Up-conversion luminescence properties of Y2O2S:Yb3+,Er3+ nanophosphors

Up-converting yttrium oxysulfide nanomaterials doped with ytterbium and erbium (Y₂O₂S:Yb³⁺,Er³⁺) were prepared with the flux method. The precursor oxide materials were prepared using the combustion synthesis. The morphology of the oxysulfides was characterized with transmission electron microscopy (TEM). The particle size distribution was 10–110 nm, depending on the heating temperature. According to the X-ray powder diffraction (XPD), the crystal structure was found hexagonal and the particle sizes estimated with the Scherrer equation agreeded with the TEM images. Upon the 970 nm infrared (IR) laser excitation, the materials yield moderate green ((²H_11/2, ⁴S_3/2) → ⁴I_15/2 transition) and strong red (⁴F_9/2 → ⁴I_15/2) luminescence. The green luminescence was enhanced with respect to the red one by an increase in both the crystallite size and erbium concentration due to the cross-relaxation (CR) processes. The most intense up-conversion luminescence was achieved with x_Yb and x_Er equal to 0.10 and 0.005, respectively. Above these concentrations, concentration quenching occurred.     

Er3+单掺与Er3+/Yb3+共掺Y2SiO5的上转换发光

报道了一种新的上转换发光材料X2型Y2SiO5:Er, Yb并研究了Yb3 浓度和泵浦功率对样品的上转换发光特性的影响:(1)随着Yb3 浓度的增加,绿、红光发射均呈先增强后减弱的变化,但相对于绿光发射,红光发射受Yb3 浓度的影响更剧烈,并且当12%(摩尔分数)Yb3 时,可以得到很纯的红光发射;(2)上转换发光强度与泵浦功率的关系表明,双光子吸收贡献样品的上转换发射.此外,讨论了可能的上转换机制.认为随着Yb3 浓度增加,Er3 的激发态吸收、Yb3 到Er3 的能量传递和Er3 的交叉弛豫对上转换发光的作用依次逐渐加强.     

纳米NaYF4:Er3+,Yb3+上转换材料的合成及其性质研究

采用溶胶-凝胶法在水相合成了纳米NaYF_4:Er~(3 ),Yb~(3 )上转换材料,980nm红外激光照射下,肉眼可观察到明亮的上转换发光。实验研究了铒、镱掺杂浓度及焙烧温度对材料合成的影响。所合成的纳米材料呈圆球形、颗粒均匀、分散性好,平均粒径70nm,可应用于生物标记。     

纤维状中空结构NaYF4:Yb3+, Er3+上转换材料的 合成及防伪应用

采用水溶性聚合物聚乙烯亚胺(PEI)调介下的水热法,一步合成了具有纤维状中空结构的六方相NaYF4:Yb3+,Er3+上转换荧光材料,并将其作为荧光填料,通过流延成膜法制备了具有上转换荧光性能的壳聚糖/聚乙烯醇(CS/PVA)荧光复合薄膜.探究了PEI配体含量和反应体系pH值对合成的上转换材料的形貌、晶型和荧光性能的影响,以及壳聚糖/聚乙烯醇荧光复合薄膜中荧光填料的最佳掺杂量.研究结果表明,在PEI含量为0.3 g且反应体系pH=5的条件下,合成的产物为具有纤维状中空结构的六方相NaYF4:Yb3+,Er3+.荧光光谱表明,合成的NaYF4:Yb3+,Er3+上转换材料在980 nm激光激发下具有优异的荧光性能.当荧光填料的掺杂质量分数为3.0％时,制备的NaYF4:Yb3+,Er3+/(CS/PVA)荧光复合薄膜具有最佳的透明度和上转换荧光特性.     

Up-conversion luminescence of the NaYF4:Yb3+,Er3+ nanomaterials prepared with the solvothermal synthesis

Up-converting NaYF₄:Yb³⁺,Er³⁺ (x_Yb: 0.20, x_Er: 0.02) nanomaterials were prepared with a microwave assisted solvothermal synthesis to study how the synthesis parameters affect the structure and up-conversion luminescence of the materials and thus their usability as labels in biomedical applications. The purity of the materials was studied with Fourier transform infra-red (FT-IR) spectroscopy and the particle size and morphology with transmission electron microscopy (TEM). The crystal structure was characterized with X-ray powder diffraction (XPD) and the crystallite sizes were calculated with the Scherrer formula. Up-conversion luminescence and luminescence decays were studied with near infra-red (NIR) laser excitation at 970 nm.The presence of the oleic acid was observed in the FT-IR spectra. The TEM images showed small quasi-spherical nanoparticles as well as long nanorods. The XPD measurements revealed that both cubic and hexagonal forms of NaYF₄ were present in the materials. The crystallite sizes ranged from ca. 20 to over 150 nm for the cubic and hexagonal phases, respectively. The characteristic up-conversion luminescence of Er³⁺ in red (640–685 nm; ⁴F_9/2 → ⁴I_15/2) and green (515–560 nm; ²H_11/2, ⁴S_3/2 → ⁴I_15/2 transitions) wavelengths was observed. The most intense luminescence and the longest luminescence emission lifetime were obtained with the material annealed for 12 h at 177 °C with 1.8 MPa pressure due to the predominance of the well-crystallized hexagonal form of NaRF₄ (R: Y, Yb, Er).     

NaYF4:Er3+和NaYF4:Yb3+/Er3+上转换荧光纳米晶的制备与表征

以EDTA为螯合剂,采用络合共沉淀法合成了NaYF4:Er3+和NaYF4:Yb3+/Er3+纳米晶.分别采用XRD、SEM、荧光分光光度计对合成的样品进行了结构、形貌和上转换荧光分析.XRD结果表明,制备的NaYF4:Er3+和NaYF4:Yb3+/Er3+均为纯立方相;SEM结果显示,制备的NaYF4:Er3+和NaYF4: Yb3+/Er3+晶粒粒径都在100nm左右,与NaYF4:Er3+相比,NaYF4:Yb3+/Er3+晶粒尺寸分布更均匀,分散性更好,符合作为荧光标记材料的要求;上转换荧光分析表明,在980nm激光器激发下,NaYF4:Yb3+/Er3+的发光强度比NaYF4:Er3+提高了1个数量级.     

Upconversion luminescence properties of nanocrystallite MgAl2O4 spinel doped with Ho3+ and Yb3+ ions

The upconversion luminescence spectra of nanocrystallite MgAl₂O₄ doped with 1% of Ho³⁺ and 5% of Yb³⁺ ions after excitation at 980 nm were measured. Influence of excitation regime either continuous or pulse on upconversion mechanisms was shown. For continuous wave (CW) laser excitation upconversion process is due to phonon assisted Excited State Absorption (ESA). For pulse laser excitation upconversion emission is due to Energy Transfer Upconversion (ETU).     

Multicolor up-conversion emissions of Tm3+/Er3+/Yb3+ tri-doped YF3 phosphors

Tm3+/Er3+/Yb3+ tri-doped yttrium fluoride (YF3) phosphors were prepared by a facile hydrothermal method. X-ray topographic analysis found that the phosphors were crystallized products. Their sizes and morphologies were characterized by scanning electron microscopy (SEM, Hitachi S-4800), which indicated that most of the YF3 phosphors were hundreds of nanometers in size. Up-conversion (UC) spectra were recorded under 980-nm diode laser excitation at room temperature with a fluorescence spectrometer (Hitachi F-4500). Plenty of UC emissions of Tm3+ and Er3+ were observed from ultraviolet to red. For Tm3+ ions, a five-photon process (approximately 291 nm and approximately 347 nm), a four-photon process (approximately 362 nm and approximately 452 nm), and a three-photon process (approximately 475 nm) were identified in the UC spectra. The UC emissions from the Er3+ were: approximately 380 nm, approximately 408 nm, approximately 521 nm, approximately 537 nm, and approximately 652 nm. Therefore, cyan-white light can be observed by the naked eye at 980-nm excitation, even under low excitation power density. By comparing the UC spectra of the phosphors annealed at different temperatures, we found that the intensity of the UC luminescence increased as annealing temperature increased. Furthermore, the spectral dependencies on Tm3+ doped concentrations were studied. The energy transfer processes and fluorescence dynamics in the tri-doped system are currently being investigated.     

Synthesis and two-color emission properties of BaGd2(MoO4)4:Eu3+,Er3+,Yb3+ phosphors

Eu³⁺, Er³⁺ and Yb³⁺ co-doped BaGd₂(MoO₄)₄ two-color emission phosphor was synthesized by the high temperature solid-state method. The structure of the sample was characterized by XRD, and its luminescence properties were investigated in detail. Under the excitation of 395 nm ultraviolet light, the BaGd₂(MoO₄)₄:Eu³⁺,Er³⁺,Yb³⁺ phosphor emitted an intense red light at 595 and 614 nm, which can be attributed to ⁵D₀ → ⁷F₁ and ⁵D₀ → ⁷F₂ transitions of Eu³⁺, respectively. The phosphor will also show bright green light under 980 nm infrared light excitation. The green emission peaks centred at 529 and 552 nm, were attributed to ⁴H_11/2 → ⁴I_15/2 and ⁴S_3/2 → ⁴I_15/2 transitions of Er³⁺, respectively. It indicated that the two-color emission can be achieved from the same BaGd₂(MoO₄)₄:Eu³⁺,Er³⁺,Yb³⁺ host system based on the different pumping source, 395 nm UV light and 980 nm infrared light, respectively. The obtained results showed that this kind of phosphor may be potential in the field of multi-color fluorescence imaging and anti-counterfeiting.     

Er3+/Tm3+/Yb3+共掺氟氧化物玻璃的上转换白光性质

采用高温固相法制备了Er3+/Yb3+、Tm3+/Yb3+和Er3+/Tm3+/Yb3+共掺杂的氟氧化物玻璃SiO2-Al2O3-Na2O-ZnF2,研究了980nm近红外激光激发下的上转换发光性质。研究表明,Er3+/Yb3+共掺样品呈现了上转换绿光和红光发射,Tm3+/Yb3+共掺样品呈现了强的上转换蓝光发射和弱的红光发射,Er3+/Tm3+/Yb3+三掺样品呈现了上转换白光发射。对上转换发光强度和激光功率的研究表明上转换绿光和红光发射是两光子吸收过程,上转换蓝光发射是三光子吸收过程。     

Yb3+ concentration dependence of upconversion luminescence in Y2Sn2O7:Yb3+/Er3+ nanophosphors

Pyrochlore Y₂Sn₂O₇ nanophosphors codoped with Er³⁺ (fixed 2 at.%) and Yb³⁺ ions (2–16 at.%) were synthesized via hydrothermal process followed by heat treatment. We investigate the infrared-to-visible upconversion (UC) luminescence properties of Er–Yb codoped Y₂Sn₂O₇. Upon 980 nm excitation at room temperature, green (at ~522 and 544 nm) and red (at ~661 nm) UC emissions were observed, which are ascribed to the (²H_11/2, ⁴S_3/2) → ⁴I_15/2 and ⁴F_9/2 → ⁴I_15/2 transitions, respectively. It has been found that the Yb³⁺-doping concentrations have greatly influenced on the UC luminescence intensity and the emission ratio of the red and green in Y₂Sn₂O₇:Yb³⁺/Er³⁺ nanophosphors. The tunable emission is due to the energy back transfer from Er³⁺ to Yb³⁺ and the cross relaxation between the two neighboring Er³⁺ ions. It is expected that the achieved single and intense red emission band may have potential application for in vivo bioimaging.     

Synthesis and luminescence properties of Na+, Li+ compensated Er3+ doped CaAl4O7 phosphors

Here the green-emitting highly luminescent Er³⁺ doped, Er³⁺-Li⁺ co-doped, Er³⁺-Na⁺ co-doped CaAl₄O₇ is synthesized by Pechini method at 1000^°C. Photoluminescence (PL) of CaAl₄O₇: Er³⁺ studies have been compared with Li⁺ co-doped CaAl₄O₇: Er³⁺ and Na⁺ co-doped CaAl₄O₇: Er³⁺. Na⁺ co-doped CaAl₄O₇:Er³⁺ shows increases in luminescence intensity compared to Li⁺ co-doped CaAl₄O₇: Er³⁺ and Er³⁺ doped CaAl₄O_7. The results suggest that CaAl₄O₇:Er³⁺ phosphor can be used as efficient green-emitting phosphor in white LED. The resultant phosphor emits green color peaking at 549 nm upon 378 nm excitation. Powder X-ray diffraction (PXRD) and photoluminescence (PL) techniques have been studied to characterize the synthesized microparticles. Further, this phosphor has good thermal stability that implies its potential to act as green phosphor in white light-emitting diodes. The effect of activator (Er³⁺), Na⁺ co-doped CaAl₄O₇:Er³⁺, and Li⁺ co-doped CaAl₄O₇:Er³⁺ phosphors luminescence spectra as well as photoluminescence life time studies were studied in detail. The results show that as the concentration of Er³⁺ in CaAl₄O₇ increases, the symmetry around the Er³⁺ ion decreases due to the creation of lattice defects in the crystal. Addition of Na⁺ and Li⁺ ions in CaAl₄O₇: Er³⁺leads to a small distortion in the local symmetry of Er³⁺ ions, thereby significantly enhancing its luminescence property. Analysis of photoluminescence life time studies of the prepared samples shows a smaller concentration quenching of Er³⁺ luminescence in charge compensated Na⁺ and Li⁺ CaAl₄O₇ phosphor.

     

Near-infrared luminescence and energy transfer in CaMoO4: Ho3+, Yb3+ phosphor

Down-conversion (DC) is a promising avenue to break Shockley–Queisser detailed balance limit, and efficient DC from one ultraviolet visible photon to two near-infrared (NIR) photons is realized in the Ho³⁺ –Yb³⁺ co-doped CaMoO₄ system. The scheelite samples have been synthesized via solid-state reaction method. Upon blue light excitation (447 nm), Ho³⁺ transfers its energy to Yb³⁺ via resonant cross-relaxation process, bringing about NIR luminescence. The visible emissions decrease as a function of Yb³⁺ contents, while NIR emission at 996 nm first increases and then decreases due to CQ at Yb³⁺ contents beyond 15 mol %. The lifetime of Ho³⁺: ⁵F₄, ⁵S₂ → ⁵I₈ with various Yb³⁺ contents is calculated as 114, 85, 73, 70, 64, 59 and 55 μs, respectively. The maximum energy transfer efficiency and the corresponding DC quantum efficiency are estimated to be 48 and 148 %. The phosphor may be a potential candidate for application in enhancing the performance of crystalline silicon solar cells.     

Effect of homogeneous coating on K+-doped NaGdF4:Er3+,Yb3+ upconversion materials

Journal of Materials Science: Materials in Electronics - The K+-doped (Na1?xKx)GdF4:Er3+,Yb3+ upconversion materials were successfully synthesized by solvothermal method. The doping of K+ was...     

Structural and optical properties of NaY(WO4)2:Tm3+,Yb3+ and NaY(WO4)2:Tm3+,Er3+,Yb3+ powders synthesized by the high-temperature solid-state method

Journal of Materials Science: Materials in Electronics - The NaY(WO4)2:Tm3+,Yb3+ (NYW:Tm3+,Yb3+) and NaY(WO4)2:Tm3+,Er3+,Yb3+ (NYW:Tm3+,Er3+,Yb3+) powders have been synthesized by the...     

Synthesis and characterization of Yb3+,Tm3+:Ba2YF7 nanocrystalline with efficient upconversion fluorescence

A novel upconversion luminescence nanocrystals Yb³⁺,Tm³⁺:Ba₂YF₇ were synthesized via the hydrothermal method. They have uniform morphology with a mean size of 30 nm even if annealed at 600 °C. Pumped by 980 nm laser diode the as-synthesized powers emit ultraviolet/blue light, which is in the range of the specific upconversion luminescent spectra of Tm³⁺ ions. After post-annealing at 600 °C in an argon atmosphere for 2 h, their upconversion luminescence intensity is 5 multiple improved and the ultraviolet/blue light can even be seen by the naked eyes under a low excitation power of 20 mW. This indicates that Ba₂YF₇ is a very effective luminescent host material. Excitation power dependences of individual upconversion emission intensity are plotted, which partly uncover the upconversion luminescence mechanism of Tm³⁺ ions.     

Preparation and upconversion luminescence of Y2SiO5:Yb3+, Ho3+ nanophosphors

X1 type monoclinic Y2SiO5:Yb3+, Ho3+ nanophosphors with fixed (varied) Ho3+ and varied (fixed) Yb3+ concentrations were synthesized by sol-gel method. The nanophosphors presented lacunaris shape with an average size of about 47 nm measured by transmission electron microscopy and scanning electron microscopy. Up-conversion emissions have been observed at 550 nm corresponding to (5F4, 5S2)-5I8 transition and 661 nm due to 5F5-5I8 transition of Ho3+ upon 980 nm excitation at room temperature. The results indicate that both green and red luminescences are based on the two-photon process through the energy transfer from Yb3+. However, the intensity of green emission is weaker than that of the red, because the 5I7 level of Ho3+ can be effectively populated. The integrated upconversion emission intensity on the Yb3+ and Ho3+ concentrations were also studied.