A broadband-sensitive upconverter: Garnet-type Ca3Ga2Ge3O12 codoped with Er3+, Y3+, Li+, Ni2+, and Nb5+

We have developed a new broadband-sensitive photon upconversion (UC) material that can be used for transparent ceramic plates mounted on the rear faces of crystalline silicon solar cells. We selected the host material of a cubic crystal structure codoped with Er³⁺ and Ni²⁺ so that the Ni²⁺ dopants were fully activated to sensitize the Er³⁺ emitters. In garnet-type Ca₃Ga₂Ge₃O₁₂ with additional codopants of Nb⁵⁺ and Li⁺ for charge compensation, all the Ni²⁺ dopants occupied the six-coordinated Ga³⁺ sites, leading to highly efficient energy transfer from the Ni²⁺ to the Er³⁺. Formation of four-coordinated Ni²⁺ that quenches the UC emission of the Er³⁺ was prevented, because Ni²⁺ cannot substitute the four-coordinated Ge⁴⁺ much smaller than Ni²⁺. Consequently, energy dissipation from the Er³⁺ to the Ni²⁺ was well reduced compared with the previously developed Gd₃Ga₅O₁₂:Er,Ni,Nb in which the Ni²⁺ dopants partially occupied the four-coordinated Ga³⁺ sites. Additional introduction of Y³⁺ and Li⁺ enhanced optical transitions and improved the UC performance, owing to more enhanced lattice distortion, along with eliminating different phases. The optimal composition (Ca_0.6Er_0.1Y_0.1Li_0.2)₃(Ga_0.98Ni_0.01Nb_0.01)₂Ge₃O₁₂ exhibited a broadband sensitivity ranging from 1.1 μm (the absorption edge of silicon) to 1.6 μm for the UC emission at 0.98 μm.     

Er3+ cross-section spectra of Er3+/Pr3+:Gd3Ga5O12 single-crystal: Pr3+-codoping effect

Fluorescence and absorption spectra at 530 nm (²H_11/2→⁴I_15/2), 560 nm (⁴S_3/2→⁴I_15/2), 660 nm (⁴F_9/2→⁴I_15/2), 980 nm (⁴I_11/2→⁴I_15/2), 1530 nm (⁴I_13/2→⁴I_15/2), and 2710 nm (⁴I_11/2→⁴I_13/2) of Er³⁺ in Gd₃Ga₅O₁₂ single-crystal codoped with Pr³⁺ have been measured. Judd-Ofelt analysis yields the intensity parameters Ω₂ = (0.68 ± 0.03) × 10⁻²⁰ cm², Ω₄ = (0.60 ± 0.07) × 10⁻²⁰ cm², and Ω₆ = (0.90 ± 0.17) × 10⁻²⁰ cm². A comparison with previously reported values of Er³⁺-only doping case shows that Pr³⁺-codoping causes slight change of both Ω₂ and Ω₄, while onefold increase of Ω₆. From calculated radiative rates and measured fluorescence spectra, Er³⁺ emission cross-section spectra were calibrated at first. Then, the absorption cross-section spectra were calculated using McCumber relation. In parallel, the absorption cross-section spectra were also obtained from the measured absorption spectrum, and compared with those obtained from the McCumber relation. The comparison shows that both methods give consistent result of absorption cross-section spectrum. Further comparison with Er³⁺-only doping case shows that Pr³⁺-codoping causes considerable change of Er³⁺ cross-section value. In spectrally mixing regions of Er³⁺ and Pr³⁺, Pr³⁺ emission affects little the determination of Er³⁺ emission cross-section as Pr³⁺ fluorescence is much weaker than Er³⁺ fluorescence due to low Pr³⁺ concentration.     

Er3+:Yb3+:Y3Al5O12单晶中Er3+离子光谱参数的计算

采用提拉法生长出光学质量的Er3 :Yb3 :Y3Al5O12(YAG)单晶,测定了晶体的吸收光谱和上转换荧光光谱,根据Judd-Ofelt理论,计算出Er3 在YAG晶体中的强度参数Ω2=1.074 1×10-20cm2,Ω4=1.295 3×1020cm2,Ω6=0.923 8×1020cm2.由此得到部分波段跃迁的荧光分支比、辐射寿命和积分发射截面积.提出将679 nm波段的4F9/2→4I15/2跃迁作为激光输出进一步研究的新通道.     

Er3+和Yb3+共掺锗硅酸盐玻璃的上转换发光性能

采用熔融-淬火法制备了基体为30SiO2-20GeO2-15Al2O3-5B2O3-30CaF2的Er3+和Yb3+共掺锗硅酸盐玻璃.采用X射线衍射仪、荧光光谱仪和热分析仪对样品进行了表征.结果表明:Er2O3含量从0.5％(摩尔分数,下同)增加到2.0％时,玻璃转变温度Tg和Tx-Tg(Tx为第一析晶温度)数值均有明显下降.Yb2O3含量从1.5％增加到4.5％时,玻璃上转换红光发光强度数量级由103提高到105,对其中1个样品在740℃热处理12h后发现,微晶化处理并未对Er的上转换发光产生有益影响.     

Tunable upconversion luminescence in new Ho3+/Yb3+-doped SrBi4Ti4O15 photochromic ceramics for switching application

Upconversion (UC) luminescence modulation is quite important in controlling and processing light for active components of light sources, photoswitches, optical memories, and optical sensing devices. In this work, we reported one kind of novel phosphor, Ho³⁺/Yb³⁺-doped SrBi₄Ti₄O₁₅ ceramics, which displayed both strong UC luminescence and obvious photochromic (PC) reaction. The UC luminescence, PC effect, and the modulation of UC performance based on PC behavior were investigated in detail. By alternating visible light irradiation and thermal stimulus, the UC luminescence could be reversibly regulated. Meanwhile, the modulation was unveiled to tightly rely on the irradiation time and thermal treatment processes. Excellent reproducibility was also achieved. In addition, as an alternative method to thermal treatment, the manipulation of luminescence by electric field was also explored. Finally, the mechanism related to the UC luminescence manipulation was illustrated. The results indicate that these samples could be potentially utilized in optical data storage and anti-counterfeiting security fields.     

Green to red and NIR tunable luminescence in heavily Er3+-doped tellurite glasses via selective energy transfer mechanism

Here, we select simple Er³⁺-doped tellurite glass as model system to systematically explore the up-conversion, down-shifting mechanisms with different excitations (980 and 447 nm), respectively. We observe for the first time, to the best of our knowledge that tunable photo-luminescence occurs from green to red and NIR region, rather than merely from the long-accepted green to red region. Direct evidence of selective energy transfer mechanism is expounded in detail, and its potential applications are demonstrated. In addition, we provide evidence that the cross-relaxation process between dopant ions can enhance photo-luminescence in Er³⁺ doped tellurite glasses with high dopant concentrations, whereas the crucial reason for emission decrease is the energy loss long-distance energy migration. These fundamental insights into the photophysical processes in heavily doped photonic glasses will broaden the applications of rare-earth-doped materials ranging from optical communications to medical imaging.     

柠檬酸凝胶法制备Er,Tm∶Yb3Al5O12纳米粉体及发光性能

以柠檬酸为燃烧剂,采用柠檬酸凝胶法制备了Er,Tm∶Yb3Al5O12(Er,Tm:YbAG)纳米粉体,其最佳的制备工艺条件:Er3+和Tm3+掺杂的摩尔分数分别为2%和1%,柠檬酸与金属硝酸盐原子总数的摩尔比为1.7∶1,煅烧温度和时间分别为950℃和2h。制备的粉体颗粒为规则球形,粒径均匀、分散性好,平均粒径约为45nm。研究了样品的发光性能,结果表明:2%Er,1%Tm∶YbAG样品的发光性能最好,在1 587、1 658和1 711nm处有较强发射峰,分别对应Er3+的4 I13/2→4 I15/2跃迁和Tm3+的3 F4→3 H6跃迁。样品的上转换光谱表明,上转换荧光峰包括了蓝光、绿光和红光。     

Power dependent upconversion in Er3+/Yb3+ co-doped BiNbO4 phosphors

In the present article, optical properties and energy upconversion in Er³⁺/Yb³⁺ co-doped BiNbO₄ matrix were investigated. The BiNbO₄ matrix was prepared using the solid-state reaction method. X-ray diffraction of the matrix shows that the crystal structure is consistent with ICSD code 74338. The grain distribution and the behavior of doping with Er³⁺ and Yb³⁺ on the sample surface were obtained by scanning electron microscope. Raman spectral characterization was carried out to examine the behavior of the vibrational modes of the samples. Upconversion emissions in the visible region at 484.5, 522, 541.5 and 670.5 nm in the matrices BiNbO₄:Er,Yb and BiNbO₄:Er were observed and analyzed as a function of 980 nm laser excitation power and rare-earth doping concentration. The results show that BiNbO₄ is a promising host material for efficient upconversion phosphors.     

Yb3+/Er3+共掺碲钨酸盐玻璃的能量传递与频率上转换发光

在970nm LD激发和Er^3 离子浓度几乎不变情况下，研究了Yb^3 ／Er^3 共掺碲钨酸盐玻璃中的能量传递和其上转换发光特性。结果表明：随掺Yb^3 浓度的增加，Yb^3 ／Er^3 间能量传递效率也增加，其值在0．52到0．60之间。在Yb^3 ／Er^3 共掺碲钨酸盐玻璃中观察到峰值分别位于533，547nm和668nm的上转换绿光和红光，它们分别来源于Er^3 离子^2H11/2→^4I15／2(533nm)，^4S3／2→^4I15／2(547nm)和^4F9/2→^4I15／2(668nm)辐射跃迁。上转换红光和绿光均为双光子过程，且随Yb^3 离子掺杂浓度的增加，上转换红绿光强度和其强度比值Ic／Ig也增加，这被认为是与激发态Er^3 与激发态Yb^3 之间的能量传递过程有关。     

Enhanced near-infrared to green upconversion from Er3+-doped oxyfluoride glass and glass ceramics containing BaGdF5 nanocrystals

In this work, effect of glass composition as well as ceramization on visible and near-infrared (NIR) luminescence properties along with their decay dynamics of Er³⁺ ions has been compared considering two different oxyfluoride glasses yielding BaF₂ and BaGdF₅ nanocrystals. Both the glass systems have exhibited an intense normal and upconversion green emission under ultraviolet (378 nm) and NIR (978 nm) excitations, respectively. A remarkable enhancement of these emission intensities is observed for gadolinium-(Gd) containing glasses. Interestingly, NIR fluorescence intensity from Er³⁺ ions at 1540 nm has showed marginal decrease in gadolinium-containing glass which is attributed to occurrence of strong excited-state absorption (ESA) due to higher fluorine content ensuing an augmentation of upconversion green emission with a concomitant decrease in NIR emission. The quadratic dependence of upconversion green emission intensity on its pump power for all the samples revealed biphotonic absorption process from ground-state ⁴I_15/2 to the excited-state ⁴I_11/2 followed by ESA of second photon to the ⁴F_7/2 level. The intense green upconversion emission as well as enhanced NIR fluorescence lifetimes indicate the suitability of these glass/glass ceramics for upconversion lasers and amplification in the third telecom window.     

Effect of ligand field symmetry on upconversion luminescence in heat‐treated LaBGeO5:Yb3+, Er3+ glass

In this paper, we report upconversion (UC) luminescence enhancement in LaBGeO₅:Yb³⁺, Er³⁺ glass‐ceramics (GCs), surface crystallized glass‐ceramics (SCGCs) and ceramics compared with the as‐melt glass fabricated by the conventional melt‐quenching technique. Based on structural investigations, we find that the nucleation and crystallization of trigonal stillwellite LaBGeO₅:Yb³⁺, Er³⁺ nanocrystals occur first at the glass surface before the following volume crystallization. The local site symmetry around rare earth (RE) ions which was evaluated using the Eu³⁺ ions as a probe together with Judd‐Ofelt theory calculations exhibits a clear increase with the devitrification of the glass. Consequently, complete crystallization of the glass leads to largest enhancement in the UC emissions of the LaBGeO₅:Yb³⁺, Er³⁺ ceramics. We ascribe the enhancement of UC luminescence in the LaBGeO₅:Yb³⁺, Er³⁺ GCs, SCGCs, and ceramics to the structural ordering and the improvement of site symmetry surrounding RE ions that minimizes the rate of nonradiative relaxation process.     

铒镱共掺钆镓石榴石激光晶体生长及荧光光谱分析

采用提拉法生长了掺10%(摩尔分数,下同)Yb3+、掺Er3+分别为3%,5%和10%的Er3+:Yb3+:Gd3Ga5O12(Er:Yb:GGG)晶体。分析了Er:Yb:GGG晶体的结构和荧光光谱。结果表明:所生长的晶体属于立方晶系,Ia3d空间群。在980nm激光激发下,晶体样品在1000～1600nm范围内存在3个较强的发射带,相应的发射峰分别位于1030,1471nm和1534nm附近。由于Yb3+对Er3+的敏化作用,随着Er3+掺量的递增,1030nm处的发射峰强度逐渐减弱,1471nm和1534nm处的发射峰强度逐渐增强。计算了各个发射峰的受激发射截面积,铒和镱离子掺量为10%的晶体(10%Er:10%Yb:GGG)的受激发射截面高达2.0073×10–18cm2,可以产生较强的1534nm人眼安全波段的激光。     

Halogen-content-dependent photoluminescence of Mn2+-doped CsPbCl3 nanocrystals

The thermodynamically viable halogen vacancy defects in CsPbCl₃ perovskite nanocrystals (NCs) are considered the main factor in weakening their optical quality. However, their separate impact on the dopant emission in Mn²⁺-doped CsPbCl₃ perovskite NCs is still under exploration owing to the absence of comparable samples. Herein, a series of Mn²⁺-doped CsPbCl₃ samples were synthesized with different oleylamine-Cl (OAm-Cl) contents based on a halogen-hot-injection strategy. It is found that the Mn²⁺ concentration of as-prepared samples fixed at 0.65%, and the Mn²⁺ photoluminescence (PL) also exhibited an OAm-Cl content-independent lifetime of ∼ 1.78 ms, implying the efficient and identical luminescence of isolated Mn²⁺ ion in all samples. In contrast, the excitonic and Mn²⁺ PL intensities of the NCs are strong related to the amount of OAm-Cl, which are attributed to the coordination effect of the suppressed excitonic nonradiative recombination owing to the passivation of chloride vacancies and the enhanced energy transfer from the host exciton to Mn²⁺ ions in the samples with sufficient OAm-Cl contents. The temperature-dependent of Mn²⁺ PL disclosed an initial increase and was followed by a decrease with increasing temperature for the samples with relatively higher OAm-Cl contents, while it monotonously decreases for the sample with lower OAm-Cl content of 0.4 mL. The different PL intensity change trend results from the effective passivation of chloride vacancies by extra OAm-Cl. Above results present here will help clarify the underlying influence mechanism of halogen vacancy on the PL properties of Mn²⁺-doped perovskite NCs, which is essential for targeted modulation of their optical properties.     

Phase evolution in Bi2O3:Yb3+/Er3+ nanoparticles with nearly single-band red upconversion luminescence

Bi₂O₃:Yb³⁺/Er³⁺ nanoparticles with flower-like morphology were easily synthesized by urea-assisted coprecipitation reactions. The influences of calcination temperature and doping concentration on the crystal phase structures of Bi₂O₃ and Bi₂O₃:x%Yb³⁺/2%Er³⁺ (x = 0–30) were systematically investigated by XRD analysis. The experimental results revealed that lanthanide doping could effectively improve the thermal stability of Bi₂O₂CO₃ samples, and the monoclinic-to-tetragonal-to-cubic phase transitions of Bi₂O₃ were implemented by controlling calcination temperatures and introducing smaller lanthanide ions (Ln³⁺) into the host lattices. Based on the analysis of TG and DSC curves, we found that the fundamental reason for this phase transition was the different stabilities of each crystalline phase under different doping conditions. Upon 980 nm laser excitation, Bi₂O₃:x%Yb³⁺/2%Er³⁺ samples presented near single-band red upconversion emission owing to the efficient energy reabsorption of the Bi₂O₃ host to Er³⁺ emission.     

Luminescent Er3+ doped transparent alumina ceramics

We report on successful preparation of Er³⁺ doped transparent alumina (0.1–0.17 at.%) exhibiting visible light photoluminescence using wet shaping method and hot isostatic pressing. The effects of dopant amount, type of doping powder and powder pre-treatment on final microstructure, real in-line transmittance and photoluminescence characteristics were studied.The real in-line transmittance ranged between 28 and 56%, depending on processing parameters. The transparency decreased with increased amount of dopant. The decrease is dependent on the type of doping powder and its pre-treatment.The photoluminescence spectra measured in both visible and NIR region showed typical emission bands due to the presence of Er³⁺ ions. The decay profiles of the ⁴S_3/2 → ⁴I_15/2 transition were fitted with a 2-exponential function, with faster component in the range of 360–700 ns and slower component around 1.6-2.4 μs. The intensity of emissions and lifetime of the ⁴S_3/2 level decrease significantly with increasing concentration of Er³⁺ ions.     

Multifunctional optical thermometry based on the stark sublevels of Er3+ in CaO-Y2O3: Yb3+/Er3+

A conventional high temperature solid state method was utilized to prepare CaO-Y₂O₃, which is a potential candidate for manufacturing crucible material to melt titanium and titanium alloys with low cost. Meanwhile, Yb³⁺ ions and Er³⁺ ions were selected as the sensitizers and activators respectively to dope into CaO-Y₂O₃, aimed at providing real-time optical thermometry during the preparation process of titanium alloys realized using fluorescence intensity ratio (FIR) technology. The results reveal that a high measurement precision can be acquired by using the Stark sublevels of Er^{3+ 4}F_9/2 to measure the temperature with a maximum absolute error of only about 3 K. In addition, by analyzing the dependence of ⁴I_13/2 → ⁴I_15/2 transition on pump power of 980 nm excitation wavelength, it was found that the laser-induced thermal effect has almost no influence on the temperature measurement conducted by using the FIR of the Stark sublevels of Er^{3+ 4}I_13/2, which means that a high excitation pump power can be used to obtain strong NIR emission and good signal-to-noise ratio for optical thermometry without the influence of the laser-induced thermal effect. All the results reveal that CaO-Y₂O₃: Yb³⁺/Er³⁺ is an excellent temperature sensing material with high measurement precision.     

Production and optical properties of Ce3+-activated and Lu3+-stabilized transparent gadolinium aluminate garnet ceramics

We first report the novel Ce³⁺-activated and Lu³⁺-stabilized gadolinium aluminate garnet (GAG) transparent ceramics derived from their precipitation precursors via a facile co-precipitation strategy using ammonium hydrogen carbonate (AHC) as the precipitant. The resulting precursors in liquid phase were substantially homogeneous solid solutions and could directly convert into sinterable garnet powders via pyrolysis. Substituting 35 at.% of Lu³⁺ for Gd³⁺ was effective to stabilize the cubic GAG garnet structure and transparent (Gd,Lu)₃Al₅O₁₂:Ce ceramics were successfully fabricated by vacuum sintering at 1715°C. The ceramic transparency was improved by optimizing the particle processing conditions and the best sample had an in-line transmittance of ~70% at 580 nm (Ce³⁺ emission center) and over 80% in partial infrared region with a fine average grain size of ~4.5 μm. Transparent (Gd,Lu)₃Al₅O₁₂:Ce ceramics have a short critical wavelength (<200 nm) and a maximal infrared cut-off at ~6.6 μm. Both the (Gd,Lu)₃Al₅O₁₂:Ce phosphor powder and the transparent ceramic exhibited characteristic yellow emission of Ce³⁺ with strong broad emission bands from 490 to 750 nm upon UV excitation into two groups of broad bands around 340 and 470 nm. The photoluminescence and photoluminescence excitation intensities as well as the quantum yield were greatly enhanced via high-temperature densification. Both the phosphor powder and ceramic bulk had short effective fluorescence lifetimes.     

Bright red upconversion luminescence from Er3+ and Yb3+ co-doped ZnO-TiO2 composite phosphor powder

ZnO-TiO₂ composites co-doped with Er³⁺ and Yb³⁺ ions were successfully synthesized by powder-solution mixing method and their upconversion (UC) luminescence was evaluated. The effect of firing temperature, ZnO/TiO₂ mixing ratio, and dopant concentration ranges on structural and UC luminescence properties was investigated. The crystal structure of the product was studied and calculated in detail by means of X-ray diffraction (XRD). Also, the site preference of Er³⁺ and Yb³⁺ ions in the host material was considered and analyzed based on XRD results and UC luminescence characteristics. Brightest UC luminescence was observed in the ZnO-TiO₂:Er³⁺,Yb³⁺ phosphor fired at 1300 °C in which the system consisted of mixed phases; Zn₂TiO₄, TiO₂, RE₂Ti₂O₇ and RE₂TiO₅ (RE = Er³⁺ and/or Yb³⁺). Under the excitation of a 980 nm laser, the two emission bands were detected in the UC emission spectrum, weak green band centered at 544 and 559 nm, and strong red band centered at 657 and 675 nm wavelengths in accordance with ²H_11/2, ⁴S_3/2 → ⁴I_15/2 and ⁴F_9/2 → ⁴I_15/2 transitions of Er³⁺ ion, respectively. The simple chemical formula equations, for explaining the site preference of Er³⁺ and Yb³⁺ ions in host crystal matrix, were generated by considering the Zn₂TiO₄ crystal structure, its crystal properties, and the effect of Er³⁺ and Yb³⁺ ions to the host crystal matrix. The UC emission intensity of the products was changed by varying ZnO/TiO₂ mixing ratios, and Er³⁺ and Yb³⁺ concentrations. The best suitable condition for emitting the brightest UC emission was 1ZnO:1TiO₂ doped with 3 mol% Er³⁺, 9 mol% Yb³⁺ fired at 1300 °C for 1 h.     

NIR photoluminescence and radioluminescence characteristics of Nd3+ doped BaTa2O6 phosphor

Barium tantalate phosphors activated with different concentrations of Nd³⁺ ion were synthesized via conventional solid state reaction method. The synthesized ceramic powders were characterized by X–ray diffraction (XRD), scanning electron microscopy‐energy dispersive spectroscopy (SEM‐EDS), laser diode (LD) excited near infrared (NIR) photoluminescence and X‐ray induced radioluminescence (RL) analyses. In XRD results, Nd³⁺ doped BaTa₂O₆ structure with tetragonal tungsten bronze (TTB) symmetry was observed to continue up to 10 mol%. In the examination of ceramic powders by SEM, grain size decreased with the increasing doping concentration. By using laser diode excited NIR photoluminescence of BaTa₂O₆:Nd³⁺ phosphor exhibited characteristic emissions at 877, 1080, and 1376 nm wavelengths due to ⁴F_3/2 → ⁴I_11/2, ⁴F_3/2 → ⁴I_11/2, and ⁴F_3/2 → ⁴I_11/2 band transitions respectively. Scintillation properties of Nd³⁺ doped samples from UV to near‐IR spectral region were carried out by the radioluminescence analysis. NIR and scintillation emissions initially increased by the doping concentration, and then decreased due to concentration quenching effect.     

Dy3+-doped Y3Al5O12 transparent ceramic for high efficiency ultraviolet excited single-phase white-emitting phosphor

A kind of Dy-doped yttrium aluminum garnet (YAG) transparent ceramic for ultraviolet excited single-phase white light-emitting phosphor was investigated, which has high-quantum efficiency (45%). The temperature field of Dy:YAG transparent ceramic was calculated by steady-state thermal simulation. Moreover, by combining with 365 nm light-emitting diodes (LED) chip directly, the Commission Internationale de l’Éclairage coordinate (x = 0.33, y = 0.35) is close to the standard equal energy white light illumination. The Dy:YAG transparent ceramic, possessing of good optical and thermal properties, is promising for applications in high-power LEDs devices.