5I8 Transition Research Articles

Nd3+ as effective sensitizing and deactivating ions for the 2.87 µm lasers in Ho3+ doped LaF3 crystal

The efficient 2.87 μm emission of Ho3+: 5I6→5I7 transition via Nd3+ sensitization in Nd,Ho:LaF3 crystal was obtained under 808 nm LD excitation for the first time. The lifetime of Ho3+:5I7 decreases dramatically from 26.28 ms to 6.41 ms via Nd3+ co-doping. The mechanism of sensitization and deactivation by Nd3+ was investigated compared with the Ho:LaF3 crystal. The absorption cross-section, emission cross-section, and fluorescence quantum efficiency were estimated and discussed. All the results indicate Nd,Ho:LaF3 crystal an attractive gain medium for solid-state lasers around 2.87 µm under an 808 nm LD pump.

Comparative study of optical properties of Ho3+ -doped RE2O3-Na2O-ZnO-TeO2 glasses

Tellurite glasses of the composition xHo2O3-(7-x)RE2O3−3Na2O-25ZnO-65TeO2 were prepared by the melt quenching-technique. Absorption (300 K) and fluorescence (300 K) spectra as well as the lifetimes from excited states are presented and discussed in details. The analysis of the absorption spectrum at 300 K has been carried out for determination of phenomenological Ωλ (λ = 2, 4, 6) Judd-Ofelt parameters. Based on the Judd-Ofelt theory, the radiative transition probabilities (AT), branching ratios (βR) and radiative lifetimes (τR) of the emitting levels of Ho3+ ion have been determined. The experimental lifetime of the 5I7 level has been significantly reduced in comparison to the radiative lifetime. It was found that the quenching of emission from the 5I7 level of the Ho3+ ion is due to self-quenching process. The stimulated and effective emission cross-sections for the 5I7→5I8 transition have been calculated. The fluorescence from the 5S2 level is strongly dependent on the activator concentration. The obtained results show that among three types of glasses, Ho3+-doped Y2O3-Na2O-ZnO-TeO2 glasses are the most promising candidates for a 2 µm laser host as well as an efficient phosphor with green luminescence.

Magnetic tuning in upconversion emission enhanced through Ag+ ions co-doped in GdF3: Ho3+/Yb3+ phosphor and a real-time temperature sensing demonstration

Herein Ho3+/Yb3+ doped GdF3 phosphor was prepared by chemical coprecipitation method. Further, during sample preparation, Ag+ ions were incorporated into the GdF3 lattice to enhance the upconversion emission. Using 980 nm excitation intense emission bands were observed at 543 nm and 650 nm corresponding to the 5F4→ 5I8 and 5F5→5I8 transitions. Incorporation of Ag+ ions has resulted in enhancement in the emission and maximum intensity was obtained for the Ag+ concentration of 10 mol%. It was supposed that Ag+ ions change the crystal field around the Ho3+ ions that result in emission enhancement. The Ag+ incorporation was also confirmed through UV–vis absorption and downconversion analysis. The effect of the magnetic field was studied on the emission intensity and an optical hysteresis loop was observed in the plot of emission intensity vs the magnetic field. The CIE color coordinate variation based temperature sensing ability of the optimized sample is also demonstrated.

Study of Anti-Stokes Luminescence of ZBLAN:Нo3+ Ceramics Excited at 1908 nm

Visualization of IR radiation of a Tm:YLF laser with a wavelength of 1908 nm in 53ZrF4–20BaF2–3LaF3–1HoF3–3AlF3–20NaF (mol %) ceramic samples is studied. The luminescence spectra of Но3+-doped ZBLAN ceramics exhibit bands in the regions of 540, 650, and 900 nm, which correspond to the 5S2 → 5I8, 5F5 → 5I8, and 5I5 → 5I8 transitions, the red band (650 nm) being most intense. The population of the upper levels of these transitions can be explained using the cascade excitation mechanism. A visualization model is developed based on balance equations for populations of the upper energy states of Но3+ ions. The population distributions are numerically estimated as functions of the excitation intensity. The obtained time dependences of the populations of the 5S2 and 5F5 states correlate with the experimental time dependences of the luminescence intensity at the 5S2 → 5I8 and 5F5 → 5I8 transitions upon pulsed excitation. The threshold power density of a Tm:YLF laser at which luminescence of the ceramic samples was observed was ~2 W/cm2.

Controllable optical properties between Ho3+: 5I7 → 5I8 and Tm3+: 3F4 → 3H6 transitions in germanosilicate glasses

Diode-pumped solid-state 2 μm lasers have seen rapid development for their efficient operation, compact size, and stable performance. In this work, doped germanosilicate (SiO2-GeO2-Ga2O3-Lu2O3) glasses with varying Tm3+/Ho3+ concentrations exhibiting excellent physical and optical characteristics were successfully prepared. Thermal and structural properties were analyzed by the measured DSC and Raman spectra. An evident efficient wide absorption band near 770–830 nm demonstrated the feasible energy transfer between Tm3+: 3F4 → 3H6 and Ho3+: 5I7 → 5I8 transitions. Meanwhile, combining with Judd-Ofelt theory, super predicted spontaneous emission probabilities were obtained, which are beneficial to obtain fine laser action for solid-state lasers. This is a first study to demonstrate that a tunable fluorescence peak (1.8–2.05 μm) can be obtained by modulating the combined effects between two luminous activation centers. Therefore, the results indicate a promising rare-earth doped glass host for solid-state 2 μm lasers.

Electrical properties improvement and excellent upconversion luminescence of PSMHYT crystals

A novel Pb(Sc1/2Nb1/2)O3-Pb(Mg1/3Nb2/3)O3-Pb(Ho1/2Nb1/2)O3-Pb(Yb1/2Nb1/2)O3-PbTiO3 (PSMHYT) crystal was grown by using the flux method. XRD and Raman scattering determined pure perovskite structure of as-grown crystals. Electrical test results showed that the crystal along [100]-orientation was of high Curie temperature Tc (192 °C), large coercive field Ec (15.90 kV/cm) and remanent polarization Pr (31.94 μC/cm2), which were higher than those of most crystals reported previously. The optical absorption at UV-VIS-NIR bands related to Ho3+ and Yb3+ was observed. Irradiated by excitation sources with different wavelengths (245, 460 and 980 nm), weak downconversion (DC) and strong upconversion (UC) luminescences were achieved, and related UC emission mechanism was also analyzed. Rich luminescence was ascribed to abundant energy levels of rare earth Ho3+. Furthermore, focused on the up-conversion process, the fluorescence lifetime (τ) from 5F4/5S2→5I8 (green) transition and total quantum yield in green and red emissions were investigated, with results of 0.1/0.039 ms and 0.39% obtained. Excellent electrical and optical properties make PSMHYT crystal a promising substitute material in transducers, sensors, and optoelectronic coupling devices.

Effect of Ho3+ concentration on the structure, morphology and optical properties of Ba0.5Mg0.5Al2O4 nanophosphor

Barium magnesium aluminate nanopowders doped with holmium (Ba0.5Mg0.5Al2O4:x% Ho3+) were successfully prepared by the sol-gel method. The Ho3+ concentration was varied up to 2 mol%. X-ray powder diffraction results showed that the Ba0.5Mg0.5Al2O4 nanopowders crystallized in the hexagonal phase of BaAl2O4. Scanning electron microscopy images suggested that the doping influences the particle morphology. Photoluminescence results showed visible emissions observed at around 422 and 733 nm which originated from intrinsic defects within the host material as well as emissions at around 491, 550, 662 and 758 nm which were attributed to the 5F3 → 5I8, 5F4/5S2 → 5I8, 5F5 → 5I8 and 5S2 → 5I7 transitions of Ho3+ respectively. Infrared emissions around 1157 and 1200 nm were attributed to the 5S2,5F4 → 5I6 and 5I6 → 5I8 transitions of Ho3+. Increasing the Ho3+ concentration up to x = 0.8% led to luminescence enhancement, while further increase led to luminescence quenching. Lifetime measurements revealed that the x = 0.8% sample with maximum emission intensity at 550 nm has a strong lifetime component of 7.79 μs and a small component of long lifetime 79 μs, while the x = 2% (maximum doped) sample exhibited some concentration quenching and the contribution of the medium (7.79 μs) component was lower. The Commission Internationale de l’Eclairage (CIE) co-ordinates showed that the emission colour could be tuned towards bluish-purple by mixing of the MgAl2O4 and BaAl2O4 components. The Ho3+ concentration influenced the proportion of green emission colour.

Removal of hydroxyl routes enhancing 2.85 μm mid-infrared luminescence in oxyfluorotellurite glass with high ZnF2 content

The near ~3 μm mid-infrared laser demonstrates real and potential applications in many military and civilian areas, but the lack of host materials with nice optical quality and the overlapped vibrations of OH– hamper the emission intensity. To eliminate the OH– absorption, ZnF2 was adopted in Yb3+/Ho3+ codoped binary TeO2-PbF2 glass to partially till totally replace PbF2. The high ZnF2 concentration would raise the glass transition temperature and enhance the thermal stability of matrix, especially enhance the intensity of 2.85 μm mid-infrared luminescence obviously. TeO2-ZnF2 glass with 45.5% ZnF2 original content has high ratio of the strength parameter Ω4/Ω6 (=2.90) and possesses higher spontaneous transition probability (45.25 S−1) along with the larger calculated emission cross section (0.96 × 10−20 cm2) corresponding Ho3+: 5I6 → 5I7 transition. Fourier transmittance of infrared spectra revealed ZnF2 could reduce the OH– concentration in glass substantially, which were favor of 2.85 μm mid-infrared emission. Our results indicated that the use of ZnF2 to effectively remove the hydroxyl groups is an efficacious way to develop near ~3 μm mid-infrared optical glass with high efficient luminescence and thermochemical reliability.

Crystal Structure of NaLuW2O8·2H2O and Down/Upconversion Luminescence of the Derived NaLu(WO4)2:Yb/Ln Phosphors (Ln = Ho, Er, Tm)

Hydrothermally reacting Lu(NO)3 and Na2WO4·2H2O at 200 °C and pH = 8 produced the new compound NaLuW2O8·2H2O, which was analyzed via the Rietveld technique to crystallize in the orthorhombic system (space group: Cmmm) with cell parameters a = 21.655(1), b = 5.1352(3), and c = 3.6320(2) Å and cell volume V = 403.87(4) Å3. The crystal structure presents -(NaO6)-(NaO6)- and -(LuO4(H2O)2WO5)-(LuO4(H2O)2WO5)- alternating layers linked together by the O2- ion common to NaO6 octahedron and WO5 triangle bipyramid. Tetragonal structured and phase-pure Na(Lu0.87Ln0.03Yb0.1)(WO4)2 phosphors (Ln = Ho, Er, and Tm) were directly produced by calcining their NaLuW2O8·2H2O analogous precursors at 600 °C for 2 h, followed by a detailed study of their downconversion/upconversion (DC/UC) photoluminescence. It was shown that the UC luminescence is dominated by a red band at ∼650 nm for Ho3+ (5F5 → 5I8 transition), green bands at ∼500-575 nm for Er3+ (2H11/2/4S3/2 → 4I15/2 transitions) and a blue band at ∼476 nm for Tm3+ (1G4 → 3H6 transition), all via a three-photon process. DC luminescence of the phosphors is characterized by a ∼545 nm green emission for Ho3+ (5F4/5S2 → 5I8 transition, λex = 453 nm), ∼500-575 nm green emissions for Er3+ (2H11/2/4S3/2 → 4I15/2 transitions, λex = 380 nm), and a ∼455 nm blue emission for Tm3+ (1D2 → 3F4 transition, λex = 360 nm), with CIE chromaticity coordinates of around (0.27, 0.71), (0.26, 0.72), and (0.15, 0.04), respectively.

Field-induced large strain and strong green photoluminescence in (Ho,Sb)-modified (Bi0.5Na0.5)0.945Ba0.065TiO3 multifunctional ferroelectric ceramics

(Ho,Sb)-modified (Bi0.5Na0.5)0.945Ba0.065TiO3 (BNBT6.5) multifunctional ferroelectric ceramics were fabricated by a conventional solid-state reaction method. Results showed that (Ho, Sb)-modified BNBT6.5 materials exhibited a bright green photoluminescence while simultaneously obtaining a large electric-field-induced strain of 0.37% (80 kV/cm) in samples with x = 0.50% due to the appearance of an ergodic relaxor phase at zero field. Under the electric field, the ergodic relaxor phase could reversibly transform to ferroelectric phase. As a result, the strain is very resistant to field cycling due to the reversible field-induced phase transition between the ergodic relaxor and ferroelectric phase, giving the materials attractive for its good fatigue resistance. Besides the excellent strain properties, (Ho, Sb)-modified BNBT6.5 host exhibits a bright photoluminescence with a strong green emission located at around 549 nm owing to the 5S2→5I8 transition under the 451 nm light excitation at room temperature. As a multifunctional material, (Ho,Sb)-modified BNBT6.5 ferroelectric materials showed great potential in optical-electro integration and coupling device applications.

Energy transfer induced 2.0 µm luminescent enhancement in Ho3+/Yb3+/Ce3+ tri-doped tellurite glass

Tellurite glasses doped with Ho3+, Ho3+/Yb3+ and Ho3+/Yb3+/Ce3+ ions have been prepared using conventional melt-quenching method, and characterized respectively by the X-ray diffraction (XRD) pattern, differential scanning calorimeter (DSC) curve, UV–vis–IR absorption spectrum, upconversion spectrum, fluorescence spectrum and fluorescence decay curve to investigate the 2.0 µm band spectroscopic properties of Ho3+, thermal stability and structural nature of glass hosts. Under the excitation of 980 nm laser diode (LD), an intense and broad 2.0 µm band infrared emission originated from the 5I7 → 5I8 transition of Ho3+ was observed in the Ho3+/Yb3+ co-doped tellurite glass and increased further with the addition of Ce3+, which is attributed to the energy transfer (ET) from Yb3+ to Ho3+ as well as the cross-relaxation (CR) between Ho3+ and Ce3+. The quantitative analyses of ET mechanism between the doped rare-earth ions, together with the investigation on the changes of upconversion emission intensity and 2.0 µm fluorescence lifetime with Ce3+ were presented to elucidate the observed 2.0 µm band luminescent enhancement. Meanwhile, important spectroscopic parameters, such as radiative transition probability, absorption and emission cross-sections, and gain coefficient for Ho3+:5I7 → 5I8 transition, were calculated from the measured absorption spectrum to evaluate the potential radiative properties. Additionally, the measured DSC curve reveals the good thermal stability and the XRD pattern confirmed the amorphous structure of prepared glass host. The results indicate that Ho3+/Yb3+/Ce3+ tri-doped tellurite glass is a potential active medium for developing 2.0 µm band infrared solid lasers.

Upconverting YbPO4:RE monospheres (RE=Ho, Er, Tm)

AbstractUniform spheres of (Yb0.98RE0.02)PO4 orthophosphate (RE=Ho, Er, and Tm, respectively) were synthesized via a homogeneous precipitation procedure mediated by SO42− anions. The as‐precipitated and 1100°C calcined products were determined via laser‐diffraction particle sizing to have the average diameters of ~2.04 ± 0.67 and 1.80 ± 0.93 μm, respectively. The upconversion luminescence of RE3+ under sensitization by the host Yb3+ was studied for the calcination products under 978 nm laser excitation, and it was found that the emissions are dominated by a red band at ~650 nm for Ho3+ (5F5 → 5I8 transition), similarly strong green (~515‐565 nm, 2H11/2/4S3/2 → 4I15/2 transition) and red (~640‐680 nm, 4F9/2 → 4I15/2 transition) bands for Er3+, and a near‐infrared band at ~800 nm for Tm3+ (3H4 → 3H6 transition). The number of laser photons needed to populate the emitting state was determined by varying the excitation power, and the possible photon reactions leading to the observed upconversion were discussed.

Effects of the annealing temperature on the structure and up-conversion photoluminescence of ZnO film

The up-conversion film is being tried to increase the photoelectric conversion efficiency of the silicon solar cell. To improve the efficiency of the photoluminescence film, the effects of the annealing temperature were investigated on the structure and photoluminescence of the ZnO up-conversion film, which was prepared using the sol-gel method and the spin-coating technique. The results show that the organic compounds and water in the ZnO film were completely eliminated when the annealing temperature reached 500 °C. The crystallinity of film is improved and the average grain size continuously increases as increasing the annealing temperature. The transmittance in the wavelength range of 400–2000 nm continuously increases as the annealing temperature increases from 500 °C to 700 °C, whilst it decreases first and then increases as the annealing temperature increases from 800 °C to 1000 °C. When the film is excited with a laser of 980 nm, there are two intense emission bands in the up-conversion emission spectra, 542-nm green light and 660-nm red light, corresponding to Ho3+: 5S2/5F4 → 5I8 and 5F5 → 5I8 transitions, respectively. In addition, the intensity of up-conversion luminescence for the film increases first and then decreases with the increase of the annealing temperature. When the annealing temperature is at 900 °C, the film consists of small round compact particles with a high degree of crystallization, reaching maximum up-conversion intensity of the film.

Efficient 2 μm emission in Er3+/Ho3+ co-doped lead silicate glasses under different excitations

Er3+ has been considered one of the most suitable sensitive ions of Ho3+ to generate 2 μm emission. In this work, luminescent properties and energy transfer mechanism of Er3+/Ho3+ co-doped lead silicate glass were systematically investigated under 980 and 1550 nm excitations, respectively. Based on the absorption spectra, the Judd-Ofelt intensity parameters, absorption and emission cross sections, and gain coefficient were calculated. The emission cross section of Ho3+: 5I7 → 5I8 transition is as large as 8 × 10−21 cm2. And the calculated maximum gain coefficient is 3.48 cm−1 at 2010 nm. In addition, the energy transfer efficiency between Er3+: 4I13/2 level and Ho3+: 5I7 level can reach 89.3% when the samples were pumped by a 980 nm laser diode. An intense 2 μm emission was obtained upon excitation of 1550 nm due to the large absorption cross section of Er3+ at 1550 nm and efficient energy transfer from Er3+: 4I13/2 level to Ho3+: 5I7 level. These results suggest that the Er3+/Ho3+ co-doped lead silicate glass has great potential for application as a mid-infrared laser material.

Upconversion Luminescence of ZnO-TiO<sub>2</sub>: Ho<sup>3+</sup>/Yb<sup>3+</sup> Phosphor Powder

Ho3+/Yb3+ co-doped ZnO-TiO2 composite system were synthesized by powder-solution mixing method and their upconversion (UC) luminescence characteristics were investigated under the 980 nm laser excitation. The effect of various ZnO/TiO2 mixing ratios, and Ho3+ and Yb3+ concentrations were also studied. The XRD patterns showed that the product fired at 1300 °C consisted of Zn2TiO4, TiO2, RE2Ti2O7, and RE2TiO5 (RE = Ho3+ and/or Yb3+) phases. The green emission centered at 538 nm wavelength was detected as the strongest emission intensity which it was in accordance with the 5F4,5S2 → 5I8 transition of Ho3+ ion. The emission intensity of the product changed by varying ZnO/TiO2 mixing ratios, and Ho3+ and Yb3+ concentrations. Brightest UC emission was observed in the sample of 1ZnO:1TiO2 (in mole) doped with 0.03 mol% Ho3+, 9 mol% Yb3+ fired at 1300 °C for 1 h. Besides, the dependence of the UC emission intensity on the excitation power indicated that the two-photon process was responsible for this UC system.

Influence of gamma radiation on enhancement of luminescent properties of GdPO4:Yb3+@SiO2 nanophosphors

The core/shell luminescent GdPO4:Yb3+@SiO2 nanophosphors have been synthesized via a facile solution combustion method. The effect of Yb3+ concentration and γ-radiation on the crystal phase, morphology and luminescent properties of nanophosphors has been studied. Upon photo excitation at 487 nm, GdPO4:Yb3+@SiO2 emits strong red luminescence at 640 nm and NIR luminescence at 731 nm corresponding to the 5F5 → 5I8 and 5F4 → 5I7 transitions, respectively. A 10-fold increase in luminescence intensity has been observed after increasing the Yb3+ content from 1% to 5%. Further, the Vis/NIR luminescence intensity of these nanophosphors had enhanced progressively 3–7 folds and 10–13 folds after exposed to 150 and 300 kGy γ-radiation, respectively. The dual advantage of Vis-NIR luminescence aided with biocompatibility makes these nanophosphors promising materials for biomedical applications.

Spectroscopic traits of holmium in magnesium zinc sulfophosphate glass host: Judd – Ofelt evaluation

Basic understanding on the spectroscopic behaviour of holmium ion (Ho3+) doped in magnesium zinc sulfophosphate glass host is essential for the development of inexpensive and eye–safe infrared solid state laser. To achieve this goal, six such glass samples were prepared using melt quenching method at varying Ho3+ ions contents. FTIR and Raman spectra were recorded to determine the structural properties of the synthesized glasses. Samples were characterized using UV–Vis–NIR absorption and photoluminescence (PL) spectroscopy to determine the Ho3+ ions concentration dependent spectral properties. The absorption spectra of the studied glasses revealed seven peaks which were allocated to the transition from the ground state (5I8) to the excited states (3H6, 5G5, 5G6, 3K8, 5F3, 5F4+5S2, 5F5, 5I6, and 5I7) of Ho3+ ion. Judd–Ofelt (J–O) intensity parameters (Ω2, Ω4, and Ω6) and radiative parameters such as transition probabilities, fluorescence branching ratio, and radiative lifetime were calculated from the measured optical spectra. The nephelauxetic ratio shows negative value signifying ionic bond between REI and the ligand. The value of J–O parameters Ω2, Ω4, Ω6 and spectroscopic quality factor were varied in the range of (4.10 − 8.05) ×10−20 cm2, (1.96−2.77) ×10−20 cm2, (1.95−2.31) ×10−20 cm2 and (1.01 − 1.25), respectively. The small of Ω2 indicated high symmetry around Ho3+ ions while the large value of Ω4 and Ω6 signified the occurrence of high rigidity of the glasses. PL emission spectra of the synthesized glasses disclosed two significant bands assigned to 5F4 → 5I8 (green) and 5F5 → 5I8 (red) transitions. The stimulated emission cross–section for the green and red luminescence was ranged respectively between (8.60 − 10.79) ×10−21 cm2 and (9.35 − 11.62) ×10−21 cm2. The proposed glasses was established to be beneficial for solid state laser application.

Intense Red-Emitting Upconversion Nanophosphors (800 nm-Driven) with a Core/Double-Shell Structure for Dual-Modal Upconversion Luminescence and Magnetic Resonance in Vivo Imaging Applications.

In this study, intense single-band red-emitting upconversion nanophosphors (UCNPs) excited with 800 nm near-infrared (NIR) light are reported. When a NaYF4:Nd,Yb active-shell is formed on the 12.7 nm sized NaGdF4:Yb,Ho,Ce UCNP core, the core/shell (C/S) UCNPs show tunable emission from green to red, depending on the Ce3+ concentration under excitation with 800 nm NIR light. Ce3+-doped C/S UCNPs (30 mol %) exhibit single-band red emission peaking at 644 nm via a 5F5 → 5I8 transition of Ho3+. A high Nd3+ concentration in the shell results in strong absorption at around 800 nm NIR light, even though the shell thickness is not large, and small-sized C/S UCNPs (16.3 nm) emit bright red light under 800 nm excitation. The formation of a thin NaGdF4 shell on the C/S UCNPs further enhances the upconversion (UC) luminescence and sub-20 nm sized core/double-shell (C/D-S) UCNPs exhibit 2.8 times stronger UC luminescence compared with C/S UCNPs. Owing to the strong UC luminescence intensity and Gd3+ ions on the surface of nanocrystals, they can be applied as a UC luminescence imaging agent and a T1 contrast agent for magnetic resonance (MR) imaging. In vivo UC luminescence and high-contrast MR images are successfully obtained by utilizing the red-emitting C/D-S UCNPs.

Efficient 2.0 μm emission in Nd3+/Ho3+ co-doped SiO2-Al2O3-Na2CO3-SrF2-CaF2 glasses for mid-infrared laser applications

Nd3+/Ho3+ co-doped SiO2-Al2O3-Na2CO3-SrF2-CaF2-Ho2O3-Nd2O3 oxyfluorosilicate glasses have been prepared by high temperature melt-quenching method. The co-doped samples exhibit fluorescence bands centered at 892, 1058, 1330 nm and 2.0 μm under the excitation of 808 nm laser diode (LD). The energy transfer mechanism between Nd3+ and Ho3+ was analyzed based on the absorption, emission and the energy level structures of Nd3+ and Ho3+ ions. In the present investigation, the energy transfer efficiency from Nd3+ to Ho3+ reached ∼50% under the excitation of 808 nm. This result indicates that Nd3+ ions can be potentially used as sensitizers for Ho3+ ions to stimulate the NIR emissions. Stimulated emission cross-section was evaluated for the prominent 5I7 → 5I8 transition of Ho3+ ion by using the Mc-Cumber theory. The spectroscopic characteristics of Nd3+/Ho3+ co-doped oxyfluorosilicate glasses are found to be suitable as optical medium for mid infrared emission at ∼2.0 μm.

Energy transfer and 2 μm emission in Tm3+/Ho3+ co-doped (Y0.87La0.1Zr0.03)2O3 nanopowders

(Y0.87La0.1Zr0.03)2O3 nanopowders doped with various concentrations of Tm3+ and Ho3+ were prepared by the citrate method. The standard cubic Y2O3 phase can be matched in the Tm3+/Ho3+ co-doped (Y0.87La0.1Zr0.03)2O3 nanopowders. The nanopowders exhibit average particle sizes of 40, 60, 80 and 100 nm after calcinated at 900, 1000, 1100 and 1200 °C, respectively. The energy transfer from Tm3+ to Ho3+ and the optimum fluorescence emission around 2 μm were investigated. Results indicate that the emission bands at around 1.86 and 1.95 μm correspond to 3F4→3H6 transition of Tm3+ and 5I7→5I8 transition of Ho3+, respectively. Better spectral properties were achieved in Tm3+/Ho3+ co-doped (Y0.87La0.1Zr0.03)2O3 nanopowders with the average size of 100 nm obtained at the conditions of the treatment of precursors calcinated at 1200 °C for 2 h doped with 1.5 mol% Tm3+ and 1 mol% Ho3+.