3H4 Transition Research Articles

Structural analysis of deeply charged Li(Ni0.95Co0.04Al0.01)O2 cathode for Li-ion battery.

LiNi0.95Co0.04Al0.01O2 (NCA95) is charged up to 4.6 V to study its structural stability at a highly delithiated state using transmission electron microscopy (TEM). The TEM analysis shows that the localized depletion of Li ions near the surface triggers the transition from the H3 phase to the H4 phase with the H4 phase with the O1 stacking appearing as a series of stacking faults even at 4.4 V. The H3 → H4 transition appears to be irreversible and leads to the initial capacity loss. In addition, intraparticle cracks are observed when charged above 4.3 V. These intraparticle microcracks, unlike interparticle cracks that become sealed upon Li-uptake, likely remain during deintercalation, compromising the mechanical stability of the cathode and lead to fast deterioration of the cycling stability. The TEM analysis of the overcharged NCA95 cathode suggests a clear limit above which the cathode can be cycled without significant capacity loss. The introduction of doping elements that promote the migration of Ni2+ ions into the Li layer would hinder the H3 → H4 transition and help suppress the intraparticle cracks.

Down-conversion luminescence and thermometric properties of novel orange-red Bi2Mo3O12:Pr3+ phosphors

Bi2Mo3O12: Pr3+ phosphors have been successfully synthesized through a one-step solid-state reaction method. The effects of Pr3+ concentration on lattice constants and optical properties were also studied. XRD patterns showed well-crystallized monoclinic structures for the prepared Bi2Mo3O12 and Bi2Mo3O12: Pr3+ samples. The UV–visible diffuse reflectance spectra indicated strong absorption in the ultraviolet region. Excitation spectra demonstrated that the Bi2Mo3O12: Pr3+ could be efficiently excited under UV light in the 250–430 nm range and blue light at 450 nm. By varying the excitation wavelength, the emission color could be tuned from orange-red to red region. The strongest emission peak is located at around 597 nm, which is attributed to the 1D2→3H4 transition of Pr3+. An optical thermometer based on fluorescence intensity ratio (FIR) shows a high sensitivity of Sr = 2.02 % K−1, indicating the developed materials have potential applications in the optical temperature sensing field.

Visible/near-infrared luminescence and concentration effects of Pr3+-doped Sr2Al2GeO7 downconversion phosphors

The Pr3+ ion has been widely doped into various materials as a red and near-infrared (NIR) emitting center for applications in lighting and solar spectrum downconversion. Herein, the preparation of a new library of Pr3+-doped Sr2Al2GeO7 phosphors was proved by powder x-ray diffraction patterns and Rietveld refinements and characterized by a scanning electron microscope with energy-dispersive x-ray spectrometry. The Sr2Al2GeO7:Pr3+ sample strongly absorbs blue photons over 420–500 nm and yields intense visible emissions with dominant peaks around 490 nm from the Pr3+ 3P0 → 3H4 transition, as well as robust NIR emission bands over 800–1200 nm. In addition to the typical transitions of 1D2 → 3F2 at 880 nm, 1G4 → 3H4 at 1000 nm, and 1D2 → 3F3,4 at 1070 nm, the distinguishable NIR emission at 929 nm was demonstrated from the 3P0 → 1G4 transition via static and dynamic spectroscopic analysis. Most interestingly, for the 3P0 blue-excited state, a considerably elevated concentration of about 10%Pr3+ was optimal for the visible/NIR emissions, in stark contrast to the diluted optimal 1%Pr3+ for the 1D2 state. The relevant cross-relaxation from the 3P0 and 1D2 states between Pr3+ was comprehensively treated by theoretical speculations and experimental results. Such concentrated Pr3+ blue activators would significantly facilitate the blue-to-NIR downconversion through a desired two-step sequential transition from the 3P0 initial state to the 1G4 intermediate level for quantum efficiency exceeding unity. The current results would consolidate the basis of concentrated Pr3+ donors to promote the novel Pr3+/Yb3+ codoping downconversion for greatly increasing Si solar cell efficiency.

Microstructures and properties of Pr,Ce:Gd2O2S ceramics fabricated from powders synthesized at different initial water bath temperatures

Crystallized precursor with stacked layered was synthesized in hot water bath using oxide powders and concentrated sulfuric acid as raw materials. Gd2O2S powders with high phase purity were obtained by reducing the precursor under flowing hydrogen atmosphere. The influence of initial bath temperature of Gd2O3 and H2SO4 on the microstructure of Gd2O2S powders was investigated. The Gd2O2S:Pr,Ce powders showed a stacked layered structure and as the initial water bath temperature increases, the particle size of the flaky powders also increases. Using the synthesized powders, Gd2O2S:Pr,Ce scintillation ceramics were fabricated through pre-sintering in vacuum followed by HIP post-treatment in argon atmosphere. The Gd2O2S:Pr,Ce ceramics fabricated from the powders synthesized at lower initial water bath temperature show a rapid densification rate during pre-sintering. The Gd2O2S:Pr,Ce ceramic sample fabricated from powders synthesized at 7°C showed the highest optical transmittance, XEL intensity, and light yield value of 25,800 ph/MeV @ 662 keV γ rays. The PL decay time of Pr3+3P0→3H4 transition was measured to be ∼2.87 μs for all ceramic samples. The effect of the initial water bath temperature on optical transmittance and light yield of Gd2O2S:Pr,Ce ceramics was also discussed.

Diode-end-pumped self-Q-switched Tm:YAlO3 laser at 2362 nm

A diode-end-pumped self-Q-switched Tm:YAlO3 laser at 2362 nm based on 3H4→3H5 transition is proposed for the first time according to the references. The max mean output power of 0.41 W with a slope efficiency of 14.1% was obtained under the absorbed pump power of 6.7 W, corresponding pulse width and pulse repetition frequency were 7.82 μs and 45.09 kHz respectively. By analyzing the laser beam spatial distribution, the self-Q-switched Tm:YAlO3 laser at 2362 nm was originated from the time-dependent lens mechanism. The present research provides an approach for generating Q-switched lasers in the 2.3 μm spectral region.

Blue-excitable orange-red-emitting M3Y(PO4)3:Pr3+ (M = Ba, Sr, Ca) phosphors for multifunctional applications.

Research on multifunctional luminescent materials has become an emerging trend for new applications of optical sensing, monitoring, anticounterfeiting, lighting, etc. Herein, a library of Pr3+-doped M3Y(PO4)3 (M = Ba, Sr, Ca) phosphors was prepared for careful spectroscopic studies in potential lighting and optical temperature sensing applications. With the help of density functional theory calculation, diffuse reflectance spectra, and steady/dynamic photoluminescence spectra, the effects of alkaline earth metals on the fluorescence properties of M3Y(PO4)3:Pr3+ were studied systematically. Under the excitation of blue ∼ 445 nm, orangish-red fluorescence of approximately 602 nm was efficiently detected due to Pr3+ 1D2 → 3H4 transition, which becomes stronger by regulating alkaline-earth elements from Ba to Sr and to Ca. An optimized Ca3Y(PO4)3:0.7%Pr3+ sample was validated with excellent thermal stability 89%@423 K and further applied to fabricate a white light emitting diode by combining with commercial YAG:Ce3+ phosphors on a 445 nm blue chip. Specifically, CIE chromaticity coordinates (0.3510, 0.3650) and correlated color temperature (∼ 4838 K) were obtained for an obvious improvement. Moreover, optical thermometry properties of Ca3Y(PO4)3:0.7%Pr3+ were explored on basis of Pr3+ 3P0-3P1 thermally coupled energy levels. Their fluorescence intensity ratios following the Boltzmann equation could be operated over 298-598 K with superior relative sensitivity ∼ 0.87% K-1 at 298 K. These interesting results for multifunctional luminescence will greatly promote the development of novel Pr3+-doped luminescent materials as well as the related photoelectric devices.

Luminescence of Yb3+ incorporated into SrTi1-xZrxO3 solid-solutions: Inquiring into the charge transfer state nature in lanthanide-doped titanates

For more than forty years, quenching of the 3P0 → 3H4 emission in favor of the 1D2 → 3H4 one in Pr3+-doped titanates has been explained by a mechanism involving a metal-to-metal charge transfer (MMCT) state, profusely designated in the literature as IVCT Pr3+/Ti4+ → Pr4+/Ti3+ state. Here, we present experimental evidence making unnecessary this mechanism and supporting theoretical results that points towards an alternative process based on a ligand-to-metal charge transfer (LMCT) O2−/Ti4+ → O−/Ti3+ state as being responsible for that quenching (Z. Barandiarán et al. J. Phys. Chem. Lett. 2017, 8, 3095). Photoluminescent spectra of Yb3+ incorporated into SrTi1-xZrxO3 solid-solutions interpreted in the framework of phenomenological models leading to vacuum referred binding energy diagrams and compared with equivalent solid solutions but doped with Pr3+, indicate that the emission of both lanthanide ions is excited through the same host state: the LMCT O2−/Ti4+ → O−/Ti3+ state. Photoluminescence spectra and decay curves performed in Pr-doped SrTiO3 as a function of the temperature suggest a thermally activated mechanism as being responsible for the quenching of the emission associated with the 3P0 → 3H4 transition.

Crystal growth, polarized spectral properties, and 2.3 µm laser performance of Tm:LuVO4 crystal

We report on the Czochralski crystal growth, polarized optical spectroscopy, and the first continuous-wave laser operation of 1.5 at.% Tm:LuVO4 crystal on the 3H4 → 3H5 transition. The polarized absorption and stimulated-emission properties of Tm3+ ions in LuVO4 were revised and the crystal-field splitting of the Tm3+ multiplets was determined by low-temperature (12 K) spectroscopy. The maximum stimulated-emission cross-section for the 3H4 → 3H5 transition is 2.48 × 10−20 cm2 at 2363 nm for π-polarization corresponding to an emission bandwidth of 28 nm. Evidence of phonon-assisted emissions of Tm3+ ions above 2 µm is presented. The broadband emission properties of the Tm:LuVO4 crystal make it promising for ultrashort pulse generation. Additionally, pumped by a 796 nm fiber-coupled laser diode, the Tm:LuVO4 laser generated a Watt-level output power at 2279-2295 nm with a slope efficiency of 9.2% and linearly polarized emission (π-polarization).

Diode-pumped continuous-wave Pr:YLF cyan laser

We demonstrate continuous-wave quasi-three-energy level laser operation in the cyan region with an LD-pumped Pr:YLF laser. Based on the 3P0→3H4 transition, a continuously tunable Pr:YLF cyan laser was realized with a wavelength tunable range of 490.41 nm–491.72 nm, corresponding to a maximum power of 72 mW–244 mW. Under the same pumping scheme, a maximum output power of 255 mW was achieved at 491 nm using Pr:YLF, corresponding to a slope efficiency of 7.2 %. To our knowledge, this is the highest power produced at room temperature by a cyan laser demonstrated with a Pr:YLF crystal. This work provides a simple and effective scheme to generate high-power cyan lasers at room temperature for various applications, such as underwater communications and fluorescence detection.

Large-Area Near-Infrared Emission Enhancement on Single Upconversion Nanoparticles by Metal Nanohole Array.

Single lanthanide (Ln) ion doped upconversion nanoparticles (UCNPs) exhibit great potential for biomolecule sensing and counting. Plasmonic structures can improve the emission efficiency of single UCNPs by modulating the energy transferring process. Yet, achieving robust and large-area single UCNP emission modulation remains a challenge, which obstructs investigation and application of single UCNPs. Here, we present a strategy using metal nanohole arrays (NHAs) to achieve energy-transfer modulation on single UCNPs simultaneously within large-area plasmonic structures. By coupling surface plasmon polaritons (SPPs) with higher-intermediate state (1D2 → 3F3, 1D2 → 3H4) transitions, we achieved a remarkable up to 10-fold enhancement in 800 nm emission, surpassing the conventional approach of coupling SPPs with an intermediate ground state (3H4 → 3H6). We numerically simulate the electrical field distribution and reveal that luminescent enhancement is robust and insensitive to the exact location of particles. It is anticipated that the strategy provides a platform for widely exploring applications in single-particle quantitative biosensing.

Diode-pumped cascade Tm:YAG laser at ∼2 μm and ∼2.3 μm

We report on the first cascade continuous-wave operation of the Tm:YAG crystals with different doping concentrations (2 at.% Tm:YAG and 3.5 at.% Tm:YAG) on the 3F4 → 3H6 (at ∼2 μm) and 3H4 → 3H5 (at ∼2.3 μm) transitions. With the lower concentration of Tm-doped YAG, the cascade laser generated a maximum total output power of 4.70 W with a higher slope efficiency of 23.9 %, out of which 0.79 W are obtained based on the 3H4 → 3H5 transition at ∼2.3 μm. Such laser that combing the two emission wavelengths makes it has potential application in some special field, e.g., gas detection.

Polarized spectral properties and 2.3 µm laser performance of the Tm:YVO4 crystal

The polarized spectral properties and ∼2.3 µm high-power continuous-wave laser operation of Tm3+-doped yttrium orthovanadate crystal (Tm:YVO4) are reported. For the 3H4 → 3H5 transition, the stimulated-emission cross-section σSE is 1.01 × 10−20 cm2 at 2276 nm corresponding to a large emission bandwidth of 52 nm (for π-polarization). Pumped by a 794 nm laser diode, the 1.5 at.% Tm:YVO4 laser delivered 5.52 W at 2.29 µm with a slope efficiency of 19.9%, a laser threshold of 8.70 W, and a linear laser polarization (π). The Tm laser operated on the cascade scheme (on the 3H4 → 3H5 and 3F4 → 3H6 transitions) which was mainly responsible for the observed high laser slope efficiency. We also report on the first passively Q-switched Tm:YVO4 laser at 2.3 µm by employing porous nano-grained cuprous selenide (PNG-Cu2Se) as a saturable absorber. The shortest pulse duration and the highest single pulse energy amounted to 706 ns and 3.65 µJ, respectively, corresponding to a pulse repetition rate of 62.8 kHz.

4.1 W continuous-wave and broadly wavelength tunable Tm-doped laser in 2.1-2.4 µm spectral region based on vibronic and electronic transitions

Efficient diode-pumped continuous-wave (CW) and wavelength tunable Tm:YAP lasers based on the vibronic and electronic transitions are investigated. A total maximum output power of 4.1 W is achieved with multi-wavelength output around 2162 nm and 2274 nm, corresponding to a slope efficiency of 29.8% for a 3 at. % Tm:YAP crystal. A maximum output power of 2.48 W with a slope efficiency of 25.4% is obtained at 2146 nm for a 4 at. % Tm:YAP crystal. Using a birefringent filter (BF), the emission wavelengths of the Tm:YAP laser are tuned over spectral ranges of 59 nm from 2115 nm to 2174 nm and 127 nm from 2267 nm to 2394 nm, respectively, which is the first demonstration of wavelength tunable Tm:YAP laser based on the electronic transition 3H4→3H5 and vibronic transition 3F4→3H6, to the best of our knowledge. The results show great potentials of the Tm:YAP crystal for realizing efficient lasers in the spectral range of 2.1-2.4 µm.

High-power 2.3 µm Tm:YLF laser with intracavity upconversion pumping by a Nd:ASL laser at 1051 nm.

A Tm:LiYF4 laser operating on the 3H4 → 3H5 transition is embedded in a high-power diode-pumped Nd:ASL laser for intracavity upconversion pumping at 1.05 µm. This leads to a record-high output power at 2.3 µm for any bulk thulium laser pumped by an upconversion process. The continuous-wave Tm:LiYF4 laser delivers 1.81 W at 2.3 µm for 32 W of laser-diode pump power, making this kind of pumping competitive with direct diode pumping. The intracavity pumping process allows for counteracting the low absorption inherent to upconversion pumping and to dispatch the thermal loads on two separate laser crystals. The proposed laser architecture also features a relatively weak heating of the Tm:LiYF4 crystal and an increased tolerance to Tm3+ absorption. This laser design opens a new paradigm that holds great promise for high-power 2.3-µm solid-state lasers based on thulium ions.

Upconversion-pumped femtosecond thulium laser at 2309 nm mode-locked by a GaSb-based SESAM

We report on a femtosecond thulium laser operating on the 3H4 → 3H5 transition with upconversion pumping around 1 µm and passively mode-locked by a GaSb-based SEmiconductor Saturable Absorber Mirror (SESAM). This laser employs a 6 at.% Tm:LiYF4 laser crystal and a polarization maintaining Yb-fiber master oscillator power amplifier at 1043 nm as a pump source addressing the 3F4 → 3F2,3 excited-state absorption transition of Tm3+ ions. In the continuous-wave regime, the Tm-laser generates 616 mW at ∼2313 nm with a slope efficiency of 10.0% (vs. the incident pump power) and a linear polarization (π). By implementing a type-I SESAM with a single ternary strained In0.33Ga0.67Sb quantum well embedded in GaSb for sustaining and stabilizing the soliton pulse shaping, the self-starting mode-locked Tm-laser generated pulses as short as 870 fs at a central wavelength of 2309.4 nm corresponding to an average output power of 208 mW at a pulse repetition rate of 105.08 MHz and excellent mode-locking stability. The output power was scaled to 450 mW at the expense of a longer pulse duration of 1.93 ps. The nonlinear parameters of the SESAM are also reported.

Growth and spectroscopic properties of Ca3(Ta,Ga)5O12:Pr3+ single crystal as a promising new laser material in the visible domain

Structurally disordered Pr3+-doped Ca3(Ta,Ga)5O12 - Pr:CTGG single crystal was grown by the Czochralski technique for the first time and its spectroscopic properties were investigated. Modified Judd-Ofelt analysis was applied to determine spectroscopic and laser emission characteristics. Based on low-temperature absorption and emission spectra, the partial energy levels of Pr3+ ions have been obtained and a multicenter structure of the optical spectra was highlighted. The electron-phonon interactions were also observed in the emission spectra corresponding to the 3P0 → 3H4 transition under different excitation wavelengths. The fluorescence decays of the 3P0 and 1D2 levels were measured. The emission cross-sections corresponding to the 3P0 → 3H4 (486.5 nm) and 3P0 → 3F2 (652.7 nm) transitions were found to be σem = 19 × 10−20 cm2 and σem = 15 × 10−20 cm2, respectively. The values for other parameters that may predict the possibility of achieving efficient laser emission, especially at 486.5 nm, such as quantum efficiency (ⴄ = 50 %), gain bandwidth (σem× Δλeff, = 32.2 × 10−26 cm3), and optical gain (σem× τmeas = 12.86 × 10−25 cm2 s) were determined. The obtained results indicate that the Pr:CTGG crystal has a high potential for obtaining efficient laser emission in the blue domain.

Type-I intermittency route to chaos in passively Q-switched Tm:YLF laser emitting at 2.3 μm

We report on an original chaotic dynamic behaviour of a passively Q-switched 2.3-μm Thulium laser operating on the 3H4 → 3H5 transition. The experiment employs a Tm:LiYF4 laser crystal within various laser cavity configurations, involving optional additional cascade laser operation on the 3F4 → 3H6 transition at 1.9 μm. The saturable absorber employed is Cr2+:ZnSe, which is exclusively saturated by the 2.3 μm laser emission. A precise analysis of the Q-switching dynamics shows a pronounced inclination of the cascade laser scheme towards chaotic operation. To investigate the origins of chaos, we originally monitor the metastable 3F4 level population using cascade laser operation at 1.9 μm, which proves to be a crucial underlying parameter for explaining the observed instabilities. This analysis allows for explaining the specific dynamics of the Q-switched 2.3 μm Tm-laser intrinsically linked to Tm3+-doped materials. A very atypical route to chaos for a Q-switched laser is demonstrated involving type I intermittencies. The obtained results are of great interest for studying the premises of chaos in pulsed solid-state lasers.

Continuous-wave and SESAM mode-locked 2.3-µm Tm:LiYF4 lasers: Upconversion pumping at 1.45 µm

A Tm:LiYF4 laser operating on the 3H4→3H5 transition with upconversion pumping at 1.45 µm generates 831 mW at 2313 nm with 34.0% slope efficiency. Mode-locked by a GaSb- based SESAM, it delivers 855-fs pulses at 104.4-MHz.

High-power intracavity upconversion pumped Tm:YLF laser emitting at 2.3 μm

A Tm:LiYF4 laser operating on the 3H4 → 3H5 transition is integrated into a high-power diode-pumped Nd:ASL laser for intracavity upconversion pumping at 1.05 μm. This architecture leads to a record-high output power at 2.3 μm ever extracted from any upconversion pumped Thulium laser. The continuous-wave Tm-laser yields 1.81 W at 2.3 μm at 32 W of laser-diode pump power at 0.8 μm, rivalling direct diode pumping. The intracavity pumping mitigates weak absorption inherent to the upconversion pumping scheme and disperses the deposited heat over two laser crystals. This laser design minimizes heating of the Tm-crystal and enhances the tolerance to Tm3+ excited-state absorption, being promising for high-power 2.3-μm solid-state lasers based on thulium ions.

Efficient high-power 2.3 μm continuous-wave laser operation of diffusion-bonded composite YVO4/Tm:GdVO4 crystals

Abstract We reported on an efficient high-power continuous-wave laser operation on the 3H4 → 3H5 transition of Tm3+ ions in a diffusion-bonded composite YVO4/Tm:GdVO4 crystal. Pumped by a laser diode at 794 nm, a maximum output power of 7.5 W was obtained from a YVO4/Tm:GdVO4 laser at 2.29 μm, corresponding to a slope efficiency of 40.3% and exceeding the Stokes limit. To the best of our knowledge, this result represents the maximum power ever achieved from a Tm laser at 2.3 μm.