Green Upconversion Luminescence Research Articles

Effect of Li+ ions doping on microstructure and upconversion luminescence of CeO2:Er3+ translucent ceramics

CeO2:1%Er, CeO2:1%Er, 5%Li and CeO2:1%Er, 10%Li translucent ceramics were fabricated for the first time. Under the 980nm diode laser excitation, the ceramics gave intense green (520–570nm) and red (640–680nm) upconversion luminescence, which were ascribed to the radiative transitions of 2H11/2, 4S3/2→4I15/2 and 4F9/2→4I15/2 of Er3+ ions, respectively. It was worthy to point out that the above upconversion luminescence intensity of CeO2:Er, Li ceramics was greatly enhanced, and the preliminary observation suggests that the transmittance of CeO2:Er, Li ceramics in the visible spectral region was improved when Li+ ions were introduced as ceramics fluxing agent. The effect of Li+ ions doping on microstructure and upconversion emission of CeO2:Er translucent ceramics was investigated and the possible reasons for these results were presented, respectively.

Tunable Upconversion Luminescence and Energy Transfer Process in BaLa2ZnO5:Er3+/Yb3+Phosphors

BaLa2ZnO5:Er3+/Yb3+has been synthesized via a high temperature solid-state method, and the tunable upconversion luminescence and energy transfer process between Yb3+and Er3+in this system have been demonstrated. Upon 980 nm laser excitation, the intense green and red emission around 527, 553, and 664 nm were observed for BaLa2ZnO5:Er3+/Yb3+, which can be assigned to the characteristic energy level transitions of2H11/2→4I15/2,4S3/2→4I15/2, and4F9/2→4I15/2of Er3+, respectively. The critical Er3+quenching concentration (QC) was determined to be about 5 mol%, and the power studies indicated that mixture of 2- and 3-photon process was responsible for the green and red upconversion luminescence.

Up-conversion and Photoluminescence in Er3+ Single Crystal MgAl-spinel

Traditional and up-conversion luminescence of MgAl2O4 single crystal doped with erbium ions obtained by the Verneuil method has been investigated. The time resolved spectral measurements of the green and red up-conversion luminescence bands show that a build-up part is present in the up-conversion luminescence kinetics. This means that energy transfer process is involved in the creation of the luminescence. Considering rather small concentration of Er3+ in the material (0.12 mass %), the expected up-conversion mechanism should be excited state absorption since the average distance between erbium ions is high. The above-mentioned considerations suggest that clustering of the activator ions is present in the material, which is supported by SEM analysis.

Er3+/Yb3+共掺杂氧氟硼硅酸盐微晶玻璃绿色上转换发光的温度特性

Er³⁺/Yb³⁺共掺杂氧氟硼硅酸盐微晶玻璃绿色上转换发光的温度特性

Controlled morphology and EDTA-induced pure green upconversion luminescence of Er3+/Ho3+-Yb3+ co-doped NaCe(MoO4)2 phosphor

An innovative route to increase the green UC emission and simultaneously suppress red UC emission in Er3+/Ho3+-Yb3+ co-doped NaCe(MoO4)2.

Ca2+掺杂对NaYF4∶Yb,Er微米晶上转换发光性能的影响

Hexagonal NaYF4∶ Yb/Er microcrystals were prepared by a facile trisodium citrate-assisted hydrothermal method. The microparticles were characterized by TEM,X-ray diffraction(XRD),and luminescent spectra. Intense green upconversion luminescence was observed under 980 nm excitation. By introducing Ca2+ dopants into the grain lattices,the upconversion luminescence intensity of NaYF4∶ Yb/Er microcrystal was improved significantly. The enhancement is proposed to originate from a modification of the crystal structure and an improvement in the crystallinity of NaYF4∶ Yb/Er microcrystals.

Upconversion luminescence properties of Er3+/Yb3+ in transparent α-Sialon ceramics

Er3+ stabilized transparent α-Sialon ceramics with upconversion (UC) luminescence properties were fabricated for the first time by hot press sintering method. The fabricated samples show better transparency as well as UC luminescence properties. Moreover, the effect of Yb2O3 as a sensitizer on UC properties was analyzed in Er-α-Sialon system. The change in Sialon phases and crystal structure were analyzed by X-ray diffraction. The chemical compositions and morphology of grains and intergranular phase were analyzed by EDS and Transmission Electron Microscopy, respectively. The UC emissions were observed around 527, 547 and 670nm corresponding to the 2H11/2, 4S3/2 and 4F9/2 transitions, respectively when excited by 980nm continuous wave (CW) laser diode. UC process in Er3+ is found to be two photon processes. Intense green UC luminescence was observed with Er3+ and low amount of Yb3+ addition but higher amount of Yb3+ addition shows higher UC luminescence in red region. The transparency was higher in higher Er2O3 and low Yb2O3 content Sialon that was around 60% in visible light region. The chromaticity was also calculated for different samples and high color purity above 90% was obtained for green and yellow emissions. The mechanical properties were also investigated in this study.

Enhanced green upconversion luminescence in Yb–Tb co-doped sintered silica nanoporous glass

We report on a new kind of green-emitting (543 nm) high-silica luminous glass, which is fabricated by sintering of Yb3+–Tb3+ co-doped nanoporous glass. The fluorescence spectra show that there is an energy transfer between Yb3+ and Tb3+. The energy transfer process can be enhanced by addition of Al3+ into the Yb3+–Tb3+ co-doped nanoporous glass, and the energy transfer rate can be enhanced more than three times than that of Yb3+–Tb3+ co-doped porous glass. The role of Al3+ has been discussed, and the fluorescence decay curve reveals that the Al3+ play an important role in the energy transfer process.

Spectroscopic properties of Er3+ ions in multicomponent tellurite glasses

In the present work, multicomponent tellurite glasses were elaborated by the melt quench technique with different concentrations of Er3+ ions. Amorphous nature of all the glasses was confirmed using X-ray diffraction patterns. The thermal parameters, such as glass transition temperature (Tg) and the onset of crystallization temperature (TX), were determined by the differential scanning calorimetry. Judd–Ofelt parameters were derived for 0.5mol% Er3+-doped glass from the absorption measurements, and in turn, used to find the radiative properties of 4S3/2, 2H11/2 and 4I11/2 levels of Er3+ ion. A green emission corresponding to 4S3/2→4I15/2 and 2H11/2→4I15/2 transitions of Er3+ ions was observed in the glasses under investigation. Efficient green upconversion luminescence was observed under 976nm excitation. The emission bands centered at 529 and 543nm confirmed that two photons contribute to the upconversion processes. We have also analyzed the dependence of downconversion as well as upconversion as a function of Er3+ ion concentration, which shows quenching of photoluminescence intensity above 0.5mol% doping. From the emission spectra, CIE color coordinates of 0.5mol% Er3+-doped glass was examined. Fluorescence decay curves for the 4S3/2→4I15/2 transition for all the doped glasses have been measured and analyzed. Absorption cross-section and calculated emission cross-section, using the McCumber method, for the 4I13/2↔4I15/2 transitions were evaluated and discussed.

Synthesis of scheelite structural Yb3+, Er3+ co-doped NaLa(MoO4)2 and its green upconversion luminescence

The polycrystalline Er3+/Yb3+ co-doped NaLa(MoO4)2 phosphor was synthesized, and its green upconversion (UC) luminescence properties were investigated in detail. Under 980-nm excitation, Er3+/Yb3+ co-doped NaLa(MoO4)2 exhibited weak red emissions near 660 nm and 670 nm and strong green UC emissions at 530 nm and 550 nm corresponding to the intra 4f transitions of Er3+ (4F9/2, 2H11/2, 4S3/2) → Er3+ (4I15/2). The optimum doping concentrations of Er3+ and Yb3+ for the highest emission intensity were determined by using X-ray diffraction (XRD) and photoluminescence (PL) analyses. The Er3+/Yb3+ (7.0/10.0 mol%) co-doped NaLa(MoO4)2 phosphor sample exhibited a strong, shiny, green emission. A possible UC mechanism for Er3+/Yb3+ co-doped NaLa(MoO4)2 depends on the pump power is discussed in detail.

Upconversion luminescence and mechanisms of Nd3+/Ho3+/Yb3+ triply doped TeO2–K2O–Nb2O5 glasses

Nd3+/Ho3+/Yb3+ triply doped TeO2–K2O–Nb2O5 glasses were synthesized by the conventional melting-quenching technique. Single green upconversion (UC) luminescence centered at 532nm, corresponding to the (5F4, 5S2)→5I8 transitions of Ho3+, was observed under 800nm excitation. However, green and red emission bands centered at 547, 662 and 758nm, corresponding to the (5F4, 5S2)→5I8, 5F5→5I8 and (5F4, 5S2)→5I7 transitions of Ho3+, respectively, were simultaneously observed under 980nm excitation. The dependence of UC luminescence intensity of Ho3+ under 800 and 980nm excitations on Yb3+ concentration was studied. It was found, under 800nm excitation, the 532nm emission intensity of Ho3+ begin to reduce when the Yb3+ concentration is higher than 0.8mol%. However, at the same concentration of Yb3+, the emission quenching was not observed under 980nm excitation. The UC mechanisms under two pumping sources were discussed in terms of the experiment results. It was found that the UC luminescence of Ho3+ mainly depends on ET under 800nm excitation; however under 980nm excitation, it mainly depends on ESA.

Structural disorder-dependent upconversion in Er3+/Yb3+-doped calcium titanate

In this work, we evaluated the photoluminescence of distinct Er/Yb-doped CaTiO3 powders prepared by the polymeric precursor method, i.e., the crystalline form (structurally ordered) and another form (structurally disordered) before structural order was reached. Upconversion luminescence and photoluminescence are correlated to structural order–disorder. The CT:Er,Yb material presents broad-band emission under UV irradiation and green upconversion luminescence under IR irradiation.

Intensive Upconversion Luminescence of Na-Codoped Rare-Earth Oxides with a Novel RE–Na Heterometallic Complex as Precursor

Four novel heterometallic RE-Na-organic frameworks, [(RE)Na3(PZTC)2(H2O)4]·2H2O (RE = Yb (1), Ho (2), Er (3), Y (4); PZTC = pyrazine-2,3,5-tricarboxylate), were synthesized via solvothermal reactions and characterized by IR, elemental analysis, and single-crystal X-ray diffraction. The results show that the four complexes are isostructural. In the frameworks, the trinuclear Na cluster and RE ion acting as nodes are bridged by the multifunctional PZTC ligand to give a 3-D framework. Codoping in the frameworks was realized due to their isostructural characteristics. The codoped complexes were calcinated at 800 °C to give rise to the corresponding oxides. Investigation of their photophysical properties shows that the upconversion luminescence (UCL) of the Ho system is green while that of the Er system is red upon excitation at 980 nm. With regard to the luminescence color and intensity, the Er system is preferable to the Ho system for application in bioimaging. Both the red and the green UCL of the Ho(3+) and Er(3+) systems involve a two-photon process. In addition, the UCL mechanism is given. The UCL comparison of Na-doped oxides with non-Na-doped oxides indicates that doping Na can greatly enhance the UCL of the Er system.

Enhanced broadband excited upconversion luminescence in Ho-doped glasses by codoping with bismuth.

We report enhanced green and red upconversion (UC) luminescence in Ho3+-doped oxyfluoride germanate glass by introducing bismuth near-infrared active centers as sensitizers. The UC excitation bands at 750 and 970 nm show a full width at half-maximum of 20 and 45 nm, respectively. Energy transfer from sensitizers, the excited-state absorption, and phonon-coupled absorption of Ho3+ jointly contribute to the enhanced UC luminescence. Our approach provides an efficient methodology to broaden the excitation bandwidth of UC luminescent materials, which may have the potential for promising application in solar cells.

Hydrothermal synthesis and up-conversion luminescence of Ho3+/Yb3+ co-doped CaF2

CaF2:Ho3+/Yb3+ nano-particles with intense green up-conversion (UC) luminescence are successfully synthesized via a facile hydrothermal approach by using NH4F as the fluoride source and Na2EDTA as a chelating reagent. Powder X-ray diffraction (XRD), transmission electron microscopy (TEM), field emission scanning electron microscopy (FE-SEM), and UC emission spectra are used to characterize the structures, shapes, and luminescent properties of the samples. The effects from fluoride sources and chelating reagents on the formations of CaF2 nano-particles are investigated, and the formation process is also deduced. Under the excitation of a 980-nm laser diode, the samples each show a green up-conversion emission centered at 540 nm corresponding to the 5S2/5F4→5I8 transitions of Ho3+. Moreover, the UC mechanisms of Ho3+/Yb3+ co-doped CaF2 nano-particles are also discussed.

White upconversion luminescence generation from Ho3+ singly doped chalcohalide glasses

Bright white light which compose of blue, green and red emission bands from Ho3+ single doped Ge–Ga–S–CsCl (CsBr) chalcohalide glasses under 900nm infrared laser excitation were observed and investigated. The calculated color coordinates proved that the light were close to the natural sunlight. The low phonon energy of the local surrounding of Ho3+ ions and short ultra-violet cut-off edge resulted in the strong blue emission, as well as the enhanced green and red upconversion luminescence. It was also found that color coordinates of these white lights were independent on the excitation intensity. The result indicated that Ho3+ ions singly doped chalcohalide glass can be promising candidate for white light source, 3-dimensional display or color tunable visible laser.

Synthesis and characterization of HA/YVO4: Yb3+, Er3+ up-conversion luminescent nano-rods

In this paper, hydroxyapatite (HA) nano-rods have been successfully functionalized by depositing YVO4: Yb3+, Er3+ up-converting nanoparticles on the surfaces via a facile sol–gel technique. 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 structure, morphology and up-conversion luminescent properties of the samples. The results indicate that the HA nano-rods have been successfully coated by YVO4: Yb3+, Er3+ up-converting nanoparticles, and the samples exhibit bright green up-conversion luminescence upon the excitation of a 980nm diode laser. Furthermore, the optical intensity of the composites can be controlled by varying the depositing cycles of YVO4: Yb3+, Er3+ up-converting nanoparticles. This up-conversion luminescent HA may find important applications in the fields of in vivo bio-imaging and a drug delivery system.

Efficient monochromatic red, green, and blue up-converted luminescence from Yb3+-doped micro-phosphors co-doped with Er3+ or Tm3+ ions

Yb3+-doped YVO4 and Y2O3 micro-phosphors co-doped with Tm3+ or Er3+ ions were prepared using a solid-state reaction method without the use of additional flux. Analysis of their crystalline properties indicates essentially complete inter-diffusion of the dopant ions into the host crystal with no evidence of impurity phases. The luminescence up-conversion properties of the micro-phosphors were investigated using 980nm laser diode excitation. Blue up-converted luminescence centred at 474nm associated with the 1G4→3H6 transition of Tm3+ is produced by the Tm3+/Yb3+ co-doped YVO4 phosphor, with an overall efficiency of luminescence up-conversion of 1.3%. The Er3+/Yb3+ co-doped YVO4 micro-phosphor produced two green up-converted luminescence emission bands centred at 526nm and 554nm corresponding to the 2H11/2→4I15/2 and 4S3/2→4I15/2 transitions of Er3+, respectively, with a total efficiency of up-converted luminescence of 6.6%. In contrast with the green-emitting Er3+/Yb3+ co-doped YVO4-based phosphor, Er3+/Yb3+ co-doped Y2O3 micro-phosphors were produced displaying almost exclusively intense red up-converted luminescence associated with the 4F9/2→4I15/2 transition of Er3+, with efficiencies of luminescence up-conversion up to 14%. Micro-phosphors were produced for which the blue, green and red up-converted luminescence in each case accounts for >94% of the total up-converted luminescence emission.

On the mechanism of persistent up-conversion luminescence in the ZrO2:Yb3+,Er3+ nanomaterials

The up-converting ZrO2:Yb3+,Er3+ nanomaterials were prepared with the combustion and sol–gel methods. The structure of the materials was cubic except for the minor monoclinic and tetragonal impurities associated with the use of the sol–gel method. The XANES results revealed only the trivalent form for both the Yb and Er dopants. The distance distributions calculated from EXAFS confirm that Er3+ and Yb3+ occupy the ZrIV site in the structure. The nanomaterials show red (650–700nm) and very weak green (520–560nm) up-conversion luminescence due to the 4F9/2→4I15/2 and (2H11/2,4S3/2)→4I15/2 transitions of Er3+, respectively. The nanomaterials obtained with the combustion synthesis yield the most intense luminescence though showing significant afterglow, as well. The thermoluminescence measurements revealed the existence of traps with depths between 0.68 and 1.03eV well matching to room temperature persistent emission. Finally, the mechanism for the persistent up-conversion luminescence was introduced based on the experimental results and discussed.

Synthesis and Up‐conversion Luminescence of Yb3+/Ln3+ (Ln = Er,Tm,Ho) Co‐Doped Strontium Cerate by Pechini Method

Novel up‐conversion (UC) luminescent nanopowders, Sr2CeO4:Yb3+,Ln3+ (Ln = Er, Tm, Ho) were prepared with Pechini method. The Sr2CeO4:Yb3+,Ln3+ (Ln = Er, Tm, Ho) nanopowders had an orthorhombic crystal structure, and showed olive‐like morphology with the length of about 260 nm and width of about 130 nm. Under 980 nm lazer excitation, the Sr2CeO4:Yb3+/Er3+, Sr2CeO4:Yb3+/Tm3+, and Sr2CeO4:Yb3+/Ho3+ nanophosphors exhibit strong green, blue, and green UC luminescence, respectively. The luminescence mechanisms for the doped lanthanide ions were thoroughly analyzed.