Synthesis and upconversion luminescence of uniform beta-NaYF4:Yb3+/Tm3+ hexagonal nanoplates

Yb3+ and Tm3+-codoped hexagonal-phase NaYF4 powders were prepared by a facile hydrothermal method. The results of X-ray powder diffraction (XRD) and scanning electron microscopy (SEM) showed that the as-prepared powders were well crystallized nanoplates with high size-uniformity. Under the excitation from a 980 nm laser diode, upconversion (UC) emissions centered at approximately 291 nm (1I6 --> 3H6), approximately 346 nm (1I6 --> 3F4), approximately 361 nm (1D2 --> 3H6), approximately 451 nm (1D2 --> 3F4), approximately 474 nm (1G4 --> 3H6), approximately 644 nm (1G4 --> 3F4), and approximately 799 nm (3H4 --> 3H6) were observed in the sample. Furthermore, the intensity dependence of UC emissions on excitation power was measured. The results indicated that populating the 1I6, 1D2, 1G4, and 3H4 states were five-photon, four-photon, three-photon, and two-photon UC processes, respectively.     

Controllable multicolor upconversion luminescence of lanthanide doped NaGdF4 nanocrystals through single laser excitation at 980 nm

Room temperature multicolor Upconversion (UC) luminescence in Yb3+, Tm3+, Er3+ ions doped NaGdF4 nanocrystals have been successfully synthesized by a hydrothermal method. As-prepared nanocrystals are highly crystalline and well-dispersed in cyclohexane to form stable and clear colloidal solutions, which demonstrates strong emission properties with a single laser excitation at 980 nm. The multicolor light consists of blue, green, and red UC radiations that correspond to transitions 1G4 --> 3H6 of Tm3+, 2H(11/2)/4S(3/2) --> 4I(15/2), and 4F(9/2) --> 4I(15/2) of Er3+ ions, respectively. The UC mechanisms were proposed based on spectral, kinetic, and pump power dependence analyses.     

Effect of concentration on the photoluminescence properties of Sm3+ and Dy3+: cadmium lithium boro tellurite glasses

Rare-earth (Sm3+ or Dy3+) ions doped cadmium lithium boro tellurite glasses have been prepared by melt quenching method for their spectral studies. From X-ray diffraction (XRD) patterns the glass amorphous nature has been confirmed. Vis-NIR absorption, excitation and emission spectra of these glasses have been analyzed systematically and also rare earth ion concentration is optimised Sm3+: CLiBT glasses have shown strong orange-reddish emission at 598 nm (4G5/2-->6H7/2) with an excitation wavelength lambda(exci) = 401 nm and Dy3+: CLiBT glasses have shown strong yellow emission at 574 nm (6F9/2-->6H13/2) with lambda(exci) = 451 nm.     

The sol-gel process synthesis of GdAl3(BO3)4:Eu3+ nanophosphors

GdAl3(BO3)4:Eu3+ red phosphors were prepared using citric acid as complex agent by sol-gel technique. The preparation conditions of the precursor synthesis, including crystallization temperature and crystallization time were investigated. Their structure and luminescence properties were characterized by X-ray diffraction (XRD) analysis and fluorescence spectrometry. The results showed that GdAl3(BO3)4:Eu3+ phosphor crystallized at 960 degrees C for 2 h have been synthesized by sol-gel method. The phosphor is distributed into hexagonal system and the lattice parameters are a = 9.2992 nm c = 7.2577 nm. The excitation spectrum of Gd(0.95)Al3(BO3)4:Eu(0.05)3+ samples is complex and the frequency scale is wide. It consists of a number of main excitation transitions namely 8S(7/2) --> 6IJ (270 nm) of Gd3+, and the others 7F0 --> 5L6 (400 nm), 7F0 --> 5D2 (472 nm) and 7F0 --> 5D1 (542 nm) of Eu3+. The main emission peaks are 614 nm and 619 nm, which are the characteristic emission peaks of Eu3+. These emission peaks correspond to the transition from 5D0 to 7F2 of Eu3+. The shape and the wavelength range of the emission spectrum are similar when the sample was excited by different excitation spectrum. Only the relative intensity of the emission peaks is different from each other.     

铋锗酸盐玻璃中铒离子的上转换光谱特性

研究了由重金属氧化物Bi2O3-GeO2-PbO组分高温融熔而成的铋锗酸盐玻璃中稀土掺杂铒离子(Er3+)的吸收光谱、上转换发光谱以及玻璃基质的红外吸收谱,着重分析了975 nm和800 nm泵浦光激励下Er3+离子的上转换发光机理.结果表明,在975 nm或800 nm泵浦光激励下,观察到了绿光(529 nm、552...     

Sensitized upconversion emissions of Tb3+ by Tm3+ in YF3 and NaYF4 nanocrystals

Yb3+-Tm3+-Tb3+-codoped YF3 and NaYF4 nanocrystals (NCs) were synthesized using a simple hydrothermal method. Under 980 nm excitation, violet and ultraviolet upconversion (UC) emissions of 5D3 --> 7FJ (J = 6, 5, 4) and 5D4 --> 7FJ (J = 6, 5, 4, 3) of Tb3+ ions were observed with the fluoride NCs. In the Yb-Tm-Tb codoped NCs, energy transfer (ET) processes from Tm3+ to Tb3+ were proposed to be the main mechanisms for the UC emissions of Tb3+ ions. They are more efficient than the phonon assisted cooperative sensitization of the Yb3+ couple proposed previously for similar material system. The analysis of power dependence indicated that populating the 5D4 level of the Tb3+ ions was a four photon UC process, which demonstrated the existence of the two step ET process of Yb3+ --> Tm3+ --> Tb3+. It was also found that UC luminescence properties of Tb3+ ions were sensitive to crystal structures.     

Visible upconversion emission of Pr3+ doped gadolinium gallium garnet nanocrystals

The luminescence properties of a Pr3+-doped gadolinium gallium garnet (GGG, Gd3Ga5O12) nanocrystalline host were investigated. Dominant blue/green emission was observed emanating from the 3P0 --> 3H4 transition after excitation using a wavelength of 457.9 nm. Continuous wave excitation into the 1D2 level of the Pr3+ ion at 606.9 nm transition produced blue upconversion luminescence spectra, ascribed to emission from the 3P1 --> 3H4 and 3P0 --> 3H4 transitions. The increase in the decay times of the observed transitions following excitation with 606.9 nm is indicative of the dominance of an energy transfer upconversion (ETU) mechanism relative to excited state absorption (ESA). Furthermore, blue, green and red upconversion emission was observed from the 3P0, 3P1 and 1D2 states following excitation into the 1G4 energy level with 980 nm. No change in the decay times of the emitting states was observed following excitation with a wavelength of 980 or 457.9 nm; hence, upconversion was determined to primarily occur through ESA. The luminescence properties of the nanocrystals are compared to a single crystal of GGG:Pr3+ (bulk) with an identical Pr3+ concentration (1%).     

The properties of upconversion luminescence on YAIO3:Er(3+) nanophosphors with different Er(3+) concentrations

We report the properties of upconversion luminescence on Yttrium aluminum perovoskite (YAIO3) doped with trivalent erbium at concentrations of 1, 2, 3, 5 and 7 mol%. The samples were synthesized by solvo-thermal reaction method and the XRD patterns conforms that the YAP:Er(3+) nanophosphors have orthorhombic phase. Efficient green and red upconversion (UC) emission of YAP:Er(3+) nanophosphors was measured under the excitation of 975 nm continuous wave diode laser, and its dynamics and pump power dependence were investigated. As concentration of Er(3+) ion increased from 1 to 7 mol%, the red UC emission increased more rapidly. It is attributed to the energy transfer (4I(11/2) --> 4I(15/2):4I(13/2) --> 4F(9/2)) and to the cross relaxation (4S(3/2) --> 4I(9/2):4I(15/2) --> 4I(13/2)) between Er(3+) ions. In this case, the green and red emissions were yielding from quadratic to linear. These conclusions obtained are confirmed by theoretical investigations based on steady-state rate equations.     

Emission properties of hydrothermal Yb(3+), Er(3+) and Yb(3+), Tm(3+)-codoped Lu2O3 nanorods: upconversion, cathodoluminescence and assessment of waveguide behavior

Yb(3+) and Ln(3+) (Ln(3+) = Er(3+) or Tm(3+)) codoped Lu(2)O(3) nanorods with cubic Ia3 symmetry have been prepared by low temperature hydrothermal procedures, and their luminescence properties and waveguide behavior analyzed by means of scanning near-field optical microscopy (SNOM). Room temperature upconversion (UC) under excitation at 980 nm and cathodoluminescence (CL) spectra were studied as a function of the Yb(+) concentration in the prepared nanorods. UC spectra revealed the strong development of Er(3+) (4)F(9/2) → (4)I(15/2) (red) and Tm(3+) (1)G(4) → (3)H(6) (blue) bands, which became the pre-eminent and even unique emissions for corresponding nanorods with the higher Yb(3+) concentration. Favored by the presence of large phonons in current nanorods, UC mechanisms that privilege the population of (4)F(9/2) and (1)G(4) emitting levels through phonon-assisted energy transfer and non-radiative relaxations account for these observed UC luminescence features. CL spectra show much more moderate development of the intensity ratio between the Er(3+) (4)F(9/2) → (4)I(15/2) (red) and (2)H(11/2), (4)S(3/2) → (4)I(15/2) (green) emissions with the increase in the Yb(3+) content, while for Yb(3+), Tm(3+)-codoped Lu(2)O(3) nanorods the dominant CL emission is Tm(3+) (1)D(2) → (3)F(4) (deep-blue). Uniform light emission along Yb(3+), Er(3+)-codoped Lu(2)O(3) rods has been observed by using SNOM photoluminescence images; however, the rods seem to be too thin for propagation of light.     

Synthesis and characterization of PVP/TbL(phen)0.5 x 7H2O nanorods

The luminescent complex terbium (III)-trimesic acid (TMA)-1,10-phenanthroline (phen) nanorod was synthesized in the polyvinylpyrrolidone (PVP) matrix by a co-precipitation method. The chemical formula of the synthesized complex was speculated to be PVP/TbL(phen)0.5 x 7H2O by inductively coupled plasma-atomic emission spectroscopy (ICP-AES), elemental analysis and Fourier-transform infrared spectroscopy (FTIR). The X-ray diffraction pattern (XRD) of PVP/TbL(phen)0.5 x 7H2O indicated that it was a crystalline complex. The transmission electron microscopy (TEM) result showed that the complex was nanorods with diameters of about 80-100 nm. The thermogravimetric curve (TGA) analysis exhibited that the complex has good stability below 400 degrees C. UV-Vis diffuse reflectance spectra showed that there is a maximum absorption at 300 nm. The photoluminescence analyses (PLA) showed that the synthesized complex emitted the characteristic green fluorescence of Tb (III) ions under ultraviolet light excitation. The emission peaks of PVP/TbL(phen)0.5 x 7H2O at 488, 542, 581, and 618 nm using 278 nm as exciting wavelength can be assigned to the 5D4 --> 7F6, 5D4 --> 7F5, 5D4 --> 7F4, and 5D4 --> 7F3 electron transitions of the Tb3+ ions, respectively.     

Energy transfer mechanisms in Yb3+-doped GdVO4 near-infrared downconversion nanophosphor

Yb3+-doped GdVO4 nanophosphor was prepared by the co-precipitation method. Under ultraviolet (UV) light excitation, strong near-infrared (NIR) emission of Yb3+ (2F(5/2) --> 2F(7/2)) around 980 nm was observed. Owing to the host absorption of GdVO4, a broad excitation band ranging from 250 to 350 nm was recorded when the Yb3+ emission was monitored, which suggests an efficient energy transfer from the host to the Yb3+ ions. The concentration dependence of the visible vanadate emission and the Yb3+ emission was investigated. The decay curve of the vanadate emission was measured under the excitation of a 266 nm pulsed laser. The decay time of the vanadate emission at 500 nm was remarkably reduced by introducing Yb3+, further verifying that the energy transfer from the vanadate host to the Yb3+ ions was very efficient. Cooperative energy transfer (CET) is discussed as the possible energy transfer process. The temperature dependence of the emission intensity and decay time were also investigated for our further discussion.     

Up-conversion emissions characteristics of non-aqueous sol-gel derived RE3Al5O12 nanocrystals

The RE3Al5O12 (REAG:Er3Al5O12, Er:Y3Al5O12 and Er:Yb3Al5O12) up-conversion (UC) nanocrystals have been prepared by the non-aqueous sol-gel method. The green and red UC emissions are attributed to the 2H(11/2), 4S(3/2) --> 4I(15/2) and 4F(9/2) --> 4I(15/2) transitions of Er3+, respectively, were obtained for all samples with a 975 nm semiconductor LD excitation. For Er3Al5O12 nanocrystals, the green and red UC emissions have similar intensities. Y and Yb ions have no evident effect on the peak positions, but strongly affected the intensities of the green and red UC emissions of the Er. A much higher intensity of the green relative to red UC emission was observed for Er:Y3Al5O12 nanocrystals, however, the red UC emission became predominant for Er:Yb3Al5O12 nanocrystals. It was suggested that the two-photon process was responsible for the green and red UC emissions mechanism for all the samples.     

Upconversion luminescence enhancement in Yb3+/Tm3+-codoped Lu2O3 nanocrystals induced by doping with Li+ ions

Lutetium oxide (Lu2O3) nanocrystals doped with 2%Yb3+, 0.5%Tm3+, and various doping concentrations of Li+ (0, 3, 5, 7, 10, 12, and 15 mol%) were prepared by the sol-gel method. The dependence on different doping concentrations of Li+ ions of the structure, morphology, and the upconversion emission intensity of the Lu2O3:2%Yb3+, 0.5%Tm3+ nanocrystals was investigated. The obtained Lu2O3 nanocrystals were systematically characterized by X-ray diffraction (XRD), field emission-scanning electron microscopy (FE-SEM), Fourier transformed infrared (FT-IR) spectra, Raman spectra, and upconversion spectra measurements. It was found that all the nanocrystals can be readily indexed to pure cubic phase of Lu2O3, indicating good crystallinity. The experimental results show that Li+ doping in Lu2O3:2%Yb3+, 0.5%Tm3+ nanocrystals can greatly enhance the upconversion emission intensity. The strong blue (490 nm) and the weak red (653 nm) emissions from the prepared nanocrystals were observed under 980 nm laser excitation, and attributed to the 1G4 --> 3H6 and 1G4 --> 3F4 transitions of Tm3+ ions, respectively. An simple analysis based on steady-state rate equations and a power-dependent study both indicate that the 1G4 levels can be populated by three-step energy transfer (ET) processes. The enhancement of the upconversion luminescence was suggested to be the consequence of the modification of the local field symmetry around the Tm3+ ion, reduced number of OH- groups, and the enlarged nanocrystal size induced by the Li+ ions.     

Intense red upconversion emission of Yb/Tm/Ho triply-doped tellurite glasses

By conventional melting and quenching methods, 3Yb2O3-0.2Tm2O3-xHo2O3 (wt%, x=0.2~1.2) was doped into an easily fiberized tellurite glass with composition of 78TeO2-10ZnO-12Na2O (mol%) to form YTH-TZN78 glasses. Under 976 nm excitation, the direct sensitizing effect of Yb ions (Yb→Ho) and indirect sensitizing and self-depopulating effects of Tm ions (Yb→Tm→Ho) were found to present intense red upconversion emission at 657 nm (Red, Ho:5F5→5I8) and were responsible for the absence of the usually observed 484 nm emission (Blue, Tm:1G4→3H36). Regardless of the dopant concentration of Ho ions, the intensity of the red emission at 657 nm (Red, Ho:5F5→5I8) is about three times stronger than that of the green one at 543 nm (Green, Ho:5S2→5I8). For this certain red emission at 657 nm, 0.4 wt% Ho2O3-doped YTH-TZN78 glass was found to present the highest emission intensity and is therefore determined as a promising active tellurite glass for red fiber laser development.     

Broadband downconversion in Bi3+, Yb3+-Co-doped YVO4 phosphor

Yttrium vanadate phosphors co-doped with Bi3+ and Yb3+ ions have been prepared via the solid-state reaction. The phosphors were characterized by various methods including X-ray diffraction, photoluminescence excitation and photoluminescence spectra. Upon ultraviolet (UV) light excitation, an intense near-infrared (NIR) emission of Yb3+ corresponding to the transition of 2F(5/2) --> 2F(7/2) peaking at 985 nm was observed as a result of energy transfer from O2(-)-V5+ or Bi3+-V5+ charge transfer state (CTS) to Yb3+. A broad excitation band ranging from 250 to 375 nm was recorded when the Yb3+ emission was monitored, which suggests an efficient energy transfer from CTS to Yb3+ ions. The dependence of Yb3+ doping concentration on the visible emission, the NIR emission and decay lifetime has been investigated. The results of visible and NIR spectral evolution with temperature indicate that the mechanism for the NIR-emission is mainly phonon-assisted energy transfer at room temperature, while the mechanism is mainly cooperative energy transfer at low temperature. The YVO4:Bi3+, Yb3+ phosphor has prospects for realizing high efficiency crystalline Si solar cells by converting broadband UV energy into NIR light.     

Up-conversion fluorescence of Tm3+ and Gd3+ in Yb3+/Tm3+ co-doped Gd2O3 nanocrystals

Through a co-precipitation method Gd(OH)3:20%Yb3+, 1%Tm3+ nanorods were synthesized. After sintered at 900 degrees C for 1 h in air, the as-prepared Gd(OH)3:20%Yb3+, 1%Tm3+ nanorods were converted into Gd2O3:20%Yb3+, 1% Tm3+ nanocrystals. Crystalline phases, sizes, and morphologies of the two samples were characterized by X-ray diffraction and field emission scanning electron microscope. The up-conversion (UC) fluorescence spectra of the Gd2O3:20%Yb3+, 1%Tm3+ nanocrystals were recorded by using a fluorescence spectrophotometer with a 980 nm continuous wave laser diode as excitation source. The nanocrystals not only present characteristic blue and ultraviolet (UV) UC emissions of activated Tm3+, but also show UV UC emissions of host Gd3+. The experimental study suggests that the excitation power has great effects on UC fluorescence properties and the energy transfer from Tm3+ to Gd3+ is very efficient.     

Preparation and luminescent properties of YVO4:Eu3+ nanofibers by electrospinning

This paper describes a procedure based on electrospinning for generating europium-doped yttrium vanadate (YVO4:Eu3+) nanofibers with diameters ranging from 30 to 50 nm. The YVO4:Eu3+ nanofibers were obtained through calcining precursory nanofibers, which were prepared through the electrospinning method. Suitable electrospinning parameters, such as concentration of PVP in solution, spinneret tip-to-collector plate distance (TCD), and applied voltage between spinneret and collector plate, are used to obtain thinner and more uniform precursory nanofibers of YVO4:Eu3+, which is important for preparing smaller diameter pure YVO4:Eu3+ nanofibers. The luminescent properties of the YVO4:Eu3+ nanofibers including excitation and emission spectra and fluorescence lifetime were studied. The excitation spectrum shows a broad band extending from 200 to 350 nm, which corresponds to the strong vanadate absorption in YVO4:Eu3+. The emission spectrum is dominated by the red 5D0 --> 7F2 hypersensitive transition of Eu3+. The fluorescence lifetime of Eu3+ 5D0 --> 7F2 (619 nm) is determined to be 493 micros at room temperature, which is basically in accordance with that in the bulk (521 micros).     

Luminescent properties of La3PO7:Eu3+ nanoparticles

La3PO7:Eu3+ samples were prepared by combustion and annealing and characterized by X-ray diffraction and transmission electron microscopy. It was found that the average size of the particles is about 80 nm. The red emission from the 5D0 --> 7F2 transition of the Eu3+ ions under ultraviolet light excitation is much stronger than the orange emission from the 5D0 --> 7F1 transition. The emission spectra, charge transfer band, laser selective excitation spectra, and time-resolved spectra indicate that symmetry of the local environment of Eu3+ lacks an inversion center and Eu3+ ions occupy at least two types of sites in the La3PO7 crystal. The superior color chromaticity compared to other phosphates and borates doped with Eu3+ means La3PO7:Eu3+ may have potential as a luminescent material.     

Ultraviolet upconversion fluorescence of Er3+ in Yb3+/Er3+-codoped Gd2O3 nanotubes

Under 980 nm excitation, room-temperature ultraviolet (UV) upconversion (UC) emissions of Er3+ from the 4G(9/2), 2K(13/2), and 2P(3/2) states were observed in Gd2O3:Yb3+/Er3+ nanotubes, which were synthesized via a simple wet-chemical route at low temperature and ambient pressure followed by a subsequent heat treatment at 800 degrees C. The experimental results exhibited that these UV emissions came from four-photon UC processes. In the Gd2O3:Yb3+/Er3+ nanocrystals, the energy transfers (ETs) from Yb3+ to Er3+ played important roles in populating the high-energy states of Er3+ ions. This material provides a possible candidate for building UV compact solid-state lasers or fiber lasers.     

表面效应对YAG:Eu3+纳米晶发光特性的影响研究

分别采用沉淀法和燃烧法制备了YAG:1%Eu3+纳米晶粉末,用XRD和TEM对样品进行了结构分析和形貌表征。室温光谱分析表明,其发射主峰位于590nm,来源于5 D0→7F1跃迁,另外来源于5 D0→7F4跃迁的709nm发射也较强。另外发现,燃烧法制备的样品在不同激发波长激发时,发射光谱峰形有显著变化。对沉淀法制备的纳米微粒经盐酸"浸蚀"表面修饰后,发现395nm激发时,676nm和693nm发光显著增强,而且693nm发射的激发谱中存在两个宽激发带。对表面修饰后样品的变温发光特性研究发现,随着温度的降低,676nm发射显著增强,而693nm发射显著减弱。对于上述现象通过纳米微粒的表面效应和缺陷态进行了分析和解释。