Yb~(3 )对Tm~(3 )间接敏化与基质晶格关系

Yb3 敏化Tm3 有两种方式 ,一种是直接敏化上转换 ,另一种是间接敏化上转换。前种直接采用 980nm激光激发 ,而后者可用 80 7nm激光激发 ,无疑后者有利于提高上转换发光的量子效率。由于基质晶格的晶体场强度不同 ,对称性有高有低 ,造成的稀土离子的能级分裂不同 ,通过分析双掺BaY2 F8,Cs3Yb2 Cl9等材料的光谱资料并结合生长的双掺Yb3 ,Tm3 ∶ZnWO4 单晶光谱的实际测试与分析 ,提出了Yb3 和Tm3 间的间接敏化共振能量传输的新观点 ,并具体分析了能形成这一上转换机制的条件。与间接敏化非共振能量传输不同 ,一是Yb3 的2 F5/2 →2 F7/2 的跃迁应与Tm3 3H4 →1 G4 能级间隔尽可能接近 ;二是Yb3 激发态能级2 F5/2 与Tm3 的3H4 能级尽可能接近。这要求基质材料的晶体场场强要弱 ,对称性要低。间接敏化共振能量传输极有可能引起光子雪崩上转换 ,这将为探索实用上转换激光晶体提供有益经验。     

Upconversion properties of Er3+, Yb3+ and Tm3+ codoped fluorophosphate glasses

Er3+, Yb3+ and Tm3+ codoped fluorophosphate glasses emitting blue, green and red upconversion luminescence at 970 nm laser diode excitation were studied. It was shown that Tm3+ behaves as the sensitizer to Er3+ for the green upconversion luminescence through the energy transfer process: Tm3+:3H4+Er3+:4I 15/2-->Er3+:4I 9/2+Tm3+:3H6, and for the red upconversion luminescence through the energy transfer process: Tm3+:3F4+Er3+:4I 11/2-->Tm3+:3H6+Er3+:4F 9/2. Moreover, Er3+ acts as quenching center for the blue upconversion luminescence of Tm3+. The sensitization of Tm3+ to Er3+ depends on the concentration of Yb3+. The intensity of blue, green and red emissions can be changed by adjusting the concentrations of the three kinds of rare earth ions. This research may provide useful information for the development of high color and spatial resolution devices and white light simulation.     

Dopant distribution in a Tm(3+)-Yb(3+) codoped silica based glass ceramic: an infrared-laser induced upconversion study

The optically active dopant distribution in a Tm(3+)-Yb(3+) doped silica based glass ceramic sample has been investigated. A systematic analysis of the upconversion fluorescence of the Tm(3+)-Yb(3+) codoped glass and glass ceramic has been performed at room temperature. Tm(3+) and Yb(3+) single doped glass and glass ceramics have also been included in the study. Upon infrared excitation at 790 nm into the (3)H(4) level of the Tm(3+) ions a blue upconversion emission is observed, which is drastically increased in the Yb(3+) codoped samples. A rate equation model confirmed the energy transfer upconversion mechanism. Based on these results, the temporal dynamic curves of the levels involved in the upconversion process, (3)H(4), (2)F(5/2), and (1)G(4) were interpreted in the glass ceramic samples. The contribution of the optically active Tm(3+) and Yb(3+) ions in the crystalline and in the vitreous phase of the glass ceramic was distinguished and the ratio of Tm(3+) ions in the crystalline phase could be quantified for the 1 mol % Tm(3+)-2.5 mol % Yb(3+) glass ceramic. A surprising result was obtained for that concentration: the main contribution to the upconversion emission of the glass ceramic is due to Tm(3+)-Yb(3+) ions in the vitreous phase.     

Yb3+/Tm3+掺杂的NaY(WO4)2纳米晶的制备及发光特性

以聚乙二醇为配位剂,用水热法制备出纳米级上转换发光粉Yb3+和Tm3+共掺杂的NaY(WO4)2。研究了不同cYb/cTm对上转换发光强度的影响,实验表明当cYb/cTm=5∶1时,上转换发光强度最强。用XRD,SEM确定了Yb3+和Tm3+共掺杂的NaY(WO4)2是四方晶系,其粒径在25~35 nm范围,且分散均匀。用980 nm半导体激光器(LD)对其进行激发,在室温下观察到了365 nm附近紫外发射峰、456 nm,476 nm附近的蓝光发射峰和648 nm附近的红光发射峰,分别对应于Tm3+离子的1D2→3H6,1D2→3F4,1G4→3H6和1G4→3F4的跃迁。根据泵浦功率与发光强度的关系得出紫外发射峰、蓝光和红光发射均为双光子过程。     

Strong blue emission from Pr3+ ions through energy transfer process from Nd3+ to Pr3+ via Yb3+ in tellurite glass

Energy transfer excited upconversion emission in Nd3+/Pr3+-codped tellurite glass have been studied on pumping with 800 nm wavelength. The upconversion emission bands from Pr3+ ion are observed at the 488, 524, 546, 612, 647, 672, 708 and 723 nm due to the (3P0 + 3P1)-->3H4, 3P1-->3H5, 3P0-->3H5, 3P0-->3H6, 3P0-->3F2, 3P1-->3F3, 3P0-->3F3 and 3P0-->3F4 transitions, respectively. The addition of ytterbium ions (Yb3+) on the upconversion emission intensity is also studied and result shows an eight times enhancement in the upconversion intensity at 488 nm from Pr3+ ions. The pump power and concentration dependence studies are also made. It is found that Yb3+ ions transfer its excitation energy to Nd3+ from which it goes to Pr3+. No direct transfer to Pr3+ is seen. This is verified by codoping Nd3+ and Pr3+ into the host.     

Tm3+/Yb3+掺杂亚碲酸盐玻璃蓝红光上转换的研究

研究了掺Tm^3 /Yb^3 亚碲酸盐玻璃室温下的上转换发光。用970nm波长的半导体激光器作为泵浦源，得到了高效率的480nm波长上转换的荧光，通过对不同掺杂浓度样品的发光比较，发现了这种玻璃上转换发光的浓度猝灭现象，找出了这种玻璃得到高效率上转换发光的适宜浓度，并对Tm^3 的浓度猝灭现象进行了分析，通过对上转换发光强度与泵浦强度关系曲线的拟合，看到这种上转换是三光子吸收过程，这与通过能级图分析得到的结果相同，另外，也对650nm波长的转换发光进行了研究。     

Intense blue up-conversion luminescence in Tm3+/Yb3+ codoped oxyfluoride glass-ceramics containing beta-PbF2 nanocrystals

Up-conversion luminescence properties of a Tm3+/Yb3+ codoped oxyfluoride glass-ceramics under 980 nm excitation are investigated. Intense blue emission centered at 476 nm, corresponding to 1G4-->3H6 transitions of Tm3+ was simultaneously observed in the transparent oxyfluoride glass ceramics at room temperature. The intensity of the blue up-conversion luminescence in a 1 mol% YbF3-containing glass-ceramic was found to be about 40 times stronger than that in the precursor oxyfluoride glass. The reason for the intense Tm3+ up-conversion luminescence in the oxyfluoride glass-ceramics is discussed. The dependence of up-conversion intensities on excitation power and possible up-conversion mechanism are also evaluated.     

一种上转换白光荧光粉的制备与发光性能研究

采用高温固相法制备了上转换白光荧光粉AlF3-YbF3:Er3+/Tm3+。通过XRD物相分析可知:上转换白光荧光粉AlF3-YbF3:Er3+/Tm3+是由三方AlF3相和正交YbF3相组成;利用发射光谱研究了该荧光粉的上转换发光性能,并且分析了当固定Er3+离子掺杂浓度时,Tm3+离子掺杂浓度对上转换白光荧光粉AlF3-YbF3:Er3+/Tm3+色度的影响,进而提出其上转换能量传递机制。结果表明:在980 nm激光激发下,波长为410 nm的紫光峰、550 nm的绿光峰和660 nm的红光峰分别对应于荧光粉中Er3+离子的2H9/2→4I15/2,4S3/2→4I15/2和4F9/2→4I15/2能级的跃迁,而波长为360 nm的紫外光峰、450 nm的蓝光峰、700 nm的红光峰,分别对应于荧光粉中Tm3+离子的1D2→3H6,1G4→3H6和1G4→3F4能级的跃迁,Er3+离子发出的光与Tm3+离子发出的光最终混合成色坐标为x=0.32,y=0.36的白光。此外,通过980 nm半导体激光器和EPM 2000 Dual-channel Joulemeter/Power meter测得该荧光粉最大上转换效率为6.90%。     

NaGd（WO4）2:Yb3+,Tm3+纳米粉的制备与上转换发光性能

以聚乙二醇为络合剂,采用水热法成功制备了NaGd(WO4)2:Yb3+,Tm3+纳米粉。运用X射线粉末衍射、扫描电镜和光谱分析对制备的样品结构和发光性能进行了表征。结果表明,NaGd(WO4)2:Yb3+,Tm3+为四方晶系,晶粒尺寸约为50 nm。在980 nm半导体激光器激发下获得了发射光谱,有3个发射峰,发光中心位于455,476和650 nm,分别对应1D2→3F4,1G4→3H6,1G4→3F4的跃迁。讨论了Yb3+,Tm3+能量转换过程和机制。泵浦功率与发光强度关系表明,455,476和650 nm的3个发射均属于三光子过程。     

Cooperative energy transfer frequency upconversion in Tb3+/Yb3+-codoped oxyfluoride glasses

In this report, we investigate the cooperative energy transfer frequency upconversion in Tb3+/Yb3+-codoped SiO2-Al(2)O(3)-Na2O-ZnF(2) oxyfluoride glasses under 980 nm diode laser excitation. The influence of both Tb3+ and Yb3+ concentration on the emission bands were investigated. With a lower Tb3+ concentration, the emission bands around 381, 416 and 438 nm, and 489, 545, 587 and 623 nm associated with (5)D(3), (5)G(6)-->(7)F(J) (J=6, 5, 4) and (5)D(4)-->(7)F(J) (J=6, 5, 4, 3) transitions were observed. However, only (5)D(4)-->(7)F(J) (J=6, 5, 4, 3) transitions appear in a higher Tb3+ concentration. The integrated upconversion luminescence intensity was examined when the temperature of sample was varied from 40 to 450 K. The dependence of the upconversion emission intensity upon the excitation power was also examined, and the upconversion mechanisms were discussed.     

Sub-10 nm hexagonal lanthanide-doped NaLuF4 upconversion nanocrystals for sensitive bioimaging in vivo

By thermal decomposition in the presence only of oleylamine, sub-10 nm hexagonal NaLuF(4)-based nanocrystals codoped with Gd(3+), Yb(3+), and Er(3+) (or Tm(3+)) have been successfully synthesized. Sub-10 nm β-NaLuF(4): 24 mol % Gd(3+), 20 mol % Yb(3+), 1 mol % Tm(3+) nanocrystals display bright upconversion luminescence (UCL) with a quantum yield of 0.47 ± 0.06% under continuous-wave excitation at 980 nm. Furthermore, through the use of β-NaLuF(4):Gd(3+),Yb(3+),Tm(3+) nanocrystals as a luminescent label, the detection limit of <50 nanocrystal-labeled cells was achieved for whole-body photoluminescent imaging of a small animal (mouse), and high-contrast UCL imaging of a whole-body black mouse with a penetration depth of ~2 cm was achieved.     

Preferential suppression of high-energy upconverted emissions of Tm3+ by Dy3+ ions in Tm3+/Dy3+/Yb3+-doped LiYF4 colloidal nanocrystals

The intensity of high energy UV and blue upconverted emissions of Tm(3+) ions in Tm(3+)/Yb(3+) co-doped LiYF(4) colloidal nanocrystals was selectively reduced compared to the NIR emission at 802 nm. This was achieved by doping a small amount of Dy(3+) ions into the host matrix.     

Strong visible up-conversion emission in Tb3+, Tm3+ and Tb3+-Tm3+ co-doped tellurite glasses sensitized by Yb3+

Up-conversion luminescence characteristics under 975 nm excitation have been investigated with Tb3+/Tm3+/Yb3+ triply doped tellurite glasses. Here, green (547 nm: (5)D(4)-->(7)F(4)) and red (660 nm: (5)D(4)-->(7)F(2)) up-conversion (UC) luminescence originating from Tb3+ is observed strongly, because of the quadratic dependences of emission intensities on the excitation power. Especially, the UC luminescence was intensified violently with the energy transfer from the Tm3+ ions involves in the Tb3+ excitation. To the Tb3+/Tm3+/Yb3+ triply doped glass system, a novel up-conversion mechanism is proposed as follows: the energy of (3)G(4) level (Tm3+) was transferred to (5)D(4) (Tb(3+)) and the 477-nm UC luminescence of Tm3+ was nearly quenched.     

Yb3+掺杂浓度对LaF3晶相及其上转换光谱的影响

LaF3微米晶的晶相(斜方相和六角相)及其上转换发光光谱可以通过精确调节Yb3+的摩尔掺杂浓度来控制。利用简单的水热法合成了Yb3+和Tm3+共掺杂的LaF3,YF3和NaYF4三种不同基质的氟化物纳米晶。XRD分析表明,当Tm3+的掺杂浓度不变,仅Yb3+的摩尔掺杂浓度从10%提高到20%,就可以使基质结构由六角相过渡到斜方相。实验结果表明,具有较大离子半径的稀土离子由于增强的偶极化率,更容易使电子云产生畸变,有利于基质斜方相结构的形成。     

Study of upconversion fluorescence property of novel Er3+/Yb3+ co-doped tellurite glasses

Er3+/Yb3+ co-doped TeO2-B2O3-Nb2O5-ZnO (TBN) glasses were prepared. The absorption spectra and upconversion luminescence spectra of TBN glasses were measured and analyzed. The upconversion emission bands centered at 530, 546 and 658 nm were observed under the excitation at 975 nm, corresponding to the transitions of 2H11/2-->4I15/2, 4S3/2-->4I15/2 and 4F9/2-->4I15/2 respectively. The ratio of red emission to green emission increases with an increasing of Yb3+ ions concentration. According to the quadratic dependence on excitation power, the possible upconversion mechanisms and processes were discussed.     

Structural and up-conversion luminescence properties in Tm3+/Yb3+-codoped heavy metal oxide-halide glasses

Tm3+/Yb3+-codoped heavy metal oxide-halide glasses have been synthesized by conventional melting and quenching method. Structural properties were obtained based on the Raman spectra, indicating that halide ion has an important influence on the phonon density and maximum phonon energy of host glasses. Intense blue and weak red emissions centered at 477 and 650 nm, corresponding to the transitions 1G4-->3H6 and 1G4-->3H4, respectively, were observed at room temperature. The possible up-conversion mechanisms are discussed and estimated. With increasing halide content, the up-conversion luminescence intensity and blue luminescence lifetimes of Tm3+ ion increase notably. Our results show that with the substitution of halide ion for oxygen ion, the decrease of phonon density and maximum phonon energy of host glasses both contribute to the enhanced up-conversion emissions.     

Synthesis of colloidal upconverting NaYF4 nanocrystals doped with Er3+, Yb3+ and Tm3+, Yb3+ via thermal decomposition of lanthanide trifluoroacetate precursors

Upconverting lanthanide-doped nanocrystals were synthesized via the thermal decomposition of trifluoroacetate precursors in a mixture of oleic acid and octadecene. This method provides highly luminescent nanoparticles through a simple one-pot technique with only one preparatory step. The Er3+, Yb3+ and Tm3+, Yb3+ doped cubic NaYF4 nanocrystals are colloidally stable in nonpolar organic solvents and exhibit green/red and blue upconversion luminescence, respectively, under 977 nm laser excitation with low power densities.     

A facile synthesis and photoluminescence properties of water-dispersible Re3+ doped CeF3 nanocrystals and solid nanocomposites with polymers

Water-dispersible Re(3+) doped CeF(3) colloidal nanocrystals with well controllable morphology and high crystallinity have been successfully synthesized through a solvothermal process. The TEM images illustrate that the Re(3+) doped CeF(3) nanocrystals are rectangular (or cubic) with a mean diameter of ~10 nm. The excellent dispersibility in some of the polar solvents including water is achieved by using polyethyleneimine as the capping agent. The amine groups of the polymer chains on one hand bind to the nanocrystal surface; on the other hand the free ones could link to functional materials including bio-molecules. The CeF(3) nanocrystals doped with Tb(3+) and Dy(3+) ions show the characteristic emission of Tb(3+ 5)D(4)-(7)F(J) (J = 6-3, with (5)D(4)-(7)F(5) green emission at 542 nm as the strongest one) and Dy(3+ 4)F(9/2)-(6)H(15/2) (blue-green color at 478 nm) and (4)F(9/2)-(6)H(13/2) (yellow color at 571 nm) transitions, respectively. The energy transfer from Ce(3+) to Tb(3+) and Dy(3+) was also investigated in detail. In vitro studies of Re(3+) doped CeF(3) colloidal nanocrystals on HepG2 cells confirm their excellent biological compatibility. The obtained solid CeF(3)?: Tb(3+)/PDMS nanocomposites are very stable and flexible and exhibit strong green photoluminescence upon UV excitation.     

Facile synthesis and multicolor luminescent properties of uniform Lu2O3:Ln (Ln=Eu3+, Tb3+, Yb3+/Er3+, Yb3+/Tm3+, and Yb3+/Ho3+) nanospheres

Multicolor Lu(2)O(3):Ln (Ln=Eu(3+), Tb(3+), Yb(3+)/Er(3+), Yb(3+)/Tm(3+), and Yb(3+)/Ho(3+)) nanocrystals (NCs) with uniform spherical morphology were prepared through a facile urea-assisted homogeneous precipitation method followed by a subsequent calcination process. X-ray diffraction (XRD), scanning electron microscopy (SEM), transmission electron microscopy (TEM), high-resolution transmission electron microscopy (HRTEM), energy-dispersive X-ray spectrum (EDS), Fourier transformed infrared (FT-IR), thermogravimetric and differential thermal analysis (TG-DTA), and photoluminescence (PL) spectra as well as kinetic decays were employed to characterize these samples. The XRD results reveal that the as-prepared nanospheres can be well indexed to cubic Lu(2)O(3) phase with high purity. The SEM images show the obtained Lu(2)O(3):Ln samples consist of regular nanospheres with the mean diameter of 95 nm. And the possible formation mechanism is also proposed. Upon ultraviolet (UV) excitation, Lu(2)O(3):Ln (Ln=Eu(3+) and Tb(3+)) NCs exhibit bright red (Eu(3+), (5)D(0)→(7)F(2)), and green (Tb(3+), (5)D(4)→(7)F(5)) down-conversion (DC) emissions. Under 980 nm NIR irradiation, Lu(2)O(3):Ln (Ln=Yb(3+)/Er(3+), Yb(3+)/Tm(3+), and Yb(3+)/Ho(3+)) NCs display the typical up-conversion (UC) emissions of green (Er(3+), (4)S(3/2),(2)H(11/2)→(4)I(15/2)), blue (Tm(3+), (1)G(4)→(3)H(6)) and yellow-green (Ho(3+), (5)F(4), (5)S(2)→(5)I(8)), respectively.     

High-resolution optical spectroscopy of Na(3)[Ln(dpa)(3)].13H(2)O with Ln = Er(3+), Tm(3+), Yb(3+)

The title compounds were synthesized and studied by solution and single-crystal absorption, luminescence, and excitation spectroscopy. The f-f luminescence is induced in the Tm(3+) and Yb(3+) complexes in solution by exciting into the (1)Pi-(1)Pi absorptions of the ligand in the UV. A single-configurational coordinate model is proposed to rationalize the nonradiative relaxation step from ligand-centered to metal-centered excited states in [Yb(dpa)(3)](3-) (dpa = 2,6-pyridinedicarboxylate). Direct f-f excitation is used in crystals of Na(3)[Tm(dpa)(3)].13H(2)O and Na(3)[Yb(dpa)(3)].13H(2)O to induce f-f luminescence. From low-temperature, high-resolution absorption, luminescence, and excitation spectra, the ligand-field splittings in the relevant states can be determined. It was impossible to induce NIR to VIS upconversion in any of the complexes. This is mainly due to the fact that nonradiative relaxation among the f-f excited states is highly competitive, even in [Yb(dpa)(3)](3-) with an energy gap between (2)F(5/2) and (2)F(7/2) of about 10000 cm(-1). It can be rationalized on the basis of an adapted energy gap law. No luminescence at all could be detected in Na(3)[Er(dpa)(3)].13H(2)O.