Transitions Of Ho Research Articles

Tunable green-red luminescence in Ho 3+/Yb 3+/Ce 3+: YF 3 nanocrystals embedded transparent glass ceramics

The Ho 3+/Yb 3+/Ce 3+:YF 3 nanocrystals embedded transparent oxyfluoride glass ceramics were successfully synthesized and the emission spectra have been measured. We changed the doped concentrations of ion Ce 3+ in the glass ceramics and unexpectedly found that the different concentrations brought forth different luminescence wavelengths, a tunable luminescence wave band from green to red, which might be useful to the tunable visible laser or display applications. In addition, excitated with wavelength 975 nm LD, the transitions of Ho 3+: 5G 4 → 5I 8 at 390 nm, 5G 5 → 5I 8 at 420 nm and 5F 3 → 5I 8 at wavelength 490 nm were observed in the glass ceramic GCCe0, while in samples GCCeJ(J=1,3,5,8), the three peaks disappeared.

Low-phonon BaF 2: Ho 3+, Tm 3+ doped crystals for 3.5–4 μm lasing

We study new pumping and sensitization scheme of 3.9 μm mid-IR laser transition ( 5I 5 → 5I 6 of Ho 3+) in the BaF 2 low-phonon crystal doped by Ho 3+ and co-doped by Tm 3+. It includes direct energy transfer from Tm 3+ to Ho 3+ governing by the 3H 4 → 3H 6; 5I 8 → 5I 5 cross-relaxation that gives ninefold increase of absorption of pumping light. We measure and analyze the lifetimes of all participated levels of Ho 3+ and Tm 3+ at low impurity concentrations, as well as energy transfer kinetics of the 3H 4 level of Tm 3+ and the 5I 6 level of Ho 3+ vs. acceptor concentration. We analyze the drawback of sensitization scheme, i.e. a self-quenching of Tm 3+ excitation governing by the 5H 4 → 3F 4; 3H 6 → 3F 4 cross-relaxation. Nevertheless, this drawback compensates by fast depletion of the 5I 6 terminal laser level with energy transfer governing by the 5I 6 → 5I 8; 3H 6 → 3H 5 cross-relaxation. As a result 3.9 μm laser transition of Ho 3+ in BaF 2: Ho 3+: Tm 3+ is not self-terminated. Moreover, efficient depletion of Ho 3+ terminal laser level with energy transfer to the initial level of 3.6 μm laser transition of Tm 3+ may cause cascade lasing in the mid-IR spectral range at two wavelengths of two different ions (Ho 3+ and Tm 3+).

Investigation of spectroscopic properties (absorption and emission) of Ho 3+ doped alkali, mixed alkali and calcium phosphate glasses

Optical absorption and emission spectra of Ho 3+ doped alkali, mixed alkali and calcium phosphate glasses of the type (69.5NH 4H 2PO 4·15Na 2HPO 4)·15R 2CO 3 (R = Li, Na and K), (69.5NH 4H 2PO 4·15Na 2HPO 4)·7.5Li 2CO 3·7.5R 2CO 3 (R = Na and K), (69.5NH 4H 2PO 4·15Na 2HPO 4)·7.5Na 2CO 3·7.5K 2CO 3 and (69.5NH 4H 2PO 4·15Na 2HPO 4)·15CaCO 3 have been studied. Variation of Judd–Ofelt intensity of parameters ( Ω λ ), peak wavelengths of the hypersensitive transitions ( λ p ), radiative transition probabilities ( A rad) and peak emission cross-sections ( σ p ) with the variation of alkalis, mixed alkalis and calcium in the phosphate glass matrix has been studied. The shift in peak wavelength of the hypersensitive transition and Judd–Ofelt intensity parameter ( Ω 2) are correlated with the structural changes in the host matrix. Radiative lifetimes ( τ R ) are estimated for certain excited states of Ho 3+ in these glass matrices. From the luminescence spectra, the emission cross-sections ( σ p ) are evaluated for the two emission transitions of Ho 3+ ion. Variation of luminescence intensities of the two transitions, absorption and emission cross-sections with the variation of alkalies, mixed alkalies and calcium in the above phosphate glass systems has been studied.

Growth and optical spectroscopy of Ho-doped KPb 2Cl 5 for infrared solid-state lasers

Results of the growth and infrared optical properties of Ho-doped KPb 2Cl 5 for potential applications in infrared (IR) solid-state lasers are reported. The investigated crystal was synthesized from commercial starting materials of PbCl 2, KCl, and HoCl 3 followed by several purification steps including normal freezing, zone-refinement, and chlorination. The Ho:KPb 2Cl 5 crystal was subsequently grown by the Bridgman technique. Following optical excitation at ∼0.89 μm, several IR emission bands were observed at room temperature with average wavelengths at 1.07, 1.18, 1.35, 1.65, 2.00, 2.89, and 3.96 μm. The emission at 3.96 μm originated from the 5I 5→ 5I 6 transition of Ho 3+ ions and exhibited a decay time of 5.0 ms at room temperature. Based on a Judd–Ofelt analysis the mid-IR emission quantum efficiency was determined to be near unity, which results in a peak emission cross-section of 0.62×10 −20 cm 2 at 3.96 μm. The obtained spectroscopic results indicate the favorable optical properties of Ho:KPb 2Cl 5 for mid-IR laser applications.

Intense green and red upconversion emissions from Ho 3+ in presence of Yb 3+ in Li:TeO 2 glass

Weak visible emission is observed at 545 nm and 660 nm on 976 nm excitation of Ho 3+ ions doped in tellurite glass. Addition of ytterbium to the doped glass causes a large increase in intensity of the green and the red emissions. In addition to these two new emissions of Ho 3+ one in the blue and the other in the NIR region are also observed. This increase in intensity is ascribed to energy transfer from ytterbium ions to holmium ions. Rate equation model has been proposed to study the upconversion emission and its dependence on pumping power. Possible upconversion mechanisms for these emissions are also discussed. Effect of changing the concentration of Yb 3+ on the emission intensity, lifetime and full width at half maximum (FWHM) in 5F 4( 5S 2) → 5I 8 transition of Ho 3+ in codoped sample has also been studied.

Absorption intensities, emission cross sections, and crystal field analysis of selected intermanifold transitions of Ho3+ in Ho3+:Y2O3 nanocrystals

Optical absorption and emission intensities are investigated for Ho3+ in nanocrystalline Ho3+:Y2O3. Room temperature absorption intensities of Ho3+(4f10) transitions in synthesized Ho3+:Y2O3 nanocrystals have been analyzed using the Judd–Ofelt (JO) approach to obtain the phenomenological intensity parameters Ω2, Ω4, and Ω6. The JO intensity parameters are used to calculate the spontaneous emission probabilities, radiative lifetimes, and branching ratios of the Ho3+ transitions from the upper multiplet manifolds to the corresponding lower-lying multiplet manifolds L2S+1J of Ho3+(4f10). The emission cross sections of the intermanifold transitions F54,S52→I58 (0.549 μm) and I56→I58 (1.204 μm) have been determined. The room temperature fluorescence lifetimes of these transitions in Ho3+:Y2O3 nanocrystals were measured. Radiative and fluorescence lifetimes are used to determine the quantum efficiency. The low temperature spectra are analyzed for the energy (Stark) level transitions of select L2S+1J multiplet manifolds of Ho3+(4f10). The comparative study of Ho3+(4f10) ions suggests that synthesized Ho3+:Y2O3 nanocrystals could be an excellent alternative to single-crystal Ho3+:Y2O3 for certain photonic applications, especially in the near infrared region.

Electro-optical characterization of Ge–Se–Te glasses

Chalcogenide bulk glasses Ge 20Se 80− x Te x for xϵ(0,15) have been prepared by systematic replacement of Se by Te. Selected glasses have been doped with Ho, Er and Pr, and samples have been characterized by transmission spectroscopy, measurements of dc electrical conductivity and low-temperature photoluminescence. Absorption coefficients have been derived from measured transmittance and estimated reflectance. Arrhenius plots of dc electrical conductivity, in the measured temperature range 300–460 K, are characterized by single activation energies roughly equal to the half of the optical gap. Activation energies deduced from Arrhenius plots reveal a systematic decrease with increasing Te content. Similarly, both absorption and low-temperature photoluminescence spectra reveal shifts of absorption edge and/or dominant luminescence band to longer wavelength due to Te → Se substitution. Samples doped with Ho and Er exhibit a strong luminescence at 1200 and 1540 nm due to 5I 6 → 5I 8 and 4I 13/2 → 4I 15/2 transitions of Ho 3+ and Er 3+ ions, respectively. Pr doped samples exhibit only a relatively weak luminescence peak at 1590 nm, which we tentatively assign to 3F 3 → 3H 4 transition of Pr 3+ ions. Absorption of the base glass luminescence at 1460 and 1520 nm has been observed at low temperature on samples doped with Pr and Er, respectively.

Investigation of 2.0 μm emission in Tm 3+ and Ho 3+ co-doped oxyfluoride tellurite glass

This paper reports 2.0 μm emission properties of Tm 3+/Ho 3+ co-doped oxyfluoride tellurite glass exited by 808 nm laser diode (LD). Mid-infrared transmittance property of glass was investigated by Fourier transform infrared (FTIR) spectrometer. The real chemical composition of investigated glass was identified by X-ray photoelectric spectroscopy (XPS). Thermal stability of the glass was determined by differential thermal analysis (DTA) measurement. The Judd–Ofelt parameters, spontaneous radiative transition probabilities, branching ratios and radiative lifetime of Ho 3+ were calculated based on the absorption spectra by using Judd–Ofelt theory. Results indicate that the maximum 2.0 μm emission intensity attributed to the 5I 7→ 5I 8 transition of Ho 3+ was achieved at 1.5 mol% Tm 2O 3 and 1 mol% Ho 2O 3 concentrations in oxyfluoride tellurite glass. OH − absorption at 3000 cm −1 was greatly depressed by introduction of 10 mol% F −. The maximum absorption and stimulated emission cross-section of Ho 3+ near 2.0 μm are 7.0×10 −21 cm 2 at 1950 nm and 8.8×10 −21 cm 2 at 2048 nm, respectively. The calculated radiative lifetime of 4.4 ms for 5I 7→ 5I 8 transition and large stimulated emission cross-section of the Tm 3+/Ho 3+ co-doped oxyfluoride tellurite glass indicate that the glass has a potential application in efficient 2.0 μm laser.

Emissions properties of Ho 3+: 5I7 → 5I8 transition sensitized by Er 3+ and Yb 3+ in fluorophosphate glasses

Emission properties of Ho 3+ at 2.0 μm and the energy transfer mechanism between Yb 3+, Er 3+ and Ho 3+ ions in fluorophosphate glasses are investigated. The measured emission spectra show that the 5 I 7 → 5 I 8 transition of Ho 3+ upon 980 nm laser diode excitation is strong. Judd–Ofelt intensity parameters ( Ω λ , λ = 2, 4, 6), spontaneous transition probability ( A rad), radiative lifetime ( τ r), absorption cross section ( σ a), stimulated emission cross section ( σ e) and FWHM × σ e peak for the transition of Ho 3+: 5 I 7 → 5 I 8 are calculated and discussed. The obtained results show that the present Yb 3+/Er 3+/Ho 3+ triply-doped fluorophosphate glass can be identified to be a promising material at 2.0 μm emission.

Gain properties of germanate glasses singly doped with Tm 3+ and Ho 3+ ions

Two kinds of germanate glasses singly doped with the ion concentration of 2.0mol.%Tm 3+ and 2.0mol.%Ho 3+, respectively, were prepared. According to McCumber theory, the absorption and stimulated emission cross-sections corresponding to the 3H 6↔ 3F 4 transitions of Tm 3+ (at 1.8 µm) and the 5I 8↔ 5I 7 transitions of Ho 3+ (at 2.0 µm) were obtained, and respective gain cross-section spectra were also computed as a function of population inversion according to absorption and emission cross-sections and the ion concentrations. For Tm 3+-doped germanate glasses, the maximum of the absorption, emission, and gain cross-sections reached a value higher than those reported for fluorozirconate, fluoride, and oxyfluoride glasses. For Ho 3+-doped germanate glasses, the maximum of absorption, emission, and gain cross-sections reached a value higher than that reported for fluorozircoaluminate glasses. Hence, these Tm 3+-doped and Ho 3+-doped germanate glasses exhibited an advantage for application in mid-infrared lasers at about 1.8 and 2.0 µm wavelength.

Spectral properties and energy transfer of Tm 3+/Ho 3+-codoped Ga 2O 3-Bi 2O 3-GeO 2-PbO glasses

The 2.0 μm emission originating from Ho 3+: 5I 7 → 5I 8 transition in Ho 3+/Tm 3+-codoped gallate-bismuth-germanium-lead glasses were investigated upon excitation with 808 nm laser diode (LD). Energy transfer (ET) process between Tm 3+: 3F 4 level and Ho 3+: 5I 7 level was also discussed. It was noted that the measured peak wavelength and stimulated emission cross-section of Ho 3+-doped bismuth-germanium-lead glasses were ∼2.02 μm and 5.1×10 −21 cm 2, respectively. Intense emission of Ho 3+ in Tm 3+/Ho 3+-codoped GBPG glass were observed, which resulted from the ET between Tm 3+: 3F 4 and Ho 3+: 5I 7 level upon excitation with 808 nm LD.

Hydrothermal Synthesis of GdVO4:Ho3+ Nanorods with a Novel White-light Emission

Abstract A novel white-light phosphor GdVO4:Ho3+ was prepared via a simple hydrothermal reaction route. Under ultraviolet excitation, the as-prepared nanocrystals showed a broad band emission and sharp lines, which are associated with the oxygen vacancies around V4+ ions and the typical f–f transitions of Ho3+ ions, respectively. The coexistence of broad emission and sharp lines results in the bright white light with a quantum yield of 28%.

The Ho(III) as structural probe for high temperature ionic liquids: RCl 3 (R = rare earth)

The electronic absorption spectra of the f ← f transitions of Ho 3+ as a probe cation doped in solid and liquid YCl 3 and TbCl 3 have been measured from room temperature to above the melting point of both compounds. In the same temperature range Raman spectroscopy has been utilized to characterize all phases present. Emphasis is given on the Ho 3+ ligand field spectra of the 5G 6 ← 5I 8 hypersensitive transition and their similarities with the known spectra of holmium chloro-elpasolite. Smooth spectral changes with nearly invariant molar absorptivities (between 30 and 40 L mol −1 cm −1) are observed upon melting YCl 3 and α-TbCl 3 which indicate that most probably the Ho 3+ is in 6-fold distorted octahedral coordination in both compounds and both phases. Drastic spectral changes are observed alongside the α-TbCl 3 to β-TbCl 3 phase transition where the coordination is altered from six to eight and the molar absorptivity quadruples. The spectra of liquid Y(Ho)Cl 3 and Tb(Ho)Cl 3 are correlated to the spectra of liquid La(Ho)Cl 3 and Gd(Ho)Cl 3 and are attributed to the ligand field states of Ho 3+ in distorted octahedral geometries. In conjunction with the molar volumes of all RCl 3 (R = rare earth) liquids which are invariant and independent of R and with Raman spectroscopic measurements for the same systems, a common possible structure of the rare earth chloride liquids is deduced and proposed.

The evolution of the ordered states of single-crystalURu2Si2 under pressure

The ‘hidden order’ (HO) and superconducting (SC) states ofURu2Si2 have been investigated via electrical resistivity measurements as a function of pressureP up to nearly 30 kbarand magnetic field H≤9 T. The field and pressure dependences of the SC state were examined for two crystals withH aligned parallel to c and a, with the latter orientation revealing an enhanced critical field.No discontinuities in either the field or pressure dependence of the SC state were found.The evolution of the HO state showed a distinct kink in the pressure dependence atPc = 15 kbar, coincident with the destruction of superconductivity. The behavior of the two orderedphases was analyzed via a model describing the competition for Fermi surfacefraction, where a portion of the Fermi surface becomes completely gapped nearPc. The evolution of the magnitude of the scattering at the HO transition is compared withthe Fermi surface fraction gapped by the HO state, and the phenomenology of a spindensity wave-like ground state is discussed as it pertains to the data presented.

Infrared Emission Properties of Ho Doped KPb2Cl5

AbstractWe report on the optical properties of Ho doped KPb2Cl5 (Ho: KPC) for potential applications as an infrared (IR) solid-state gain medium. The investigated crystal was synthesized from commercial starting materials of PbCl2, KCl, and HoCl3 followed by several purification steps including directional freezing, zone-refinement, and chlorination. The Ho: KPC crystal was subsequently grown by Bridgman technique. Following optical excitation at 885 nm, several IR emission bands were observed at room-temperature with average wavelengths at 1.07, 1.18, 1.35, 1.65, 2.00, 2.94, and 3.96 μm. The emission at 3.96 μm originated from the 5I5 -> 5I6 transitions of Ho3+ and was further evaluated for possible applications in mid-IR lasers. The decay time of the 5I5 excited state was measured to be 5.0 ms at room-temperature. The long 5I5 lifetime is favorable for laser applications and indicates that non-radiative multi-phonon relaxations are small in Ho: KPC. Based on a Judd-Ofelt analysis, the emission quantum efficiency was determined to be near unity resulting in a peak emission cross-section of 0.62×10-20 cm2 at 3.96 μm. A drawback for laser applications is the long decay time of the lower 5I6 state with a value of 4.8 ms . Since the 3.96 μm transition terminates in the 5I6 level, its long lifetime will lead to population bottlenecking, which limits possible mid-IR lasing to pulsed and quasi-cw operation.

Lattice strain dependent optical transitions in Ho3+-ion doped barium strontium titanate thin films

The influence of lattice strain on the strength of dipoles in the Ho3+-doped barium-strontium titanate (BST) thin films has been analyzed. Thin films were produced by using the sol–gel technique on Si substrate. The resulting stress due to fabrication process was quantified by analyzing the {200} planes of the cubic perovskite structure and comparing them with the data for bulk materials. The influence of strain and changes due to Ho3+-ion doping were characterized by Raman and visible photoluminescence spectroscopy, which clearly show the evidence for the increased tetragonality due to weaker dipole interaction at B-sites of cubic perovskite in the presence of Ho3+-ions at concentrations larger than 3 mol%. The film strain can therefore be controlled to enhance the intensity of emitted light at 650 nm.

The Ho3+ Hypersensitive Transitions as Structural Probes for Molten Rare-Earth Ahlorides

The electronic absorption spectra of the f ← f transitions of Ho3+ in solid and molten Cs2NaHoCl6 elpasolite and in Y(Ho)Cl3 have been measured from room temperature up to above the melting point of both compounds. Emphasis is given on the ligand field spectra of the 5G6 ← 5I8 hypersensitive transition. Smooth spectra changes are observed upon melting the solids. In conjuction with Raman spectroscopic measurements the absorption spectra are attributed to HoCl 3− 6 octahedra in distorted geometries. The spectra of molten Y(Ho)Cl3 are correlated to the elpasolite spectra as well as with the spectra of La(Ho)Cl3 and Gd(Ho)Cl3 to deduce the possible structure of the host rare-earth chlorides.

Magnetocaloric effect, specific heat and adiabatic temperature change of HoxEr1−xN (x=0.25, 0.5, 0.75)

Sample of Ho x Er 1− x N ( x = 0.25, 0.5, 0.75) were synthesized by hot isostatic pressing of alloy blocks in nitrogen gas and their specific heat were measured under zero-field and 5 T. The peak value of the specific heat associated with the ferro–para magnetic transition of Ho x Er 1− x N was lager than that of Er 3 Ni which is used commercially as a magnetic regenerator for the Gifford–McMahon refrigerator. Magnetic entropy change Δ S and adiabatic temperature range Δ T were evaluated from entropy curves under zero-field and 5 T. Both the properties were very promising from viewpoints of application of rare-earth mononitride to the magnetic refrigerant and/or regenerator working at cryogenic temperatures around their Curie's temperature.

Blue, green, yellow and red upconversion fluorescence in Tm3+/Ho3+:Cs2NaGdCl6 crystals under 785nm laser excitation

Abstract 1% Tm 3+ , 10% Ho 3+ single-doped and 10% Tm 3+ , 10% Ho 3+ co-doped Cs 2 NaGdCl 6 samples were synthesized by Morss method E. Under 785 nm semiconductor laser pumping, the upconversion fluorescence in Tm 3+ single-doped and Tm 3+ , Ho 3+ co-doped Cs 2 NaGdCl 6 was investigated at room temperature. For 1% Tm 3+ -doped sample, three upconversion emission bands near 483 nm, 658 nm and 701 nm were obtained and assigned to be 1 G 4 → 3 H 6 , 1 G 4 → 3 F 4 and 3 F 3 → 3 H 6 , respectively. For 10% Tm 3+ , 10% Ho 3+ co-doped sample, four strong upconverted emissions near 492 nm (blue), 543 nm (green), 588 nm (yellow) and 657 nm (red) were measured and assigned to be 5 F 3 → 5 I 8 , 5 S 2 → 5 I 8 , 5 G 4 → 5 I 6 and 5 F 5 → 5 I 8 transitions of Ho 3+ ions. With the help of the measuring power dependence of all these upconversion emissions, a reasonable upconversion mechanism model responsible for them was presented. The analysis of these upconversion emissions confirmed the efficient energy transfer from Tm 3+ ( 3 F 4 ) to Ho 3+ ( 5 I 7 ) ions.

Ligand Field States and Vibrational Modes of Solid and Molten Elpasolite: Cs2NaHoCl6

Electronic absorption and Raman spectra of solid and molten Cs2NaHoCl6 elpasolite have been measured in the temperature range 20 - 780 ◦C. The Raman spectra of the solid indicate that there is no phase transition above room temperature. It appears, that the internal vibrational modes of the solid are transferred into the melt, indicating that the [HoCl6]3− “octahedra” are the predominant species. The 5G6 ← 5I8 and 3H6 ← 5I8 hypersensitive transitions of Ho(III) in elpasolite have been studied and analyzed in terms of the ligand field splittings of these states in the octahedral [HoCl6]3− field. The temperature-induced changes in the spectra are attributed to the presence of “hot” bands arising from sets (“zones”) of energy levels in the ground 5I8 state. The continuous and smooth spectral changes observed upon melting indicate the presence of [HoCl6]3−octahedra in both phases.