Luminescent properties of SrBPO5:Dy3+ and effect of Co-doping with Tm3+

A series of phosphors SrBPO₅:Dy³⁺ and SrBPO₅:Dy³⁺,Tm³⁺ was synthesized by traditional solid-state high-temperature method and was characterized by X-ray diffraction (XRD) and fluorescence spectrophotometry. For SrBPO₅:Dy³⁺ material, the f-f transitions of Dy³⁺ ions were assigned and discussed, and the optimal doping concentration of Dy³⁺ was found. As a result of co-doping SrBPO₅:Dy³⁺ with Tm³⁺, the phosphors SrBPO₅:Dy³⁺,Tm³⁺ can be effectively excited by 360 nm ultraviolet (UV), and exhibit color-tunable emission from blue to yellowish-white region with different doping concentration. The present study can pave the way for the creation of efficient UV phosphors using Dy³⁺,Tm³⁺ co-doped systems for near-UV InGaN-based light emitting diodes (LEDs).     

颜色可调Sr3Y（BO3）3∶Tm3+，Dy3+荧光粉的发光性能及能量传递

采用高温固相法制备了Sr_3Y(BO_3)_3:xTm~(3+),yDy~(3+)荧光粉,并通过XRD、SEM和荧光光谱仪对样品的物相、微观形貌、发光性能、能量传递机制和CIE色坐标进行了分析。结果表明:Sr_3Y(BO_3)_3:xTm~(3+)荧光粉在监测波长为359 nm时发射蓝光,Tm~(3+)的浓度淬灭点为x=0.08;在Sr_3Y(BO_3)_3:0.08Tm~(3+),yDy~(3+)荧光粉中,随着Dy~(3+)掺杂浓度的增加,Tm~(3+)的发光强度降低而Dy~(3+)发光强度却先增加后降低,Dy~(3+)的浓度淬灭点为y=0.1;通过改变Dy~(3+)掺杂浓度或改变激发光的波长,均可实现发射光的颜色可调;在Tm~(3+)-Dy~(3+)离子之间存在能量传递。当Dy~(3+)掺杂浓度(物质的量分数)为0.15时能量传递效率达75.14%,能量传递机制为电偶极-电偶极相互作用。     

Luminescence properties of Dy3+ or/and Sm3+ doped LiLa(WO4)2 phosphors and energy transfer from Dy3+ to Sm3+

The Dy³⁺ or/and Sm³⁺ doped LiLa(WO₄)₂ phosphors are synthesized by a facile solid state reaction method. The phase and luminescence properties of the phosphors are investigated. The powder X-ray diffraction (XRD) results show that the phosphor has a tetragonal phase crystal structure. The quenching concentration of single doped Dy³⁺ and Sm³⁺ in the LiLa(WO₄)₂ are determined to be 6% and 3%, respectively. Under the excitation of 404 nm, warm white light is obtained in the co-doped phosphors. With the concentration of Sm³⁺ increasing, the correlated color temperature (CCT) gradually decreases from 3090 to 2453 K. Two kinds of energy transfer may exist at the same time. The overlap between the emission spectrum of Dy³⁺ and the excitation spectrum of Sm³⁺ reveals that the energy of Dy³⁺ can transfer to Sm³⁺ via radiation. Another way of energy transfer, that is non-radiative energy transfer, is attributed to the excited state of Dy³⁺ (⁴F_9/2) slightly higher than that of Sm³⁺ (⁴I_19/2). The calculation results show that non-radiative energy transfer process from Dy³⁺ to Sm³⁺ ions is predominated by quadrupole–quadrupole interaction.     

Photoluminescence properties of rare earths (Eu3+, Tb3+, Dy3+ and Tm3+) activated NaInW2O8 wolframite host lattice

The photoluminescence (PL) studies on NaIn_1?xRE_xW₂O₈, with RE=Eu³⁺, Tb³⁺, Dy³⁺ and Tm³⁺ phases have shown that the relative contribution of the host lattice and of the intra-f–f emission of the activators to the PL varies with the nature of the rare earth cation. In the case of Dy³⁺ and Tm³⁺ activators, with yellow and blue emission, respectively, the energy transfer from host to the activator plays a major role. In contrast for Eu³⁺, with intense red emission, the host absorption is less pronounced and the intra-f–f transitions of the Eu³⁺ ions play a major role, whereas for Tb³⁺ intra-f–f transitions are only observed, giving rise to green emission.     

White light emission from Tm/Dy co-doped oxyfluoride germanate glasses under UV light excitation

In this paper, we report on the absorption and photoluminescence properties of Tm³⁺/Dy³⁺ ions co-doped oxyfluoride germanate glasses for white light emission. The X-ray diffraction (XRD) and differential thermal analysis (DTA) profiles of the host glass have been carried out to confirm its structure and thermal stability. From the measured absorption spectra, Judd-Ofelt (J-O) intensity parameters (Ω₂, Ω₄ and Ω₆) have been evaluated for Tm³⁺ and Dy³⁺ ions. A combination of blue, yellow and red emissions has emerged in these glasses, which allows the observation of bright white light when the glasses are excited by the ultraviolet light. The white light luminescence colour could be changed by varying the excitation wavelength. Also, various colours of luminescence, including white light, can be easily tuned by adjusting the concentrations of Tm³⁺ or Dy³⁺ ions in the co-doped glasses. Concentration quenching effect was also investigated and possible energy transfer mechanism from Dy³⁺→Tm³⁺ ions was explained which is also confirmed by the decay lifetime measurements.     

Novel red-emitting phosphors, (Mg(1−x−y)MnxDyy)Al2Si2O8 and (Mg(1−x−y)MnxTmy)Al2Si2O8

Mn⁴⁺ doped and Dy³⁺, Tm³⁺ co-doped MgAl₂Si₂O₈-based phosphors were prepared by conventional solid state reaction at 1,300 °C. They were characterized by thermogravimetry, differential thermal analysis, X-ray powder diffraction, photoluminescence, and scanning electron microscopy. The luminescence mechanism of the phosphors, which showed broad red emission bands in the range of 600–715 nm and had a different maximum intensity when activated by UV illumination, was discussed. Such a red emission can be attributed to the ²E → ⁴A₂ transitions of Mn⁴⁺.     

Er3+-Tm3+-Yb3+ tri-doped CaMoO4 upconverting phosphors in optical devices applications

The structural and optical properties of the Er³⁺-Tm³⁺-Yb³⁺codoped CaMoO₄ phosphors prepared by chemical route have been explored. The crystalline structures of the prepared phosphors have been investigated with the help of X-ray diffraction analysis. The presence of different vibrational modes and absorption bands arising due to the transitions from the ground state to different excited states of rare earth ions have been identified using the Raman and UV-VIS-NIR absorption spectra of the developed phosphor, respectively. The concentration quenching effect on the luminescence property of the prepared materials has been explained in detail. The upconversion luminescence property of the Er³⁺-Tm³⁺-Yb³⁺codoped CaMoO₄ phosphor annealed at different temperatures under 980 nm and 808 nm excitations have been reported. The energy transfer Er³⁺ → Tm³⁺, Yb³⁺ → Er³⁺ and Tm³⁺ has been found to be responsible for efficient UC emission. The dipole-dipole interaction is observed to be responsible for the concentration quenching of the luminescence intensity. The effect of annealing temperature on the upconversion luminescence property has been explained in detail. The results suggest that the developed tri-doped phosphor may be suitable in making the efficient NIR to visible upconverter and lighting based optical devices.     

Tunable white light-emission of a CaW1?x Mo x O4:Tm3+, Tb3+, Eu3+ phosphor prepared by a Pechini sol–gel method

A white light-emitting CaW_1?x Mo _x O₄:Tm³⁺, Tb³⁺, Eu³⁺ phosphor was prepared by a Pechini sol?Cgel method. The incorporation of Mo⁶⁺ into the CaWO₄ host matrix can broaden its excitation range and promote tunability to its emission. When the CaW_1?x Mo _x O₄ system is triply-doped with Tm³⁺, Tb³⁺, and Eu³⁺ ions, energy transfer occurs from both WO₄ ^2? and MoO₄ ^2? groups to Tm³⁺ and Tb³⁺ ions. A significant red-shift in the excitation of Eu³⁺ allows the resulting emission to be tunable between cool, natural, and warm white light by varying the excitation wavelength. The undoped and triply-doped CaW_1?x Mo _x O₄ phosphors were characterized by X-ray diffraction, scanning electron microscopy, photoluminescence excitation and emission spectra, and CIE chromaticity (x, y) coordinates.     

Enhanced photoluminescence of Ba2GdNbO6: Eu/Dy phosphors by Li doping

The Ba₂GdNbO₆: Eu³⁺/Dy³⁺ and Li⁺-doped Ba₂GdNbO₆: Eu³⁺/Dy³⁺ phosphors were prepared by solid-state reaction process. X-ray diffraction (XRD), field emission scanning electron microscopy (FE-SEM) and photoluminescence (PL) as well as lifetimes, was utilized to characterize the resulting phosphors. Under the excitation of ultraviolet light, the Ba₂GdNbO₆: Eu³⁺/Dy³⁺ and Li⁺-doped Ba₂GdNbO₆: Eu³⁺/Dy³⁺ show the characteristic emissions of Eu³⁺ (⁵D₀-⁷F_1,2,3 transitions dominated by ⁵D₀-⁷F₁ at 593 nm) and Dy³⁺ (⁴F_9/2-⁶H_15/2,_13/2 transitions dominated by ⁴F_9/2-⁶H_15/2 at 494 nm), respectively. The incorporation of Li⁺ ions into the Ba₂GdNbO₆: Eu³⁺/Dy³⁺ phosphors has enhanced the PL intensities depending on the doping concentration of Li⁺, and the highest emission was obtained in Ba₂Gd_0.9NbO₆: 0.10Eu³⁺, 0.01Li⁺ and Ba₂Gd_0.95NbO₆: 0.05Dy³⁺, 0.07Li⁺, respectively. An energy level diagram was proposed to explain the luminescence process in the phosphors.     

Energy Transfer from Ce3+ to Tb3+/Dy3+/Mn2+ in Ca9Ga(PO4)7 Phosphors: Synthesis,Structure and Tunable Multicolor Luminescent Properties

A series of Ca₉Ga(PO₄)₇:Ce³⁺/Tb³⁺/Dy³⁺/Mn²⁺ phosphors with tunable color, in which Ce³⁺ acts as the sensitizer, was synthesized. Energy transfer (ET) from Ce³⁺ to Tb³⁺/Dy³⁺/Mn²⁺ was investigated in detail. Tb³⁺/Dy³⁺/Mn²⁺ single-doped Ca₉Ga(PO₄)₇ can exhibit green, yellow, and red emission, respectively. Incorporating Ce³⁺ into a Tb³⁺/Dy³⁺/Mn²⁺ single-doped Ca₉Ga(PO₄)₇ phosphor can remarkably promote the luminous efficiency of the Tb³⁺/Dy³⁺/Mn²⁺ ions. This enhancement originates from an efficient ET from Ce³⁺ to Tb³⁺/Dy³⁺/Mn²⁺. The ET was validated by luminescence spectra, decay dynamics, and schematic energy levels. Moreover, the intensity ratio of red emission of Mn²⁺ to violet emission of Ce³⁺ was analyzed based on energy-transfer and lifetime measurements. In Ce³⁺-Tb³⁺, Ce³⁺-Dy³⁺, and Ce³⁺-Mn²⁺ doped Ca₉Ga(PO₄)₇, the emitting color changed from violet to green, yellow, and red, respectively, which indicates the potential use of this new tunable phosphor in UV light-emitting diodes.     

Microwave synthesis and photoluminescent properties of Sr2CeO4/Ln3+ (Ln = Er, Ho, Tm)

Sr₂CeO₄/Ln³⁺ (Ln = Er, Ho, Tm) phosphors were synthesized with the microwave radiation method for the first time. The luminescent properties of the samples were investigated and the up-conversion luminescence of Er³⁺, Ho³⁺ and Tm³⁺ doped Sr₂CeO₄ phosphors was observed. The spectra indicate that the energy transfer takes place from the triplet excited state of MLCT (metal-to-ligand charge transfer) state for Sr₂CeO₄ (sensitizer) to the rare earth ions (activator). __________ Translated from Journal of Hebei Normal University (Natural Science Edition), 2007, 31(2): 212–216 [译自: 河北师范大学学报 (自然科学版)]     

Reddish-orange,neutral and warm white emissions in Eu3+, Dy3+ and Dy3+/Eu3+ doped CdO-GeO2-TeO2 glasses

Eu³⁺, Dy³⁺ and Dy³⁺/Eu³⁺ doped CdO-GeO₂-TeO₂ glasses were prepared using the melt-quenching process and analyzed by X-diffraction, Raman spectroscopy, excitation and emission spectra, and emission decay time profiles. The lack of X ray diffraction peaks revealed that all samples are amorphous. Vibrational modes associated with TeOTe and GeOGe related bonds and molecular oxygen were detected by Raman spectroscopy. The luminescence characteristics were studied upon excitations that correspond with the emission of InGaN (370–420 nm) based LEDs. The Eu³⁺ singly doped glass displayed reddish-orange global emission, with x = 0.601 and y = 0.349 CIE1931 chromaticity coordinates, upon 393 nm excitation. Neutral emission with x = 0.373 and y = 0.412 CIE1931 chromaticity coordinates and correlated color temperature (CCT) of 4400 K, was achieved in the Dy³⁺ singly doped glass excited at 388 nm. The Dy³⁺/Eu³⁺ co-doped glass exhibited warm, neutral and soft warm white emissions with CCT values of 3435, 4153 and 2740 K, under excitations at 382, 388 and 393 nm, respectively, depending mainly on the Dy³⁺ and Eu³⁺ relative excitation. The Dy³⁺ excitation bands observed in the Dy³⁺/Eu³⁺ glass by monitoring the 611 nm Eu³⁺ emission, suggest that Dy³⁺ → Eu³⁺ energy transfer takes place, despite the fact that the Dy³⁺ emission decays in the Dy³⁺ and Dy³⁺/Eu³⁺ doped glass, remain without changes. The shortening of Eu³⁺ decay in presence of Dy³⁺ was attributed to an Eu³⁺ → Dy³⁺ non-radiative energy transfer process, which according with the Inokuti-Hirayama model might be dominated through an electric quadrupole-quadrupole interaction, with efficiency and probability of 5.5% and 51.6 s⁻¹, respectively.     

Upconversion Luminescence through Cooperative and Energy-Transfer Mechanisms in Yb3+-Metal-Organic Frameworks

Lanthanide-doped metal–organic frameworks (Ln-MOFs) have versatile luminescence properties, however it is challenging to achieve lanthanide-based upconversion luminescence in these materials. Here, 1,3,5-benzenetricarboxylic acid (BTC) and trivalent Yb³⁺ ions were used to generate crystalline Yb-BTC MOF 1D-microrods with upconversion luminescence under near infrared excitation via cooperative luminescence. Subsequently, the Yb-BTC MOFs were doped with a variety of different lanthanides to evaluate the potential for Yb³⁺-based upconversion and energy transfer. Yb-BTC MOFs doped with Er³⁺, Ho³⁺, Tb³⁺, and Eu³⁺ ions exhibit both the cooperative luminescence from Yb³⁺ and the characteristic emission bands of these ions under 980 nm irradiation. In contrast, only the 497 nm upconversion emission band from Yb³⁺ is observed in the MOFs doped with Tm³⁺, Pr³⁺, Sm³⁺, and Dy³⁺. The effects of different dopants on the efficiency of cooperative luminescence were established and will provide guidance for the exploitation of Ln-MOFs exhibiting upconversion.     

CaWO4:xEu3+,ySm3+,zLi+红色荧光粉的制备及光学性能

采用微波固相法制备了CaWO₄：xEu³⁺,ySm³⁺,zLi⁺红色荧光粉。测量样品的XRD图、激发谱、发射谱及发光衰减曲线,研究并分析了Eu³⁺、Sm³⁺、Li⁺的掺杂浓度,对样品微结构、光致发光特性、能量传递及能级寿命的影响。结果表明,Eu³⁺、Sm³⁺、Li⁺掺杂并未引起合成粉体改变晶相,仍为CaWO₄单一四方晶系结构。Eu³⁺、Sm³⁺共掺样品中,Sm³⁺掺杂为3%时,Sm³⁺对Eu³⁺的能量传递最有效。Li⁺掺杂起到了助熔剂和敏化剂的作用,使样品发光更强。在394 nm激发下,与CaWO₄：3%Eu³⁺样品比较,3%Eu³⁺、3%Sm³⁺共掺CaWO₄及3%Eu³⁺、3%Sm³⁺、1%Li⁺共掺CaWO₄样品的发光分别增强2倍及2.4倍。同一激发波长下,单掺Eu³⁺样品寿命最短,Sm³⁺、Eu³⁺共掺样品随Sm³⁺浓度增加,寿命先减小后增加,且掺杂了Li⁺的样品比不掺Li⁺的样品⁵D₀能级寿命有所增加。     

Rare-earth-doped glasses for fiber amplifiers in broadband telecommunication

Rare-earth-doped optical amplifiers have a great potential for broadband Wavelength-Division-Multiplexed (WDM) telecommunication by tailoring host glass compositions. In order to design the emission spectra of doped rare-earth ions, it is important to understand the relationship between the local ligand field and various optical properties of specific 4f-levels, such as the radiative transition probability, the nonradiative decay probability, which dominate the spectral line width and quantum efficiency of amplification transitions. For the Er³⁺:1.55 μm transition, the role of the Judd–Ofelt Ω₆ parameters is presented, which is correlated to the Er–ligand bond covalency in glasses. The Tm³⁺: 1.46-μm transition shows quantum efficiency over 90% high enough for the S-band application, in heavy metal oxide glasses with moderate phonon energy and wider spectra than fluorides. A way to improve population inversion by selective energy transfer with codoped lanthanide ions is presented. Finally, the energy level structures and resultant spectral properties of Pr³⁺, Nd³⁺ and Dy³⁺ ions, 1.3-μm-active ions, are compared. The hypersensitivity of Dy³⁺ transitions appears especially in chalcogenide glasses, where the nonradiative loss due to multiphonon decay is also minimized. In conclusion, glass materials have opportunities to vary the radiative cross section, quantum efficiency, and gain flatness, which are important for novel amplifiers in the future DWDM system.     

Luminescence in La3TaO4Cl6

The luminescence properties of La₃TaO₄Cl₆ are reported and discussed. The rare earth ions Sm³⁺, Eu³⁺, Tb³⁺, Dy³⁺, and Tm³⁺ show characteristic absorption and emission lines. For Sm³⁺ and Eu³⁺, broad absorption bands are also observed and are attributed to charge-transfer transitions. The line emissions of Tb³⁺ are only from ⁵D₄, even at low (1 at.%) concentration. Broad excitation and emission bands were observed with In³⁺. These bands are attributed to In³⁺Ta⁵⁺ → In⁴⁺Ta⁴⁺ charge-transfer transitions. An additional broad absorption at 250 and 280 nm leading to broad emission at 410 nm is ascribed to OH⁻ impurities.     

Vacuum ultraviolet and near-infrared excited luminescence properties of Ca3(PO4)2:RE, Na (RE=Tb, Yb, Er, Tm, and Ho)

Tb³⁺, Yb³⁺, Tm³⁺, Er³⁺, and Ho³⁺ doped Ca₃(PO₄)₂ were synthesized by solid-state reaction, and their luminescence properties were studied by spectra techniques. Tb³⁺-doped samples can exhibit intense green emission under VUV excitation, and the brightness for the optimal Tb³⁺ content is comparable with that of the commercial Zn₂SiO₄:Mn²⁺ green phosphor. Under near-infrared laser excitation, the upconversion luminescence spectra of Yb³⁺, Tm³⁺, Er³⁺, and Ho³⁺ doped samples demonstrate that the red, green, and blue tricolored fluorescence could be obtained by codoping Yb³⁺-Ho³⁺, Yb³⁺-Er³⁺, and Yb³⁺-Tm³⁺ in Ca₃(PO₄)₂, respectively. Good white upconversion emission with CIE chromaticity coordinates (0.358, 0.362) is achieved by quadri-doping Yb³⁺-Tm³⁺-Er³⁺-Ho³⁺ in Ca₃(PO₄)₂, in which the cross-relaxation process between Er³⁺ and Tm³⁺, producing the ¹D₂-³F₄ transition of Tm³⁺, is found. The upconversion mechanisms are elucidated through the laser power dependence of the upconverted emissions and the energy level diagrams.     

Photoluminescent properties of white-light-emitting Li6Y(BO3)3:Dy3+ phosphor

In this study, lithium yttrium borate (LYBO) phosphor was doped with various concentrations of trivalent dysprosium ions. To produce these phosphors, the raw materials were sintered. The phase conformation, crystallinity, grain size, and overall morphology of the synthesized phosphors were studied with X-ray diffraction and scanning electron microscopy. The optimized LYBO phosphor, i.e., the LYBO phosphor that exhibited the highest X-ray- and ultraviolet (UV)-induced photoluminescent intensities, had a Dy³⁺ concentration of 4 mol%. Photoluminescence analysis showed that this phosphor could be easily excited with near-UV light (300–400 nm). The dominant photoluminescence bands were found in the blue (480 nm) and yellow (577 nm) regions of the visible spectrum. The light yield of the X-ray-induced luminescence of the optimized Li₆Y(BO₃)₃:Dy³⁺ was found to be 66% of that of the commercially available X-ray imaging material, Gd₂O₂S:Tb³⁺ (GOS). The chromaticity coordinates of the Li₆Y(BO₃)₃:Dy³⁺ phosphor were x = 0.34 and y = 0.32, which agree well with achromatic white (x = 0.33, y = 0.33). The results of this study show that the synthesized Li₆Y(BO₃)₃:Dy³⁺ phosphor could be used as X-ray imaging material.     

不同掺杂浓度Tm3+：LiLuF4单晶的1800 nm荧光发射

采用坩埚下降法生长了Tm³⁺掺杂浓度为0.45%,0.90%,1.63%与3.25%（摩尔分数,x）的LiLuF₄单晶.测试了样品的电感耦合等离子体原子发射光谱（ICP-AES）、X射线衍射（XRD）谱、吸收光谱（1400-2000 nm）,并且分析比较了808 nm半导体激光器（LD）激发下荧光光谱. 结果表明：当Tm³⁺的浓度从0.45%变化到3.25%时,1800 nm处的荧光强度呈现了先增后减的趋势,当掺杂浓度约为0.90%时达到最大值,而位于1470 nm处的荧光强度则呈现了相反的趋势. Tm³⁺：³F₄能级的荧光衰减寿命随着掺杂浓度的增加不断减小. 1800 nm处的这种荧光强度变化归结于Tm³⁺离子间的交叉驰豫效应（³H₆,³H₄→³F₄,³F₄）和自身的浓度猝灭效应. 同时计算得到了浓度为0.90%的样品在1890 nm处的最大发射截面为0.392×10^-20 cm². 并且根据Judd-Ofelt 理论所得寿命和测定的荧光寿命计算得到了³F₄→³H₆的最大量子效率约为120%.     

Synthesis,Structure, and Photoluminescence Properties of Novel KBaSc2(PO4)3:Ce3+/Eu2+/Tb3+ Phosphors for White‐Light‐Emitting Diodes

A series of novel KBaSc₂(PO₄)₃:Ce³⁺/Eu²⁺/Tb³⁺phosphors are prepared using a solid‐state reaction. X‐ray diffraction analysis and Rietveld structure refinement are used to check the phase purity and crystal structure of the prepared samples. Ce³⁺‐ and Eu²⁺‐doped phosphors both have broad excitation and emission bands, owing to the spin‐ and orbital‐allowed electron transition between the 4f and 5d energy levels. By co‐doping the KBaSc₂(PO₄)₃:Eu²⁺ and KBaSc₂(PO₄)₃:Ce³⁺ phosphors with Tb³⁺ ions, tunable colors from blue to green can be obtained. The critical distance between the Eu²⁺ and Tb³⁺ ions is calculated by a concentration quenching method and the energy‐transfer mechanism for Eu²⁺→Tb³⁺ is studied by utilizing the Inokuti–Hirayama model. In addition, the quantum efficiencies of the prepared samples are measured. The results indicate that KBaSc₂(PO₄)₃:Eu²⁺,Tb³⁺ and KBaSc₂(PO₄)₃:Ce³⁺,Tb³⁺ phosphors might have potential applications in UV‐excited white‐light‐emitting diodes.