Transition Of Tm Research Articles

Upconversion Luminescence Enhancement in Yb3+/Tm3+-Codoped Lu2O3 Nanocrystals Induced by Doping with Li+ Ions

Lutetium oxide (Lu2O3) nanocrystals doped with 2%Yb3+, 0.5%Tm3+, and various doping concentrations of Li+ (0, 3, 5, 7, 10, 12, and 15 mol%) were prepared by the sol-gel method. The dependence on different doping concentrations of Li+ ions of the structure, morphology, and the upconversion emission intensity of the Lu2O3:2%Yb3+, 0.5%Tm3+ nanocrystals was investigated. The obtained Lu2O3 nanocrystals were systematically characterized by X-ray diffraction (XRD), field emission-scanning electron microscopy (FE-SEM), Fourier transformed infrared (FT-IR) spectra, Raman spectra, and upconversion spectra measurements. It was found that all the nanocrystals can be readily indexed to pure cubic phase of Lu2O3, indicating good crystallinity. The experimental results show that Li+ doping in Lu2O3:2%Yb3+, 0.5%Tm3+ nanocrystals can greatly enhance the upconversion emission intensity. The strong blue (490 nm) and the weak red (653 nm) emissions from the prepared nanocrystals were observed under 980 nm laser excitation, and attributed to the 1G4 --> 3H6 and 1G4 --> 3F4 transitions of Tm3+ ions, respectively. An simple analysis based on steady-state rate equations and a power-dependent study both indicate that the 1G4 levels can be populated by three-step energy transfer (ET) processes. The enhancement of the upconversion luminescence was suggested to be the consequence of the modification of the local field symmetry around the Tm3+ ion, reduced number of OH- groups, and the enlarged nanocrystal size induced by the Li+ ions.

Investigations of optical and scintillation properties of Tm 3+-doped YAlO 3

Pure, 0.1, 0.5 and 1 mol% Tm-doped YAP single crystalline scintillators were grown by the μ-PD method. The XRD analysis confirmed the lattice constants decrease with the Tm concentration. In the transmittance measurement, the absorption bands due to the Tm 3+ 4f–4f transitions were observed at 265, 360, 485, 690 and 800 nm and they were ascribed to the transition from the 3H 6 ground state to its 1I 6, 1D 2, 1G 4, 3F 3 and 3H 4 excited states, respectively. Strong emission peak due to the 1I 6– 3F 4 transition of Tm 3+ appeared at 350 nm under X-ray irradiation. The photoluminescence decay time constants related to this transition were evaluated to be from 15.3 to 17.3 μs and the scintillation decay time constants under gamma-ray excitation were estimated to be from 17.5 to 18.8 μs. The Tm 1% doped crystal exhibited the highest light yield of 15, 100 ± 1500 photons/MeV when excited by 137Cs gamma-ray radiation.

Vacuum ultraviolet and near-infrared excited luminescence properties of Ca 3(PO 4) 2: RE3+, Na + ( RE=Tb, Yb, Er, Tm, and Ho)

Tb 3+, Yb 3+, Tm 3+, Er 3+, and Ho 3+ doped Ca 3(PO 4) 2 were synthesized by solid-state reaction, and their luminescence properties were studied by spectra techniques. Tb 3+-doped samples can exhibit intense green emission under VUV excitation, and the brightness for the optimal Tb 3+ content is comparable with that of the commercial Zn 2SiO 4:Mn 2+ green phosphor. Under near-infrared laser excitation, the upconversion luminescence spectra of Yb 3+, Tm 3+, Er 3+, and Ho 3+ doped samples demonstrate that the red, green, and blue tricolored fluorescence could be obtained by codoping Yb 3+–Ho 3+, Yb 3+–Er 3+, and Yb 3+–Tm 3+ in Ca 3(PO 4) 2, respectively. Good white upconversion emission with CIE chromaticity coordinates (0.358, 0.362) is achieved by quadri-doping Yb 3+–Tm 3+–Er 3+–Ho 3+ in Ca 3(PO 4) 2, in which the cross-relaxation process between Er 3+ and Tm 3+, producing the 1 D 2– 3 F 4 transition of Tm 3+, is found. The upconversion mechanisms are elucidated through the laser power dependence of the upconverted emissions and the energy level diagrams.

Impact of spin-up forcing on vegetation states simulated by a dynamic global vegetation model coupled with a land surface model

A dynamic global vegetation model (DGVM) coupled with a land surface model (LSM) is generally initialized using a spin-up process to derive a physically-consistent initial condition. Spin-up forcing, which is the atmospheric forcing used to drive the coupled model to equilibrium solutions in the spin-up process, varies across earlier studies. In the present study, the impact of the spin-up forcing in the initialization stage on the fractional coverages (FCs) of plant functional type (PFT) in the subsequent simulation stage are assessed in seven classic climate regions by a modified Community Land Model’s Dynamic Global Vegetation Model (CLM-DGVM). Results show that the impact of spin-up forcing is considerable in all regions except the tropical rainforest climate region (TR) and the wet temperate climate region (WM). In the tropical monsoon climate region (TM), the TR and TM transition region (TR-TM), the dry temperate climate region (DM), the highland climate region (H), and the boreal forest climate region (BF), where FCs are affected by climate non-negligibly, the discrepancies in initial FCs, which represent long-term cumulative response of vegetation to different climate anomalies, are large. Moreover, the large discrepancies in initial FCs usually decay slowly because there are trees or shrubs in the five regions. The intrinsic growth timescales of FCs for tree PFTs and shrub PFTs are long, and the variation of FCs of tree PFTs or shrub PFTs can affect that of grass PFTs.

Scintillation characteristics of Tm3+ in Ca3(BO3)2 crystals

Abstract Basic optical properties and radiation responses of undoped, Tm 3+ 1.0% and 2.0% activated Ca 3 (BO 3 ) 2 (CBO) crystalline scintillator prepared by the micro-pulling down (μ-PD) method are reported. Tm 3+ : CBO crystals showed three weak absorption bands around 190, 260 and 350 nm, owing to the Tm 3+ 4f–4f transition. Strong blue luminescence peaks at 360 and 460 nm which are ascribed to the 1 D 2 – 3 H 6 and 1 D 2 – 3 F 4 transitions of Tm 3+ respectively were observed under 241 Am 5.5 MeV α-ray excitation. The scintillation light yield of 2.0% Tm 3+ -doped CBO crystal was evaluated to be about 250 ph/n from the 252 Cf excited pulse height spectrum.

Frequency up-conversion luminescence properties and mechanism of Tm3+/Er3+/Yb3+ co-doped oxyfluorogermanate glasses

Oxyfluoride glasses were developed with composition 60GeO2·10AlF3·25BaF2·(1.95−x) GdF3· 3YbF3·0.05TmF3·xErF3 (x = 0.02, 0.05, 0.08, 0.11, 0.14, 0.17) in mole percent. Intense blue (476 nm), green (524 and 546 nm) and red (658 nm) emissions which identified from the 1 G 4→3 H 6 transition of Tm3+ and the (2 H 11/2, 4 S 3/2) → 4 I 15/2, 4 F 9/2→4 I 15/2 transitions of Er3+, respectively, were simultaneously observed under 980 nm excitation at room temperature. The results show that multicolor luminescence including white light can be adjustably tuned by changing doping concentrations of Er3+ ion or the excitation power. In addition, the energy transfer processes among Tm3+, Er3+ and Yb3+ ions, and up-conversion mechanisms are discussed.

Phase transitions in biodegradable films based on blends of gelatin and poly (vinyl alcohol)

The aim of this work was to study the effect of the hydrolysis degree (HD) and the concentration (CPVA) of two types of poly (vinyl alcohol) (PVA) and the effect of the type and the concentration of plasticizers on the phase properties of biodegradable films based on blends of gelatin and PVA, using a response-surface methodology. The films were made by casting and the studied properties were their glass (Tg) and melting (Tm) transition temperatures, which were determined by diferential scanning calorimetry (DSC). For the data obtained on the first scan, the fitting of the linear model was statistically significant and predictive only for the second melting temperature. In this case, the most important effect on the second Tm of the first scan was due to the HD of the PVA. In relation to the second scan, the linear model could be fit to Tg data with only two statistically significant parameters. Both the PVA and plasticizer concentrations had an important effect on Tg. Concerning the second Tm of the second scan, the linear model was fit to data with two statistically significant parameters, namely the HD and the plasticizer concentration. But, the most important effect was provoked by the HD of the PVA.

Role of Al 2O 3 in upconversion and NIR emission in Tm 3+ and Er 3+ codoped calcium fluoro phosphorous silicate glass system

In this study, the principal role of Al 2O 3 on the features of the photoluminescence spectra of Tm 3+ ion and upconversion phenomenon in Tm 3+ and Er 3+ codoped CaF 2−Al 2O 3−P 2O 5−SiO 2 glass system has been investigated. The concentration of Al 2O 3 is varied from 2 to 10 mol% while that of Er 3+ and Tm 3+ is fixed. IR and Raman spectral studies have indicated that there is a gradual increase in the degree of disorder in the glass network with increase in the concentration of Al 2O 3 up to 6.0 mol%. This is attributed to the presence of Al 3+ ions in octahedral positions in larger proportions. When the glasses are doped with Tm 3+ ions, the blue and red emissions were observed, whereas in Er 3+ doped glasses blue, green and red emissions were observed. When the glasses are codoped with Tm 3+ and Er 3+ ions and excited at 790 nm, all the three emission lines were observed to be reinforced, especially in the glasses mixed with 6.0 mol% of Al 2O 3. The IR emission band detected at about 1.8 μm due to 3F 4→ 3H 6 transition of Tm 3+ ions is also observed to be strengthened due to codoping. The reasons for enhancement in the intensity of various emission bands due to codoping have been identified and discussed with the help of rate equations for various emission transitions.

Monodisperse Nonionic Isoprenoid-Type Hexahydrofarnesyl Ethylene Oxide Surfactants: High Throughput Lyotropic Liquid Crystalline Phase Determination

The neat and lyotropic phase behavior of eight new ethylene oxide amphiphiles (EO = 1-8) with a hexahydrofarnesyl chain (3,7,11-trimethyldodecyl) and narrow polydispersity (>98.5% purity) is reported. Below five EO units the behavior of the neat surfactants show only a glass transition, Tg ∼ -90 °C. Above four EO units, crystallization (Tcrys) and crystal-isotropic liquid (Tm) transitions are also observed that increase with degree of ethoxylation of the surfactant headgroup. The lyotropic liquid crystalline phase behavior spans a complex spectrum of surfactant-water interfacial curvatures. Specifically, inverse phases are present below ambient temperatures for EO < 4, with HFarn(EO)2 exhibiting an inverse hexagonal (H(II)) phase stable to dilution. The phase diagram of HFarn(EO)3 displays both the gyroid (Ia3d) and double diamond (Pn3m) inverse bicontinuous cubic phases, with the latter being thermodynamically stable in excess water within the physiological regime. There is a strong preference for planar bilayer structures at intermediate headgroup ethoxylation, with the crossover to normal phases occurring at HFarn(EO)(7-8) which exhibits normal hexagonal (H(I)) and cubic (Q(I)) phases at ambient temperatures. The toxicity of colloidal dispersions of these EO amphiphiles was assayed against normal breast epithelial (HMEpiC) and breast cancer (MCF7) cell lines. The IC50 of the EO amphiphiles was similar in both cell lines with moderate toxicity ranging from ca. <5 to 140 μM in an in vitro cell viability assay. Observations are qualitatively rationalized in terms of the molecular geometry of the surfactant. The physicochemical behavior of the HFarnesyl ethylene oxide amphiphiles is compared to other ethylene oxide surfactants.

δ-Phase to defect fluorite (order–disorder) transition in the R2O3–MO2 (R=Sc, Tm, Lu; M=Zr, Hf) systems

Abstract We have studied the δ-phase to defect fluorite F * (order–disorder) transition in the R 4 M 3 O 12 (R = Sc, Tm, Lu; M = Zr, Hf) compounds. The temperature of the δ– F * phase transition in Tm 4 Zr 3 O 12 is ∼1600 °C. The rate of this transition in R 4 Zr 3 O 12 (R = Sc, Tm, Lu) decreases markedly with decreasing difference in ionic radius between the R 3+ and Zr 4+ , leading to stabilization of the δ-phases R 4 Zr 3 O 12 with R = Sc and Lu at high temperatures (∼1600 °C). During slow cooling (5 °C/h), the high-temperature defect fluorites F *-R 2 Hf 2 O 7 (R = Tm, Lu) decompose reversibly to form the δ-phases R 4 Hf 3 O 12 . Some of the materials studied exhibit microdomains formation effects, typical of the fluorite-related oxide compounds in the R 2 O 3 –MO 2 (M = Ti, Zr, Hf) systems of the heavy rare earths. The high-temperature defect fluorites F *-R 4 M 3 O 12 (R = Tm, Lu; M = Zr, Hf) as a rule contain antiphase microdomains of δ-R 4 Zr 3 O 12 . After slow cooling (5 °C/h), such microdomains are large enough for the δ-phase to be detected by X-ray diffraction. The conductivity data for R 4 M 3 O 12 (R = Sc, Tm, Lu; M = Zr, Hf) and Ln 2 Hf 2 O 7 (Ln = Dy, Lu) prepared by different procedures show that the rhombohedral phases δ-R 4 M 3 O 12 (R = Sc, Tm, Lu; M = Zr, Hf) are poorer conductors than the defect fluorites, with 740 °C conductivity from 10 −6 to 10 −5 S/cm. The conductivity drops with decreasing rare-earth ionic radius and, judging from the E a values obtained (1.04–1.37 eV), is dominated by oxygen ion transport. The highest conductivity, ∼6 × 10 −4 S/cm at 740 °C, is offered by the rapidly cooled F *-Dy 2 Hf 2 O 7 . In the fluorite homologous series, oxygen ion conductivity decreases in the order defect pyrochlore > defect fluorite > δ-phase.

Influence of precipitant solution pH on the structural, morphological and upconversion luminescent properties of Lu 2O 3:2%Yb, 0.2%Tm nanopowders

Lutetium oxide nanopowders codoped with Tm 3+ and Yb 3+ were synthesized by the reverse-strike co-precipitation method. Effects of precipitant solution pH on the structural, morphological and upconversion luminescent properties of Lu 2O 3:2%Yb, 0.2%Tm nanopowders had been investigated. The results show that pH value of the precipitant (NH 4HCO 3) solution has a significant effect on the particle size, morphology and upconversion emission intensity of the Lu 2O 3:2%Yb, 0.2%Tm nanopowders. All the samples obtained from different pH value of precipitant solution can be readily indexed to pure cubic phase of Lu 2O 3, indicating good crystallinity. The upconversion emission intensity of Lu 2O 3:2%Yb, 0.2%Tm nanopowders obtained from the precipitant solution with pH=11 is the strongest. The enhancement of the upconversion luminescence is suggested to be the consequence of reducing the number of OH − groups and the enlarged nanopowder size. The strong blue, weak red and near infrared emissions from the prepared nanopowders were observed under 980 nm laser excitation, and attributed to the 1G 4→ 3H 6, 1G 4→ 3F 4 and 3H 4→ 3H 6 transitions of Tm 3+ ion, respectively.

Effect of temperature on spectroscopic features relevant to laser performance of YVO_4:Tm^3+, GdVO_4:Tm^3+, and LuVO_4:Tm^3+ crystals

Optical spectra and luminescence decay curves were measured for thulium-doped YVO(4), GdVO(4), and LuVO(4) single crystals as a function of temperature in the 300-670 K temperature region. In spite of structural similarity, the three systems studied display significantly different transition intensities and nonradiative relaxation rates. It was found, in particular, that the peak value of the pump band absorption intensity diminishes by about 30% for Tm:YVO(4) and Tm:GdVO(4), and the effective emission cross section for the laser transition of Tm(3+) diminishes by a factor of 2 roughly when temperature increases from 300 to 500 K. An unusually small quantum efficiency of the upper laser level in Tm:LuVO(4) has been derived from the analysis of luminescence decay curves.

Intense blue photoluminescence of the Tm 3+/Yb 3+ co-doped single-crystalline hexagonal phase NaYF 4 nanorods

In this paper, Tm 3+/Yb 3+ co-doped NaYF 4 single-crystalline nanorods were prepared via a rational hydrothermal method using oleic acid as a stabilizing agent. The microstructure analysis revealed that the as-prepared samples presented a pure hexagonal phase NaYF 4 structure with high quality rod-like morphology by means of X-ray diffraction (XRD) and transmission electron microscopy (TEM). Under 980 nm excitation, the intense blue and weaker red upconversion emissions of the NaYF 4: 1%Tm 3+/ x%Yb 3+ ( x = 2, 5, 10 and 15) samples centered at 450, 477, 649 and 690 nm were observed, which were attributed to the 1D 2 → 3F 4, 1G 4 → 3H 6, 1G 4 → 3F 4 and 3F 3 → 3H 6 transitions of Tm 3+, respectively. Moreover, the photograph of the 1%Tm 3+/10%Yb 3+ co-doped NaYF 4 nanorods exhibited a strong eye-visible blue emission. The upconversion luminescence mechanisms for the Tm 3+/Yb 3+ co-doped hexagonal phase NaYF 4 nanorods were analyzed. In addition, the effect of Yb 3+ ions concentrations on the photoluminescence properties of the Tm 3+/Yb 3+ co-doped hexagonal phase NaYF 4 nano-rods were investigated in detail.

Mid-infrared emission characteristics and energy transfer processes in doubly doped Tm, Tb: KPb 2Br 5 and Tm, Nd: KPb 2Br 5

We present spectroscopic studies on the ∼5 μm mid-infrared emission and energy transfer properties of Tb 3+ doped KPb 2Br 5 and Nd 3+ doped KPb 2Br 5 sensitized by Tm 3+ ions. A series of co-doped Tm, Tb: KPb 2Br 5 and Tm, Nd: KPb 2Br 5 samples were prepared from purified starting materials of PbBr 2, KBr, and rare-earth bromides. Resonant excitation into the 3H 6 → 3F 4 absorption transition of Tm 3+ at ∼1.76 μm resulted in an enhanced 5 μm emission from Tb 3+ and Nd 3+ ions in Tm, Tb: KPb 2Br 5 and Tm, Nd: KPb 2Br 5, respectively. The existence of energy transfer between Tm → Tb and Tm → Nd in KPB was further evidenced by the quenching of the emission decay times of the 3F 4 → 3H 6 transition of Tm 3+ in doubly doped Tm, Tb: KPb 2Br 5 and Tm, Nd: KPb 2Br 5 compared to singly doped Tm: KPb 2Br 5.

650-nm laser emission under upconversion pumping at 1.064 μm in Tm+3: ZBLAN fiber laser

We report for the first time continuous wave (CW) red laser emission in Tm+3-doped ZBLAN fiber laser, operated at 650 nm (1G4 → 3F4 transition of Tm+3). The excitation uses a three step upconversion scheme. The pump source is a Nd:YAG laser operated at 1.064 μm. A laser output power of CW 80 mW was obtained for 1.42 W of launched pump power. The slope efficiency with respect to launched pump power was measured to be 7.7%. The temporal behavior of the emitted laser is also addressed.

Upconversion luminescence of Yb 3+/Ho 3+/Er 3+/Tm 3+ co-doped KGd(WO 4) 2 powders

Different lanthanide ions (Yb 3+/Ho 3+/Er 3+/Tm 3+) codoped KGd(WO 4) 2 phosphors were prepared by high-temperature solid-state reaction. The upconversion luminescence properties of two-ion and three-ion co-doped KGd(WO 4) 2 phosphors were investigated in detail. The concentration quenching effect of the two-ion co-doped KGd(WO 4) 2 phosphors was studied, and the optimum concentration of Ho 3+, Er 3+ and Tm 3+ are 2 mol.%, 2 mol.% and 3 mol.%, respectively. The Yb 3+/Ho 3+/Tm 3+ co-doped KGd(WO 4) 2 sample is the best white upconversion luminescence material among three-ion co-doped KGd(WO 4) 2 phosphors. The CIE coordinates for the samples were calculated, and chromaticity coordinates were close to white light regions. The upconversion luminescence mechanism of the samples was discussed. The upconversion luminescence of Ho 3+ and Er 3+ was both produced through two-photon process. The emissions of Ho 3+ at 546 and 654 nm originated from the transition of Ho 3+ ( 5S 2→ 5I 8 and 5F 5→ 5I 8), while those of Er 3+ at 530 and 551 nm were attributed to the transition of Er 3+ ( 2I 11/2→ 4I 15/2 and 4S 3/2→ 4I 15/2). The upconversion luminescence mechanism of Tm 3+ was a three-photon process. The blue emission of Tm 3+ was due to the transition of Tm 3+ ( 1G 4→ 3H 6).

Photoluminescence and energy transfer of Tm3+ doped LiIn (WO4)2 blue phosphors

Abstract Room temperature steady and time resolved emission spectra of LiIn1−xTmx(WO4)2 (where thulium concentration is 0, 0.5, 1, 5 and 10 at%) blue phosphors, under UV excitation energy have been investigated. The concentration quenching effect on the blue emission, due to the (WO4)−2 groups and 1G4→3H6 emission transition of Tm3+ were studied. Two energy transfer mechanisms are shown. The first takes place between excited (WO4)−2 groups and the 1G4 energy level of Tm3+, and is mainly analyzed by phonon-assisted energy transfer. The second mechanism is due to an energy transfer from the excited Tm3+ ions to the surrounding ground state Tm3+ ions. The non-exponential decay curves of the 1G4 level observed for higher concentrations are analyzed by the Inokuti–Hirayama model. We think that the quenching effect between Tm3+ ions is mainly linked to the dipole–dipole interactions.

Spectroscopic properties Eu3+ doped and Tm3+/Yb3+ codoped oxyfluoride glass ceramics containing Ba2GdF7 nanocrystals

Abstract Transparent Eu3+ doped and Tm3+/Yb3+ codoped oxyfluoride glass ceramics were prepared and spectroscopic properties were investigated. The XRD and TEM results demonstrated the formation of Ba2GdF7 nanocrystals, and the reduction of the ratio β between 5 D 0 → 7 F 2 and 5 D 0 → 7 F 1 transitions of Eu3+ ions evidenced rare-earth ions incorporation into Ba2GdF7 nanocrystals. For Tm3+/Yb3+ codoped glass ceramic, unusual ultraviolet upconversion emissions from 6 P J → 8 S 7 / 2 transition of Gd3+ at 308 nm and 1 D 2 → 3 H 6 , 1 D 2 → 3 F 4 and 1 G 4 → 3 H 6 transitions of Tm3+ at 359 nm, 449 nm and 476 nm were observed under 980 nm excitation, respectively. And upconversion mechanism of Tm3+–Yb3–Gd3++ system was analyzed.

ChemInform Abstract: Investigation of LiXO3 (X: Nb, Ta) Crystals Doped with Luminescent Ions. Recent Results

Abstract Processes of transfer of excitation from levels populated by diode laser pumping to upper laser levels in LiTaO 3 :Tm and LiTaO 3 :Ho are considered. Stimulated emission cross section for the 3 F 4 – 4 H 6 transition of Tm and for the 5 I 7 – 5 I 8 transition of Ho in lithium tantalate have been evaluated. Preliminary data concerning the contribution of radiative transitions and multiphonon relaxation to the decay of excited states of Er, Tm and Ho in LiNbO 3 and LiTaO 3 are compared.

Growth, optical parameters, and spectroscopic properties of crystals of disordered scheelite-like molybdates NaLa x Gd1 − x (MoO4)2 (x = 0–1) activated by Tm3+ ions

Polarized optical absorption spectra in the range of 450–2000 nm have been recorded for the Czochralski-grown concentration series of single crystals of mixed scheelite-like molybdates NaLa x Gd1 − x (MoO4)2(x = 0–1) activated by Tm3+ ions. The intensity parameters Ω t (t = 2, 4, 6) of the crystals grown were determined by the Judd-Ofelt method, and the values found were used to estimate the probabilities and emission branching ratios for a number of radiative transitions of Tm3+ ions. The main optical constants of an Na0.909La0.490Gd0.498Tm0.035Mo2.020O8.048 crystal were found and the temperature dependences of the refractive index for the ordinary and extraordinary waves were investigated in the temperature range of 293–373 K. The spectral dependences of the emission cross section for the expected 3 F 4 → 3 H 6 laser transition of Tm3+ ions in an Na0.908La0.301Gd0.676Tm0.048Mo2.019O8.043 crystal were measured in the spectral range of 1500–2000 nm. The gain cross section of the active medium on the 3 F 4 → 3 H 6 laser transition of Tm3+ ions in this crystal was calculated using the spectral dependences of the absorption and emission cross sections.