The fluorescence properties of Yb3+ and Er3+ Co-doped YAl3(BO3)4 powders prepared by sol-gel method

Yb³⁺ and Er³⁺ co-doped YAB powders were prepared by sol-gel method. The structure and fluorescence properties were investigated. XRD pattern indicated that the single phase was obtained at 1150°C and the structure belonged to rhombohedral. Under 379 nm excitation, two emissions around 983 nm and 1531 nm were observed and the effect of Yb³⁺ ion concentration on the emission intensity was discussed. The energy transfer was observed under 930 nm excitation and the energy transfer efficiencies for all samples were calculated. The lifetimes of ² F _5/2 level of Yb³⁺ ion and ⁴ I _13/2 level of Er³⁺ ion were measured and the effect of Yb³⁺ ion concentration on the lifetime was also discussed. The results indicated that there was an additional mechanism for the decay of ⁴ I _13/2 level in powder samples. The Yb³⁺ and Er³⁺ co-doped YAB powders should be a potential candidate for ceramic laser materials.     

Variation in luminescence behavior of Yb3+ doped GdAlO3 phosphor with gradual increase in Yb3+ concentration

The present paper reports the combustion synthesis of Yb³⁺ doped GdAlO₃ phosphors. The structural characterization and luminescence spectra of Yb³⁺ doped GdAlO₃ phosphors have been discussed. The effects of variable concentration of Yb³⁺ on Photoluminescence (PL) behavior were studied. The structural characterization was done by X-ray diffraction (XRD) and Transmission electron microscope technique (TEM). The good connectivity with grains and the semi-sphere line structure was found by TEM. The functional group analysis was carried out by Fourier transform infrared (FTIR) spectroscopic techniques. The prepared phosphor gives emission spectra in visible as well as NIR region. Both emissions were studied as a function of Yb³⁺ concentration. The emission intensity variation with Yb³⁺ ion concentration for visible and NIR region were discussed separately. The NIR emission luminescence of GdAlO₃:Yb³⁺ phosphor luminescence continuously increases with increasing Yb³⁺ ion concentration.     

Upconversion white-light emission in Ho3+/Yb3+/Tm3+ codoped LiNbO3 polycrystals

Ho³⁺/Yb³⁺/Tm³⁺ codoped LiNbO₃ polycrystals exhibiting upconversion white-light under 980 nm excitation have been successfully fabricated by the high temperature solid-state reaction method. CIE coordinate of the Ho³⁺/Yb³⁺/Tm³⁺/LiNbO₃ polycrystal is (0.34, 0.35), which is very close to the standard equal energy white-light illuminate (0.33, 0.33). Efficient green, red, and blue upconversion emissions have been observed. The luminescent decay dynamics are studied, and rate equations for the blue, green, and red emissions are set up to analyze the upconversion luminescence mechanism. The present results demonstrate that the competition between the linear decay and the upconversion process for the depletion of the intermediate excited states plays an important role in upconversion mechanism. The LiNbO₃ with upconversion white-light will be a promising luminous material.     

Down-conversion process in Tb3+–Yb3+ co-doped Calibo glasses

The down-conversion process in Tb³⁺–Yb³⁺ co-doped Calibo glasses was studied. The emission, excitation and time-resolved measurements indicated the existence of an energy conversion through the excitation of Tb³⁺ ions to near-infrared emission by Yb³⁺ ions. The emission intensity dependence on excitation power confirms that the one-photon process is responsible for the Yb³⁺ emission. An enhanced Yb³⁺ emission was observed with Yb³⁺ doping and an optimal energy transfer efficiency of 32% was obtained before reaching near-infrared emission quenching. The mechanism of the non-resonant energy transfer from Tb³⁺ to Yb³⁺ is discussed in terms of the Tb³⁺–Yb³⁺ cross-relaxation and multiphonon decay processes.     

Down-conversion near infrared emission in Pr, Yb co-doped Y2O3 transparent ceramics

Pr³⁺, Yb³⁺ co-doped Y₂O₃ transparent ceramics have been prepared by the solid state reaction and vacuum sintering. Down-conversion near infrared emission has been demonstrated upon a 482 nm excitation. The energy of the 482 nm blue photon was first absorbed by Pr³⁺ and then delivered to Yb³⁺. Possible energy transfer mechanisms from Pr³⁺ to Yb³⁺ have been discussed. Under the 482 nm excitation, the Pr⁴⁺-Yb²⁺ charge transfer state would not seriously influence the energy transfer process. The dominant one should be either the cooperative down-conversion or the two-step photon emission. The efficient down-conversion near infrared emission has potential application in enhancing the conversion efficiency of crystalline silicon solar cells.     

Preparation and fluorescence properties of Yb3+ and Er3+ co-doped GdAlO3 phosphors

Yb³⁺ and Er³⁺ co-doped GdAlO₃ phosphors are prepared by the sol–gel method. The effect of doping concentration on the structure and fluorescence properties is investigated by X-ray diffraction (XRD) and photoluminescence, respectively. XRD pattern indicates that the sample structure belongs to orthorhombic. The photoluminescence results show that both green and red fluorescence emission and upconversion emission intensities decrease with an increase in Yb³⁺ concentration due to the cross-relaxation process between Yb³⁺ and Er³⁺ ions. Based on the emission spectra, the mechanism of the upconversion emission is discussed, and we concluded that the upconversion emission is a two-photon process.     

NIR to visible frequency upconversion in Er3+ and Yb3+ codoped ZrO2 phosphor

The ZrO₂:Er³⁺ codoped with Yb³⁺ phosphor powders have been prepared by the urea combustion route. Formation of the compounds ZrO₂:Er³⁺ and ZrO₂:Er³⁺, Yb³⁺ was confirmed by XRD. The frequency upconversion emissions in the green and red regions upon excitation with a CW diode laser at ～978 nm are reported. Codoping with Yb³⁺ enhances the emission intensities of the triply ionized erbium in the green and red spectral regions by about ～130 and ～820 times respectively. The emission properties of the ZrO₂:Er³⁺ phosphor powders are discussed on the basis of excited state absorption, energy transfer, and cross-relaxation energy transfer mechanisms.     

Visible upconversion emission and non-radiative direct Yb to Er energy transfer processes in nanocrystalline ZrO2:Yb,Er

Wide band gap Yb³⁺ and Er³⁺ codoped ZrO₂ nanocrystals have been synthesized by a modified sol-gel method. Under 967 nm excitation strong green and red upconversion emission is observed for several Er³⁺ to Yb³⁺ ions concentration ratios. A simple microscopic rate equation model is used to study the effects of non-radiative direct Yb³⁺ to Er³⁺ energy transfer processes on the visible and near infrared fluorescence decay trends of both Er³⁺ and Yb³⁺ ions. The microscopic rate equation model takes into account the crystalline phase as well as the size of nanocrystals. Nanocrystals phase and size were estimated from XRD patterns. The rate equation model succeeds to fit simultaneously all visible and near infrared fluorescence decay profiles. The dipole-dipole interaction parameters that drive the non-radiative energy transfer processes depend on doping concentration due to crystallite phase changes. In addition the non-radiative relaxation rate (⁴I_11/2→⁴I_13/2) is found to be greater than that estimated by the Judd-Ofelt parameters due to the action of surface impurities. Results suggest that non-radiative direct Yb³⁺ to Er³⁺ energy transfer processes in ZrO₂:Yb,Er are extremely efficient.     

From optical spectroscopy to a concentration quenching model and a theoretical approach to laser optimization for Yb3+-doped YLiF4 crystals

A spectroscopic characterization was carried out to identify crystal-field levels for magnetic-dipole transitions of Yb³⁺ ions located in the Y³⁺ dodecahedral S₄ crystallographic site in YLiF₄ (YLF) crystals which were grown either by the Czochralski technique or by the laser heated pedestal growth (LHPG) technique. The concentration dependence of the measured decay time of the ²F_5/2 excited level of Yb³⁺ was analysed in order to understand relevant concentration quenching mechanisms. Under Yb³⁺ ion infrared pumping, self-trapping and up-conversion non-radiative energy transfer to trace rare-earth impurities (Er³⁺, Tm³⁺) has been observed over the visible region and interpreted by a limited-diffusion process within the Yb³⁺ doping ion subsystem to the impurities. The principal parameters useful for a theoretical approach for potential laser applications of Yb³⁺-doped YLiF₄ crystals have also been given.     

Cooperative luminescence and absorption in ytterbium doped aluminosilicate glass optical fibres and preforms

The cooperative luminescence and absorption properties of Yb³⁺ doped aluminosilicate glass optical fibres and preforms are investigated in detail. In accordance with previous investigations, both the visible cooperative luminescence and the infrared luminescence decay measurements have been resolved into a single exponential decay component. We show that for a glass with similar Yb³⁺ dopant concentration but more Al³⁺, the glass emits less visible luminescence. Absorption loss measurements completed on fibre samples revealed a broad absorption in the 350-500 nm range, which we propose is due to a combination of Yb²⁺ absorption and cooperative absorption from Yb³⁺ ion pairs.     

Growth, spectroscopic characteristics and laser potential of Yb3+:Ca3La2(BO3)4 crystal

Crystal of Yb³⁺-doped Ca₃La₂(BO₃)₄ has been grown by the Czochralski technique. The room temperature absorption and fluorescence spectra of the crystal have been investigated. The result showed that this crystal exhibits broad absorption and emission with the FWHM of 11 nm at 978 nm and 66 nm FWHM at 1025 nm, respectively. The stimulated emission cross-section of Yb³⁺ ions were calculated using the reciprocity method and Fuchtbauer-Ladenburg method, respectively. The room temperature fluorescence decay curves of ² F _5/2 manifold of Yb³⁺ ions were recorded for both crystal and powder samples. The effect of radiation tapping on the spectroscopic properties is discussed. The result that the lifetime of the powder sample is shorter than that of the bulk sample demonstrates the existence of radiation trapping effect. The laser potentiality was also evaluated and the results show that this crystal is a good candidate for tunable and ultrashort pulse lasers.     

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.     

Eu~(2+)-Yb~(3+)共掺磷酸盐玻璃中的合作能量传递(英文)

报道了在Eu2+-Yb3+共掺磷酸盐中,一个紫外光子(320nm)通过下转换发光变成两个近红外光子(约1 000nm)的现象.测试了不同样品的吸收、激发和发射光谱,证明了在本玻璃体系中量子剪裁现象的存在;Eu2+离子5d-4f能级发光的衰减曲线证明Eu2+到Yb3+之间的合作能量传递;用I-H理论模型拟合衰减曲线说明了能量传递的过程.最后计算出了能量传递的效率,当Yb3+浓度为1.0mol%时效率为23.05%,当其增加到2.0mol%时,能量传递效率提高到了53.6%.     

共沉淀法制备Y2SiO5∶Er3+ ,Yb3+ ,Tm3+及其上转换发光性能研究

采用化学共沉淀法制备了系列Y_1.98-2xYb_2x Er_0.02SiO₅(0.00≤x≤0.15)以及Y_1.736Yb_0.24Er_0.02Tm_0.004SiO₅上转换发光材料,比较了室温下Y_1.98-2xYb_2x Er_0.02 SiO₅ (x=0.00,0.08)样品在400—1600 nm范围内的吸收光谱,测量了所有样品在976 nm OPO激光器激发下的上转换发射光谱,以及Er³⁺离子⁴S_3/2(⁴F_9/2)→⁴I_15/2,Tm³⁺离子¹G₄→³H₆荧光衰减曲线和不同激发功率下的上转换蓝光发射强度,从而分析讨论了Er³⁺,Tm³⁺在Y₂SiO₅中的上转换发光机理.研究结果表明:在1250 ℃相对较低的温度下合成了X2型单斜晶系Y₂SiO₅ ∶Ln³⁺(Ln³⁺=Er³⁺,Yb³⁺,Tm³⁺),Yb³⁺的敏化显著增强了样品在976 nm附近的吸收能力,并大幅度加宽了该处的吸收带.分析上转换发射光谱发现:上转换绿光和红光强度都随着Yb³⁺浓度的增加先增强后减弱,但红光的猝灭浓度较高,归因于Er³⁺→Yb³⁺反向能量传递ETU4和Yb³⁺→Er³⁺正向能量传递ETU3过程的发生;上转换蓝光发射是三光子吸收过程,是通过Yb³⁺,Tm³⁺之间三次声子辅助的能量转移方式实现的. 关键词： 上转换 共沉淀 2SiO₅∶Er³⁺')" href="#">Y₂SiO₅∶Er³⁺ 3+')" href="#">Yb³⁺ 3+')" href="#">Tm³⁺     

EPR,ENDOR and optical spectroscopy of Yb3+ ion in KZnF3 single crystals

The paramagnetic center of tetragonal symmetry formed by the Yb³⁺ ion in the KZnF₃ crystal has been studied using methods of EPR, ENDOR and optical spectroscopy. The location of the impurity ion and the structural model of the complex differing from the model of the Yb³⁺ center in KMgF₃ have been established. The empirical scheme of the energy levels of the Yb³⁺ ion has been found. The parameters of its interaction with the crystal electrostatic field and the hyperfine interaction with ligands of the nearest environment have been determined. The parameters of the crystal field were used for the analysis of the distortions of the crystal lattice in the vicinity of Yb³⁺. The parameters of the transferred hyperfine interaction have been calculated for the distances between Yb³⁺ and F⁻ ions of the nearest environment obtained taking into account the found distortions. They are in good agreement with the experimental values.     

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.     

Upconversion white-light emission in Ho³⁺/Yb³⁺/Tm³⁺ tridoped LiNbO₃ single crystal

Ho³⁺/Yb³⁺/Tm³⁺ tridoped LiNbO₃ single crystal exhibiting intense upconversion white light under 980?nm excitation has been successfully fabricated by the Czochralski method. The tridoped LiNbO₃ single crystal offers power dependent color tuning properties by simply changing excitation power. Efficient three-photon blue upconversion emission and two-photon green and red upconversion emissions have been observed. In addition, the red emission of Ho³⁺ originates dominantly from the nonradiative decay of green emission. The LiNbO₃ with upconversion white light will be a potential laser candidate material.     

Desvitrification on an oxyfluoride glass doped with Tm3+ and Yb3+ ions under Ar laser irradiation

Desvitrification in a Tm³⁺ and Yb³⁺ codoped oxyfluoride glass has been obtained by exciting with a continuous Argon laser radiation increasing the average laser power from 144 to 2900 mW. Excitation spectra inside a locally damaged zone in a 1 mol% Tm³⁺ and 2.5 mol% Yb³⁺ codoped glass have been measured under excitation in the wavelength range 750–830 nm detecting the ²F_5/2 (Yb³⁺) level. This curve is the result of the contribution of two different kinds of centers, the fluoride nanocrystals and the glassy phase of the glass ceramic sample created due to the irradiation. The weight of the contributions of each of the centers depends on the excitation wavelength, and from the analysis of the decay of the luminescence it can be concluded that approximately 80% of the Tm³⁺ ions are located in the nanocrystals and therefore less than 20% in the glassy phase.     

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。     

Energy transfer between Yb3+ and Er3+ ions in an Er,Yb:YAl3(BO3)4 crystal

The electron-excitation energy transfer between Er³⁺ and Yb³⁺ ions in Er,Yb:YAl₃(BO₃)₄ crystals has been investigated. Crystals with different concentrations of active ions have been grown, and their luminescence decay kinetics in the spectral range near 1 μm have been experimentally measured. The energy-transfer microparameters have been calculated. It is shown that, to correctly describe the energy transfer in Er,Yb:YAl₃(BO₃)₄ crystals, one must take into account the interactions of higher orders than dipole-dipole interactions.