Near-infrared quantum cutting in Ho3+/Yb3+ codoped nanostructured glass ceramic

A first-order quantum cutting luminescence of Ho3+/Yb3+ couples, which are incorporated in the YF3 nanocrystals embedded in transparent glass ceramic, is reported for the first time, to our knowledge. When Ho3+ is excited with one blue photon, it was experimentally demonstrated that the resonant energy transfer from Ho3+ to Yb3+ occurs, leading to the near-infrared quantum cutting with one Ho3+ photon emitting at 1180?nm and one Yb3+ photon at 980?nm. The theoretical quantum efficiency is evaluated to be 159%.     

Broadband spectral conversion due to cooperative and phonon-assistant energy transfer from ZnO to Yb3+

The broadband spectral conversion from near-UV absorption into near-infrared emission around 1???m is reported in the ZnO?CLiYbO₂ hybrid phosphor, which is the benefit from the efficient energy transfer from ZnO to the Yb³⁺ ions that are specifically located at the interfacial diffusion regions between ZnO and LiYbO₂, rather than those in LiYbO₂ crystals. The Li⁺-related and Yb³⁺-related defect energy levels are formed inside the ZnO band gap in the ZnO?CLiYbO₂ hybrid phosphor; the former act as the quenching centers for the excitons in ZnO and meanwhile the efficient energy donors for Yb³⁺ ions, and the latter are responsible for the red shift of ZnO visible emission when the excitation energy is lower than E _g. The excitation power dependence of Yb³⁺ emission intensities is measured to investigate the number of photons that are involved in the energy transfer process, which reveals that there are two channels for the sensitizing of Yb³⁺: One is due to the energy transfer by the recombination of electrons and holes, which is a cooperative energy transfer process, and the other is via the energy feeding from the Li⁺-related energy levels, which is a phonon-assistant energy transfer process.     

Near-infrared downconversion through energy transfer from \mathrm{VO}_{4}^{3-} group to Yb3+ in Yb3+ doped YP0.9V0.1O4

Through the study of photoluminescence spectra, fluorescence decay curves, concentration-dependent luminescence and low temperature luminescence, the energy transfer from isolated $\mathrm{VO}_{4}^{3-}$ group to Yb³⁺ is investigated in Yb³⁺ doped YP_0.9V_0.1O₄. The experimental results show that the energy transfer from $\mathrm{VO}_{4}^{3-}$ group to Yb³⁺ is very efficient. Cooperative energy transfer, through which one high-energy photon absorbed by $\mathrm{VO}_{4}^{3-}$ group is converted to two near-infrared photons emitted by Yb³⁺ ions, is proposed to be the energy transfer process. This efficient ultra-violet to near-infrared downconversion could have potential application in improving the efficiency of silicon-based solar cell.     

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     

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.     

Radiationless energy transfer between Yb3+, Nd3+, and Pr3+ in a silicate glass

The glass contains two or three rare-earth elements. The concentration dependence of the intensity and lifetime of the luminescence is used to discuss Yb-Nd, Yb-Pr, and Nd-Pr interactions and energy-transfer modes. The quenching action oi Pr is found to exceed the sensitizing action for Yb.We are indebted to P. P. Feofilov for direction in this work and to V. P. Kolobkov for valuable discussions on the results.     

Tb3+、Yb3+共掺BaGd2ZnO5荧光粉的制备及其近红外量子剪裁研究

采用高温固相法合成了Tb3+、Yb3+共掺杂的BaGd2ZnO5荧光粉。XRD测量数据表明合成的样品为纯相。在Tb3+特征激发(297 nm)下得到了Yb3+的特征发射(977 nm),并且对Tb3+与Yb3+能级图进行分析,证明Tb3+到Yb3+为合作能量传递。测量了不同Yb3+浓度下Tb3+的5D4能级(544 nm)的发光寿命曲线,计算得到Tb3+与Yb3+的能量传递效率和量子效率,最高量子效率为125.5%。Yb3+的发射与硅太阳能电池的吸收匹配,该材料有可能应用于硅太阳能电池以提高其转换效率。     

Tm3+/Ho3+共掺碲酸盐玻璃的2.0μm发光特性及能量传递

研究了Tm3+/Ho3+共掺TeO2-WO3-ZnO玻璃在808 nm激光二极管抽运下的2.0μm发光特性及Tm3+与Ho3+之间的能量传递.应用Judd-Ofelt理论计算了Ho3+在碲酸盐玻璃中的谱线强度参量Ωt(t=2,4,6)、自发辐射概率Ar、辐射寿命τr等.计算了Ho3+的吸收截面σa(λ)和受激发射截面σa(λ).结果表明:碲酸盐玻璃中Tm3+→Ho3+正向能量传递系数大约是Tm3+←Ho3+反向能量传递系数的18倍.Ho3+离子的5I7能级的寿命为3.9 ms,2.0 μm处的最大发射截面为9.15×10-21cm2.在O.5 mol%Tm2O3和0.15 mol%Ho2O3共掺的碲酸盐玻璃中能获得2.0μm的最大增益.通过比较氟化物、碲酸盐和镓铋酸盐重金属氧化物等玻璃中Ho3+的量子效率η,σe×τm值和增益系数G(λ)等,发现Tm3+/Ho3+共掺碲酸盐玻璃是一种理想的2.0μm激光器用基质玻璃.     

Multicolor upconversion emission from Tm3++Ho3++Yb3+ codoped tellurite glass on NIR excitations

Multicolor emission has been produced using 798 nm and 980  nm laser excitation in a Tm³⁺+Ho³⁺+Yb³⁺ codoped tellurite based glass. This glass generates simultaneously red, green and blue (RGB) emission on 798 nm excitation. Multicolor emission thus obtained was tuned to white luminescence by adjusting the Ho³⁺ ion concentration. There is a close match between the calculated color coordinate for the white luminescence obtained here and the point of equal energy which represents white in the 1931 CIE chromaticity diagram. The 980 nm excitation of the same sample on the other hand gives intense green and red emission and the glass appears greenish.     

Energy transfer from Tm3+ to Pr3+ in barium borate glass

The system of Tm³⁺ and Pr³⁺ in barium borate glass is investigated for finding out the mechanism of nonradiative energy transfer at room temperature. The various constants for this system relevant to the energy transfer are also calculated.     

Enhanced luminescence in transparent glass ceramics containing BaYF5: Ce3+ nanocrystals

Ce³⁺ doped transparent glass ceramics containing BaYF₅ nanocrystals were prepared by controlled heat treatment of 45SiO₂–15Al₂O₃–10Na₂O–24BaF₂–6Y₂O₃–0.5Ce₂O₃ (mol%) glass. X-ray diffraction and transmission electron microscopy data have revealed the formation of BaYF₅ nanocrystals. Both photoluminescence and X-ray excited luminescence spectra have shown a blue-shift of the emission band of Ce³⁺ on ceramization, which is consistent with the Ce³⁺ environment evolving from a glassy oxide to a fluoride phase. The luminescent intensity of Ce³⁺ ions in the transparent glass ceramics is greatly enhanced compared with the precursor glass under ultraviolet and X-ray excitation. This could be attributed to the Ce³⁺ ions present in the BaYF₅ crystalline phase.     

Survey and research on up-conversion emission character and energy transition of Yb/Er/Tm co-doped phosphate glass and glass ceramic

By conventional high-temperature melting method, Yb³⁺/Er³⁺/Tm³⁺ co-doped phosphate glass was synthesized. After annealing the precursor glass, the phosphate glass ceramic (GC) was obtained. By measuring the X-ray diffraction (XRD) spectrum, it is proved that the LiYbP₄O₁₂ and Li₆P₆O₁₈ nano-crystals have existed in the phosphate GC. The up-conversion (UC) emission intensity of the GC is obvious stronger compared to that of the glass. The reason is that the shorter distance between rare earth ions in the glass ceramic increases the energy transitions from the sensitized ions (Yb³⁺) to the luminous ions (Er³⁺ and Tm³⁺). By studying the dependence of UC emissions on the pump power, the 523 and 546 nm green emissions of Er³⁺ ions in the glass are two-photon processes. But in the glass ceramic, they are two/three-photon processes. The phenomenon implies that a three-photon process has participated in the population of the two green emissions. Using Dexter theory, we discuss the energy transitions of Er³⁺ and Tm³⁺. The results indicate the energy transition of Tm³⁺ to Er³⁺ is very strong in the GC, which changes the population mechanism of UC emissions of Er³⁺.     

Color variety of up-conversion emission of Er3+/Yb3+ co-doped phosphate glass ceramics

The sample of Er³⁺/Yb³⁺ co-doped phosphate glass ceramic was prepared. At 975 nm laser diode (LD) excitation, the strong up-conversion (UC) emissions were observed, which were the UC green emission at 510–570 nm and the UC red emission at 636–692 nm, respectively. At low pump power (126 mW), the red emission is primary, and the color purity R_cp is 0.81. With the increasing of pump power, the emission color gradually varies from red to green. The intensity of the green emission is stronger compared to that of the red emission at high power (868 mW), and the color purity R_cp is 0.76. Thus, this material can be applied to fluorescence anti-counterfeiting by the color variety of UC emission under different pump power.     

Near-infrared quantum cutting in Yb3+ ion doped strontium vanadate

The materials Sr_3−x(VO₄)_2:xYb were successfully synthesized by co-precipitation method varying the concentration of Yb³⁺ ions from 0 to 0.06 mol. It was characterize by powder X-ray powder diffraction (XRD) and surface morphology was studied by scanning electronic microscope (SEM). The photoluminescence (PL) properties were studied by spectrophotometers in near infra red (NIR) and ultra violet visible (UV–VIS) region. The Yb³⁺ ion doped tristrontium vanadate (Sr₃(VO₄)₂) phosphors that can convert a photon of UV region (349 nm) into photons of NIR region (978, 996 and 1026 nm). Hence this phosphor could be used as a quantum cutting (QC) luminescent convertor in front of crystalline silicon solar cell (c-Si) panels to reduce thermalization loss due to spectral mismatch of the solar cells. The theoretical value of quantum efficiency (QE) was calculated from steady time decay measurement and the maximum efficiency approached up to 144.43%. The Sr_(3−x) (VO₄)_2:xYb can be potentiality used for betterment of photovoltaic (PV) technology.     

Enhancement of Tb emission by non-radiative energy transfer from Dy in silicate glass

A study of energy transfer was performed in dysprosium-terbium-doped silicate glasses at room temperature. Enhancement of the Tb³⁺ emission and a decrease in the Dy³⁺ emission are observed as a result of energy transfer from Dy³⁺ ions to Tb³⁺ ions. The energy transfer efficiencies, transfer probabilities, as well as average donor-acceptor distances were also calculated. It is concluded that the energy transfer mechanism between Dy³⁺ and Tb³⁺ ion is mainly electric dipole-dipole in nature.     

Upconversion emission in CaTiO3:Er3+ nanocrystals

CaTiO₃:Er³⁺ (5%) nanocrystals were obtained by sol–gel method under acidic conditions. The sizes of nanocrystals were 40 nm. Strong green anti-Stokes emission was observed after excitation of the ⁴I_9/2 and ⁴I_11/2 level. The emission is due to excited state absorption (ESA) and energy transfer upconversion (ETU).     

Up-conversion luminescence properties and energy transfer of Er~(3+)/Yb~(3+)co-doped oxyfluoride glass ceramic containing CaF_2 nano-crystals

The Er3+/Yb3+co-doped transparent oxyfluoride glass-ceramics containing CaF2nano-crystals were successfully prepared. After heat treatments, transmission electron microscopy(TEM) images showed that CaF2nano-crystals of 20–30 nm in diameter precipitated uniformly in the glass matrix. Comparing with the host glass, high efficiency upconversion luminescence of Er3+at 540 nm and 658 nm was observed in the glass ceramics under the excitation of 980 nm. Moreover,the size of the precipitated nano-crystals can be controlled by heat-treatment temperature and time. With the increase of the nano-crystal size, the intensity of the red emission increased more rapidly than that of the green emission. The energy transfer process of Er3+and Yb3+was convinced and the possible mechanism of Er3+up-conversion was discussed.     

Tm3+/Ho3+共掺碲酸盐玻璃的2.0μm发光特性及能量传递

研究了Tm³⁺/Ho³⁺共掺TeO₂-WO₃-ZnO玻璃在808 nm激光二极管抽运下的2.0μm发光特性及Tm³+与Ho³⁺之间的能量传递.应用Judd-Ofelt理论计算了Ho³⁺在碲酸盐玻璃中的谱线强度参量Ω_t (t=2,4,6)、自发辐射概率A_r、辐射寿命τ_r等.计算了Ho³⁺的吸收截面σ_a(λ)和受激发射截面σ_e(λ).结果表明：碲酸盐玻璃中Tm³⁺→Ho³⁺正向能量传递系数大约是Tm³⁺←Ho³⁺反向能量传递系数的18倍.Ho³⁺离子的⁵I₇能级的寿命为3.9ms，2.0μm处的最大发射截面为9.15×10^-21cm².在0.5mol% Tm₂O₃和0.15mol% Ho₂O₃共掺的碲酸盐玻璃中能获得2.0μm的最大增益.通过比较氟化物、碲酸盐和镓铋酸盐重金属氧化物等玻璃中Ho³⁺的量子效率η，σ_e×τ_m值和增益系数G(λ)等，发现Tm³⁺/Ho³⁺共掺碲酸盐玻璃是一种理想的2.0μm激光器用基质玻璃. 关键词： 2.0μm发光 能量传递 增益 碲酸盐玻璃     

高光强激发下Er3+/Yb3+共掺TiBa玻璃的绿光上转换发光

制备了Er3+Yb3+共掺微米级高折射率TiBa玻璃颗粒和微球,玻璃基材主要成分为TiO2BaCO3Ba(NO3)2CaCO3SiO2等,掺入1mol%Er2O3+3mol%Yb2O3.用976nm激光激发测量了它们的上转换绿光发射,发现当抽运功率大于30mW(功率密度约为1000W·cm-2)时,524nm峰的强度大于547nm峰的强度,随功率的增大,其强度差越来越大,实验判断,这是由于材料吸收抽运光而升温所致 关键词： 上转换发光 掺Er3+Yb3+玻璃 微球