Transparent luminescent bulk nanocomposites of polysiloxane embedded with CdS nanocrystallines by a direct dispersion process

Transparent luminescent bulk nanocomposites of polysiloxane (PSO) embedded with semiconductor nanocrystals (NCs) have been fabricated by the direct dispersion of CdS NCs in alkyl-(poly)siloxane (APS) followed by co-polymerization. The non-polar characteristics of the APS precursor are compatible with the CdS NC surface (oleylamine), which allows the direct dispersion of the CdS NCs without the need of any surfactant exchange. Chemical crosslinking of the NC-APS dispersion via hydrosilylation between Si-H and the vinyl group in APS immobilizes the CdS NCs in the polysiloxane network. Net-shaped three-dimensional bulk transparent polysiloxane/CdS NC composites were obtained by liquid casting of the NC-precursor dispersion and chemical crosslinking. The PSO/CdS NC composites show visible luminescence under ultraviolet excitation and the luminescent color is tunable from blue to red by controlling the NC concentration in the composite. Photoluminescence spectral analyses reveal the origin of the luminescence as being from the defect emission of the CdS NCs (550-900 nm) and an emission from the PSO matrix (380-550 nm). The luminescent spectra covered a wide range from the ultraviolet to the near-infrared region. The luminescence of the PSO/CdS NC nanocomposites was stable without any apparent degradation after exposure to air for a long time. This simple direct dispersion process is feasible for the fabrication of luminescent nanocomposites with useful optical properties for potential applications in optics and photoelectron devices.     

Dy~(3+)在ZnO–SiO_2玻璃中的发光特性(英文)

通过溶胶–凝胶法制备xZnO–(100–x)SiO2(x=0,5,10,20,摩尔分数)玻璃,研究ZnO含量对Dy3+发光强度的影响,并且研究Dy3+在紫外光和飞秒激光激发下的发光特性。结果表明:当ZnO摩尔(下同)含量为0、5%和10%,Dy3+的发光强度几乎不变,当ZnO含量达到20%时,Dy3+的发光强度显著增强,归因于基质微结构的明显改变。研究了飞秒激光激发时,Dy3+在ZnO–SiO2玻璃中的上转换发光特性。在飞秒激光(800nm)激发下,观察到强Dy3+的上转换发光。Dy3+的发光强度与泵浦光强度的依赖关系表明:上转换发光过程为双光子机制为主,根据Dy3+的能级,Dy3+在SiO2和ZnO–SiO2玻璃中的上转换发光的机制归因于激发态吸收。     

一种新型的红色荧光粉——Ca4GdO（BO3）3：Eu^3＋

采用高温固相法制备了一种新型的红色荧光粉——Ca4GdO（BO3）3：Eu^3＋．研究了它在X射线、真空紫外和紫外激发下的发光性能，研究表明，样品无论是在X射线、真空紫外还是在紫外的激发条件下，样品都能发出很强的红光．它的主发射峰在610nm，而且其它位置的发射峰都很弱；它很容易被254nm、172nm和X射线所激发而发出很强的红光，因此是一种具有潜在应用价值的红色荧光粉．研究表明Gd^3＋离子与激活剂（Eu^3＋）存在着一种能量传递的过程，而这种能量的传递过程可能跟二次吸收有关．     

Preparation of stable luminescent poly(methyl methacrylate)–europium complex nanospheres and application in the detection of hydrogen peroxide with the biocatalytic growth of gold nanoparticles

A simple and effective solvent swelling method was developed for the preparation of poly(methyl methacrylate) (PMMA)/europium (Eu) complex hybrid nanospheres. Transmission electron microscopy and dynamic light scattering results indicate that the as‐prepared PMMA–Eu nanoparticles had a spherical morphology, with a narrow particle size distribution ranging from 100–200 nm. The PMMA–Eu nanospheres exhibited strong red emissions with a maximum peak at 612 nm under UV excitation, and the luminescence lifetime of the Eu complex was enhanced after it was swollen into PMMA nanospheres. Furthermore, the luminescence intensity of the PMMA–Eu nanospheres was very stable in various severe media, including aqueous solutions with various pHs, 1 mM Ca²⁺, 1 mM Fe²⁺, 1 mM Cu²⁺, 0.1M phosphate‐buffered saline solution, 1 mM citric acid solution, 1 mM lysine, and 1 mM glutamic acid. After the nanospheres were incubated at various temperatures for 1 h, the luminescence properties remained stable when the temperature was less than 40°C yet decreased slightly between 40 and 60°C and decreased rapidly at higher temperatures. These luminescent nanospheres were successfully applied in the luminescence‐sensing assay of hydrogen peroxide and exhibited a high sensitivity and broad linear concentration range. Because of their unique luminescence properties, the as‐synthesized PMMA–Eu nanospheres are expected to have great potential for use as luminescent labels or probes for long‐time imaging and analysis in which severe media situations are present. © 2012 Wiley Periodicals, Inc. J. Appl. Polym. Sci., 2013     

掺Bi的MgO-CaO-Al_2O_3-SiO_2玻璃的吸收和近红外发光特性

研究了4种不同Bi_2O_3掺杂量(0.5%,1%,2%和3%,摩尔分数)的23MgO-11CaO-15Al_2O_3-51SiO_2(摩尔比)玻璃的发光特性。测量了吸收光谱、荧光光谱和荧光寿命。通过电子顺磁共振图谱观察了玻璃受γ辐射前后结构的变化,探讨了玻璃颜色变化和近红外发光的机理。结果表明:在500nm激发下,随着Bi_2O_3掺杂量从1%到3%的逐渐增加,发光波长发生红移,荧光半高宽从312nm增加到352 nm;最优的Bi_2O_3掺杂量为1%,玻璃的受激发射截面和荧光寿命的乘积为3.10×10~(-24)cm~2·s;γ辐射后发光强度的增加和玻璃颜色加深的现象说明Bi掺杂玻璃的近红外发光中心可能是低价态的Bi离子或者Bi团簇。     

熔盐法制备片状Y_2O_3:Eu的研究

为扩展荧光粉的适用范围,采用均相沉淀-熔盐法合成了片状Y2O3:Eu红色荧光粉,制备了表面平整光滑、分散性好的片状Y2O3:Eu3+晶体,大小尺寸为1.5×2.5μm、厚度为100~200 nm,是具有纳米级厚度的薄片。其样品沉淀剂的滴定速度也对前驱体的粒度有较大影响,C2O42-的浓度为0.5 mol/L。对荧光粉的发光性能进行了分析,通过测量激发和发射光谱,于611 nm(5D0→7F2)产生高效的强发射。确定了合成条件对Y2O3:Eu形貌、粒径及发光性能的关系。     

Structural,optical and temperature dependent photoluminescence properties of Cr3+-activated LaGaO3 persistent phosphor for optical thermometry

Cr³⁺ doped LaGaO₃ phosphor was prepared by hydrothermal reaction method with post-annealing treatment. XRD pattern showed the pure orthorhombic phase of LaGaO₃ at an annealing temperature of 1000 °C. TEM image showed the particles in the range 40-120 nm. The bandgap energy and Urbach tail increased in the doped sample as compared to the undoped sample as estimated from UV–visible diffuse reflectance spectra. PL excitation spectra showed peaks in UV, blue and orange regions. The emission spectra showed broadband with peaks in the NIR region due to emission from ⁴T₂ and ²E states. The intermediate strength of the crystal field has been calculated from the estimated spectroscopic parameter. The average lifetime was found to be in the ms range. Afterglow decay was also recorded. From the low-temperature PL, the zero phonon line, stokes shift energy, vibrational energy and Huang-Rhys parameter were calculated. With rising the temperature, PL emission peak intensity and lifetime values decreased and FWHM increased because of increased numbers of electrons in ⁴T₂ state and increasing non-radiative transition. Temperature-dependent peak intensity ratios and lifetime values were utilized for temperature sensing applications in below room temperature and above room temperature. The results indicate the possibility of present phosphor to be used as optical nanothermometer.     

Preparation and luminescent properties of highly transparent Y3Ga5O12:M3+ (M = Dy,Cr) ceramics

YGG:Dy and YGG:Cr polycrystalline ceramics were prepared via a solid-state reaction-two step sintering approach. The crystalline structure, phase evolution, morphologies and luminescence properties of as prepared transparent ceramics were intensively investigated. In-line transmittance of YGG:Dy and YGG:Cr transparent ceramics can reach up to 70.6% and 67.3% at 1200 nm, respectively. For YGG:Dy transparent ceramic, three emission bands centered at 492 nm, 581 nm and 669 nm can be observed under excitation of 353 nm. Its CIE color coordinate is (0.3182, 0.3326) under UV irradiation, which is a promising UV-converting candidate for WLEDs. While the emission peak of YGG:Cr transparent ceramic is at about 709 nm, which can be one of the candidate materials applied in red-emitting LEDs with excellent color rendering index. The experimental results demonstrate that Y₃Ga₅O₁₂:M³⁺ (M = Dy, Cr) transparent ceramics are promising novel luminescent materials for LEDs.     

Fluorescence of poly(di-n-alkylsilane)s in room-temperature solution

A comprehensive study of the electronic absorption and emission spectra and the fluorescence quantum yield and lifetime of seven poly(di-n-alkylsilane)s and of three isotopically labelled poly(di-n-hexylsilane)s in hydrocarbon solution at room temperature is reported. Also reported are fluorescence polarization and carbon tetrachloride quenching of fluorescence of poly(di-n-hexylsilane). The observed fluorescence spectra, quantum yield, and polarization depend on the selected excitation energy in a very characteristic fashion, whereas the fluorescence lifetime does not; however, it depends on the selected emission energy. These characteristic dependencies are qualitatively accounted for by the previously proposed segment distribution model if one assumes that the photophysical behavior at higher excitation energies is strongly affected by the presence of a low-lying weakly allowed state in short-segment chromophores and the behavior at lower excitation energies is dictated by the selective excitation of emitting long-segment chromophores.     

Experimental evaluation of the luminescence performance of fired clay brick coated with SrAl2O4:Eu/Dy phosphor

This study evaluates the luminescence performance of fired clay bricks coated with SrAl₂O₄:Eu/Dy phosphor. To do so, SrAl₂O₄:Eu/Dy phosphor was first produced using the traditional solid-state reaction synthesis technique. The prepared phosphor was then used for coating fired clay bricks to analyze the luminescence performance via spectral analysis, decay characteristics, and microstructure of the bricks. The results reveal that excitation and emission spectra of the phosphor coated bricks range from 200 to 480 nm and 455 to 650 nm, respectively, suggesting that the phosphor coated bricks have the capacity of absorbing light with a wide range of wavelengths. The peak wavelength projected at 511 nm in the emission spectrum is achieved, which indicates 4f⁶5 d¹-4f⁷ transition of Europium (Eu²⁺). The repeated excitation and deexcitation of Eu²⁺ by using hole traps and trap levels offered by Dysprosium (Dy³⁺), exist between the ground and the excited state of Eu²⁺ leads to luminescent phenomenon. Moreover, the decay characteristics has revealed that phosphor coated bricks can emit light for a considerable amount of time (>8.5 min) upon the removal of the excitation source. The results reveal that phosphor coated bricks has the potential of increasing energy efficiency of residential and commercial buildings.     

Controlled synthesis and optical spectroscopy of lanthanide-doped KLaF₄ nanocrystals

KLaF(4), as a good host matrix for trivalent lanthanide (Ln(3+)) ions to fabricate upconversion (UC) or downconversion (DC) phosphors, has been rarely reported. Herein, monodisperse (～10 nm) cubic-phase Ln(3+)-doped KLaF(4) nanocrystals (NCs) were synthesized via a facile thermal decomposition method. Upon excitation at 980 nm, UC luminescence properties of KLaF(4):Ln(3+)/Yb(3+) (Ln = Tm, Ho, Er) NCs were comprehensively surveyed. Particularly, after coating an inert KLaF(4) shell, the green and red UC luminescence intensity of KLaF(4):Er(3+)/Yb(3+) NCs was enhanced ～35 times, and the corresponding UC lifetimes of (4)S(3/2) and (4)F(9/2) levels of Er(3+) were observed significantly prolonged from 42 and 68 μs in core-only NCs to 87 and 136 μs in core/shell counterparts. Furthermore, intense DC luminescence was also achieved in Ce(3+)/Tb(3+) and Eu(3+) doped KLaF(4) NCs, with absolute quantum yields of 39.8% (Tb(3+)) and 17.3% (Eu(3+)). The luminescence lifetimes of (5)D(0) (Eu(3+)) and (5)D(4) (Tb(3+)) were determined to be 4.2 and 4.7 ms, respectively. Water-soluble Ln(3+)-doped KLaF(4) NCs featuring excellent monodispersion, long luminescence lifetime, and high UC/DC efficiency may have versatile and promising applications as luminescent nano-biolabels.     

Photoluminescence of Ag Nanoparticles and Tm3+ Ions in the Bismuth Germanate Glasses for the Blue Light‐Excited W‐LED

Materials containing rare‐earth ions and Ag nanoparticles (NPs) have been widely applied due to prior demonstration of increase in their luminescence properties. Here, Tm³⁺ ions‐doped bismuth germanate glasses were synthesized by a chemical reduction method based on the conventional melting‐quenching technique. The Ag NPs were facilely precipitated in the glass matrix by the chemical reduction method during the annealing process. TEM image shows that the Ag NPs are closely dispersed in the glass matrix. The luminescence properties and energy‐transfer mechanism were systematically investigated by means of absorption, emission, and excitation spectra. Significant enhancements of Tm³⁺ ions emission and a broad emission band centered at 568 nm caused by Ag NPs are observed upon 474‐nm excitation. Our research may illustrate the interactions between Tm³⁺ ions and Ag NPs and provide a simplified way to synthesize the high‐efficiency luminescent materials for the blue light‐excited W‐LEDs.     

Synthesis and photoluminescence properties of a novel red phosphor SrLaGaO4:Mn4+

A novel Mn⁴⁺-doped strontium lanthanum gallate red phosphor SrLaGaO₄:Mn⁴⁺ has been successfully prepared via the conventional solid-state reaction method. Phase purity, photoluminescence excitation/emission spectra, concentration quenching, decay curves, and temperature-dependent photoluminescence have been investigated systematically. SrLaGaO₄:Mn⁴⁺ phosphor exhibits broad excitation band from 250 to 600 nm and emits intense red light centered at 716 nm arising from spin-forbidden transition, ²E → ⁴A₂ of Mn⁴⁺. The optimal dopant concentration of Mn⁴⁺ is determined to be 0.2 mol%. Dipole-dipole interaction is supposed to be the mechanism of concentration quenching. The crystal-field strength Dq, the Racah parameters B and C, and the nephelauxetic ratio β₁ of SrLaGaO₄:Mn⁴⁺ have been calculated according to its luminescent spectra. Our systematic investigation on this new phosphor can provide a reference for the development of red-emitting phosphor.     

多元光色稀土夜光纤维的制备及性能

为进一步促进稀土夜光纤维的光色多元化,改善其光色单一性问题,本文以SrAl₂O₄∶Eu²⁺, Dy³⁺ 和 Sr₂MgSi₂O₇∶Eu²⁺, Dy³⁺为共同发光中心,通过硅烷偶联剂作为分子桥将光转换剂结合到发光材料表面,采用聚丙烯腈成纤聚合物为基体,通过溶液纺丝法制备一种激发后在黑暗状态下可以发出多元光色的夜光纤维,制备了一种兼顾红色发光特性和持久发光性能的夜光纤维,并对其性能进行了研究。结果显示,红色光转换剂的添加没有对发光材料以及成纤聚合物的物相结构造成破坏,并且复合夜光纤维的激发光谱和发射光谱都向长波长移动,光谱发生红移;从余辉衰减曲线可知,随着光转换剂添加量的增加,纤维余辉亮度随之降低;此外,夜光纤维的光色红移程度会随着红色光转换剂质量分数的增加而增强。     

Effect of “Ph–NH–CH2–” group on the luminescence properties of sol–gel silica xerogel

The effect of Ph–NH–CH₂– group (Ph: phenyl) on the luminescence properties of silica xerogel by sol–gel method has been investigated. The absorption spectra, excitation spectra and emission spectra of Ph–NH–CH₂– group embedded in the network of silica xerogel have a red shift with increasing the ratios of Ph–NH–CH₂– group in the samples. The relative photoluminescence (PL) intensity of the hybrid silica xerogel sample decreases with increasing the ratios of Ph–NH–CH₂– group. From the complex luminescent centers, the novel luminescence properties have been observed from the hybrid silica xerogel sample containing Ph–NH–CH₂– group.     

Eu掺杂YAG微晶玻璃的制备及光谱性能

采用熔融法制备了Eu掺杂的YAG微晶玻璃.通过XRD和FESEM,研究了纯相YAG晶体的析出和Eu掺杂前后YAG晶体的微结构变化,通过荧光光谱和CIE色坐标研究微晶玻璃的发光性能.结果表明:在1050℃热处理开始析出了纯相YAG晶体,晶粒尺寸20~60 nm.在短波和长波紫外光激发下都能同时得到Eu3+和Eu2+的特征发射峰,但长波紫外激发下的发光强度是短波激发下的数十倍.随着Eu掺杂浓度的增加,Eu2+发光强度明显增强, Eu3+发光强度先增强后降低.通过改变激发波长和Eu掺杂浓度,最后得到微晶玻璃样品的CIE色坐标为(0.3326, 0.3005),接近白光坐标.因此通过单掺杂Eu可以得到白光发光的YAG微晶玻璃.     

Multi‐Dimensional Quantum Nanostructures with Polarization Properties for Display Applications

Colloidal semiconductor nanocrystals (NCs), or quantum nanostructures with various dimensions and morphologies, are excellent emerging solution‐processable luminescent materials for display applications. The future of semiconductor NCs in the display market strongly relies on the development of low energy consuming devices. Replacing spherical NCs with multi‐dimensional nanostructures that emit linearly or circularly polarized light with high color purity and brightness, can significantly enhance the performance and efficiency of future display devices. In this review, we highlight some recent advances of colloidal syntheses of multi‐dimensional quantum nanostructures and their implementation as polarized light sources. The most representative examples are quasi‐one‐dimensional (q‐1D) CdSe/CdS dot‐in‐rods with strong linearly polarized emission for liquid crystal display technologies, and two‐dimensional (2D) nanoplatelets with enhanced circular dichroism signals as potential circularly polarized luminescence sources for electroluminescence applications.     

Luminescent properties of SrAl2O4: Eu,Dy material prepared by the gel method

SrAl₂O₄:Eu,Dy materials were first prepared by the gel method. Compared with samples prepared by solid state reactions, the grain size of the gel method is greatly reduced to nanometer grade. A clear blue shift occurs in the excitation and emission spectra of nano SrAl₂O₄:Eu,Dy, of which the peak of the excitation and emission spectra are at 323 and 500 nm respectively. The brightness of nano SrAl₂O₄:Eu,Dy is greatly reduced. The blue shift and the change of luminescent intensity in nano SrAl₂O₄:Eu,Dy materials can be attributed to the effect of surface energy.     

Fluorescence of poly(di-n-alkylsilane)s in room-temperature solution

A comprehensive study of the electronic absorption and emission spectra and the fluorescence quantum yield and lifetime of seven poly(di-n-alkylsilane)s and of three isotopically labelled poly(di-n-hexylsilane)s in hydrocarbon solution at room temperature is reported. Also reported are fluorescence polarization and carbon tetrachloride quenching of fluorescence of poly(di-n-hexylsilane). The observed fluorescence spectra, quantum yield, and polarization depend on the selected excitation energy in a very characteristic fashion, whereas the fluorescence lifetime does not; however, it depends on the selected emission energy. These characteristic dependencies are qualitatively accounted for by the previously proposed segment distribution model if one assumes that the photophysical behavior at higher excitation energies is strongly affected by the presence of a low-lying weakly allowed state in short-segment chromophores and the behavior at lower excitation energies is dictated by the selective excitation of emitting long-segment chromophores.     

Synthesis and photoluminescence properties of MgAl(PO4)O:Eu red phosphor for white LEDs

Eu³⁺-activated MgAl(PO₄)O:phosphor has been synthesized by a high temperature solid state reaction and efficient red emission under near-ultraviolet excitation is observed. The emission spectrum shows a dominant peak at 594 nm due to the ⁵D₀→⁷F₁ transition of Eu³⁺. The excitation spectrum is coupled well with the emission of UV LED (350–410 nm). The effect of Eu³⁺ concentration on the luminescent properties of MgAl(PO₄)O:Eu³⁺ and the mechanism of concentration quenching of Eu³⁺ are studied. The results show that MgAl(PO₄)O:Eu³⁺ is a promising red-emitting phosphor for white LEDs.