Eu掺杂SiO2纳米基质的发光特性

采用溶胶-凝胶(sol-gel)法制备了Eu掺杂的SiO₂干凝胶,分别用光致发光(PL)光谱、透射电镜(TEM)、扫描电镜(SEM)、红外吸收(IR)谱等分析手段对样品进行了表征,研究了SiO₂的基质中Eu³⁺、Eu²⁺的发光特性以及退火温度对发射光谱的影响,并对其发光机理进行了分析。结果表明,样品掺杂均匀,颗粒尺寸大约在50~80 nm,硼(B)离子进入SiO₂网格,成为了基质的一部分,改变了基质的网络结构。当采用258 nm激发样品时,随着退火温度的升高,红光发射强度先增强后减弱。对于经800 ℃退火处理的样品红光发射最强,出现了576 nm(⁵D₀ →⁷F₀),620 nm(⁵D₀ →⁷F₂),658 nm(⁵D₀ →⁷F₃)3条谱线,其中主峰位于 620 nm红光发射,对应于Eu³⁺离子的⁵D₀ →⁷F₂超灵敏跃迁,进一步说明B离子参与到基质中,形成了Si—O—B键,导致Eu³⁺离子所处配位环境的对称性降低,从而有利于Eu³⁺离子的特征发射;当采用271 nm激发样品时,随着退火温度的升高,蓝光发射强度先增强后减弱,经850 ℃退火的样品400~500 nm蓝光发射最强,归属于Eu²⁺的5d→4f的跃迁发射,证明在铝离子(Al³⁺)存在的情形下,在高温退火过程中Al³⁺部分取代Si⁴⁺形成AlO^-₄基团,掺杂Eu³⁺填补AlO^-₄基团附近的空位,增加了Eu³⁺周围的AlO^-₄四面体中氧原子的电子给予能力,使得Eu³⁺还原成Eu²⁺,从而得到了较强的蓝光发射。但是,当退火温度达到900 ℃时,由于稀土离子发生位置的迁移形成团簇红光和蓝光都明显地降低。     

LiMBO3 : Dy3+材料的发光特性

采用固相法制备了LiM(M=Ca, Sr, Ba)BO₃ : Dy³⁺材料,并研究了材料的发光特性。LiM(M=Ca, Sr, Ba)BO₃ : Dy³⁺材料的发射光谱均呈多峰发射,对应于Ca,Sr,Ba,其主发射峰分别是Dy³⁺的⁴F_9/2→⁶H_15/2(484,486,486 nm),⁶H_13/2(577,578,578 nm)和⁶H_11/2(668,668,666 nm)跃迁。监测黄色发射峰时,所得激发光 谱峰值位置相同,主激发峰分别为331,368, 397,433,462,478 nm,对应Dy³⁺的⁶H_15/2→ ⁴D_7/2,⁶P_7/2,⁶M_21/2,⁴G_11/2,⁴I_15/2和⁶F_9/2跃迁。研究了敏化剂Ce³⁺及电荷补偿剂Li⁺、Na⁺和K⁺对LiM(M=Ca, Sr, Ba)BO₃ : Dy³⁺材料发光强度的影响。结果显示:加入敏化剂Ce³⁺提高了材料的发光强度,发光强度最大处对应的Ce³⁺浓度为3%;加入电荷补偿剂Li⁺、Na⁺和K⁺后,材料的发光强度也得到了明显提高,但发光强度最大处对应的Li⁺、Na⁺和K⁺浓度不同,依次为4%、4%和3%。     

Y0.795-xGdxYb0.2Tm0.005F3纳米晶合成及 Tm3+和Gd3+的上转换发光

利用水热法合成了氟化物Y_0.795-xGd_xYb_0.2Tm_0.005F₃ (x=0.0,0.1,0.2,0.5,0.8)纳米晶。研究了退火后系列样品的上转换发光性质以及激发态辐射跃迁寿命。在980 nm激发下,Y_0.795-xGd_xYb_0.2Tm_0.005F₃纳米微晶样品中观察到了Tm³⁺的蓝光上转换发射及紫色、紫外发射增强现象,同时还观察到Gd³⁺的⁶D_9/2、⁶I_J、⁶P_5/2及⁶P_7/2到基态⁸S_7/2的发射。实验结果表明:样品半个波长量级的颗粒尺寸是Tm³⁺紫外上转换增强以及Tm³⁺到Gd³⁺发生有效能量传递的重要因素。     

纳米晶Gd2O3 ∶ Eu3+的制备与发光性质

利用共沉淀法制备了纳米晶Gd₂O₃ : Eu³⁺发光粉体。 在不同掺杂浓度、不同煅烧温度的系列样品中,均观测到Eu³⁺离子的特征发射。样品的晶相与发射性质的研究表明:所制备的样品经800~1 300 ℃热处理后,晶相为立方相,1 400 ℃时开始向单斜相转变。荧光强度与Eu³⁺离子掺杂浓度关系研究表明:在不同掺杂浓度中,Eu³⁺离子浓度为4%时其相对发射强度最强。在三个不同的煅烧温度中,经800 ℃煅烧的样品其发光效果最好。此外还观察到电荷转移激发态以及基质、Gd³⁺与Eu³⁺之间的能量传递。激发谱包含三部分,即电荷转移带、Eu³⁺的4f内壳层电子跃迁和Gd³⁺的激发谱。     

Tm3+和 Yb3+共掺杂PGETYA玻璃的直接敏化上转换发光

制备了一种稀土离子掺杂的PGETYA氟氧玻璃材料,它不仅具有较高的上转换发光效率,而且还避免了氟化物基质的缺点。其组分为58.52PbF₂-34.43GeO₂-3Al₂O₃ -0.05Tm₂O₃-4Yb₂O₃,以共掺杂Tm³⁺和Yb³⁺离子为上转换研究的对象。测量了该玻璃系统在980 nm LD激发下的上转换发光光谱,观察到很强的476 nm的蓝色荧光,它来源于Tm³⁺离子的¹G₄→³H₆跃迁。同时,还有两个较弱的红色荧光来源于Tm³⁺离子的¹G₄→³H₄和³F₃→³H₆跃迁。对上转换发光强度与泵浦电流关系曲线的拟合结果表明:此材料的蓝色上转换为三光子过程,红色上转换为双光子过程。     

BaMgAl10O17 : Eu2+发射光谱的谱峰形状

BaMgAl₁₀O₁₇ : Eu²⁺(BAM)是三基色荧光灯和等离子显示用荧光粉中的蓝色组分。用晶格弛豫和多声子跃迁理论研究了BAM发射光谱的谱峰分布。结果表明可以用三个高斯函数很好地拟合BAM的宽带发射。BAM的宽带发射可能由分布在BaMgAl₁₀O₁₇晶格中三个不同位置的Eu²⁺的能级跃迁构成。三个Eu的发光中心分别是Beevers-Ross位和anti-Beevers-Ross 位,第三个Eu²⁺的发光中心可能是位于尖晶石基块中的mid-oxygen(m_o)位。     

Pr3+ 掺杂透明氟氧化物玻璃陶瓷的光谱特性

用不同的激发波长532,514.5,476.5 nm,研究稀土Pr³⁺ 掺杂的透明氟氧化物玻璃陶瓷中Pr³⁺ 在LaF₃ 微晶环境和玻璃环境中的不同的荧光行为。对于微晶中的Pr³⁺ 离子,当用532 nm 和514.5 nm激发玻璃陶瓷时,观察到从³P₀ 能级到³H₅ 能级的发射,和¹D₂ 能级到基态³H₄能级,³P₀ 能级到³H₆ 能级的发射。我们认为微晶中Pr³⁺ 离子的³P₀ 能级上的电子布局是依靠电声子耦合-多声子辅助来实现的。为了进行比较,用476.5 nm 共振激发玻璃及微晶中Pr³⁺ 离子的³P₀ 能级,观察到³P₀ 能级到很多低能级如:³H₅、 ³H₆、³F₂的跃迁。而当在532 nm 和514.5 nm 非选择激发时,只有 ³P₀ 能级到³H₅ 能级的发射存在。我们认为这是由于不同的激光波长选择激发了不同环境中的Pr³⁺ 离子,532 nm 和514.5 nm 激发线选择激发了电声子耦合环境强中Pr³⁺ 离子。不同Pr³⁺ 离子掺杂摩尔分数分别为0.005%,0.05%,0.5%的发射光谱的研究还表明,这些电声子耦合环境强中的Pr³⁺ 离子浓度很高,很容易发生浓度猝灭现象。最后,用拉曼光谱研究了这类玻璃陶瓷的结晶性为和振动特性。     

Ca9R(VO4)7 : Eu3+ 发光粉的发光特性

采用高温固相法制备了Eu³⁺离子激活的Ca₉R(VO₄)₇(R = Y, La, Gd)红色发光粉,并利用荧光光谱对发光粉的特性进行研究。激发光谱中,Ca₉Y(VO₄)₇ : Eu³⁺ , Ca₉La(VO₄)₇ : Eu³⁺和Ca₉Gd(VO₄)₇ : Eu³⁺都有两个宽的VO^3-₄激发带和Eu³⁺的特征激发峰。发射光谱中,在Ca₉Y(VO₄)₇ : Eu³⁺ 和Ca₉La(VO₄)₇ : Eu³⁺中的350~550 nm范围内出现VO^3-₄的发射带,而在Ca₉Gd(VO₄)₇ : Eu³⁺中却没有观察到VO^3-₄的发射。在这三种发光粉中,Ca₉Gd(VO₄)₇ : Eu³⁺的发光强度远远高于其它两种,这是由于Gd³⁺的存在有效地使能量通过Gd³⁺ →VO^3-₄ → Eu³⁺及Gd³⁺ → Eu³⁺的两种方式进行能量传递,从而提高了Eu³⁺发光效率。     

SrB4 O7 : Eu磷光粉的制备及其发光性能

采用高温固相法合成了SrB₄O₇ : Eu荧光粉,并研究了不同原料、掺杂浓度、煅烧温度等因素对其发光性能的影响。发射光谱测试结果表明:SrB₄O₇ : Eu荧光粉的最佳Eu掺杂浓度为2%左右,进一步增大掺杂浓度会导致浓度猝灭。煅烧温度对基质组成影响较大,随着温度的升高,基质中BO₄四面体所占比例增大,有利于Eu³⁺离子的还原。以水合硼酸锶为原料制得样品的发光强度高于以SrCO₃和H₃BO₃为原料制得样品的发光强度。     

共沉淀法制备NaYF4 : Tm3+,Yb3+的上转换发光

通过共沉淀法制备Tm³⁺和Yb³⁺掺杂的NaYF₄上转换发光材料。其中Tm³⁺和Yb³⁺的摩尔分数分别为0.01%,0.1%。在室温下测试了NaYF₄ : Tm³⁺,Yb³⁺材料在300~1 100 nm的吸收光谱。利用X射线衍射(XRD),扫描电镜(SEM)测试了合成材料的物相结构和微观形貌。结果表明:NaYF₄ : Tm³⁺,Yb³⁺材料为六方相晶体,其颗粒大小约为50~60 nm,产物结晶良好,含有少量杂相。在798 nm近红外光激发下,测试了样品的上转换发光光谱。观察到了蓝、绿色上转换发光。讨论了上转换发光的可能机理,蓝光主要来源于Tm³⁺的激发态¹G₄到基态³H₆的跃迁,绿光来源于Tm³⁺的¹D₂→³H₅跃迁。     

Luminescent properties of red-emitting LiSr4B3O(9−3x/2)Nx:Eu2+ phosphor for white-LEDs

An Eu²⁺-activated oxynitride LiSr_(4?y)B₃O_(9?3x/2)N_x:yEu²⁺ red-emitting phosphor was synthesized by solid-state reactions. The synthesized phosphor crystallized in a cubic system with space group Ia–3d. The LiSr₄B₃O_(9?3x/2)N_x:Eu²⁺ phosphors exhibited a broad red emission band with a peak at 610 nm and a full width at half maximum of 106 nm under 410 nm excitation, which is ascribed to the 4f⁶5d¹→4f⁷ transition of Eu²⁺. The optimal doped nitrogen concentration was observed to be x=0.75. The average decay times of two different emission centers were estimated to be 568 and 489 ns in the LiSr_3.99B₃O_8.25N_0.5:0.01Eu²⁺ phosphors, respectively. Concentration quenching of Eu²⁺ ions occurred at y=0.07, and the critical distance was determined as 17.86 Å. The non-radiative transitions via dipole–dipole interactions resulted in the concentration quenching of Eu²⁺-site emission centers in the LiSr₄B₃O₉ host. These results indicate LiSr₄B₃O_(9?3x/2)N_x:Eu²⁺ phosphor is promising for application in white near-UV LEDs.     

Morphology-dependent luminescence behavior of Y<Subscript>2-x</Subscript>Gd<Subscript>x</Subscript>O<Subscript>3</Subscript>:Eu<Superscript>3+</Superscript> thin-film phosphors grown by a laser ablation

Y_2-xGd_xO₃:Eu³⁺ luminescent thin films have been grown on Al₂O₃(0001) substrates using pulsed laser deposition. Films grown under different deposition conditions have been characterized using microstructural and luminescence measurements. The crystallinity, surface morphology and photoluminescence (PL) of the films are highly dependent on the amount of Gd present. The photoluminescence (PL) brightness data obtained from Y_2-xGd_xO₃:Eu³⁺ films grown under optimized conditions have indicated that Al₂O₃(0001) is one of the most promising substrates for the growth of high-quality Y_2-xGd_xO₃:Eu³⁺ thin-film red phosphors. In particular, the incorporation of Gd into the Y₂O₃ lattice could induce a remarkable increase of PL. The highest emission intensity was observed with Y_1.35Gd_0.60Eu_0.05O₃, whose brightness was increased by a factor of 3.1 in comparison with that of Y₂O₃:Eu³⁺ films. This phosphor may be promising for application in flat-panel displays. PACS 78.20.-e; 78.55.-m; 78.66.-w     

Synthesis and luminescence properties of europium doped YBa3B9O18

Europium (Eu³⁺) doped YBa₃B₉O₁₈ were synthesized by conventional solid state solidification methods. (Y_1−xEu_x)Ba₃B₉O₁₈ formed solid solutions in the range of x=0–1.0. The luminescence property measurements upon excitation in ultraviolet–visible range show well-known Eu³⁺ excitation and emission. The charge transfer excitation band of Eu³⁺ dominates the excitation spectra. The emission spectrum of Eu³⁺ ions consists mainly of several groups of lines in the 550–720 nm region, due to the transitions from the ⁵D₀ level to the levels ⁷F_J (J=0, 1, 2, 3, 4) of Eu³⁺ ions. The dependence of luminescence intensity on Eu³⁺ concentration shows no concentration quenching for fully concentrated EuBa₃B₉O₁₈. Eu³⁺ doped YBa₃B₉O₁₈ are promising phosphors for applications in displays and optical devices.     

Synthesis and Luminescent Properties of M<Subscript>2</Subscript>V<Subscript>2</Subscript>O<Subscript>7</Subscript>: Eu (M=Sr,Ba) Nanophosphors

A solution combustion route for the synthesis of Eu³⁺-activated M₂V₂O₇ (M = Sr, Ba) and their luminescent properties have been investigated. Structure and luminescent characteristics of Sr₂V₂O₇:Eu³⁺ and Ba₂V₂O₇:Eu³⁺ nanophosphors have been studied by x-ray diffraction, scanning electron microscopy, transmission electron microscopy, fluorescence spectrometry and Fourier transform infra-red spectroscopy. The incorporation of Eu³⁺ activator in these nanoparticles has been checked by luminescence characteristics. These nanoparticles have displayed red color under a UV source which is due to characteristics transition of Eu³⁺ from ⁵D₀ → ⁷F₂ at 613 nm in both Sr₂V₂O₇:Eu³⁺ and Ba₂V₂O₇:Eu³⁺ nanophosphors. In addition, the optimal Eu³⁺ - doped contents of Sr_2(1-x)Eu_2xV₂O₇ and Ba_2(1-x)Eu_2xV₂O₇ nanophosphors for both were 4 mol%.     

Synthesis and luminescent properties of BaGd2O4:Dy3+, an novel scintillating phosphor

The BaGd_2?x O₄:xDy³⁺ (0 ≤ x ≤ 0.08) phosphors were synthesized at 1,300 °C in air by the solid-state reaction route. The as-synthesized phosphors were characterized by X-ray powder diffraction, photoluminescence excitation spectra, photoluminescence (PL) spectra, X-ray excited luminescence (XEL) spectra, and thermoluminescence (TL) spectra. It is found that the quenching concentration of Dy³⁺ ions in BaGd₂O₄ host is dependent on the selected excitation wavelength. The optimal PL intensity for the investigated BaGd_2?x O₄:xDy³⁺ phosphors is found to be x = 0.01, 0.02, and 0.04, upon excitation by 234, 277, and 350 nm ultraviolet light, respectively. The energy transfer among Dy³⁺ ions upon excitation by 350 nm is confirmed to be an electric dipole–dipole interaction mechanism based on the fitting of Huang’s rule. In addition, the intensive XEL from BaGd₂O₄:Dy³⁺ phosphor is observed by the naked eyes at room temperature, and TL properties of the investigated phosphors are analyzed and discussed. All the results imply that the investigated phosphors could be a promising scintillating phosphor.     

Synthesis and photoluminescence characteristics of (Sr, Ca)3B2O6:Eu for application in white light-emitting diodes

A series of yellow-green (Sr, Ca)₃B₂O₆:Eu phosphors have been synthesized using precursors prepared via a facile sol-gel route. The solid-solution phases crystallized to materials with the formula of Sr_3−x−yCa_xEu_yB₂O₆ with varied Ca²⁺ and Eu²⁺ contents. The emission peak centered at 540 nm under near-UV excitation exhibited a broad-band distribution in the range of 450-650 nm. The dependences of the luminescence intensity on the contents of Ca²⁺ substitution and Eu²⁺ dopant were also investigated. The composition in the host lattice sensitively affected the chromaticity index. Sr_1.21Ca_1.7Eu_0.09B₂O₆ (SCB:0.09Eu) was shown to possess the highest intensity and broadest emission band. Calcining temperature was shown to greatly influence the luminescent properties of SCB:0.09Eu. It is concluded that SCB:0.09Eu can be used as an efficient yellow-green phosphor for white light-emitting diodes (white LEDs) applications.     

Phosphor-converted light-emitting diode based on ZnO-based heterojunction

A phosphor-converted light-emitting diode (LED) was realized by coating BaMg₂Al₁₆O₂₇:Eu²⁺·Mn²⁺ and (SrCaPO₄)·B₂O₃:Eu²⁺·Na⁺ phosphors onto an n-ZnO/i-MgO/p-GaN heterojunction diode. Two emission bands at around 450 and 520 nm were observed in the phosphor-converted LED under the injection of continuous current. By analyzing the optical properties of the heterojunction diode and phosphors, it is concluded that the emission at 450 nm comes from (SrCaPO₄)·B₂O₃:Eu²⁺·Na⁺ phosphor, while the one at 520 nm comes from BaMg₂Al₁₆O₂₇:Eu²⁺·Mn²⁺ phosphor under the excitation of the light emitted from the n-ZnO/i-MgO/p-GaN heterojunction diode. The results reported in this paper may provide a route to ZnO-based phosphor-converted LEDs for future lighting or displaying purpose.     

Preparation and luminescent properties of BaCa2Si3O9:Eu

A blue emitting phosphor of the triclinic BaCa₂Si₃O₉:Eu²⁺ was prepared by the combustion-assisted synthesis method and an efficient blue emission ranging from the ultraviolet to visible was observed. The luminescence and crystallinity were investigated using luminescence spectrometry and X-ray diffractometry (XRD), respectively. The emission spectrum shows a single intensive band centered at 445 nm, which corresponds to the 4f⁶5d¹→4f⁷ transition of Eu²⁺. The excitation spectrum is a broad extending from 260 to 450 nm, which matches the emission of ultraviolet light-emitting diodes (UV-LEDs). The critical quenching concentration of Eu²⁺ in BaCa₂Si₃O₉:Eu²⁺ phosphor is about 0.05 mol. The corresponding concentration quenching mechanism is verified to be a dipole-dipole interaction. The CIE of the optimized sample Ba_0.95Ca₂Si₃O₉:Eu_0.05²⁺ was (x, y)=(0.164, 0.111). The result indicates that BaCa₂Si₃O₉:Eu²⁺ can be potentially useful as a UV radiation-converting phosphor for white light-emitting diodes (LEDs).     

Improved photoluminescence of pulsed-laser-ablated Y<Subscript>1-x</Subscript>Gd<Subscript>x</Subscript>VO<Subscript>4</Subscript>:Eu<Superscript>3+</Superscript> thin film phosphors by Gd substitution

Gd-substituted Y_1-xGd_xVO₄:Eu³⁺ luminescent thin films have been grown on Al₂O₃(0001) substrates using pulsed-laser deposition. The films grown under different deposition conditions have been characterized using microstructural and luminescent measurements. The crystallinity, surface morphology, and photoluminescence (PL) of the films are highly dependent on the amount of Gd. The photoluminescence (PL) brightness data obtained from Y_1-xGd_xVO₄:Eu³⁺ films grown under optimized conditions have indicated that the PL brightness is more dependent on the surface roughness than the crystallinity of the films. In particular, the incorporation of Gd into the YVO₄ lattice could induce a remarkable increase of PL. The highest emission intensity was observed with Y_0.57Gd_0.40Eu_0.03VO₄ thin film whose brightness was increased by a factor of 2.5 and 1.9 in comparison with that of YVO₄:Eu³⁺ and GdVO₄:Eu³⁺ films, respectively. This phosphor have application to flat panel displays. PACS 78.20.-e; 78.55.-m; 78.66.-w     

Compositional-dependent lead borate based glasses doped with Eu ions: Synthesis and spectroscopic properties

New multicomponent lead borate based glasses with various PbO/B₂O₃ weight ratio were prepared. The glass samples were analyzed in detail by using Raman and IR absorption spectroscopy. Optical properties of Eu³⁺ ions have been investigated in lead borate based systems, in which PbO/B₂O₃ weight ratios were changed from 1:2 to 8:1 in glass composition. The values of the phonon energy of the host and ⁵D₀ lifetime of Eu³⁺ decrease, whereas absorption and emission intensities, as well as bonding parameter increase with increasing PbO concentration. Additionally, spectral lines are shifted in direction to the lower frequency region. Non-monotonic dependence of the fluorescence intensity ratio R (⁵D₀-⁷F₂/⁵D₀-⁷F₁) upon PbO/B₂O₃ content has been observed in contrast to bonding parameter that is also non-linear but monotonic. Some structural and spectroscopic aspects for Eu-doped lead borate based glasses are presented.