Synthesis and Spectroscopic Properties of GdAl3(BO3)4 Poly-crystals Codoped with Yb3+ and Eu3+

GdAl3(BO3)4 polycrystals co-doped with Yb3+ and Eu3+ has been synthesised by combustion method with urea. Upon the excitation at 465 nm (Eu3+/7F6-->5D2 transition), emission bands centered at 590, 613, 697 and 702 nm in the wavelength region of 550-750 nm have clearly been observed, assigned to the electronic transitions of 5D0-->7FJ (J=1, 2, 4 and 5) of Eu3+ ions, respectively. Meanwhile, an intense emission centred at 980 nm along with a shoulder at 1,040 nm has also been observed by exploiting a cross-relaxation process between the transitions of Eu3+/5D0-->7F6 and Yb3+/2F7/2-->2F5/2. On the contrary, an intense red up-conversion emission centred at 613 nm originated from the 5D0-->7F2 transition of Eu3+ has been observed upon excitation with 980 nm laser diode. The quadratic dependence of the red up-conversion intensity on the pump-laser power reveals a cooperative energy transfer mechanism from a pair of Yb3+ ions to one Eu3+ ion.     

YAB晶体中Yb3+到Er3+的能量传递

1.55 μm波段是光通讯的一个重要波段,而且对人眼安全,有高的大气透过率,因此可以广泛应用于通讯和遥感测距等领域。由于Er³⁺离子对商品化的InGaAs激光二极管的抽运波长不能有效吸收,因此一般通过在基质中共掺杂Yb³⁺和Er³⁺离子来获得1.55 μm波段激光输出。采用助熔剂法生长了不同Yb³⁺和Er³⁺掺杂浓度的YAl₃(BO₃)₄(YAB)晶体。运用速率方程模型研究了晶体中Yb³⁺到Er³⁺能量传递过程,得到了根据Yb³⁺离子的荧光寿命计算能量传递系数的简单计算公式。计算了不同掺杂离子浓度的YAB晶体中的能量传递系数等相关参数。结果表明,在YAB晶体中,Yb³⁺到Er³⁺能量传递非常有效,YAB晶体可以作为一种能获得1.55 μm激光输出的良好介质材料。     

Infrared-to-visible upconversion emission of Er3+/Yb3+-codoped SrMoO4 phosphors as wide-range temperature sensor

Er³⁺/Yb³⁺-codoped SrMoO₄ phosphors were prepared by a high-temperature solid-state reaction method. At room temperature, all the as-prepared samples exhibited strong upconversion properties and the emission intensity increased dramatically with the increase of Yb³⁺ ion concentration, reaching its maximum value when the concentration was 5 mol%. The dependence of emission intensity on the pump power suggested that the upconversion emission was a two-photon process. Furthermore, the optical temperature sensing properties based on green upconversion emissions of the SrMoO₄:0.01Er³⁺/0.05Yb³⁺ phosphor were studied. It is found that the SrMoO₄:0.01Er³⁺/0.05Yb³⁺ phosphor can be operated over a very wide temperature range of 93–773 K with a maximum sensitivity of ∼0.0128 K⁻¹, indicating that low- and high-temperature thermometry can be simultaneously realized in this phosphor.     

Yb^3＋离子摩尔分数对Yb：GAB晶体辐射陷阱的影响

测量了一系列Yb3+摩尔分数(0.125...1)在Yb3+:GdAl3(BO3)4 晶体(Yb:GAB)的室温偏振吸收光谱、发射光谱.为了揭示和消除辐射陷阱对Yb3+光谱性质的影响,分别测量了块状、粉末和稀释粉末样品的发射光谱.为了比较不同摩尔分数和不同方式辐射陷阱的影响,采用倒易法(RM)和Fuchtbauer-Ladenburg公式(FL)来计算发射截面.实验结果表明:随着Yb3+离子摩尔分数的增加,辐射陷阱效应对发射光谱的影响越来越严重.在发射光谱中,随着Yb3+离子摩尔分数的增加,短波段发射变弱,长波段发射变强,因此,提出了Yb:GAB 晶体中发射光谱的重心波长移动Δλ与 Yb3+离子摩尔分数之间的经验关系来定量分析Yb3+离子摩尔分数变化对辐射陷阱的影响;采用稀释法能够很好消除辐射陷阱对发射光谱的影响,而粉末法对于低Yb3+浓度的样品能够比较好地消除辐射陷阱的影响,块状样品直接测量很难消除辐射陷阱的影响.     

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.     

CaWO4：Sm3+荧光粉的发光性质及其能量传递机理

采用沉淀法制备了不同Sm³⁺掺杂浓度的白钨矿结构CaWO₄荧光粉材料. 对CaWO₄:Sm³⁺ 材料的光致发光性质的研究结果表明, 在404 nm光照下样品可以实现色纯度较高的红光发射, 而短波紫外240 nm光照下除Sm³⁺的特征发射外还能观察到CaWO₄自激发发射, 能够获得较强的白光; 实验发现Sm³⁺掺杂浓度为2%时样品的发光强度最高; 通过对实验数据的分析确定了Sm³⁺之间的能量传递类型为电偶极-电偶极相互作用, 并计算了能量传递的临界距离大约为2.0 nm. 关键词： 光致发光 4：Sm³⁺')" href="#">CaWO₄：Sm³⁺ 荧光寿命 能量传递     

Nd3+ → Yb3+ energy transfer in a codoped metaphosphate glass as a model for Yb3+ laser operation around 980 nm

A complete spectroscopic investigation of a metaphosphate glass with composition Pb(PO₃)₂ doped with various amounts of Nd³⁺ and Yb³⁺ (1 up to 10 at.%) is reported. Efficient Nd³⁺ → Yb³⁺ energy transfers occur both radiatively and non-radiatively, the latter being dominant and partly resonant and partly phonon-assisted by phonons of the order of 950 cm⁻¹, which fits well with the reported Raman spectrum of the material. These transfers mainly concern the ⁴F_3/2 → ⁴I_9/2 emission and the ²F_7/2 → ²F_5/2 absorption transitions of the Nd³⁺ and Yb³⁺ ions around 900 nm, respectively. They are analysed both via spectral and temporal data. The results show that about 5% Nd³⁺ and 5% Yb³⁺ ions have to be incorporated to reach energy transfers exceeding about 65%, which is in agreement with data recently reported in the case of a YAl₃(BO₃)₄ crystal. Simulations based on the obtained data show that laser thresholds of a few tens of mW should be easily attainable by operating the materials in a channel waveguide configuration.     

Dual-polarization and dual-wavelength diode-pumped laser operation from a birefringent Yb3+-doped GdAl3(BO3)4 nonlinear crystal

From two positions of the concave output mirror of the laser cavity, diode-pumped ordinary or extraordinary polarization lasing of an Yb³⁺-doped GdAl₃(BO₃)₄ nonlinear birefringent crystal is obtained. Translating the mirror at an intermediate position, simultaneous ordinary and extraordinary polarization lasing at 1046 (2.5 nm FWHM) and 1040 nm (2.2 nm FWHM), respectively, is obtained with up to 53% slope efficiency. Using a YAG:Cr⁴⁺ saturable absorber for passive Q-switching the cavity, ordinary and extraordinary pulses are obtained with an energy as high as 236 μJ and with about 30 ns duration. The two pulses of orthogonal polarizations can be separated by up to a few hundred ns, depending on the experimental conditions. The simultaneity of the pulses is observed but is difficult to maintain. A model constituted by two coupled equations reproduces reasonably well the experimental data. Repetition rates up to 3 kHz have been explored, corresponding to 4.65 W absorbed pump power. PACS 42.55.Xi; 42.60.Gd; 42.25.Ja     

Microwave sol-gel process of KGd(WO4)2:Ho3+/Yb3 phosphors and their upconversion photoluminescence properties

Double tungstate KGd_1−x(WO₄)₂:Ho³⁺/Yb³⁺ phosphors with doping concentrations of Ho³⁺ and Yb³⁺ (x=Ho³⁺+Yb³⁺, Ho³⁺=0.05, 0.1, 0.2 and Yb³⁺=0.2, 0.45) were successfully synthesized by the microwave sol–gel method, and the upconversion mechanisms were investigated in detail. The synthesized particles formed after heat-treatment at 900 °C for 16 h showed a well crystallized morphology with particle sizes of 2–5 μm. Under excitation at 980 nm, the UC intensities of KGd_0.7(WO₄)₂:Ho_0.1Yb_0.2 and KGd_0.5(WO₄)₂Ho_0.05Yb_0.45 particles exhibited yellow emissions based on a strong 550-nm emission band in the green region and a strong 655-nm emission band in the red region, which were assigned to the ⁵S₂/⁵F₄→⁵I₈ and ⁵F₅→⁵I₈ transitions, respectively. The Raman spectra of the doped particles indicated the presence of strong peaks at higher frequencies of 764, 812, 904, 984, 1050, 1106, 1250 and 1340 cm⁻¹ induced by the disorder of the [WO₄]²⁻ groups with the incorporation of the Ho³⁺ and Yb³⁺ elements into the crystal lattice or by a new phase formation.     

Tm^3＋和Yb^3＋共掺五磷酸盐非晶中的间接敏化上转换

本文报道在约７９８ｎｍ的半导体激光泵浦下，Ｔｍ＾３＋，Ｙｂ＾３＋共渗五磷酸盐非晶的蓝光发射。激光被样品吸收而直接激发Ｔｍ＾２＋离子至＾３Ｆ４能级。从Ｔｍ＾３＋向Ｙｂ＾３＋的能量传递，接着从Ｙｂ＾３＋向Ｔｍ＾３＋的能量传递把Ｔｍ＾３＋离子激发至＾１Ｇ４能级。分析表明，声子在上转换过程中起了很大作用。     

Infrared-to-visible up-conversion luminescence and energy transfer of RE3+/Yb3+(RE = Ho,Tm) co-doped SrIn2O4

Near-infrared excited up-conversion phosphors of RE³⁺/Yb³⁺(RE = Ho, Tm) co-doped SrIn₂O₄ were synthesized by a solid-state reaction method. X-ray diffraction analysis revealed the phase composition of those samples, and the up-conversion spectroscopic properties were studied in terms of up-conversion emission spectra. Under 980 nm near-infrared laser excitation, strong green emission with the peak at 546 nm was observed in SrIn₂O₄: Ho³⁺/Yb³⁺, which can be assigned to the characteristic ⁵S₂(⁵F₄) → ⁵I₈ transition of Ho³⁺. Furthermore, SrIn₂O₄: Tm³⁺/Yb³⁺ showed bright blue emission with the peak at 486 nm, which is associated with the ¹G₄ → ³H₆ transition of Tm³⁺. The UC power studies indicated that the luminescence of SrIn₂O₄: Ho³⁺/Yb³⁺ and SrIn₂O₄: Tm³⁺/Yb³⁺ are attributed to two-photon and three-photon process, respectively. The possible UC luminescence mechanism and energy transfer in SrIn₂O₄: RE³⁺/Yb³⁺ were discussed.     

Optical bifurcated fiber diode-pumping for two-wavelength laser operation with the Yb3+-doped GdAl3(BO3)4 birefringent crystal

Thanks to diode pumping through an optical bifurcated fiber, we take benefit of the birefringence of the Yb³⁺-doped GdAl₃(BO₃)₄ crystal to get two-polarization and two-wavelength laser operation both in CW and in passive Q-switch regimes. Typical differential slopes are 54% and 30% respectively for the o- and e-waves. In the pulse regime the two o- and e-pulses are synchronous but not simultaneous. Free running laser emissions near 1040 and 1046 nm for the e- and o-waves respectively were obtained with 2.5 nm FWHM.     

钒酸钇的基质施主合作能量传递导致的镱离子的近红外量子剪裁发光

稀土材料的红外和可见量子剪裁对于寻找更好能量效率的发光材料来说都是一个激动人心的发展。发光效率的最大上限值能从100%提高到200%甚至更高。在第一代晶硅太阳能电池与第二代薄膜太阳能电池之后第三代的聚光太阳能电池已成为目前的重点发展方向。现在,利用稀土材料的近红外量子剪裁发光效应有可能较好的解决太阳光谱与太阳能电池光电响应之间存在的光谱失配的问题,因此有可能较大幅度的提高太阳能电池的发电效率,因而具有重要的意义与价值。研究了钒酸钇晶体基质中Yb3+离子的近红外量子剪裁发光现象,测量了从可见到红外的钒酸钇晶体的发光谱、激发谱与荧光寿命,测量发现钒酸钇晶体基质能带在约322.0nm光激发时能导致有效的从钒酸钇晶体基质到Yb3+离子的二级合作能量传递,进而导致了很强的Yb3+离子的985.5nm2 F5/2→2 F7/2的近红外量子剪裁发光,同时,钒酸钇晶体基质的位于430.0nm的发光强度大幅降低。测量发现:(A)Yb(1.5)∶YVO4晶体的430.0nm的荧光寿命值为τA=3.785μs;(B)YVO4晶体的430.0nm的荧光寿命值为τB=22.72μs;研究计算发现总的理论量子剪裁效率上限值为η1.5%Yb=183.3%。     

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.     

Calcination temperature optimization,energy transfer mechanism and fluorescence temperature dependence of KLa(MoO4)2:Eu3+ phosphors

The optimum calcination temperature for KLa(MoO₄)₂:Eu³⁺ phosphor was confirmed to be 1000 °C via checking the XRD patterns, SEM images and fluorescence spectra for the samples derived from solid state reaction. The energy transfer behavior between Eu³⁺ ions was studied. It was found that electric dipole–dipole interaction is responsible for the fluorescence quenching of ⁵D₂ and ⁵D₁ levels, but exchange interaction is in charge of ⁵D₀ fluorescence quenching. It was also observed that color coordinates of the studied phosphor can be tuned when the doping concentration is relatively low. The fluorescence thermal quenching process was investigated. It was found the thermal quenching followed well crossover model. Judd–Ofelt parameters of Eu³⁺ in KLa(MoO₄)₂ were obtained, and the optical transition properties were further discussed.     

Towards efficient upconversion and downconversion of NaYF4:Ho3+,Yb3+ phosphors

NaYF₄ microcrystals co-doped with Ho³⁺ and Yb³⁺ were prepared by a facile hydrothermal synthesis. The products were characterized by X-ray diffractometer, scanning electron microscopy, and photoluminescence spectroscopy. Upon excitation with a 980 nm laser diode, the sample shows an intense green upconversion emission centered at 540 nm corresponding to the ⁵S₂→⁵I₈ transition of Ho³⁺. The quadratic dependence of the green emission intensity on the excitation power reveals a two-phonon upconversion process. On the contrary, upon excitation with 448 nm, both visible and near-infrared emissions peaked at 483, 540, 644, 749, and 978 nm are simultaneously observed, which could be assigned to the electronic transitions of Ho³⁺: ⁵F₃→⁵I₈, ⁵S₂→⁵I₈, ⁵F₅→⁵I₈, ⁵S₂→⁵I₇, and Yb³⁺: ²F_5/2→²F_7/2, respectively. The energy transfer processes between Ho³⁺ and Yb³⁺ ions and the involved mechanisms have been investigated and discussed.     

1180 nm Raman laser operation of end-pumping Nd:GdAl3(BO3)4/SrWO4 crystal

We present an end-pumped continuous-wave Raman laser at 1180 nm with a 60 mm long pure crystal SrWO₄ and an Nd:GdAl₃(BO₃)₄ crystal. The highest output power Raman laser at 1180 nm is 15.5 mW corresponding to the pump power of 1.75 W. Results indicate that the intense self-doubling frequency effect of GdAl₃(BO₃)₄ reduces the 1180 nm Raman laser output.     

Optical parameters and upconversion fluorescence in Tm3+/Yb3+ codoped tellurite glass

Tm³⁺/Yb³⁺ codoped tellurite glass has been prepared. Density, refractive index, optical absorption, Judd-Ofelt parameters and spontaneous transition probabilities of Tm³⁺ have been measured and calculated, respectively. Intense blue three-photon upconversion fluorescence and S-band (1470 nm) fluorescence were investigated under the excitation of a 980 nm diode laser at room temperature. Judd-Ofelt parameters, strong blue three-photon upcoversion emission of Tm³⁺ in glass indicate that Tm³+/Yb³⁺ codoped tellurite glass is a promising blue color upconversion optical and laser material. In addition, experiment results showed the 980 nm laser was more efficient than 808 nm laser when pumping Tm³⁺/Yb³⁺ codoped tellurite glass, Tm³⁺/Yb³⁺ codoped tellurite glass also could be a promising material for S-band amplification.     

Dy3+掺杂EuAl3(BO3)4晶体的荧光性质

制备了EuAl3(BO3)4晶体和Dy3+:EuAl3(BO3)4晶体，并且研究了它们的荧光性质．EuAl3(BO3)4晶体具有强的红光发射．在Dy3+掺杂的EuAl3(BO3)4晶体中，Dy3+对Eu3+的荧光有很强的敏化作用，提出了敏化作用的机制是能量的共振传递．Dy3+敏化作用的最佳掺杂浓度为0.2，高于0.2时，由于Dy3+的浓度焠灭效应，DyxEu1-xAl3(BO3)4晶体中Eu3+的613 nm发射峰强度急剧下降．     

Fluorescence emission spectrum and energy transfer in Eu and Mn co-doped Ba2Ca(BO3)2 phosphors

Eu²⁺ and Mn²⁺ co-doped Ba₂Ca(BO₃)₂ phosphors yield two emission bands consisting of green and red components under the excitation of 360 nm, which shows a great potential for white LEDs. Effective energy transfer occurs in Eu²⁺/Mn²⁺ co-doped Ba₂Ca(BO₃)₂ host due to the large spectral overlap between the emission of Eu²⁺ and the excitation of Mn²⁺. The energy transfer from Eu²⁺ to Mn²⁺ is thoroughly investigated by their excitation, emission and photoluminescence decay behaviors, and is demonstrated to be via the dipole–quadrupole interaction.