2之间发生了键合作用,形成了Ti-O-Si键;TEM显示样品的颗粒大小约为35 nm,是具有一定的单分散性的球形颗粒;XRD和SAED结果表明,样品退火至700℃后仍为单一的锐钛矿相,这说明微量硅的加入对二氧化钛的锐钛矿相有热稳定的作用.当微量的Si4+进入TiO2的晶格,取代部分Ti4+的位置时,形成了结构等电子陷阱.通过对样品的激发光谱、发射光谱分析,发现这种结构有利于将基质吸收的能量传递到发光中心,使Eu3+的465nm处7F0→5D2激发效率最高,成为最灵敏的激发线.     

Synthesis and luminescence properties of Eu3+,Bi3+-doped BaWO4 phosphors

BaWO₄:Eu³⁺,Bi³⁺ phosphors have been prepared by the conventional high-temperature solid-state reaction and chemical precipitation. The materials were characterized by X-ray diffraction (XRD), scanning electron microscopy (SEM), and photoluminescence (PL) technologies. When the phosphors are prepared by the high-temperature solidstate reaction, Bi³⁺ doping into BaWO₄:Eu³⁺ can increase the emission intensity of 613 nm. However, maximum emission at about 595 nm was observed in Eu³⁺,Bi³⁺-doped BaWO₄ phosphors prepared by the chemical precipitation. The decay constants (monitored at 595 and/or 613 nm) are within 45–100 s. The color purity of the Ba_0:865WO₄: Eu_0:11,Bi_0:025 phosphor (prepared by chemical precipitation) was 100%. The emission mechanism of Eu³⁺,Bi³⁺ in the BaWO₄ phosphors is briefly discussed.     

Eu2+激活的Ca3SiO5绿色荧光粉的制备和发光特性研究

研究了Eu2+激活的绿色发光材料Ca3SiO5的制备条件和发光性质. Eu2+中心形成主峰值为501 nm和次峰值为570 nm的特征宽带,两峰值叠加形成发射峰值为502 nm的绿色发射光谱带. 利用这些光谱结果和Van Uitert 经验公式,确认Ca3SiO5:Eu2+中存在两种性质有差异的Eu2+发光中心,它们分别占据基质中八配位的Ca2+(Ⅰ)格位和四配位的Ca2+(Ⅱ)格位. 其激发光谱分布在250-450 nm的波长范围,峰值位于375 nm处,可以被InGaN管芯产生的350-410 nm辐射有效激发.     

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.     

Eu2+的掺杂浓度对BaAl2Si2O8:Eu2+荧光粉发光特性的影响

采用化学共沉淀法一次煅烧工艺合成了BaAl2Si2O8:Eu2+蓝色荧光粉.用X射线衍射仪和荧光分光光度计等对BaAl2Si2O8:Eu2+蓝色荧光粉的相结构、发光性能进行了测试.结果表明:化学共沉淀法一次煅烧工艺合成的BaAl2Si2O8:Eu2+蓝色荧光粉为单相;其激发光谱分布在240-410 nm的波长范围,峰值位于320 nm处,可以被InGaN管芯产生的350-410 nm辐射有效激发;在365 nm近紫外光的激发下,测得其发射光谱是位于465 nm附近的宽带峰.BaAl2Si2O8:Eu2+蓝色荧光粉的发光强度随Eu2+浓度的增大逐渐加强,当Eu2+掺杂的摩尔分数为3.5%时,发光强度达到最大值,而后随掺杂浓度的增加而减小,发生浓度猝灭;根据Dexter能量共振理论,该浓度猝灭是由于Eu2+的离子间交换相互作用引起的.     

Mg5SnB2O10:Eu3+,Bi3+—一种用于发光二极管的红色荧光粉的制备及其发光性能的研究

采用高温固相法成功合成了单一相的Eu³⁺,Bi³⁺共掺的Mg₅SnB₂O₁₀红色荧光粉,并通过X射线衍射、漫反射光谱、光致发光光谱等手段对该体系的结构及其发光特性进行了测试和研究.激发光谱表明,该荧光粉在393 nm呈现Eu³⁺的⁷Fo—⁵L₆特征激发,可以与用于发光二极管的近紫外芯片很好地匹配.在393 nm激发下,其发射光谱在591,612,701 nm处呈现Eu³⁺的⁵Do—⁷F₁,⁵Do—⁷F₂,⁵D₀—⁷F₄的特征发射.并且当固定Eu³⁺的浓度时,随着Bi³⁺含量的增加,发现Bi³⁺,Eu³⁺在这一体系中存在能量传递现象,系列样品发光强度大幅度提高.通过研究系列样品在不同Bi³⁺,Eu³⁺掺杂浓度下的发光性能,得出最佳样品为Mg_4.89Eu_0.1Bi_0.01SnB₂O₁₀,其积分强度达到了商用Y₂O₂S:Eu³⁺的1.1倍.     

Eu2+掺杂CaSi2O2N2荧光粉发光性能

采用固相反应法合成了组成为Ca_1-xEu_xSi₂O₂N₂的Eu²⁺掺杂CaSi₂O₂N₂荧光粉.通过荧光光谱对样品的发光性能进行了研究,发现Eu²⁺掺杂CaSi₂O₂N₂荧光粉发射光谱为宽波段的单峰结构,主要包含绿光和黄光区,发射峰在556~568 nm.从发射光谱的宽带特征来看,CaSi₂O₂N₂:Eu²⁺的发射主要对应着Eu²⁺离子4f⁶5d→4f⁷跃迁.从激发光谱所覆盖的范围还可以看到,样品可以有效的被UV蓝-光激发,这意味着该类荧光粉在白光LED方面有可能得到广泛的应用.另外,样品的发光性能与激发离子的浓度有着很大关系.激发离子浓度增大时,发射光谱会发生明显红移.利用这一性质,可以通过改变Eu²⁺浓度来调节荧光粉的发光范围,从而满足不同场合的需要.同时,Eu²⁺浓度提高,样品发射光谱的强度也会随之增强,在x=0.06时发射强度达到最大值,之后继续增加Eu²⁺浓度,强度不仅没有增加反而降低,即出现浓度猝灭现象.     

Synthesis,characterization and studies of radiative properties on Eu3+-doped ZnAl2O4

Eu³⁺-doped ZnAl₂O₄ phosphors were successfully synthesized in air atmosphere at 900 °C. The phosphors were characterized using X-ray diffraction (XRD), scanning electron microscopy (SEM), thermally stimulated luminescence (TSL) and photoluminescence (PL) techniques. The average particle size of the system as determined from SEM was found to be 100–150 nm (for samples annealed at 900 °C). PL spectra of the doped phosphors showed emission peaks corresponding to Eu³⁺ ions. Lifetime studies revealed Eu³⁺ ions to be in two different sites. The asymmetric ratio (I₆₁₆/I₅₉₂) was observed to be about 3.75. This suggested that Eu³⁺ ion entered the host mainly substituting Al³⁺ site distorting the local environment and is partly located on surface of the phosphors. A prominent glow peak at 430 K was observed in the TSL of γ-irradiated Eu³⁺-doped ZnAl₂O₄ phosphors. Trap parameters for this peak have been determined and the probable mechanism for the glow peak is proposed. CIE chromaticity coordinates for the system were evaluated. It was observed that, the system could be employed as a potential red emitting phosphor. Commercial utility of the phosphor was investigated by comparing it with commercial red phosphor. The PL intensity of the as prepared phosphors was 63% of that of the commercial phosphor. Apart from this, various radiative properties such as the Judd–Ofelt intensity parameters, spontaneous emission probabilities, luminescence branching ratios, radiative lifetimes and quantum efficiency were evaluated for the system.     

Electrical properties of V2O5-doped TlI

This paper reports the effect of heterogeneously doped vanadia on the ionic conductivity of thallium iodide (TlI). These compounds have been prepared and studied by X-ray diffraction, differential scanning calorimetry, scanning electron microscopy and electrical conductivity. The materials were found to be binary phase systems with the vanadia particles dispersed in the grains of TlI. The electrical conductivity shows an upward trend in the composition range x=0.1–0.5; however, with further increase in vanadia content, conductivity decreases. This behavior is attributed to disordering phenomena at interface boundaries and space-charge layers formed in the bulk grains of TlI. In addition to this, the increased content of vanadia in the system leads to the disappearance of the β?α phase transition of TlI, which is usually observed in the pure compound.     

A study of the luminescence properties of Eu -doped borate crystal and glass

Eu³⁺-doped La₂O₃-3B₂O₃ crystal and glass were prepared by solid state reaction under different calcination temperature. The emission spectrum, phonon sideband (PSB), charge transfer band (C.T.B.) and lifetime of the Eu³⁺ ion in the two materials, with the same composition but with different phase, were investigated. With excitation at 394 nm light, the glass presented intense 618 nm red luminescence; however, the crystal gave 696 nm red luminescence. This difference is ascribed to the discrepancy of the local structure around the Eu³⁺ ion in the crystal and glass. To clarify the discrepancy, the coordination of Eu³⁺ in the borate glass and crystal was investigated. The results show that Eu³⁺ ions formed a complex Eu³⁺-O²⁻-B³⁺ bond in glass; however, in the crystal, it formed a complex Eu³⁺-O²⁻-La³⁺ bond. The lifetime of Eu³⁺ ions in the crystal and the glass is 3.08 ms and 1.98 ms, respectively. This indicates that the discrepancy in the local structure around the Eu³⁺ ions between the crystal and the glass leads to different fluorescence properties.     

Effect of Sr2+-doping on structure and luminescence properties of BaAl2Si2O8:Eu2+ phosphors

Sr²⁺ doped BaAl₂Si₂O₈:Eu²⁺ phosphor was synthesized by chemical co-precipitation method. With the increase of Sr²⁺ concentration, the phase structure of (Ba_0.965 ? xSr_xEu_0.035)Al₂Si₂O₈ changes from hexagonal phase to monoclinic phase owing to large activation energy in SrAl₂Si₂O₈ system. (Ba_0.965 ? xSr_xEu_0.035)Al₂Si₂O₈ phosphor exhibits a broad blue band peaking at 425 nm due to the 4f⁶5d–4f⁷(⁸S_7/2) transition of Eu²⁺ ions. The emission intensity increases, accompanied by the blue shift of emission maximum from 459 to 417 nm with the Sr²⁺ doping concentration increasing. The optimal concentration of Sr²⁺ ion is 40%, and the phosphor shows high color stability in CIE chromaticity diagram. The result indicates that Sr²⁺ doped phosphor not only can enhance the relative intensity but also can adjust the chromaticity coordinate.     

铅激活二硅酸钡合成条件的研究

在一定量的激活剂PbO2和助熔剂BaCl2,BaSO4存在下,通过碳酸钡和二氧化硅之间的固相反应制备光致发光材料二硅酸钡铅BaSi2O5:Pb2+。为了使获得的产品是具有上述化学计量的化合物,以及具有最好的发光性能,我们用正交设计方法安排了一系列条件试验。试验结果指出,在合成二硅酸钡铅发光材料的反应中,反应温度和SiO2/BaCO3的摩尔比是最重要的因素。反应温度应高于1100℃,SiO2/BaCO3的摩尔比应在2.3—2.8之间。其它重要因素有:激活剂PbO2加入量在0.04—0.17摩尔之间对产物发光强度均无明显影响,以0.08摩尔为最好。由于PbO2在高温时分解及挥发,实际进入晶体的Pb2+量仅为0.8%(摩尔百分)。助熔剂BaCl2及BaSO4的加入量分别以0.16摩尔及0.17摩尔为最好。灼烧时间以5小时为最好。根据最佳条件所制备得到BaSi2O5:Pb2+发光材料在254nm激发下,它的发射光谱峰值为351.9nm,半高宽为39nm,它的发光强度为国内同类商品的111%,为日本东芝SPD-8S的108%。用它制作紫外荧光灯管时,涂敷性能也较好。     

Eu~(3+)/Yb~(3+)共掺杂ZrO_2粉末的制备和发光性质研究

利用共沉淀方法制备了Eu3+/Yb3+单掺和共掺的ZrO2粉体材料,研究了煅烧温度和掺杂浓度对结构和发光性质的影响。XRD结果表明:所制备单掺样品含有单斜相和四方相2种不同结构,随着热处理温度的升高,四方相向单斜相转变,经1 150℃处理后,四方相消失,呈现单一的单斜相;Yb3+离子的掺入有稳定ZrO2四方相的作用,随着掺杂浓度的增加,单斜相转变为四方相。由于晶相的不同,Eu3+处在四方相和单斜相2种发光中心,二者发光性质不同。Eu3+/Yb3+共掺后,在270 nm激发Eu3+时,观测到了Yb3+在近红外波段(980 nm)的发光,同时证实Eu3+的激发光谱和Yb3+的激发光谱相一致,表明存在Eu3+到Yb3+的能量传递,交叉弛豫和共合作能量传递过程是其可能的能量传递机理。     

助熔剂BaF2在制备BaSi2O5:Pb2+过程中的机理

采用高温固相合成法制备出BaSi₂O₅:Pb²⁺荧光体。考察了BaF₂的加入量对产物紫外发射强度的影响。用差示扫描量热分析,X射线衍射,光致发光光谱研究了掺入助熔剂BaF₂后BaSi₂O₅:Pb²⁺紫外发射强度显著增强的机理,并从热力学角度对实验结果作了分析。研究表明少量BaF₂的掺入加快了反应速度;降低了BaSi₂O₅:Pb²⁺形成温度,在高温下与SiO₂反应生成SiF₄气体,生成的SiF₄再与BaCO₃反应形成结晶良好的BaSi₂O₅:Pb²⁺荧光体。