Hydrothermal synthesis and the enhanced blue upconversion luminescence of NaYF4:Nd3+,Tm3+,Yb3+

Nd³⁺, Tm³⁺ and Yb³⁺ co-doped NaYF₄ upconversion (UC) material was synthesized by the hydrothermal method. The structure of the sample was characterized by the X-ray diffraction, and its UC luminescence properties were investigated in detail. Under the 980 nm semiconductor laser excitation, its UC spectra exhibited distinct emission peaks at 451 nm, 475 nm and 646 nm respectively. On the basis of the comparison of UC spectra between NaYF₄:Nd³⁺,Tm³⁺,Yb³⁺ and NaYF₄:Tm³⁺,Yb³⁺, it was indicated that the existence of Nd³⁺ ion enhanced the blue emission intensity. The law of luminescence intensity versus pump power proved that the blue emission at 475 nm, and the red emission at 646 nm were the two-photon processes, while the blue emission at 451 nm was a three-photon process.     

Quantum cutting mechanism in NaYF4:Tb3+, Yb3+

A quantum cutting mechanism for the sublinear near-IR power dependence property in Tb3+-Yb3+ codoped NaYF4 powders were investigated both experimentally and theoretically. The slopes of Yb3+ luminescence intensity versus excitation power were fitted to be between 0.5 and 1. We have developed a quantum cutting rate equation model to explain the anomalous sublinear phenomenon and an assessment factor was introduced to help understand the physical mechanism. Experimental results showed that the linear downconversion process combined with second-order nonlinear process induced the sublinear power dependence property with the latter to be the dominant process.     

基于NaYF_4:Yb~(3+),Er~(3+)上转换发光材料的色彩设计

采用共沉淀法制备β-NaYF4:Yb3+,Er3+。X射线衍射图谱结果表明退火有利于β相生长。样品在970nm处有一强烈吸收峰,利用980nm激光激发样品,实现红、绿、蓝三色上转换发光;其中蓝光相对较弱,红、绿光的发射峰分别为521,539,659nm。速率方程表明红、绿发射对应跃迁均是双光子过程,实验结果与理论分析相符。此外,对红、绿发射带面积比的研究表明激发功率和Yb3+掺杂量影响发光颜色;进而可实现简便的色彩设计。     

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。     

Synthesis of biocompatible uniform NaYF4:Yb3+,Er3+ nanocrystals and their characteristic photoluminescence

For biological application, lanthanide ion doped upconverting nanocrystals should be modified to be biocompatible. Here, we show a viable and efficient procedure for producing biocompatible NaYF₄:Yb³⁺,Er³⁺ upconverting nanocrystals. The uniform NaYF₄:Yb,Er upconverting nanocrystals were firstly synthesized by a mild chemical procedure, which were subsequently coated with a layer of polyethylene-glycol (PEG) to be biocompatible. The photoluminescent intensity of the PEG coated NaYF₄:Yb,Er nanocrystals varies nonlinearly with increasing the thickness of the PEG coating. In particular, it was noted that the Intensity Ratio of Red to Green Emission (IRRGE) of PEG coated NaYF₄:Yb,Er was highly depended on the excitation power density: IRRGE keeping almost constant with increasing the excitation power density below 826 W/cm², but remarkably increasing when increasing the excitation power density above 826 W/cm². For this unique phenomenon, the excitation and emission mechanisms related to PEG coating were discussed.     

氨基磷酸辅助的水热合成NaYF4:Yb3+,Er3+纳米晶及其上转换发光

以氨基磷酸为螯合剂,通过共沉淀与水热法相结合,成功地制备出NaYF4:Yb3+,Er3+纳米晶.研究结果表明:水热前后NaYF4:Yb3+,Er3+纳米晶均为立方相结构,其颗粒大小约为80nm.在980 nm近红外光激发下,实现了样品的上转换发光.样品的上转换绿红光发射带归因于Er3+的2H11/2,4S3/2→4 I15/2和4F9/2 →4I15/2能级的跃迁.水热处理后的样品的上转换发光强度与水热处理前相比有了很大的增强.水热处理后,样品表面的有机配体的减少和样品结晶度的提高是样品上转换发光显著增强的主要原因.     

Microwave sol-gel process of KGd(WO4)2:Ho3+/Yb3 phosphors and their upconversion photoluminescence properties

Double tungstate KGd_1−x(WO₄)₂:Ho³⁺/Yb³⁺ phosphors with doping concentrations of Ho³⁺ and Yb³⁺ (x=Ho³⁺+Yb³⁺, Ho³⁺=0.05, 0.1, 0.2 and Yb³⁺=0.2, 0.45) were successfully synthesized by the microwave sol–gel method, and the upconversion mechanisms were investigated in detail. The synthesized particles formed after heat-treatment at 900 °C for 16 h showed a well crystallized morphology with particle sizes of 2–5 μm. Under excitation at 980 nm, the UC intensities of KGd_0.7(WO₄)₂:Ho_0.1Yb_0.2 and KGd_0.5(WO₄)₂Ho_0.05Yb_0.45 particles exhibited yellow emissions based on a strong 550-nm emission band in the green region and a strong 655-nm emission band in the red region, which were assigned to the ⁵S₂/⁵F₄→⁵I₈ and ⁵F₅→⁵I₈ transitions, respectively. The Raman spectra of the doped particles indicated the presence of strong peaks at higher frequencies of 764, 812, 904, 984, 1050, 1106, 1250 and 1340 cm⁻¹ induced by the disorder of the [WO₄]²⁻ groups with the incorporation of the Ho³⁺ and Yb³⁺ elements into the crystal lattice or by a new phase formation.     

KLa(MoO_4)_2∶Yb~(3+),Ho~(3+),Tm~(3+)白光荧光粉的制备及性能研究

采用水热法成功制备了Yb~(3+),Ho~(3+),Tm~(3+)三掺的多晶KLa(Mo O4)2荧光粉。在980 nm激光激发下,KLa(MoO_4)_2∶Yb~(3+),Ho~(3+),Tm~(3+)发出裸眼可见的明亮白光,这其中包括Tm~(3+)离子发出的蓝光(~475 nm)、Ho~(3+)离子发出的绿光(~540 nm)和红光(~651 nm)。根据色度坐标系计算得出的坐标点可以看出,随着Ho~(3+)/Tm~(3+)掺杂浓度之比的增加,KLa(Mo O_4)_2∶Yb~(3+),Ho~(3+),Tm~(3+)所发出的白光呈现从冷白光到暖白光的变化。最后详细讨论了KLa(Mo O_4)_2∶Yb~(3+),Ho~(3+),Tm~(3+)荧光粉可能的发光机制。     

YPO4∶Ho3+,Yb3+,Tm3+微纳米管的合成及上转换白光发射

水热法合成了均匀管状Tm3+,Ho3+和Yb3+三掺的YPO4微纳米管,在波长为980nm的近红外光激发下能够发射出红绿蓝三条可见光谱带以及中心波长位于795nm的近红外发射带,从而实现上转换白光发射。通过TEM,XRD和荧光光谱等表征手段对合成的Tm3+,Ho3+和Yb3+三掺YPO4微纳米管进行了结构和性能分析,结果表明,合成的YPO4微纳米管为纯净六方相,水热反应温度对荧光材料的发射光谱有较明显的影响,然而对材料物相的影响却不大。在相同反应温度下,随着掺杂稀土离子浓度的升高,相应发射峰的强度并不是单调的增强,而是由于浓度猝灭和交叉弛豫等因素呈现非单调性的变化。探讨了可能的上转换发射机制。这种上转换发射强度可调控荧光材料在三维固体显示、上转换荧光照明以及荧光探测等领域有潜在的应用。     

Infrared-to-visible upconversion emission of Er3+/Yb3+-codoped SrMoO4 phosphors as wide-range temperature sensor

Er³⁺/Yb³⁺-codoped SrMoO₄ phosphors were prepared by a high-temperature solid-state reaction method. At room temperature, all the as-prepared samples exhibited strong upconversion properties and the emission intensity increased dramatically with the increase of Yb³⁺ ion concentration, reaching its maximum value when the concentration was 5 mol%. The dependence of emission intensity on the pump power suggested that the upconversion emission was a two-photon process. Furthermore, the optical temperature sensing properties based on green upconversion emissions of the SrMoO₄:0.01Er³⁺/0.05Yb³⁺ phosphor were studied. It is found that the SrMoO₄:0.01Er³⁺/0.05Yb³⁺ phosphor can be operated over a very wide temperature range of 93–773 K with a maximum sensitivity of ∼0.0128 K⁻¹, indicating that low- and high-temperature thermometry can be simultaneously realized in this phosphor.     

Broadband downconversion based near-infrared quantum cutting via cooperative energy transfer in YNbO4:Bi3+, Yb3+ phosphor

YNbO₄:Bi³⁺, Yb³⁺ phosphor was prepared to study the quantum cutting process of converting one ultraviolet photon into two near-infrared photons. An intense near-infrared emission of Yb³⁺:²F_5/2 → ²F_7/2 around 1 μm was observed under the ultraviolet excitation belonging to the broadband absorption of the [NbO₄]^3- group and the Bi³⁺ ion. The photoluminescence spectra and decay lifetime measurements indicate efficient energy transfer from Bi³⁺ to Yb³⁺ ions, which is attributed to be of a cooperative energy transfer mechanism. The YNbO₄:Bi³⁺, Yb³⁺ phosphor with optimized doping concentration may be applicable in improving the efficiency of silicon-based solar cells.     

Photoluminescence in Gd2O3: Er3+, Yb3+ upconversion inverse opal

Photoluminescence properties of Gd₂O₃: Er³⁺, Yb³⁺ upconversion inverse opal photonic crystals were investigated. The photoluminescence spectra of the inverse opal show strong dependence on upconversion emission intensity and the corresponding photonic band-gaps of the inverse opal. Significant suppression of the green or red upconversion emission was observed if the photonic band-gap overlaps with the Er³⁺ ions emission band. The color purity of the red or green emission was improved in the inverse opal by the suppression of green or red UC emission. We believe that the present work will be valuable for not only the foundational study of upconversion emission modification but also new optical devices in upconversion lighting and display.     

Gd3+掺杂对NaYF4:Yb3+,Tm3+/Er3+ 纳米材料上转换荧光性能的影响

利用温和的溶剂热方法合成了具有上转换发光性能的Yb³⁺-Tm³⁺和Yb³⁺-Er³⁺共掺的纳米NaYGdF₄。在该体系中,通过调节Gd³⁺在基质中的掺杂量可以有效地控制产物的相变、尺寸以及上转换荧光性能。XRD和TEM分析结果表明,Gd³⁺的掺入在促进NaYF₄纳米颗粒由立方相到六方相转变的同时有助于减小其尺寸。上转换光谱研究表明,在Yb³⁺-Tm³⁺和Yb³⁺-Er³⁺共掺体系中,可通过优化Gd³⁺的掺杂量来有效提高产物的上转换荧光强度。同时,通过研究Tm³⁺和Er³⁺在不同可见光波段的发光强度与泵浦功率的关系探讨了上转换发光的机制。     

NaYF4:Eu3+,Tm3+,Yb3+材料中Stokes和反Stokes发光研究

合成了Eu3+,Tm3+和Yb3+掺杂的NaYF4材料.360 nm光激发呈蓝色发光,峰值位于452 nm,对应Tm3+的1D2→3F4跃迁;395 nm光激发旱橙色发光,峰值位于591 nm,对应Eu3+的5D0→7F1跃迁;409 nml光激发呈红色发光,峰值位于613 nm,对应Eu3+的5D0→7F2跃迁;980 nm光激发呈蓝色和红色发光,发光峰位于474和646 nm.蓝光来源Tm3+的1G4→3H6跃迁,红光来源Tm3+的1G4→3F4跃迁.在双对数曲线中,蓝光474 nm和红光646 nm的斜率分别为2.1和2.4,在980 nm光激发下,蓝光和红光发射都是双光子过程.还研究了材料的吸收光谱,并利用X射线衍射,扫描电镜测试了材料的物相结构和微观彤貌.结果表明:NaYF4:Eu3+,Tm3+,Yb3+材料具有较规则的六方相结构,结品良好.     

Avidin conjugation to up-conversion phosphor NaYF4:Yb3+, Er3+ by the oxidation of the oligosaccharide chains

NaYF₄:Yb³⁺, Er³⁺ nanoparticles were successfully prepared by a polyol process using diethyleneglycol (DEG) as solvent. After being functionalized with SiO₂–NH₂ layer, these NaYF₄:Yb³⁺, Er³⁺ nanoparticles can conjugate with activated avidin molecules (activated by the oxidation of the oligosaccharide chain). The as-formed NaYF₄:Yb³⁺, Er³⁺ nanoparticles, NaYF₄:Yb³⁺, Er³⁺ nanoparticles functionalized with amino groups, avidin conjugated amino-functionalized NaYF₄:Yb³⁺, Er³⁺ nanoparticles were characterized by X-ray diffraction (XRD), transmission electron microscopy (TEM), atomic force microscopy (AFM), Fourier transform infrared (FT-IR), UV/Vis absorption spectra, and up-conversion luminescence spectra, respectively. The biofunctionalization of the NaYF₄:Yb³⁺, Er³⁺ nanoparticles has less effect on their luminescence properties, i.e., they still show the up-conversion emission (from Er³⁺, with ⁴S_3/2 → ⁴I_15/2 at ~540 nm and ⁴F_9/2 → ⁴I_15/2 at ~653 nm), indicative of the great potential for these NaYF₄:Yb³⁺, Er³⁺ nanoparticles to be used as fluorescence probes for biological system.     

In2O3:H03+,Yb3+纳米晶的制备与上转换发光

以乙二醇为溶剂,采用低温溶剂热法制备了H03+/Yb3+共掺杂In2O3纳米晶.利用X射线晶体衍射 (XRD)、透射电子显微镜(TEM)对粒子的结构和形貌进行表征,结果表明,合成的样品为纯的立方相In2O3,颗粒尺寸约为30nm.通过上转换发光(UCL)光谱研究了粒子的上转换发光性质,在980nm半导体激光激 发下,In2O3:H03+,Yb3+纳米晶发射出强的绿色和弱的红色上转换发光,分别归属于H03+离子(5 F4,5S2)→5I8 和5F5→5I8跃迁.研究了不同H03+和yb3+离子掺杂浓度对上转换发光性能的影响,确定了H03+和yb3+最 佳掺杂摩尔分数分别为3%和4%.双对数曲线显示,绿光和红光的发射过程均为双光子吸收过程.对样品 的上转换发光机制进行了初步讨论.     

Blue upconversion luminescence of CaMoO4:Li+/Yb3+/Tm3+ phosphors prepared by complex citrate method

Li⁺/Tm³⁺/Yb³⁺ co-doped CaMoO₄ upconversion (UC) phosphor was prepared by complex citrate-gel method and UC luminescence properties were investigated. Li⁺/Tm³⁺/Yb³⁺ co-doped CaMoO₄ has intense blue emission induced by ¹G₄??³H₆ transition at 476?nm that is improved 10 times more than that of Li⁺ undoped sample and weak red emission at 647 nm generated by ³F₂??³H₆ transition under excitation at 980?nm. The optimum doping concentration of Li⁺ ions was investigated and UC mechanism of Li⁺/Tm³⁺/Yb³⁺ co-doped CaMoO₄ was discussed in detail.     

Shape controllable synthesis and enhanced upconversion photoluminescence of β-NaGdF_4:Yb~(3+), Er~(3+) nanocrystals by introducing Mg~(2+)

Different concentrations of Mg~(2+) -doped hexagonal phase NaGdF_4:Yb~(3+), Er~(3+)nanocrystals(NCs) were synthesized by a modified solvothermal method. Successful codoping of Mg~(2+)ions in upconversion nanoparticles(UCNPs) was supported by XRD, SEM, EDS, and PL analyses. The effects of Mg~(2+)doping on the morphology and the intensity of the upconversion(UC) emission were discussed in detail. It turned out that with the concentration of Mg~(2+)increasing, the morphology of the nanoparticles turn to change gradually and the UC emission was increasing gradually as well. Notably the UC fluorescence intensities of Er~(3+)were gradually improved owing to the codoped Mg~(2+)and then achieved a maximum level as the concentration of Mg~(2+)ions was 60 mol% from the amendment of the crystal structure of β-NaGdF_4:Yb~(3+),Er~(3+)nanoparticles. Moreover, the UC luminescence properties of the rare-earth(Yb3+, Er~(3+)) ions codoped NaGdF_4 nanocrystals were investigated in detail under 980-nm excitation.     

Cooperative energy transfer and frequency upconversion in Yb3+-Tb 3+ and Nd 3+-Yb 3+-Tb 3+ codoped GdAl3(BO3)4 phosphors

Polycrystalline GdAl₃(BO₃)₄ phosphors codoped with Yb³⁺/Tb³⁺ and/or Nd³⁺/Yb³⁺/Tb³⁺ have been synthesized by combustion method. Upon excitation with a 980 nm laser diode, an intense green upconversion luminescence has been observed in GdAl₃(BO₃)₄:Yb,Tb phosphor. The quadratic dependence of the luminescence on the pump-laser power indicating a cooperative energy transfer process. Meanwhile, it is noticed that upon excitation with 808 nm laser diode, intense luminescence has clearly been detected in GdAl₃(BO₃)₄:Nd,Yb,Tb phosphor. The luminescence intensity exhibits also a quadratic dependence on incident pump-laser power. However, no green-emission has been observed in GdAl₃(BO₃)₄ phosphors codoped with Yb³⁺/Tb³⁺ or Nd³⁺/Tb³⁺ respectively upon excited at 808 nm laser diode. A proposed upconversion mechanism involving energy transfer from Nd³⁺ to Yb³⁺, and then a cooperative energy transfer process from two excited Yb³⁺ to Tb³⁺ has been presented.     

Quantum cutting in CaYAlO4: Pr3+, Yb3+

The deposition of a thin layer of a quantum-cutter material on top of silicon-based solar cells seems to be a promising solution to reduce the thermalization losses. This mechanism has been reported in materials codoped with Pr3+-Yb3+, where Pr3+ can sensitize two Yb3+ ions for one absorbed blue photon. In the present Letter, we analyze precisely energy transfers between Pr3+ and Yb3+ in CaYAlO4, and we measure a quantum-cutting rate of 145%. We show that a very efficient back transfer from Yb3+ toward the (1)G4 level of Pr3+ ion leads to a strong reduction of the quantum yield.