Upconversion luminescence and mechanisms in Yb-sensitized Tm-doped oxyhalide tellurite glasses

Effect of Yb₂O₃ content on upconversion luminescence and mechanisms in Yb³⁺-sensitized Tm³⁺-doped oxyhalide tellurite glasses were investigated under 980 nm excitation. Intense blue and relatively weak red upconversion emission centered at 476 and 649 nm corresponding to the transitions ¹G₄→³H₆ and ¹G₄→³H₄ of Tm³⁺, respectively, are simultaneously observed at room temperature. The results show that upconversion blue and red emission intensities of Tm³⁺ first increase, reach its maximum at Yb₂O₃%=3 mol%, and then decrease with increasing Yb₂O₃ content. The effect of Yb₂O₃ content on upconversion intensity is discussed, and possible effect mechanisms are evaluated. The investigated results were conducing to increase upconversion luminescence efficiency of Tm³⁺.     

Upconversion studies in rare earth ions-doped lanthanide materials

In the present work, results of upconversion emission in various powder samples have been discussed. The powder upconversion phosphors such as La₂O₃:Er³⁺/Yb³⁺, LaF₃:Er³⁺/Yb³⁺, CeO₂:Er³⁺/Yb³⁺, CeF₃:Er³⁺/Yb³⁺ were prepared and their upconversion emission, using 976 nm wavelength excitation, was investigated in depth. These phosphors have shown good upconversion emission in the visible region except for the CeF₃:Er³⁺/Yb³⁺ phosphor. Two intense bands around 525 and 550 nm due to the ² H _11/2 →⁴ I _15/2 and ⁴ S _3/2 →⁴ I _15/2 transitions, respectively, are found to be in a thermally coupled state in these samples. The intensity ratio of these two bands permitted us to estimate the temperature of the environment. The pump power studies of the emission bands of these samples are also made to understand the dynamics of the upconversion emission.     

Er,Yb:YAG微晶玻璃发光特性的研究

高温熔制Er³⁺，Yb³⁺离子掺杂CaO-Y₂O₃-Al₂O₃-SiO₂系统玻璃，并进行微晶化处理，研究了微晶玻璃中Er³⁺离子的发光及上转换发光特性，分析了微晶玻璃上转换发光机理.结果表明：原始玻璃经热处理得到了Er,Yb:YAG微晶玻璃，微晶玻璃中Er³⁺离子在室温下⁴I_13/2→⁴I_15/2跃迁产生横盖1450—1650nm区间的超宽带荧光，荧光半高宽达180nm，这可能由于YAG微晶相中Er³⁺离子与玻璃相中残留Er³⁺离子的共同发光；Er³⁺与Yb³⁺离子局域基质声子能量的降低使微晶玻璃Er³⁺离子上转换发光强度与原始玻璃相比显著提高，绿光、红光上转换荧光强度比玻璃样品分别增强约7和3倍；微晶化后Er³⁺，Yb³⁺离子局域环境发生变化也导致微晶玻璃中Er³⁺离子绿光、红光上转换发光相对强度发生变化. 关键词： 铒 镱:钇铝石榴石 微晶玻璃 荧光光谱     

High Quantum Yield Single‐Band Green Upconversion in La2O3:Yb3+, Ho3+ Microcrystals for Anticounterfeiting and Plastic Recycling

Single‐band green upconversion (UC) with high green purity and color stability is urgently required for plastic recycling and anticounterfeiting. However, it is very difficult to obtain single‐band green emission for benchmark Yb³⁺/Er³⁺ activated UC materials (such as NaYF₄:Yb³⁺,Er³⁺) due to the strong accompanying red UC. Herein, highly efficient and stable single‐band green UC is reported in La₂O₃:Yb³⁺/Ho³⁺ (LYH) microcrystals with record high absolute UC quantum yield (UCQY) of 2.6% for single‐band green UC. LYH yields pure green UC with large and stable intensity ratio, I_Green/I_Red ≈ 18. LYH presents not only higher UCQY for a single‐band green UC but also much more pure and stable green UC than the benchmark UC materials such as NaYF₄:Yb³⁺,Er³⁺ and Gd₂O₂S:Yb³⁺,Er³⁺. These results suggest that the newly developed LYH can, in principle, be promising for anticounterfeiting and plastic recycling. Its proof‐of‐concept is demonstrated as a security label based on a transparent institute logo.     

Photoconductivity in Yb-doped oxides at high excitation densities

Photoconductivity has been found in the dielectric laser materials Yb³⁺:YAG and Yb³⁺:Lu₂O₃ under 940?nm irradiation with an unexpected high photocurrent up to several 100 nanoampères. The nonlinear intensity dependence points to the occurrence of a cooperative upconversion mechanism with 2?C3 excited Yb³⁺-ions in YAG and 2 excited Yb³⁺-ions in Lu₂O₃ being involved. According to the results two tentative models of this upconversion process are discussed.     

Upconversion luminescence of Tm^3＋/Yb^3＋ codoped oxyfluoride glasses

Novel oxyfluoride glasses are developed with the composition of 30SiO2-15Al2O3-28PbF2-22CdF2-0.1TmF3 - xYbF3 - （4.9 - x） AlF3（x=0, 0.5, 1.0, 1.5, 2.0） in tool fraction, Furthermore, the upconversion luminescence characteristics under a 970nm excitation are investigated. Intense blue, red and near infrared luminescences peaked at 453nm, 476nm, 647nm and 789nm, which correspond to the transitions of Tm^3＋： ^1D2 →^3F4, ^1G4 →^3H6, ^1G4 →^3F4, and ^3H4 →^3H6, respectively, are observed. Due to the sensitization of Yb^3＋ ions, all the upconversion luminescence intensities are enhanced considerably with Yb^3＋ concentration increasing. The upconversion mechanisms are discussed based on the energy matching rule and quadratic dependence on excitation power. The results indicate that the dominant mechanism is the excited state absorption for those upconversion emissions.     

Up and down conversion fluorescence studies on combustion synthesized Yb/Yb: MO-Al2O3 (M=Ca, Sr and Ba) phosphors

The ytterbium ions doped MO-Al₂O₃ (M=Ca, Sr and Ba) phosphors have been synthesized through combustion technique and their up and down conversion fluorescence properties have been studied and compared. The samples were calcinated at different temperatures and their FTIR and XRD spectra have shown a close relationship. With 976 nm excitation all these phosphors show cooperative upconversion emission at 488 nm from the pairs of two Yb³⁺ ions along with an unexpected broad upconversion band in the blue green region and has been assigned to arise from the defect centers. Contrary to this upconversion emission, calcium aluminate phosphor exhibits bright and very broad down-conversion fluorescence (FWHM≈160 nm) upon UV (266 nm) excitation due to Yb²⁺ ions. The inter-conversion between the 3+ and 2+ valence states of Yb ion has been observed on calcinations of samples in open atmosphere and has been correlated to the emission properties. The Yb²⁺ ions containing calcium aluminate phosphor has been found suitable for producing broad band light in the visible region (white light). Lifetime of the emitting states of Yb³⁺ and Yb²⁺ ions have also been measured and discussed.     

980 nm激发下Er3+/Yb3+共掺杂ZrO2-Al2O3粉末的上转换发光特性

通过固相反应法制备了Er³⁺/Yb³⁺共掺杂ZrO₂-Al₂O₃粉末的样品，并对样品在980nm激光激发下的上转换发光特性进行了研究.从发射光谱可以发现，在可见光范围内有3个强的发光带，一个位于654nm附近的红光带和两个分别位于545nm、525nm附近的绿光带，分别对应于Er³⁺离子的以下辐射跃迁：⁴F_9/2→⁴I_15/2、⁴S_3/2→⁴I_15/2、 ²H_11/2→⁴I_15/2.其中又以Er³⁺离子的⁴F_9/2→⁴I_15/2跃迁产生的红色荧光辐射最强.对其上转换发光机制进行了分析，发现这三个发光过程都是双光子过程.对样品粉末进行了XRD检测，发现ZrO₂主要以立方相为主，并且计算得到了这种立方结构的晶格常数.Al₂O₃固溶于ZrO₂中，Al³⁺嵌入ZrO₂后产生氧空位，导致ZrO₂晶体的对称性降低，这种结构变化更有利于提高上转换效率，即上转换发光强度增强. 关键词： 3+/Yb³⁺')" href="#">Er³⁺/Yb³⁺ 上转换 2-Al₂O₃')" href="#">ZrO₂-Al₂O₃ 荧光 稀土     

Effect of Yb3+ concentration on photoluminescence properties of cubic Gd2O3 phosphor

Yb³⁺ doped phosphor of Gd₂O₃ (Gd₂O₃:Yb³⁺) have been prepared by solid state reaction method. The structure and the particle size have been determined by X-ray powder diffraction measurements. The average particle size of the phosphor is in between 35 and 50 nm. The particle size and structure of the phosphor was further confirmed by TEM analysis. The visible and NIR luminescence spectra were recorded under the 980 nm laser excitation. The visible upconversion luminescence of Yb³⁺ ion was due to cooperative luminescence and the presence of rare earth impurity ions. The cooperative upconversion and NIR luminescence spectra as a function of Yb³⁺ ion concentration were measured and the emission intensity variation with Yb³⁺ ion concentration was discussed. Yb³⁺ energy migration quenched the cooperative luminescence of Gd₂O₃:Yb³⁺ phosphor with doping level over 5%, while the NIR emission luminescence continuously increases with increasing Yb³⁺ ion concentration.     

Broadband amplification and upconversion luminescence properties of Er/Yb co-doped fluorophosphate glass

Broadband and upconversion properties were studied in Er³⁺/Yb³⁺ co-doped fluorophosphate glasses. Large Ω₆ and S_ed/(S_ed+S_md) values and the flat gain profile over 1530-1585 nm indicate the good broadband properties of the glass system. And a premise of using Ω₆ as a parameter to estimate the broadband properties of the glasses is proposed for the first time to our knowledge. Results showed that fluorescence intensity, upconversion luminescence intensity, the intensity ratio of red/green light (656 nm/545 nm) are closely related to the Yb³⁺:Er³⁺ ratio and Er³⁺ concentration, and the corresponding calculated lifetime of ⁴F_9/2 and ⁴S_3/2 states for red and green upconversion samples proves this conclusion. The upconversion mechanism is also discussed.     

Visible upconversion and infrared luminescence investigations of Al<Subscript>2</Subscript>O<Subscript>3</Subscript> powders doped with Er<Superscript>3+</Superscript>, Yb<Superscript>3+</Superscript> and Zn<Superscript>2+</Superscript> ions

Alumina (Al₂O₃) powders doped with Er³⁺, Yb³⁺ and Zn²⁺ ions have been prepared by a low-temperature combustion synthesis technique. The phase purity and crystalline structure of the combustion products are confirmed by powder X-ray diffraction. An efficient frequency upconversion in the visible region and the emission in the infrared (IR) region respectively corresponding to the ²H_11/2, ⁴S_3/2→⁴I_15/2, ⁴F_9/2→⁴I_15/2 and ⁴I_13/2→⁴I_15/2 transitions upon direct excitation with a CW laser lasing at ∼980 nm are discussed. The enhancement observed in the intensity of the upconversion emission bands in the visible region and the emission band in the IR region due to the presence of Yb³⁺ and Zn²⁺ in Er³⁺:Al₂O₃ powders is reported and explained in detail.     

Upconversion luminescence of Er/Yb-codoped natrium-germanium-bismuth glasses

The absorption and upconversion fluorescence spectra of a series of Er³⁺/Yb³⁺-codoped natrium-germanium-bismuth glasses have been studied. The transition probabilities, excited state lifetimes, and the branching ratios have been predicted for Er³⁺ based on the Judd-Ofelt theory. At room temperature, an upconversion efficiency of 6.1×10⁻² has been obtained for the green emission from the glass with 0.5 wt% Er₂O₃ and 3.0 wt% Yb₂O₃ pumped by 980 nm radiation with an intensity of 270 W/cm². And the “standardized” efficiency for green upconversion light is higher than that reported in lead-germanate, lead-tellurite-germanate, and silicate glasses. The results indicate that the Er³⁺/Yb³⁺-codoped natrium-germanium-bismuth oxide glass may be a potential material for developing upconversion optic devices.     

Upconversion luminescence of colloidal solution of Y2O3 nano-particles doped with trivalent rare-earth ions

We have studied upconversion luminescence of colloidal solution of Y₂O₃ nano-particles codoped with 1 mol% Er³⁺ and 5 mol% Yb³⁺. Y₂O₃ nano-particles codoped with 1 mol% Er³⁺ and 5 mol% Yb³⁺ show sintering and agglomeration, because they are synthesized by firing a hydroxy carbonate precursor. Colloidal solution of Y₂O₃ nano-particles codoped with 1 mol% Er³⁺ and 5 mol% Yb³⁺ is prepared through two-step dispersion process and the average diameter of the primary nano-particles is about 50 nm. Under excitation with 980-nm laser diode, upconversion luminescence of colloidal solution of the primary Y₂O₃ nano-particles codoped with 1 mol% Er³⁺ and 5 mol% Yb³⁺ in methyl isobuthyl ketone strongly appeared near 660 nm and weakly near 550 nm.     

Upconversion properties of Er^3＋/Yb^3＋ co-doped TeO2-Nb2O5-Li2O glasses

The Er^3＋/Yb^3＋ co-doped TeO2-Nb2O5-Li2O glass is prepared by conventional melting method, and its upconversion spectra are measured. The intense green upconversion luminescence upon excitation with a 976 nm laser diode is observed with the naked eyes. The dependence of luminescence intensity on the ratio of Yb^3＋/Er^3＋ is discussed in detail, and the relationship between the ratio of green luminescence intensity to red luminescence intensity and the ratio of Yb^3＋/Er^3＋ is also studied, The luminescence intensity increases with the ratio of Yb^3＋/Er^3＋ increasing. The ratio of Yb^3＋/Er^3＋ plays a more important role than the concentration of Er^3＋ in determining the upconversion luminescence intensity. The ratio of green luminescence intensity to red luminescence intensity reaches a maximum when ratio of Yb^3＋/Er^3＋ is 3. Thus the glass could be one of the potential candidates for LD pumping solid-state lasers.     

Multifunctional Er3+–Yb3+ codoped Gd2O3 nanocrystalline phosphor synthesized through optimized combustion route

This paper reports the synthesis of high upconversion luminescent Gd₂O₃: Er³⁺, Yb³⁺ nanophosphor through optimized combustion route using urea as a reducing agent. The paper also reports the first observation of upconversion emission bands extending upto the UV region (335, 366 and 380 nm) in Er³⁺–Yb³⁺ co-doped phosphor materials. The fuel to oxidizer ratio has been varied to obtain the maximum upconversion luminescence. Three high intensity bands are found at 408, 523–548 and 667 nm due to the ⁴G_11/2 → ⁴I_15/2, ²H_11/2, ⁴S_3/2 → ⁴I_15/2 and ⁴F_9/2 → ⁴I_15/2 transitions, respectively, along with the other bands. Input excitation power dependence has been studied for different transitions, and the saturation effect and decrease in the slope of different transitions at higher input pump power has been explained. Heat treatments of the samples show change in crystallite phase/size and relative upconversion luminescence intensities of blue, green and red bands. The color of the phosphor emission has shown to be tunable with change in the crystal structure as well as on excitation laser power and Er³⁺–Yb³⁺ concentration. The property of color tunability of the phosphor material has been used to record the fingerprint in different colors. Also, the future prospect of the nanocrystalline phosphor material as a sensor for temperature, using FIR method, has been explored.     

Synthesis and luminescence properties of Gd6MoO12:Yb3+, Er3+ phosphor with enhanced photoluminescence by Li+ doping

Yb³⁺/Er³⁺ co-doped Gd₆MoO₁₂ and Yb³⁺/Er³⁺/Li⁺ tri-doped Gd₆MoO₁₂ phosphors were prepared by adjusting the annealing temperature via the high temperature solid-state method. Under the excitation of 980 nm semiconductor, the upconversion luminescence properties were investigated and discussed. In the experimental process, we get the optimum Yb³⁺ concentration and the concentration quench effect will happen while the concentration extends the given region. According to the Yb³⁺ concentration quenching effects, the critical distance between Yb³⁺ ions had been calculated. The measured UC luminescence exhibited a strong red emission near 660 nm and green emission at 530 nm and 550 nm, which are due to the transitions of Er³⁺(⁴F_9/2, ²H_11/2, ⁴S_3/2) → Er³⁺(⁴I_15/2). Then the effect of excitation power density in different regions on the upconversion mechanisms was investigated and the calculated results demonstrate that the green and red upconversion is a two-photon process. A possible mechanism was discussed. After Li⁺ ions mixing, the upconversion emission enhanced largely, and the optimum Li⁺ concentration was obtained while fixed the Yb³⁺ and Er³⁺ on the above optimum concentration. This enhancement owns to the decrease of the local symmetry around Er³⁺ after Li⁺ ions doping into the system. This result indicates that Li⁺ is a promising candidate for improving luminescence in some case.     

Infrared-to-visible upconversion in Er and Er/Yb activated Sb2O4 nanopowders prepared by sol-gel route

We prepared Er³⁺ doped and Er³⁺/Yb³⁺ codoped Sb₂O₄ nanocrystals by the sol-gel method. The Raman, X-ray diffraction (XRD), transmission electron microscope (TEM), and photoluminescence spectra of the samples were studied. The phonon energy of the Sb₂O₄ nanocrystals is very low (the maximum value being 461 cm⁻¹). The upconversion (UC) red emission of the Er³⁺/Yb³⁺ codoped sample is very strong at 975 nm laser diode excitation. The Sb₂O₄ nanocrystals will be a promising luminous material.     

Magnetic properties of Yb Mo O and Gd Mo O from rare earth Mössbauer measurements

Using ¹⁷⁰Yb and ¹⁵⁵Gd M?ssbauer measurements down to ∼ 0.03 K, we have examined the semiconducting pyrochlore Yb₂Mo₂O₇ where the Mo intra-sublattice interaction is anti-ferromagnetic and the metallic pyrochlore Gd₂Mo₂O₇ where this interaction is ferromagnetic. Additional information was obtained from susceptibility, magnetisation and ¹⁷²Yb perturbed angular correlation measurements. The microscopic measurements evidence lattice disorder which is important in Yb₂Mo₂O₇ and modest in Gd₂Mo₂O₇. Magnetic irreversibilities occur at 17 K in Yb₂Mo₂O₇ and at 75 K in Gd₂Mo₂O₇ and below these temperatures the rare earths carry magnetic moments which are induced through couplings with the Mo sublattice. In Gd₂Mo₂O₇, we observe the steady state Gd hyperfine populations at 0.027 K are out of thermal equilibrium, indicating that Gd and Mo spin fluctuations persist at very low temperatures. Frustration is thus operative in this essentially isotropic pyrochlore where the dominant Mo intra-sublattice interaction is ferromagnetic. Received 13 January 2003 Published online 4 June 2003 RID="a" ID="a"e-mail: hodges@drecam.saclay.cea.fr     

The phase transition, hygroscopicity, and thermal expansion properties of Yb2-xAlxMo3O12

Materials with the formula Yb2-xAlxMo3O12 （x = 0.1, 0.2, 0.3, 0.4, 0.5, 0.7, 0.9, 1.0, 1.1, 1.3, 1.5, and 1.8） were synthesized and their structures, phase transitions, and hygroscopicity investigated using X-ray powder diffraction, Raman spectroscopy, and thermal analysis. It is shown that Yb2-xAlxMo3012 solid solutions crystallize in a single monoclinic phase for 1.7 〈 x 〈 2.0 and in a single orthorhombic phase for 0.0 〈 x 〈 0,4, and exhibit the characteristics of both monoclinic and orthorhombic structures outside these compositional ranges. The monoclinic to orthorhonlbic phase transition temperature of A12Mo3012 can be reduced by partial substitution of A13＋ by Yb3＋, and the Yb2-zAlxMo3012 （0.0 〈 x 〈 2.0） materials are hydrated at room temperature and contain two kinds of water species. One of these interacts strongly with and hinders the motions of the polyhedra, while the other does not. The partial substitution of A13＋ for Yb3＋ in Yb2Mo3012 decreases its hygroscopicity, and the linear thermal expansion coefficients after complete removal of water species are measured to be -9.1 x 10-6/K, -5.5 x 10-6/K, 5.74 x 10-6/K, and 9.5 x 10 6/K for Ybl.sAlo.2（MoO4）3, Yb1.6Alo.4（MoO4）3, Ybo.4All.6（Mo04）3, and Ybo.2Al1.8（MoO4）3, respectively.     

Energy transfer and infrared-to-visible upconversion luminescence of Er/Yb-codoped halide modified tellurite glasses

We report on the energy transfer and frequency upconversion spectroscopic properties of Er³⁺-doped and Er³⁺/Yb³⁺-codoped TeO₂-ZnO-Na₂O-PbCl₂ halide modified tellurite glasses upon excitation with 808 and 978 nm laser diode. Three intense emissions centered at around 529, 546 and 657 nm, alongwith a very weak blue emission at 410 nm have clearly been observed for the Er³⁺/Yb³⁺-codoped halide modified tellurite glasses upon excitation at 978 nm and the involved mechanisms are explained. The quadratic dependence of fluorescence on excitation laser power confirms the fact that the two-photon contribute to the infrared to green-red upconversion emissions. And the blue upconversion at 410 nm involved a sequential three-photon absorption process.