White up-conversion emission in Ho/Tm/Yb tri-doped glass ceramics embedding BaF2 nanocrystals

Ho³⁺/Tm³⁺/Yb³⁺ tri-doped glass ceramics with white light emitting have been developed and demonstrated. Pumped by 980 nm laser diode (LD), intensive red, green and blue up-conversions (UC) were obtained. The green emission is assigned to Ho³⁺ ion and the blue emission is assigned to Tm³⁺ ion, whereas the red emission is the combination contribution of the Ho³⁺ and Tm³⁺ ions. The RGB intensities could be adjusted by tuning the rare-earth ion concentration and pump power intensity. Thus, multicolor of the luminescence, including perfect white light with CIE-X=0.329 and CIE-Y=0.342 in the 1931 CIE chromaticity diagram can be obtained in 0.15 Ho³⁺/0.2Tm³⁺/3Yb³⁺ tri-doped glass ceramics embedding BaF₂ nanocrystals pumped by a single infrared laser diode source of 980 nm at 500 mW. The up-conversion luminescence mechanism of Yb³⁺ sensitize Ho³⁺ and Tm³⁺ ions and the energy transfer from Ho³⁺ to Tm³⁺ in oxy-fluoride silicate glass ceramics were analyzed.     

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⁺     

The up-conversion properties of Yb and Er doped Y4Al2O9 phosphors

Er³⁺ doped and Yb³⁺/Er³⁺ co-doped Y₄Al₂O₉ phosphors are prepared by the sol-gel method. The effect of dopant concentration on the structure and up-conversion properties is investigated by X-ray diffraction (XRD) and photoluminescence, respectively. XRD pattern indicates that the sample structure belongs to monoclinic. Under 980 nm excitation, the green and red up-conversion emissions are observed and the emission intensities depended on the Yb³⁺ ion concentration. The green up-conversion emissions decrease with the increase of Yb³⁺ concentration, while red emission increases as Yb³⁺ concentration increases from 0 to 8 at% and then decreases at high Yb³⁺ concentration. The mechanisms of the up-conversion emissions are discussed and results shows that in Er³⁺ and Yb³⁺/Er³⁺ co-doped system, cross-relaxation (CR) and energy transfer (ET) processes play an important role for the green and red up-conversion emissions.     

Enhancement of upconversion luminescence in Tm/Er/Yb-codoped glass ceramic containing LiYF4 nanocrystals

A transparent Er³⁺–Tm³⁺–Yb³⁺ tri-doped oxyfluoride glass ceramics containing LiYF₄ nanocrystals were prepared. Under 980 nm laser diode (LD) pumping, intensive red, green and blue upconversion (UC) was obtained. The blue, green, and red UC radiations correspond to the 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. This is similar to that in Tm³⁺–Yb³⁺ and/or Er³⁺–Yb³⁺ co-doped glass ceramics. However, the blue UC radiations of the Er³⁺–Yb³⁺ co-doped glass ceramics is two-photon process due to cooperative energy transfer. The UC mechanisms were proposed based on spectral, kinetic, and pump power dependence analyses.     

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.     

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.     

Study on up-conversion emissions of Yb/Tm co-doped GdF3 and NaGdF4

The Yb³⁺/Tm³⁺ co-doped GdF₃ and NaGdF₄ samples were synthesized through a combination method of a co-precipitation and an argon atmosphere annealing procedures. X-ray diffraction analysis indicated that the Yb³⁺/Tm³⁺ co-doped GdF₃ sample crystallized well and was orthorhombic phase, and the Yb³⁺/Tm³⁺ co-doped NaGdF₄ sample was hexagonal phase. With a 980-nm semiconductor continuous wave laser diode as the excitation source, the up-conversion emission spectra of the two samples in the wavelength range of 240-510 nm were recorded. In the up-conversion emissions of the samples, Yb³⁺ transferred energies to Tm³⁺ resulting in their ultraviolet, violet, and blue up-conversion emissions. And, Tm³⁺ simultaneously transferred energies to Gd³⁺, which finally resulted in ultraviolet up-conversion emissions of Gd³⁺. The study on the excitation power dependence of up-conversion fluorescence intensity indicated that there were multi-photon (three-, four-, five-, and six-) processes in the up-conversion emissions of the samples. And the up-conversion emissions of Gd³⁺ and Tm³⁺ in the Yb³⁺/Tm³⁺ co-doped GdF₃ and NaGdF₄ samples were compared studied, too.     

Upconversion emission enhancement in Er/Yb-codoped BaTiO3 nanocrystals by tridoping with Li ions

Er³⁺/Yb³⁺/Li⁺-tridoped BaTiO₃ nanocrystals were prepared by a sol-gel method to improve the upconversion (UC) luminescence of rare-earth doped BaTiO₃ nanoparticles. Effects of Li⁺ ion on the UC emission properties of the Er³⁺/Yb³⁺/Li⁺-tridoped BaTiO₃ nanocrystals were investigated. The results indicated that tridoping with Li⁺ ion enhanced the visible green and red UC emissions of Er³⁺/Yb³⁺-codoped BaTiO₃ nanocrystals under the excitation of a 976 nm laser diode. X-ray diffraction and decay time of the UC luminescence were studied to explain the reasons of the enhancement of UC emission intensity. X-ray diffraction results gave evidence that tridoping with Li⁺ ion decreased the local symmetry of crystal field around Er³⁺, which increased the intra-4f transitions of Er³⁺ ion. Moreover, lifetimes in the intermediate ⁴ S_3/2 and ⁴I_11/2 (Er) states were enhanced by Li⁺ ion incorporation in the lattice. Therefore, it can be concluded that Li⁺ ion in rare-earth doped nanocrystals is effective in enhancing the UC emission intensity.     

Optical character of Er/Yb co-doped P2O5-CaO-Na2O-Al2O3-AgO phosphate glass

The up-conversion (UC) and near infrared (NIR) luminescence of Er³⁺/Yb³⁺ co-doped phosphate glass are investigated. In the UC emission range, the 523 nm, 546 nm green emissions and the 659 nm red emission are observed. With the increasing pump power, the intensity ratios of I₅₂₃/I₆₅₉, I₅₄₆/I₆₅₉ and I₅₂₃/I₅₄₆ increase gradually. The phenomenon is reasonably interpreted by theoretical analysis based on steady state rate equations. The emission cross section of the infrared emission at 1546 nm is larger (about 6.7 × 10^− 21 cm²), which is suitable for making fiber amplifier.     

Up-conversion photoluminescence characteristics of Yb3+:Er3+:Tm3+ co-doped borosilicate glasses

Yb3+:Er3+:Tm3+ co-doped borosilicate glasses are prepared.Their strong up-conversion photoluminescence spectra in a range from ultra-violet to near-infrared,which are excited by a 978-nm laser diode,are measured,and the mechanisms of energy transfer among Yb3+,Er3+ and Tm3+ ions are discussed.The results show that there is an unexpected wavelength at 900-nm emission from Yb3+ Stark splitting levels to pump Tm3+ ions and there exists an optimum pump power.The concentration of the Tm3+ dopant gives rise to a prominent effect on the intensity of visible and near-infrared emissions for the Yb3+:Er3+:Tm3+ co-doped borosilicate glasses.     

Tm3+/Yb3+共掺碲酸盐玻璃的近红外发光及能量传递机理

采用高温熔融法制备了组分为TeO₂-ZnO-Na₂O的Tm³⁺离子单掺和Tm³⁺/Yb³⁺共掺碲酸盐玻璃,应用Judd-Ofelt理论计算分析了玻璃样品的强度参量Ω_t(t=2, 4, 6),自发辐射跃迁几率A,荧光分支比β和荧光辐射寿命τ_rad等光谱参量,测量得到了不同Yb³⁺离子掺杂浓度下玻璃样品的Tm³⁺离子上转换发光谱.结果显示,在980 nm泵浦光激励下玻璃样品发射出强烈的近红外上转换荧光.对Tm³⁺离子上转换发光分析表明,强烈的Tm³⁺离子近红外上转换发光主要来自于Yb³⁺/Yb³⁺离子间的共振能量传递以及基于单声子和双声子辅助的Yb³⁺/Tm³⁺离子间的非共振能量传递过程,并进一步计算得到了声子贡献比和能量传递系数.最后,计算分析了Tm³⁺:³F₄→³H₆能级间跃迁的1.8 μm波段吸收截面、受激发射截面和增益系数.研究表明,Yb³⁺/Tm³⁺共掺TeO₂-ZnO-Na₂O玻璃可以作为近红外波段固体激光器的潜在增益基质.     

Emission analysis of Pr and Tm: Ca2Gd2W3O14 phosphors

5 mol% of Pr³⁺ and Tm³⁺ ions activated calcium gadolinium tungstate (Ca₂Gd₂W₃O₁₄₎ phosphors were synthesized by traditional solid state reaction method. Crystalline phase structure was identified from the X-ray diffraction (XRD) profiles. From the scanning electron microscopy (SEM) images, we have observed the agglomeration of the particles, and average grain size is around 40-300 nm. Using the energy dispersive X-ray analysis (EDAX) and Fourier transform infrared (FTIR) spectra, identified the elements and functional groups present in the prepared phosphors. The emission spectrum of Pr³⁺: Ca₂Gd₂W₃O₁₄ powder phosphors have shown an intense red emission at 615 nm with the excitation wavelength λ_exci=450 nm and thus these red color emitting powder phosphors are used as one of the components in the preparation of WLEDs. The excitation spectrum of Tm³⁺: Ca₂Gd₂W₃O₁₄ powder phosphor has shown a ligand to metal charge transfer (W-O) band (LMCT) within the WO₄²⁻ group. Emission spectrum of Tm³⁺: Ca₂Gd₂W₃O₁₄ phosphors have shown blue emissions at 453 nm (¹D₂→³F₄).     

Upconversion emission enhancement of TiO2 coated lanthanide-doped Y2O3 nanoparticles

To investigate the upconversion emission,this paper synthesizes Tm3+ and Yb3+ codoped Y2O3 nanoparticles,and then coats them with TiO2 shells for different coating times.The spectral results of TiO2 coated nanoparticles indicate that upconversion emission intensities have respectively been enhanced 3.2,5.4,and 2.2 times for coating times of 30,60 and 90 min at an excitation power density of 3.21×102 W.cm 2,in comparison with the emission intensity of non-coated nanoparticles.Therefore it can be concluded that the intense upconversion emission of Y2O3:Tm3+,Yb3+ nanoparticles can be achieved by coating the particle surfaces with a shell of specific thickness.     

Er3+，Er3+/Yb3+掺杂氟化镧超微材料的光谱特性与上转换发光

采用共沉淀法制备了Er³⁺掺杂和Er³⁺/Yb³⁺共掺杂LaF₃超微材料,所制备的样品的颗粒呈球形,尺寸为250nm左右.计算得到Er³⁺单掺杂样品中对应着⁴S_3/2和⁴F_9/2能级的发光量子效率分别为67.0%和71.9%.研究发现,随着Yb³⁺离子浓度的增加 关键词： 3+')" href="#">Er³⁺ 3+')" href="#">Yb³⁺ 发光 能量传递     

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     

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.     

Upconversion Based Tunable White-Light Generation in Ln:Y<Subscript>2</Subscript>O<Subscript>3</Subscript> Nanocrystalline Phosphor (Ln = Tm/Er/Yb)

We report the generation of efficient white light based on upconversion (UC) in Tm³⁺/Er³⁺/Yb³⁺:Y₂O₃ nanocrystalline phosphor synthesized by simple and cost effective solution combustion technique on 976 nm laser excitation. The calculated color coordinates (using 1931 CIE standard) for samples annealed at different temperatures vary from (0.16, 0.30) to (0.32, 0.33) with dopant concentration, annealing temperature and the pump power; thus providing a wide color tunability including the white one. White emission is observed even at a very low laser power (60 mW). The maximum upconversion efficiency obtained for white emission is 2.79% with the color coordinates (0.30, 0.32) at laser power of 420 mW which is quite close to the standard white color coordinates.     

Novel green-emitting Na2CaPO4F:Eu phosphors for near-ultraviolet white light-emitting diodes

In this study, green-emitting Na₂CaPO₄F:Eu²⁺ phosphors were synthesized by solid-state reactions. The excitation spectra of the phosphors showed a broad hump between 250 and 450 nm; the spectra match well with the near-ultraviolet (NUV) emission spectra of light-emitting diodes (LEDs). The emission spectrum showed an intense broad emission band centered at 506 nm. White LEDs were fabricated by integrating a 390 nm NUV chip comprising blue-emitting BaMgAl₁₀O₁₇:Eu²⁺, green-emitting Na₂CaPO₄F:0.02 Eu²⁺, and red-emitting CaAlSiN₃:Eu²⁺ phosphors into a single package; the white LEDs exhibited white light with a correlated color temperature of 5540 K, a color-rendering index of 90.75, and color coordinates (0.332, 0.365) close to those of ideal white light.     

Synthesis and luminescence properties of Eu, Ce and Tb-activated Sr3La2(BO3)4 under UV excitation

The spectroscopic properties in UV-excitable range for the phosphors of Sr₃La₂(BO₃)₄:RE³⁺ (RE³⁺=Eu³⁺, Ce³⁺, Tb³⁺) were investigated. The phosphors were synthesized by conventional solid-state reactions. The photoluminescence (PL) spectra and commission international de I'Eclairage (CIE) coordinates of Sr₃La₂(BO₃)₄:RE³⁺ were investigated. The f-d transitions of Eu³⁺, Ce³⁺ and Tb³⁺ in the host lattices are assumed and corroborated. The PL and PL excitation (PLE) spectra indicate that the main emission wavelength of Sr₃La₂(BO₃)₄:Eu³⁺ is 611 nm, and Sr₃La₂(BO₃)₄:Ce³⁺ shows dominating emission peak at 425 nm, while Sr₃La₂(BO₃)₄:Tb³⁺ displays green emission at 487, 542, 582 and 620 nm. These phosphors were prepared by simple solid-state reaction at 1000 °C. There are lower reactive temperature and more convenient than commercial phosphors. The Sr₃La₂(BO₃)₄:Tb³⁺ applied to cold cathode fluorescent lamp was found to emit green light and have a major peak wavelength at around 542 nm. These phosphors may provide a new kind of luminescent materials under ultraviolet excitation.     

Upconversion and color tunability in Tm/Ho/Yb doped low phonon energy bismuth tellurite glasses

Low phonon energy Tm³⁺/Ho³⁺/Yb³⁺ triply doped bismuth tellurite glasses exhibiting multicolor upconversion fluorescences have been fabricated and characterized. The multicolor fluorescence composed of three primary colors green, red and blue upconversion emissions from Ho³⁺ and Tm³⁺ has been investigated. By adjusting the excitation power, the fluorescence colors can be tuned from multicolor to white color, and the dependence of color tunability on pump power has been presented in the CIE 1931 chromaticity diagram. With the increase in pumping power, the color coordinates move along the down-left direction and hit the equal energy point. The upconversion and color tunability via changing the pump power of infrared excitation in Tm³⁺/Ho³⁺/Yb³⁺ triply doped bismuth tellurite glasses will lead to new breakthrough in the field of three-dimensional solid-state displays and white-light emitting devices.