Luminescence kinetics of LiNbO3:Yb3+-Er3+, LiNbO3:Er3+, and LiNbO3:Yb3+ crystals under selective excitations in the impurity subsystem

The results of investigations of luminescent radiations’ kinetic characteristics for LiNbO₃:Yb³⁺-Er³⁺, LiNbO₃:Er³⁺, and LiNbO₃:Yb³⁺ crystals under optical excitations at 532 nm and 1064 nm wavelengths are presented. The shapes and times of rise and damping of luminescent signals at 550 nm, 980 nm and 1555 nm wavelengths under selective excitations in the impurity subsystem of the investigated materials are determined. Comparison of the temporal characteristics of luminescent responses of LiNbO₃ crystals doped separately with Yb³⁺ and Er³⁺ ions with those of the LiNbO₃:Yb³⁺-Er³⁺ crystal allows identifying the contributions from different energy transfer processes of optical excitation taking place in the impurity subsystem of the material.     

Preparation and characterization of stable aqueous suspensions of up-converting Er3+/Yb3+-doped LiNbO3 nanocrystals

The preparation of LiNbO₃:Er³⁺/Yb³⁺ nanocrystals and their up-conversion properties have been studied. It is demonstrated that polyethyleneimine- (PEI) assisted dispersion procedures allow obtaining stable aqueous LiNbO₃:Er³⁺/Yb³⁺ powder suspensions, with average size particles well below the micron range (100–200 nm) and the isoelectric point of the suspension reaching values well above pH 7. After excitation of Yb³⁺ ions at a wavelength of 980 nm, the suspensions exhibit efficient, and stable, IR-to-visible (green and red) up-conversion properties, easily observed by the naked eye, very similar to those of the starting crystalline bulk material.     

Structural and optical characterization of Er3+/Yb3+-doped LiNbO3

We report the dependence of the unit-cell parameters and the extraordinary and ordinary refractive indices of Er³⁺/Yb³⁺-codoped LiNbO₃ crystals. Both properties depend in a non-monotonic manner on the Er³⁺/Yb³⁺ content. A singularity was observed at concentrations of 1.1-1.2 mol. % in the crystal (0.6-0.7 mol. % in the melt). In the same way the Er and Yb concentration influences the periodically poled lithium niobate formation. The observed behavior of refractive indices and unit-cell parameters of Er³⁺/Yb³⁺-codoped LiNbO₃ crystals could be explained in terms of the RE³⁺-ion concentration affecting the Li-vacancy concentration and the RE³⁺-ion positions in the crystal. Received: 21 May 2001 / Revised version: 22 August 2001 / Published online: 23 October 2001     

Photoluminescence of LiNbO3 crystals doped with Er3+ and Yb3+ ions

Results of cooperative phenomena investigations in the impurity subsystem of lithium niobate crystals doped with Er³⁺ and co-doped with Yb³⁺ impurity ions under continuous wave and pulsed excitation at 975 nm and 1064 nm wavelengths are presented. Dependences of some spectroscopic characteristics on the intensity of laser pumping are studied. Based on the pair centers model the analysis of the cooperative luminescence behavior in LiNbO₃:Yb³⁺+Er³⁺ crystals is performed.     

Dynamics of the Yb3+ to Er3+ energy transfer in LiNbO3

The energy transfer dynamics between Yb³⁺ and Er³⁺ ions in lithium niobate is investigated after ytterbium-pulsed excitation at 920 nm. The sensitisation of the LiNbO₃:Er³⁺ system with Yb³⁺ ions does not modify the lifetime of the ⁴I_13/2 erbium level (1.5-μm emission), whereas it induces a marked, concentration-dependent change in the lifetime of the ²F_5/2 (Yb³⁺) and ⁴S_3/2 (Er³⁺) multiplets (1060-nm and 550-nm emissions, respectively). The results are analysed by using the rate-equation formalism and cross-relaxation model for the energy transfer. Received: 15 October 1998 / Revised version: 24 November 1998 / Published online: 24 February 1999     

A study of the quantum efficiency of multichannel relaxation in LiNbO<Subscript>3</Subscript>:Yb,Er crystals

Luminescence spectra of gradient-activated LiNbO₃:Yb, Er crystals with predefined concentration profiles of the optical centers are studied in different spectral regions. The process of electronic excitation energy transfer in the Yb³⁺–Er³⁺ system inside the LiNbO₃ matrix is calculated and dependences of the quantum efficiency of the up-conversion processes for the green and red luminescences of erbium ions on the time of excitation energy deactivation are obtained.     

Arrays of micro-cavities activated with laser ions

We have combined different rare earth ions (Er³⁺, Nd³⁺ and Yb³⁺) in two dimensional ferroelectric patterns to obtain periodical fluorescent arrays. High refractive-index Er³⁺ doped CaTiO₃ nanocrystals have been embedded into Nd³⁺ or Yb³⁺ doped LiNbO₃ substrates pre-patterned with a two dimensional arrays of micro-voids. The process of incorporation and consolidation of the optically active nanoparticles into the alternate domain structures leads to luminescent ring-shaped arrangements with innovative geometries and to a micrometer spatial control of the trivalent rare earth ion emitters. Multicolor emission systems and the possibility of chromatic switching at the micrometer scale among the different compounds forming the two dimensional structure is demonstrated.     

Preparation and characterization of upconversion luminescent LaF3:Yb,Er/LaF3 core/shell nanocrystals

LaF₃:Yb³⁺,Er³⁺/LaF₃ core/shell nanocrystals were successfully synthesized using solvothermal method. The crystal structure, morphology and photoluminescence properties of as-prepared nanocrystals were investigated in detail. XRD patterns show that the obtained LaF₃:Yb³⁺,Er³⁺ core and LaF₃:Yb³⁺,Er³⁺/LaF₃ core/shell nanocrystals exhibit hexagonal structure. The average particle size is about 9.3 nm and 11.4 nm for core and core/shell nanocrystals, respectively. Compared with LaF₃:Yb³⁺,Er³⁺ nanocrystals, both the upconversion emission intensity and the lifetime increase in LaF₃:Yb³⁺,Er³⁺/LaF₃ core/shell nanocrystals. The enhancement can be attributed to the LaF₃ shell which can eliminate the nonradiative centers on the surface of LaF₃:Yb³⁺,Er³⁺ nanocrystals.     

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.     

Avidin conjugation to up-conversion phosphor NaYF4:Yb3+, Er3+ by the oxidation of the oligosaccharide chains

NaYF₄:Yb³⁺, Er³⁺ nanoparticles were successfully prepared by a polyol process using diethyleneglycol (DEG) as solvent. After being functionalized with SiO₂–NH₂ layer, these NaYF₄:Yb³⁺, Er³⁺ nanoparticles can conjugate with activated avidin molecules (activated by the oxidation of the oligosaccharide chain). The as-formed NaYF₄:Yb³⁺, Er³⁺ nanoparticles, NaYF₄:Yb³⁺, Er³⁺ nanoparticles functionalized with amino groups, avidin conjugated amino-functionalized NaYF₄:Yb³⁺, Er³⁺ nanoparticles were characterized by X-ray diffraction (XRD), transmission electron microscopy (TEM), atomic force microscopy (AFM), Fourier transform infrared (FT-IR), UV/Vis absorption spectra, and up-conversion luminescence spectra, respectively. The biofunctionalization of the NaYF₄:Yb³⁺, Er³⁺ nanoparticles has less effect on their luminescence properties, i.e., they still show the up-conversion emission (from Er³⁺, with ⁴S_3/2 → ⁴I_15/2 at ~540 nm and ⁴F_9/2 → ⁴I_15/2 at ~653 nm), indicative of the great potential for these NaYF₄:Yb³⁺, Er³⁺ nanoparticles to be used as fluorescence probes for biological system.     

Ti扩散Er3+:LiNbO3沟道波导的模式分析

本文采用有效折射率方法对Ti扩散Er³⁺:LiNbO₃沟道波导的模式特性进行了分析,分析中考虑了Er³⁺:LiNbO₃晶体的各向异性,并与变分法分析进行了比较,二者结果相一致。     

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.     

ESR study of rare-earth ions with the effective spin of 1/2 in LiNbO3 crystals

Rare-earth ions of Nd³⁺ and Er³⁺ in nearly stoichiometric and MgO-doped LiNbO₃ crystals, respectively, have been investigated by employing an X-band electron spin resonance (ESR) spectrometer. The grown crystal was heated in Li-rich powder at 1100°C in order to make it nearly stoichiometric by the vapor transport equilibrium technique. Due to the fact that the ESR linewidth is much narrower in the stoichiometric crystal than in the congruent LiNbO₃, we were able to determine the hyperfine constants of¹⁴³Nd and¹⁴⁵Nd at 4 K. By codoping MgO into LiNbO₃, a new Er³⁺ center has been observed with a differentg-tensor. We propose that the new Er³⁺ center in Mg-doped LiNbO₃ occupies the niobium site due to the local excessive Mg²⁺ ion at the lithium site, whereas Nd³⁺ and Er³⁺ in congruent crystals reside at the lithium site. The proposal is consistent with theg-value anisotropy.     

Synthesis and characterization of core-shell structured SiO2@YVO4:Yb,Er microspheres

In this paper, the core-shell structured SiO₂@YVO₄:Yb³⁺,Er³⁺ microspheres have been successfully prepared via a facile sol-gel process followed by a heat treatment. X-ray diffraction, field emission scanning electron microscopy, energy disperse X-ray spectroscopy, transmission electron microscopy, Fourier transform infrared spectroscopy, and photoluminescence spectra were used to characterize the samples. The results reveal that the SiO₂ spheres have been successfully coated by YVO₄:Yb³⁺,Er³⁺ phosphors to form core-shell structures and the size of obtained microspheres has a uniform distribution. Additionally, the samples exhibit bright green luminescence under the excitation of a 980 nm laser diode. The photoluminescence intensity increases with the number of coatings. These core-shell structured SiO₂@YVO₄:Yb³⁺,Er³⁺ microspheres may have great potential in the fields of infrared detection and display devices.     

Spectral properties and energy transfer of Yb,Er:GdVO4 crystal

GdVO₄ single crystal co-doped with Yb³⁺ and Er³⁺ was grown by the Czochralski method. The X-ray powder diffraction pattern of Yb,Er:GdVO₄ crystal confirms that the as-grown crystal is isostructural with pure GdVO₄ crystal. Its polarized absorption spectra and non-polarized fluorescence spectra were measured at room temperature. The absorption band at 984 nm for π-polarization has an FWHM of about 36 nm, which is favorable for InGaAs LD laser pumping. The spectrum properties of Er³⁺ in Yb,Er:GdVO₄ crystal were investigated based on Judd–Ofelt theory. There is strong energy transfer from Yb³⁺ to Er³⁺ in this crystal. When excited with 980 nm radiation, this crystal emitted strong fluorescence at about 1529 nm and 552.5 nm. The total energy transfer rate and efficiency from Yb³⁺ to Er³⁺ is 3.33 ms^-1 and 67%, respectively. The energy transfer between Er³⁺ and Yb³⁺ ions is a multistep transfer process, and was investigated based on a random-walk model. The investigation result shows that there is strong cooperative-sensitization effect from Yb³⁺ to Er³⁺, which is the main upconversion energy-transfer process in this crystal. PACS 42.70.Hj; 81.10.Fq; 42.55.Rz     

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.     

Yb3+敏化的Er3+/Ho3+共掺碲酸盐玻璃的上转换发光研究

用高温熔融法制备了系列Er³⁺/Yb³⁺共掺，Ho³⁺/Yb³⁺共掺，和Er³⁺/Yb³⁺/Ho³⁺三掺碲酸盐玻璃，在975nm激光抽运下三种掺杂玻璃中都出现了较强的绿光和红光上转换.研究了Yb³⁺离子对Er³⁺和Ho³⁺离子上转换发光强度的影响以及Yb³⁺→Er关键词： 3+/Yb³⁺/Ho³⁺共掺')" href="#">Er³⁺/Yb³⁺/Ho³⁺共掺 碲酸盐玻璃 光谱性质 上转换     

Facile synthesis of well-dispersed SrF2:Yb/Er upconversion nanocrystals in oleate complex systems

Well oil-dispersible SrF₂:Yb³⁺/Er³⁺ upconversion (UC) nanocrystals (NCs) were easily synthesized in the water-ethanol-oleic acid-sodium oleate complex systems. The as-prepared NCs all show size-uniformity, and their sizes, morphologies can be controlled by varying the solvent and reaction time, and rectangular SrF₂:Yb³⁺/Er³⁺ nanosheets with the sizes of 5-25 nm can be obtained. The possible mechanism on the nucleation and growth of nanocrystals occurred at the oleic acid/sodium oleate interface was also discussed. The size and morphology dependent UC luminescence behaviors have been observed in SrF₂:Yb³⁺/Er³⁺ NCs, and their UC luminescence transitions were proposed. The as-prepared UC nanocrystals are expected to fulfill the demand for biological applications.     

Green,blue, red,near-infrared up-conversion luminescence of Yb<Superscript>3+</Superscript>/Er<Superscript>3+</Superscript>/Tm<Superscript>3+</Superscript> co-doped YVO<Subscript>4</Subscript> nanoparticles

YVO₄:Yb³⁺,Er³⁺; YVO₄:Yb³⁺,Tm³⁺; and YVO₄:Yb³⁺,Er³⁺,Tm³⁺ were all synthesized via sol-gel method with a subsequent thermal treatment. Specifically, YVO₄:Yb³⁺,Er³⁺,Tm³⁺ phosphors were prepared with different annealing temperatures to study the influence of temperature. The transmission electron microscope (TEM), scanning electron microscope (SEM), X-ray diffractometer (XRD), and photoluminescent (PL) spectrofluorometer were used to investigate the morphology, crystal structure, and up-conversion luminescent properties of all samples. In summary, all samples were granular-like nanoparticles and well crystallized with the same tetragonal phase as YVO₄. Under the irradiation at 980 nm, YVO₄:Yb³⁺,Er³⁺ phosphors can generate green emission at 525 and 553 nm and red emission at 657 nm, while YVO₄:Yb³⁺,Tm³⁺ phosphors can generate blue emission at 476 nm, red emission at 648 nm, and near-infrared emission at 800 nm. Notably, YVO₄:Yb³⁺,Er³⁺,Tm³⁺ samples can exhibit green emission, blue emission, red emission, and near-infrared emission at the same time, which might endow the as-prepared samples with potential applications in many fields, such as luminous paint, infrared detection, and biological label.     

NIR to visible upconversion in Er/Yb co-doped CaYAl3O7 phosphor obtained by solution combustion process

Using the combustion synthesis, CaYAl₃O₇:Er³⁺ phosphor powders co-doped with Yb³⁺ have been prepared at low temperatures (550 °C) in a few minutes. Formation of the compound was confirmed by X-ray powder diffraction. Near-infrared to visible upconversion fluorescence emission in the Er³⁺ doped CaYAl₃O₇ phosphor powder has been observed. The effect of co-doping with triply ionized ytterbium in the CaYAl₃O₇:Er³⁺ phosphor has been studied and the process involved is discussed.