5I7 Level Research Articles

Improved temperature sensing performance of YAG: Ho3+/Yb3+ by doping Ce3+ ions based on up-conversion luminescence

The YAG: Ho3+/xCe3+/Yb3+(x = 0.0, 0.2, 0.5, 1.0 mol%) up-conversion luminescence (UCL) materials were prepared with a melting method utilizing CO2 lasers. The UCL spectra of the prepared samples were measured under the excitation of a 980 nm laser diode. Since the energy gaps between 5I6 and 5I7 levels, 5F4/5S2 and 5F5 levels, 5F2,3/3K8 and 5F4/5S2 levels of Ho3+ match well with the energy gap between 5F5/2 and 5F7/2 levels of Ce3+, the generation of three cross-relaxation (CR) processes between Ho3+ and Ce3+ enables the doping of Ce3+ ions to tune the intensity and intensity ratio of the green emission to the red emission of the YAG: Ho3+/Yb3+ sample. The temperature sensing performances of the samples were analyzed. When both the temperature measurement range and sensitivity are considered, the YAG: Ho3+/0.2 mol%Ce3+/Yb3+ sample may be a more promising candidate for the temperature sensing material, the temperature measurement range of which is 298–1023 K, and the maximum absolute sensitivity and relative sensitivity are 0.0514 K-1 and 0.0094 K-1, respectively.

2.9 µm lasing from a Ho3+/Pr3+ co-doped AlF3-based glass fiber pumped by a 1150 nm laser.

Ho3+/Pr3+ co-doped AlF3-based glass fibers were fabricated by using a rod-in-tube method based on the matrix glass composition of AlF3-BaF2-CaF2-YF3-SrF2-MgF2-LiF-ZrF4-PbF2. Under the pump of a 1150 mW Raman fiber laser, a 2.9 µm laser was observed in a 19 cm long Ho3+/Pr3+ co-doped AlF3-based glass fiber with an output power of 173 mW and a slope efficiency of 10.4%. Ho3+/Pr3+ co-doped AlF3-based glasses were fabricated to investigate the deactivation effects of Pr3+ ions on the Ho3+:5I7 level. Our results showed that the Ho3+/Pr3+ co-doped AlF3-based glass fibers are potential gain media for ∼2.9µm lasers.

Enhanced mid-infrared emissions of Ho3+/Er3+ co-doped Na5Y9F32 single crystal by introduction of Pr3+ ions

The Na5Y9F32 fluoride single crystals tri-doped with ∼1 mol% Ho3+/∼1 mol% Er3+, and various concentrations of Pr3+ (0, 0.5, 0.8 and 1.0 mol%) were successfully grown by a modified Bridgman method. The absorption, Raman, emission spectra and fluorescence decay curves of Pr3+/Ho3+/Er3+ tri-doped Na5Y9F32 single crystals were studied systematically. The intensity parameters (Ω2 = 1.96 × 10−20 cm2, Ω4 = 1.66 × 10−20 cm2, Ω6 = 1.46 × 10−20 cm2) of Er3+ ions and emission cross-sections at ∼2.7 μm (1.76×10−20 cm2) and ∼2.9 μm (1.34×10−20 cm2) were calculated according to the measured absorption spectra. The emission intensities at ∼2.7 μm of Er3+: 4I11/2 → 4I13/2 and ∼2.9 μm of Ho3+: 5I6→5I7 were enhanced gradually as increase of Pr3+ concentrations from 0 to 1.0 mol% under excitation of 800 nm laser diode (LD). However, the ∼2.0 μm of Ho3+: 5I7→5I8 and ∼1.5 μm of Er3+: 4I13/2 → 4I15/2 were gradually reduced. The introduction of Pr3+ can greatly reduce the lifetimes of Er3+: 4I13/2 and Ho3+: 5I7. The energy transfer from Er3+: 4I13/2 to Ho3+: 5I7 level and depopulating Er3+: 4I13/2 and Ho3+: 5I7 levels under the action of Pr3+ ions are responsible for the enhancement of ∼2.7 and ∼2.9 μm emissions. The Pr3+/Ho3+/Er3+ tri-doped Na5Y9F32 single crystal may become a new choice for ∼3.0 μm mid-infrared solid-state laser.

Yb,Ho,Pr:GYTO晶体生长、结构及光谱性能（特邀）

A new mid infrared laser material Yb,Ho,Pr:GYTO crystal was grown successfully using Czochralski method for the first time. The structural parameters were obtained by the X-ray Rietveld refinement method. The X-ray rocking curves of the (100), (010), and (001) diffraction face of Yb,Ho,Pr:GYTO crystal were measured. The full widths at half maximum of those diffraction peaks are 0.036°, 0.013°, and 0.077°, respectively, which indicates a high crystalline quality of the as-grown crystal. Laser Ablation Inductively-Coupled Plasma Mass Spectrometry was used to measure the concentrations of Yb3+, Ho3+, Pr3+, and Y3+ ions in the Yb,Ho,Pr:GdYTaO4 crystal. The effective segregation coefficients of Yb3+, Ho3+, Pr3+, and Y3+ in Yb,Ho,Pr:GYTO crystal are 0.624, 1.220, 1.350, and 0.977, respectively. The room-temperature polarhosized absorption spectra of Yb,Ho,Pr:GdYTaO4 was measured and the corresponding absorption transitions were assigned. The 2.9 μm fluorescence spectrum excited by 940 nm LD presents that the strongest emission is located at 2908 nm. In addition, the Yb-Ho-Pr energy transfer mechanism in GYTO was also demonstrated. Compared with Ho:GYTO crystal, the lifetime of 5I7 level of Yb,Ho,Pr:GYTO crystal is reduced by 87.13%, which is close to that of the upper level 5I6, indicating that Yb,Ho,Pr:GYTO crystal is easier to realize population inversion and laser output.

Triple-wavelength lasing at 1.50 μm, 1.84 μm and 2.08 μm in a Ho3+/Tm3+ co-doped fluorozirconate glass microsphere

Simultaneous 1.50 μm, 1.84 μm and 2.08 μm laser emission is observed in a Ho3+/Tm3+ co-doped ZrF4–BaF2–YF3–AlF3 (ZBYA) fluoride glass microsphere when pumped using a 793 nm laser diode. The ZBYA fluoride glass microsphere was prepared using a CO2 laser heating method and whispering-gallery modes (WGM) were excited when the pump light was coupled using a tapered fiber. The introduction of Ho3+ ions reduced the population of the long-lived Tm3+:3F4 level and removed the 3H4→ 3F4 self-termination effect, resulting in the population of the Ho3+:5I7 level through a resonant energy transfer process. As the 793 nm laser pump power grows, lasing occurs initially at 2.08 μm, followed by the cascade outputs at 1.50 μm and 1.84 μm.

Growth, structure, and spectroscopic properties of an Yb3+, Ho3+ co-doped LuYAG single crystal for 2.91 μm laser

Yb3+ and Ho3+ co-doped Lu2.55Y0.45Al5O12 (Yb,Ho:LuYAG) crystal with a size of Φ 28 mm × 120 mm was successfully grown by the Czochralski method. The lattice parameters of the as-grown Yb,Ho:LuYAG crystal were obtained by Rietveld refinement with the XRD data. The result of X-ray rocking curve indicated that the grown crystal has a high crystalline quality. From strong absorption band near 935 nm and emission bands within 2700–3000 nm, we found that the Yb3+ ions can be acted as the sensitizer for the activator ions Ho3+. Furthermore, the lifetimes of the 5I6 and 5I7 levels of the Ho3+ ions were 68.25 μs and 7.58 ms, respectively. These results indicated that the Yb,Ho:LuYAG crystal is a promising gain material for 2.91 μm laser pumped by a 940 nm LD.

Enhanced 2.0 µm emission in Nd3+/Yb3+/Ho3+ tri-doped tellurite glass: Role of Yb3+ as a bridge

In this paper, Nd3+/Yb3+/Ho3+ tri-doped scheme was developed and the enhanced 2.0 µm band emission of Ho3+ by introducing the third Yb3+ into Nd3+/Ho3+ co-doped tellurite glass was obtained. Under the excitation of 808 nm laser diode (LD), the near-infrared emission spectrum displayed that the 2.0 µm band peak intensity was increased by about 2.4 times when introducing 1 mol% amount of Yb2O3, which is attributed to the newly established energy transfer channel of Nd3+ → Yb3+ → Ho3+. The decrease of Nd3+:4F3/2 level lifetime and increase of Ho3+:5I7 level lifetime evaluated from the fluorescence decay curves demonstrated the observed luminescent phenomenon. The mechanism analysis about energy transfer together with micro-coefficient calculation were carried out to understand the role of Yb3+ as a bridge and phonon assistance in the accomplishment of energy transfers among Nd3+, Yb3+ and Ho3+. Meanwhile, the 2.0 µm band spectroscopic property of Ho3+, the structural information and thermal stability of tellurite glass were investigated by application of Judd-Ofelt theory, and measurements of XRD pattern and DSC curve respectively. The obtained results indicate that Nd3+/Yb3+/Ho3+ tri-doped tellurite glass with good thermal stability is a promising candidate material in improving 2.0 µm band emission performance of Ho3+.

Efficient Ho:(Sc0.5Y0.5)2SiO5 laser at 2.1 µm in-band pumped by Tm fiber laser.

In this paper, we demonstrate a new 2.1-µm Ho:(Sc0.5Y0.5)2SiO5 (Ho:SYSO) laser at room temperature. The absorption and emission spectra of Ho:SYSO crystal were studied at temperature of 300 K. The strongest absorption peak of 5I7 level of Ho ions in SYSO crystal is located at 1943 nm with cross section of 0.79 × 10-20 cm2. The maximum emission cross section of 1.74 × 10-20 cm2 is located at 2032 nm. A 1940.3-nm narrow-linewidth Tm fiber was used to pump the Ho:SYSO crystal. At absorbed pump power of 20.4 W, the continuous wave Ho:SYSO laser yielded 10.3 W maximum output power at 2097.67 nm and 54.7% slope efficiency respect with absorbed pump power. In addition, we have estimated the beam quality factor (M2) of Ho:SYSO laser to be 1.7 near maximum output level.

Growth and spectroscopic properties of Ho3+ doped GdYTaO4 single crystal

A promising 2.9 µm Ho:GdYTaO4 laser crystal was grown successfully by the Czochralski method for the first time. The crystal belongs to the monoclinic space group of I2/a (No. 15) and high crystalline quality is demonstrated by X-ray rocking curves. The spectral properties of Ho:GdYTaO4 crystal at room temperature are investigated. Based on the Judd–Ofelt theory, the intensity parameters, spontaneous transition probabilities, fluorescence branching ratios, and radiative lifetimes are obtained in detail. The strongest emission peak is located at 2848 nm, and the full width at half maximum is about 15 nm. The experimental lifetimes of 5I6 and 5I7 levels are 0.31 and 8.08 ms, respectively. Moreover, the Stark levels of 5I6, 5I7, and 5I8 are identified and the splitting values are calculated to be 254.1, 226.7, and 370. 4 cm−1, respectively.

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.

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.

Dual effects of Nd3+ in Nd3+/Ho3+:CaLaGa3O7 crystal on 2.86 µm emission

Enhanced 2.86 µm emission corresponding to Ho3+: 5I6→5I7 was achieved in Nd3+/Ho3+ codoped CaLaGa3O7 crystal for the first time. The detailed spectroscopic properties and energy transfer mechanism of the as-grown crystal were investigated. The results show that the Nd3+ ion is not only a very good sensitizer in a Ho3+ doped CaLaGa3O7 crystal, but also an appropriate deactivated ion with efficient depopulation of the Ho3+: 5I7 level for enhancing the 2.86 µm fluorescence emission. And the energy transfer efficiency of Ho3+: 5I7→Nd3+: 4I13/2 is estimated to be 93%, which indicates that the self-termination effect for the 2.86 µm holmium laser is suppressed successfully in Nd3+/Ho3+: CaLaGa3O7 crystal. Besides, the thermal properties of Nd3+: CaLaGa3O7 crystal were also studied. In conclusion, the introduction of Nd3+ is favorable for achieving an enhanced 2.86 µm emission in Nd3+/Ho3+: CaLaGa3O7 crystal, which can act as a new promising candidate for mid-infrared lasers.

Positive influence of Sm3+ ion on the ~ 2.85 µm emission in Yb3+/Ho3+ co-doped silica-germanate glass

In present work, a novel sensitized ion: Sm3+ activated Yb3+/Ho3+ co-doped silica-germanate glasses have been synthesized by melt quenching method. Absorption spectra and mid-infrared photo-luminescence of prepared glasses were characterized and compared in parallel. Quintuple enhancement of ~ 2.85 µm emission was achieved successfully in Yb3+/Ho3+ co-doped silica-germanate glass with 0.3 mol% Sm3+ addition, which also possesses a large stimulated emission cross section (14.9 × 10–21 cm2). Sensitized effect of Sm3+ and efficient energy transfer (ET) mechanism of Ho3+:5I7→Sm3+:6H13/2 in the co-doped silica-germanate glasses were investigated under 980 nm laser diode excitation. Moreover, decay profiles of Ho3+:5I7 level were measured to further examine the high ET efficiency (η) of Ho3+:5I7 to Sm3+:6H13/2, which confirmed the efficient population inversion of Ho3+ ~ 2.85 µm emission. All results indicate that the Yb3+/Ho3+/Sm3+ tri-doped silica-germanate glass is a promising candidate material for improving the Ho3+ ~ 2.85 µm fiber laser performance.

Growth, structure and optical properties of Yb/Ho: CaLaGa3O7 laser crystal

Yb/Ho: CaLaGa3O7 as mid-IR laser crystal was successfully grown by the Czochralski method for the first time. The effects of Yb3+ on the structure parameters and spectroscopic properties have been investigated. In comparison with Ho3+ singly-doped CaLaGa3O7 crystal, Yb3+ not only enhances 2.86 µm emission but also depopulates the Ho3+: 5I7 level in Yb/Ho: CaLaGa3O7 crystal, which is beneficial to the possible population inversion for Ho3+: 5I6→5I7. Results indicate that the prepared Yb/Ho: CaLaGa3O7 crystal is a promising candidate for 2.86 μm mid-infrared laser applications.

2.75 μm spectroscopic properties and energy transfer mechanism in Er/Ho codoped fluorotellurite glasses

We report a detailed spectroscopic investigation of a series of fluorotellurite glasses with different Er3+ ions concentration in system 50TeO2-27BaF2-9ZnF2-8YF3-3MgF2-3NaF-xErF3-1HoF3(x = 1,2,3 mol%). Intense 2 μm emission and 2.75 μm emission with high absorption and emission cross-section were observed under 980 nm LD pumping, and the maximum gain coefficient around 2750 nm was as high as 2.41 cm−1, suggesting the prepared glasses are a competitive candidate for mid-infrared laser materials. Besides, it was found that the trend of 2 μm and 2.75 μm emission intensity varied with Er3+ ions concentration was different. Energy transfer process was discussed subsequently to explain this phenomenon. Furthermore, we quantitatively investigate the energy transfer efficiency from Er3+: 4I13/2 level to Ho3+: 5I7 level.

2.8\u2009\u03bcm emission and OH quenching analysis in Ho3+ doped fluorotellurite-germanate glasses sensitized by Yb3+ and Er3+

The use of Yb3+ and Er3+ co-doping with Ho3+ to enhance and broaden the Ho3+: 5I6 → 5I7 ~2.8 μm emissions are investigated in the fluorotellurite-germanate glasses. An intense ~3 μm emission with a full width at half maximum (FWHM) of 245 nm is achieved in the Er3+/Ho3+/Yb3+ triply-doped fluorotellurite-germanate glass upon excitation at 980 nm. The glass not only possesses considerably low OH− absorption coefficient (0.189 cm−1), but also exhibits low phonon energy (704 cm−1). Moreover, the measured lifetime of Ho3+: 5I6 level is as high as 0.218 ms. In addition, the energy transfer rate to hydroxyl groups and quantum efficiency (η) of 5I6 level were calculated in detail by fitting the variations of lifetimes vs. the OH− concentrations. The formation ability and thermal stability of glasses have been improved by introducing GeO2 into fluorotellurite glasses. Results reveal that Er3+/Ho3+/Yb3+ triply-doped fluorotellurite-germanate glass is a potential kind of laser glass for efficient 3 μm laser.

Mid-infrared fluorescence properties, structure and energy transfer around 2 µm in Tm3+/Ho3+ co-doped tellurite glass

Tm3+/Ho3+ doped tellurite glasses with good thermal stability and low phonon energy are prepared. 1.8µm fluorescence, enhanced near 2µm fluorescence and a weak 2.3µm fluorescence are observed in the Tm3+/Ho3+ co-doped glasses. The energy transfer mechanism between Tm3+ and Ho3+ has been analyzed according to the absorption spectra, the emission spectra and the level structures of Tm3+ and Ho3+ ions. The decay lifetime of 1.8µm and 2µm fluorescence in Tm3+/Ho3+ co-doped tellurite glass are 0.38ms and 2.46ms, respectively. Moreover, the energy transfer efficiency between Tm3+:3F4 and Ho3+:5I7 levels is calculated and compared. Additionally, the calculated forward energy transfer coefficient CTm-Ho is about five times as large as the reverse energy transfer coefficient CHo-Tm. Results demonstrate that the Tm3+/Ho3+ doped tellurite glass has excellent spectroscopic properties and can be an attractive candidate for 2µm laser.

Growth, spectroscopy, and laser performance of a radiation-resistant Cr,Yb,Ho,Pr:GYSGG crystal for 2.84 µm mid-infrared laser

A new Cr3+, Yb3+, Ho3+, and Pr3+ co-doped GYSGG (Gd2YSc2Ga3O12) single crystal with a size of Φ 26mm × 80mm was grown successfully using the Czochralski method for the first time. Absorption spectrum is studied, and main absorption bands are centered at 449, 638, and 934nm. The fluorescence spectrum shows a broad emission band around 2.8µm, indicating the Cr3+ and Yb3+ ions can act as the sensitizer for the Ho3+ ions. The fluorescence lifetimes of the 5I6 and 5I7 levels of the Ho3+ ions are fitted to be 0.39 and 5.31ms, respectively. By comparison with those of the Cr,Yb,Ho:GYSGG crystal, the Pr3+ ions acting as the deactivator can decrease efficiently the lifetime of the lower laser level 5I7 of the Ho3+ ions. Additionally, a flash lamp pumping 2.84µm laser with maximum average power of 257mW is achieved. These results indicate the Cr,Yb,Ho,Pr:GYSGG crystal is a new promising radiation-resistant laser gain medium applied in radiant environment.

Improvement of Green Upconversion Monochromaticity by Doping Eu3+ in Lu2O3:Yb3+/Ho3+ Powders with Detailed Investigation of the Energy Transfer Mechanism.

The monochromaticity improvement of green upconversion (UC) in Lu2O3:Yb3+/Ho3+ powders has been successfully realized by tridoping Eu3+. The integral area ratio of green emission to red emission of Ho3+ increases 4.3 times with increasing Eu3+ doping concentration from 0 to 20 mol %. The energy transfer (ET) mechanism in the Yb3+/Ho3+/Eu3+ tridoping system has been investigated carefully by visible and near-infrared (NIR) emission spectra along with the decay curves, revealing the existence of ET from the Ho3+5F4/5S2 level tothe Eu3+5D0 level and ET from the Ho3+5I6 level to the Eu3+7F6 level. In addition, the population routes of the red-emitting Ho3+5F5 level in the Yb3+/Ho3+ codoped system under 980 nm wavelength excitation have also been explored. The ET process from the Yb3+2F5/2 level to the Ho3+5I7 level and the cross-relaxation process between two nearby Ho3+ ions in the 5F4/5S2 level and 5I7 level, respectively, have been demonstrated to be the dominant approaches for populating the Ho3+5F5 level. The multiphonon relaxation process originating from the Ho3+5F4/5S2 level is useless to populate the Ho3+5F5 level. As the energy level gap between the Ho3+5I7 level and Ho3+5I8 level matches well with that between Eu3+7F6 level and Eu3+7F0 level, the energy of the Ho3+5I7 level can be easily transferred to the Eu3+7F6 level by an approximate resonant ET process, resulting in a serious decrease in the red UC emission intensity. Since this ET process is more efficient than the ET from the Ho3+5F4/5S2 level to the Eu3+5D0 level as well as the ET from the Ho3+5I6 level to the Eu3+7F6 level, the integral area ratio of green emission to red emission of Ho3+ has been improved significantly.

Upconversion luminescence of Ca1−xHoxF2+x and Sr0.98−xEr0.02HoxF2.02+x powders upon excitation by an infrared laser

Fluorite-type Ca1−xHoxF2+x and Sr0.98−xEr0.02HoxF2.02+x powders were synthesized using the co-precipitation from water solution technique. The upconversion luminescence of Ca1−xHoxF2+x and Sr0.98−xEr0.02HoxF2.02+x powders in the visible spectral region upon excitation of 5I7 level Ho3+ ions and 4I13/2 level Er3+ ions were studied for the first time. The possibility of visualizing near IR laser radiation using Ca1−xHoxF2+x and Sr0.98−xEr0.02HoxF2.02+x powders is proposed. Optimal compositions of Ca1−xHoxF2+x and Sr0.98−xEr0.02HoxF2.02+x powders for application as visualizers are discussed.