Two- and three-photon upconversion of LaOBr:Er

In this work, the LaOBr:Er³⁺ (0.1%) powders were prepared by solid state reaction. The structural properties of LaOBr:Er³⁺ were characterized by X-ray diffraction (XRD), Fourier transform infrared spectroscopy (FT-IR) and Raman spectroscopy. The results show that LaOBr:Er³⁺ has low phonon energy, which indicate that LaOBr:Er³⁺ may have high luminescent efficiency. Under excitation into ⁴I_11/2 level of Er³⁺ ions by 980 nm laser, the two- and three-photon upconverted luminescence of LaOBr:Er³⁺ were recorded. The most intense emissions were come from the ²H_11/2, ⁴S_3/2 → ⁴I_15/2 transitions. The upconversion mechanisms were studied in detail through laser power dependence, and results show that excited state absorption is responsible for the upconversion. The upconversion properties indicate that LaOBr:Er³⁺ may be used in upconversion phosphors.     

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.     

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.     

Fluorescence spectroscopy of Er3+:LaOBr prepared by NH4Br solid state reaction

The steady luminescent materials La_1−xEr_xOBr (x = 0, 0.0003, 0.01) were synthesized by a new NH₄Br solid state reaction, and the structures were studied using XRD and Raman methods. Under 514.5 nm Ar⁺ laser excitation, the upconversion fluorescence spectra in LaOBr:Er³⁺ were recorded and investigated. It was found that four upconverted emission bands with peaks at 388 nm, 399 nm, 405 nm (violet) and 477 nm (blue) were observed. All these upconverted emissions were assigned, and the upconversion mechanism was deduced to be excited state absorption (ESA), by analyzing the energy level structures of Er³⁺ ions and measuring the power dependence of upconverted emission intensities.     

Synthesis and characterization of Y2O3:Er3+ upconversion materials with nanoporous structures

Y2O3:Er3+ upconversion materials with nanoporous structures were prepared by a hydrothermal method following a post-thermal treatment. The structure and morphology of the materials were characterized by X-ray diffraction (XRD) and field-emission scanning electron microscopy (FESEM). The results indicated that the as-obtained Y2O3:Er3+ powders were of cubic-phase structure, and the nanoporous structure was formed in the annealing process. The optical results indicated that high annealing temperature could improve the upconversion properties, but it could destroy the nanoporous structure. Under 980 nm excitation, red (4F(9/2) --> 4I(15/2) and green (2H(11/2), 4S(3/2) --> 4I(15/2)) upconversion luminescence was observed. The studies on the intensity dependence of upconversion emission indicated that two-photon processes were responsible for the green and red upconversion luminescence. This kind of multifunctional material has potential applications in nanocontainers for use as biomolecule and drugs carriers.     

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...     

Fabrication of Er3+-doped LaOCl nanostructures with upconversion and near-infrared luminescence performances

LaOCl:Er³⁺ nanofibers and nanobelts were prepared by electrospinning combined with a double-crucible chlorination technique using NH₄Cl powders as chlorinating agent. X-ray powder diffraction analysis indicated that LaOCl:Er³⁺ nanostructures were tetragonal with space group P4/nmm. Scanning electron microscope analysis and histograms revealed that diameter of LaOCl:Er³⁺ nanofibers and the width of nanobelts respectively were 161.15 ± 18.11 nm and 6.11 ± 0.19 μm under the 95 % confidence level, and the thickness of nanobelts was 116 nm. Up-conversion (UC) emission spectra analysis manifested that LaOCl:Er³⁺ nanostructures exhibited strong green and red UC emission centering at 525, 548 and 671 nm, respectively attributed to ²H_11/2 → ⁴I_15/2, ⁴S_3/2 → ⁴I_15/2 and ⁴F_9/2 → ⁴I_l5/2 energy levels transitions of Er³⁺ ions under the excitation of a 980-nm diode laser. It was found that the relative intensities of green and red emissions vary obviously with the changing of concentration of Er³⁺ ions, and the optimum molar percentage of Er³⁺/(La³⁺+Er³⁺) ions was 5 % in the LaOCl:Er³⁺ nanostructures. The LaOCl:x %Er³⁺ nanobelts have higher UC emission (both red and green) intensity than the counterpart nanofibers. Moreover, the near-infrared characteristic emissions of LaOCl:Er³⁺ nanostructures were achieved under the excitation of a 532-nm laser. Commission Internationale de L’Eclairage analysis demonstrated that color-tuned luminescence can be obtained by changing doping concentration of Er³⁺ ions, which could be applied in the fields of optical telecommunication and optoelectronic devices. The UC luminescent mechanism of LaOCl:Er³⁺ nanostructures were also proposed.     

Multicolor upconversion of Er3+/Tm3+/Yb3+ doped oxyfluoride glass ceramics

Er³⁺/Tm³⁺/Yb³⁺ tridoped oxyfluoride glass ceramics was synthesized in a general way. Under 980 nm LD pumping, intense red, green and blue upconversion was obtained. And with those primary colors, multicolor luminescence was observed in oxyfluoride glass ceramics with various dopant concentrations. The red and green upconversion is consistent with ⁴F_9/2 → ⁴I_15/2 and ²H_11/2, ⁴S_3/2 → ⁴I_15/2 transition of Er³⁺ respectively. While the blue upconversion originates from ¹G₄ → ³H₆ transition of Tm³⁺. This is similar to that in Er³⁺/Yb³⁺ and/or Tm³⁺/Yb³⁺ codoped glass ceramics. However the upconversion of Tm³⁺ is enhanced by the energy transfer between Er³⁺ and Tm³⁺.     

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.     

Electrospinning preparation of LaOBr:Tb3+ nanostructures and their photoluminescence properties

Tb³⁺-doped LaOBr nanostructures including nanofibers, nanobelts, and hollow nanofibers were synthesized for the first time via calcinating the electrospun polyvinyl pyrrolidone/[La(NO₃)₃ + Tb(NO₃)₃ + NH₄Br] composites. X-ray diffraction analysis revealed that LaOBr:Tb³⁺ nanostructures are tetragonal in structure with space group of P4/nmm. The morphologies and sizes of LaOBr:Tb³⁺ nanostructures were investigated using scanning electron microscope and transmission electron microscope. Under the excitation of 254-nm ultraviolet light, LaOBr:Tb³⁺ nanostructures exhibit the green emissions of predominant peak at 543 nm, which is ascribed to ⁵D₄ → ⁷F₅ transition of Tb³⁺ ions. It is found that the optimum doping concentration of Tb³⁺ ions in the LaOBr:Tb³⁺ nanofibers is 3 %. Interestingly, we found that the luminescence intensity of hollow nanofibers is obviously greater than that of nanofibers and nanobelts for LaOBr:Tb³⁺ under the same measuring conditions. Moreover, the luminescence of LaOBr:Tb³⁺ nanostructures are located in the green region in Commission Internationale de L’Eclairage chromaticity coordinates diagram. The formation mechanisms of LaOBr:Tb³⁺ nanofibers, nanobelts, and hollow nanofibers were also proposed. LaOBr:Tb³⁺ nanostructures are promising nanomaterials for applications in the fields of light display systems and optoelectronic devices.     

Temperature-dependent light upconversion and thermometric properties of Er3+/Yb3+-codoped SrMoO4 sintered ceramics

Journal of Materials Science - A series of Sr1?x?yErxYbyMoO4 phosphor compositions codoped with Er3+ (x?=?1 mol%) and varying Yb3+...     

Properties of Er3+-doped phosphate glasses and glass fibres and efficient infrared to visible upconversion

Some thermomechanical properties such as expansion, transition temperature and high-temperature viscosity of phosphate glasses with different P₂O₅ and BaO compositions have been measured. Absorption and fluorescence spectra of the phosphate glasses with different Er³⁺ doping have also been measured. The Er³⁺ doping concentration with respect to the maximal fluorescence intensity is 0.75 mol %. The attenuation of the fibre at a wavelength of 1.53 m is 12.8 db m^–1. Upconversion of 1.064 m NdYAG laser pulses into intense green 547 and 667 nm light in the 0.75 mol % Er³⁺-doped phosphate glass fibre has been achieved. The output power of the two fluorescence signals of green 547 nm and red 667 nm are 178 and 42 W, respectively, with an upconversion efficiency of 1.78×10^–2% and 4.2×10^–3% respectively.     

Ca3(PO4)2:Er3+,Yb3+: An upconversion phosphor for in vivo imaging

Using a sol-gel process, we have synthesized compounds isostructural with the biogenic mineral whitlockite and containing calcium phosphate, β-Ca₃(PO₄)₂, codoped with Er³⁺ and Yb³⁺ in various concentrations and ratios. Their particle size was determined to be ～42–57 nm by atomic force microscopy and ～93 nm by dynamic light scattering. The particles were shown to be weak anion exchangers (their zeta potential is ?13.3 mV). The observed luminescence of the β-Ca₃(PO₄)₂:Er³⁺,Yb³⁺ phosphates in the visible spectral region (λ = 0.525, 0.550, and 0.650 μm) under IR excitation (λ = 0.98 μm) is due to the upconversion mechanism and is acceptable for in vivo imaging in terms of safety (green emission) and intensity. Biocompatibility testing results demonstrate that the β-Ca₃(PO₄)₂:Er³⁺,Yb³⁺ phosphates meet the relevant biosafety and nontoxicity criteria.     

Frequency upconversion properties of Er3+/Yb3+-codoped lead–germanium–bismuth oxide glasses

The frequency upconversion properties of Er³⁺/Yb³⁺-codoped heavy metal oxide lead–germanium–bismuth oxide glasses under 975 nm excitation are investigated. Intense green and red emission bands centered at 536, 556 and 672 nm, corresponding to the ²H_11/2 → ⁴I_15/2, ⁴S_3/2 → ⁴I_15/2 and ⁴F_9/2 → ⁴I_15/2 transitions of Er³⁺, respectively, were simultaneously observed at room temperature. The influences of PbO on upconversion intensity for the green (536 and 556 nm) and red (672 nm) emissions were compared and discussed. The optimized rare earth doping ratio of Er³⁺ and Yb³⁺ is 1:5 for these glasses, which results in the stronger upconversion fluorescence intensities. The dependence of intensities of upconversion emission on excitation power and possible upconversion mechanisms were evaluated and analyzed. The structure of glass has been investigated by means of infrared (IR) spectral analysis. The results indicate that the Er³⁺/Yb³⁺-codoped heavy metal oxide lead–germanium–bismuth oxide glasses may be a potential materials for developing upconversion fiber optic devices.     

掺铒TeO2-Nb2O5-ZnO系统玻璃的上转换发光性能

稀土离子掺杂碲酸盐系统玻璃是一类应用前景良好的上转换发光材料.研究了含铒TeO2-Nb2O5-ZnO系统玻璃在980nm抽运下的上转换光谱,结果发现存在3个上转换荧光谱带,分别对应于2H11/2→4I15/2、4S3/2→4I15/2和4F9/2→4I15/2,而且Er3 含量的增加可明显提高材料在530、550和660nm附近的发光性能.少量的ZnO引入既可以大幅提升材料的上转换发光强度,又能保持铌碲酸盐玻璃良好的化学稳定性.材料的发光机制主要是激发态吸收(ESA)和能量转移(ET),最大声子能量的降低是上转换发光增强的主要原因.     

Synthesis and upconversion properties of GdOBr:Er phosphors

GdOBr:Er³⁺ phosphors were synthesized by a simple solid-state reaction method. Under 980 nm and (or) 785 nm laser excitation, GdOBr:Er³⁺ (1%) samples present strong green and red upconverted emissions. The upconversion mechanisms were studied in detail through laser power dependence and excited state absorption process is discussed as the possible upconversion mechanisms. More interesting, the bright green upconverted emission is visible to the naked eye for GdOBr:Er³⁺ (1%) samples even excited by 1 mW 980 nm laser. Such phenomenon indicates that GdOBr:Er³⁺ may be used as upconversion phosphors.     

Optical high temperature sensor based on enhanced green upconversion emissions in Er3+-Yb3+-Li+ codoped TiO2 powders

The Er3+-Yb3+-Li+ codoped TiO2 powders have been prepared by sol-gel method. The strong enhancement of green and red upconversion emissions were obtained for Er3+-Yb3+ codoped TiO2 by additional Li+ codoping and investigated using 976 nm semiconductor laser diode excitation. The enhanced upconversion emissions by the addition of Li+ resulted from the formation of Li compound with lower crystal field symmetry. The fluorescence intensity ratio (FIR) of green upconversion emissions from the transitions of 2H(11/2) --> 4I(15/2) and 4S(3/2) --> 4I(15/2) of Er3+ in the Er3+-Yb3+-Li+ codoped TiO2 has been studied as a function of temperature in the range of 300-925 K, and the maximum sensitivity was determined to be 0.0025 K(-1). Er3+-Yb3+-Li+ codoped TiO2 material with the highest operating temperature up to 925 K, has higher temperature sensitivity and fluorescence efficiency being a promising candidate for applications in optical high temperature sensor.     

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.     

Controllable synthesis of tetragonal LiScF4:Yb3+, Er3+ nanocrystals and its upconversion photoluminescence properties: Lithium scandium fluoride nanocrystals

Tetragonal rare-earth ions codoped LiScF₄ nanocrystals have been synthesized by a modified solvothermal method. The results revealed that the phase and morphology can be tailored through varying the synthesis conditions, such as reaction temperature and time. Meanwhile, the UC fluorescence emission spectra were measured. It turned out that the UC emission intensity can be significantly influenced by reaction temperature and time. Different from the NaYF₄:20%Yb³⁺,2%Er³⁺ nanocrystals that usually emit green emission, yellow color emission can be observed in the LiScF₄:20%Yb³⁺,2%Er³⁺ samples under 980 nm excitation, which illustrates that the obtained new phase LiScF₄ is suitable as a promising host for efficient UC fluorescence generation and tunable UC emission spectra. Moreover, the UC mechanism was investigated in detail.