3P1 State Research Articles

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.

From nonemission to nearly unity quantum yield: Breaking parity-forbidden transitions in rubidium indium chloride through 5s2 lone pair Sb-doping

Halide perovskites doped with ns2 metal ions have stimulated widespread research owing to their efficient and stable self-trapped emissions. Here we observe the strictly forbidden transition 3P0→1S0 is broken and afford nearly unity triplet orange self-trapped excitons (O-STEs) emission, through 5 s2 lone pair Sb cation doping in host Rb2InCl5·H2O single crystal. In particular, additional triplet blue self-trapped excitons (B-STEs) emission centered at 475 nm, stemming from partially allowed 3P1→1S0, is also observed. Spectroscopic characterization along with literature analysis demonstrates that the behavior of forbidden transition breaking originates from the mixing of 3P0 and 3P1 states. First-principles density-functional theory (DFT) calculations as well confirm the involvement of atomic orbitals in bandgap construction, as evidence of 5s5p-5 s2 transition, affording the STEs emission. Combining the efficient, stable broad emission Rb2In96.39 %Cl5·H2O: 3.61 % Sb3+ crystal with Cs3Cu2Cl5 and Cs3Cu2I5 phosphors, a lead-free white light-emitting diode with a high color rendering index of 93.4 has been achieved. Furthermore, the unique sensitive and steep temperature dependence photoluminescence (PL) lifetimes may prompt this type of self-trapped zero-dimensional (0D) perovskites to great potential in the field of thermometry application.

The electronic structures and optical properties induced by spin-orbit-coupling in LiPbPO4 compound

Phosphate materials are excellent candidates for nonlinear optical materials, thus necessitating a comprehensive and in-depth study of them. Here, inspired by the interesting phenomenon induced by the spin-orbit coupling (SOC) effect, we extend it to LiPbPO4 compounds using a first-principles approach to probe the influence of SOC on the electronic structure and optical properties of post-transition metal compounds. The results show that only the bottom of the conduction band shows an energy level splitting with the inclusion of SOC, which is analyzed to come from the SOC in the Pb 6p state since the SOC in the O 2p state is very weak. The splitting of the conduction band triggers the decrease of the band gap and the change of the optical properties. The performance analysis shows that both the refractive index and the second harmonic generation (SHG) coefficient are enhanced with the inclusion of SOC, however, the change in the birefringence is insignificant, and it is further found that the enhanced SHG coefficient values are closer to the experimental values. In conclusion, our study reveals the impact of SOC effect on the electronic structure and optical properties of LiPbPO4 compounds, contributing to a deeper understanding of the nonlinear optical in post-transition metal compounds.

Spectroscopy of the 5s5p3P0→5s5d3D1 transition of strontium using laser cooled atoms

This article presents spectroscopy results of the 5s5p3P0→5s5d3D1 transition in all isotopes of laser cooled Sr atoms and the utility of this transition for repumping application. By employing the 5s5p3P0→5s5d3D1 (483 nm) transition in combination with the excitation of 5s5p3P2→5s6s3S1 (707 nm) transition, we observe a significant increase (∼13 fold) in the steady state number of atoms in the magneto-optic trap. This enhancement is attributed to the efficient repumping of Sr atoms that have decayed into the dark 5s5p3P2 state by returning them to the ground state 5s21S0 without any loss into the other states. The absolute transition frequencies were measured with an absolute accuracy of 30 MHz. To support our measurements, we performed Fock-space relativistic coupled-cluster calculations of the relevant parameters in Sr To further increase the accuracy of the calculated properties, corrections from the Breit, quantum electrodynamical and perturbative triples were also included. The calculated branching ratio for the repumping state confirms the significantly increased population in the 3P1 state. Thereby, leading to an increase of population of atoms trapped due to the enhanced repumping. Our calculated hyperfine-splitting energies are in excellent agreement with the measured values. Moreover, our calculated isotope shifts in the transition frequencies are in good agreement with our measured values.

Enhancement of ultraviolet upconversion photoluminescence of Y7O6F9:Pr, Gd induced by Li+ codoping☆

Ultraviolet upconversion photoluminescence materials have great potential in various fields, but the improvement of the upconversion efficiency is challenging. Codoping of Li+ is considered as an effective strategy and widely used to improve the photoluminescence properties of phosphors. In this paper, Li+ is introduced into a Y7O6F9:Pr3+,Gd3+ system. The effect of Li + codoping on the phase purity, crystal structure, microstructure, downshifting and upconversion photoluminescence as well as the decay dynamic of the phosphors was studied. It is revealed that the overall photoluminescence efficiency and the energy transfer efficiency from Pr3+ to Gd3+ are greatly promoted. The downshifting and upconversion photoluminescence increase by 2.58 and 10 times as 6 mol% of Li+ is codoped. The photoluminescence decay dynamic study shows that the 3P0 state decays slower in the Li + -containing phosphor than the Li+-free one. The improvement of the photoluminescence properties is due to the increase of the crystallinity and the reduce of the quenching center.

Measuring the nuclear magnetic quadrupole moment of optically trapped ytterbium atoms in the metastable state

We propose a scheme to measure a nuclear magnetic quadrupole moment (MQM), a CP -violating electromagnetic moment that appears in the nuclear sector, using the long-lived 3P2 metastable state in neutral 173Yb atoms. Laser-cooling and trapping techniques enable us to prepare ultracold 173Yb atoms in the 3P2 state trapped in an optical lattice or an optical tweezer array, providing an ideal experimental platform with long spin coherence time. In addition, our relativistic configuration interaction calculation for the 3P2 electronic wavefunction reveals a large magnetic field gradient generated by the atomic electrons in this state, which amplifies the measurable effect of an MQM. Our scheme could lead to an improvement of more than one order of magnitude in MQM sensitivity compared to the best previous measurement (Murthy et al 1989 Phys. Rev. Lett. 63, 965).

Cationic substitution engineering induced Multi-Color light emitting of bismuth in Tantalate used for WLED

Revealing and predicting the photoluminescence behavior of trivalent bismuth activated phosphors is very important for exploiting high-quality photoluminescent materials and modulating their luminescence properties, since it commonly performs multi-type electronic transitions. In this work, the chosen matrix of Gd3TaO7, which contains only one highly symmetrical cationic crystallographic site, is favorable for analyzing luminescence behavior of Bi3+ ions, and Bi3+-activated Gd3TaO7 can emit bright green light under the near-ultraviolet (NUV) light or low voltage electron beam excitation. The cationic substitution engineering of rare earths Ln (Ln = Lu, Y and La) replacing Gd3+ ions was carried out for further regulation of spectra, and multi-color light emitting was successfully realized. However, their unusual photoluminescence properties bring a novel comprehension for the photoluminescence behavior of Bi3+ ions in this system. For well rationalizing this phenomenon, the first-principles calculation was carried out for revealing their electronic structure, combined with their geometry optimization. The results indicate multi factors have contribution in modulating the luminescence behavior of Bi3+ ions, especially the interaction between 3P1 state, metal-to-metal charge transfer state and Bi-Bi dimers. The result is favorable for us to exactly adjust the luminescence properties of Bi3+ ions.

Structural and luminescent performance and optical thermometry of Pr3+ doped SrWO4 down-conversion phosphors

A series of Pr3+ doped SrWO4 phosphors were synthesized using solid-state reaction routes. The phase composition, photoluminescence and temperature sensitivities of as-prepared materials were investigated. Rietveld refinement of measured XRD data was applied to analyze the lattice parameters. The optical transition was elaborated using UV–visible diffuse reflectance spectra and photoluminescence spectra. The photoluminescence measurements confirmed the strong visible light emission from the developed phosphors under both UV excitation at 250 nm and blue excitation at 450 nm. Notably, the maximum emission intensity was observed at a Pr3+ doping concentration of 2 mol%. Furthermore, the fluorescence intensity ratio (FIR) technique was employed, focusing on the emissions originating from the 3P0 and 1D2 state of Pr3+ within the temperature range of 298–598 K. Two FIR groups were adopted in this case, which can verify each other to achieve self-calibration. Typically, SrWO4:0.02Pr3+ exhibited remarkable performance as a temperature sensor, displaying an absolute sensitivity (Sa) of 3.11%K−1 and a relative sensitivity (Sr) of 0.81%K−1. As a result, the significant temperature-dependent PL and remarkable down-conversion luminescence make the SrWO4:Pr3+ material a promising candidate for optical thermometers and UV to visible converters of solar cell applications.

Investigation of the 6s6p3P2-6s7s3S1 transition of ytterbium atoms with modulation-transfer spectroscopy

We perform the precise measurement of the 6s6p3P2-6s7s3S1 transition frequencies of the neutral ytterbium (Yb) atoms by using the modulation transfer spectroscopy. High-resolution dispersive signals of all isotopes except low-abundance 168Yb (F = 2-F = 1) and 171Yb (F = 5/2-F = 3/2) are obtained. The frequencies of locked laser are measured using an optical comb, and the obtained results are traced to the absolute transition frequency of the 171Yb 1S0-3P0 clock. We measure the isotope shifts relative to 174Yb and evaluate the systematic shifts. The absolute frequency of the 6s6p3P2-6s7s3S1 transition in 174Yb is determined to be 389260605.8 ± 3.2 MHz, which has a huge deviation from the existing data in the studies. Based on the obtained transition frequencies, we calculate the hyperfine constants of the 3P2 and 3S1 states. This research will provide valuable data for the ytterbium-related experiments and improve the reported transition frequencies with higher precision.

Continuous outcoupling of ultracold strontium atoms combining three different traps

We have demonstrated the continuous outcoupling of ultracold 88Sr atoms using a moving optical lattice. While Sr atoms are Zeeman-slowed and magneto-optically trapped on the 1S0–1P1 transition, the atoms relaxed to the 5s5p 3P2 metastable state are magnetically trapped and Doppler cooled on the 5s5p 3P2–5s4d 3D3 transition at 2.92 μm. By optically pumping the atoms to the 5s5p 3P0 state, we outcouple the atoms by a moving optical lattice. Such a continuous atomic source enables superradiant lasers and the zero-dead-time operation of atom interferometers and optical lattice clocks.

Cascade and yoked superfluorescence detected by sum frequency generation spectroscopy.

We investigated the superfluorescent decay process of dense rubidium atomic vapor in a cell. Using a femtosecond laser pulse, the atoms were excited from the 5S ground state to the 6P state. The 2.73μm and 1.37μm fields were generated on the cascaded decay, 6P → 6S → 5P, which further stimulated the 780 nm forward emission on the 5P → 5S transition. Using sum frequency generation (SFG) spectroscopy, we observed all emission fields and the time delay between them, with sufficient temporal resolution. The experimental results were successfully reproduced using semiclassical simulations.

Coherent dynamics in a five-level atomic system

The coherent control of multi-partite quantum systems presents one of the central prerequisites in state-of-the-art quantum information processing. With the added benefit of inherent high-fidelity detection capability, atomic quantum systems in high-energy internal states, such as metastable noble gas atoms, promote themselves as ideal candidates for advancing quantum science in fundamental aspects and technological applications. Using laser-cooled neon atoms in the metastable 3P2 state of state 1s 22s 22p 53s (LS-coupling notation) (Racah notation: 2 P 3/23s[3/2]2) with five m J -sublevels, experimental methods for the preparation of all Zeeman sublevels |m J ⟩ = |+2⟩, |+1⟩, |0⟩, |−1⟩, |−2⟩ as well as the coherent control of superposition states in the five-level system |+2⟩, …, |−2⟩, in the three-level system |+2⟩, |+1⟩, |0⟩, and in the two-level system |+2⟩, |+1⟩ are presented. The methods are based on optimized radio frequency and laser pulse sequences. The state evolution is described with a simple, semiclassical model. The coherence properties of the prepared states are studied using Ramsey and spin echo measurements.

A novel blue excited white light emitting SrWO4: Pr3+ phosphor for single phase white-LED applications

A series of white light emitting Pr3+ activated SrWO4 phosphors are synthesized by most facile solid state reaction routes. The structural properties are investigated by X-ray diffraction (XRD) spectroscopy, Field Emission Scanning Electron Microscopy (FESEM), Energy dispersive X-ray (EDX) spectroscopy, Fourier transform infrared (FTIR) spectroscopy and X-ray photoemission spectroscopy (XPS). The optical properties are elaborated in detail using UV–visible–NIR spectroscopy and Photoluminescence (PL) spectroscopy. Rietveld refinement of obtained XRD data is performed to investigate the crystal structure and crystallographic parameters. The photoluminescence measurements ensure that the developed phosphors emit bright white light under UV excitation of 242 nm and blue excitation of 448 nm. The maximum emission intensity is achieved at 3 mol% doping of Pr3+, followed by concentration quenching due to dipole-dipole interactions. The decay of electrons from the most populated 3P0 state in all the samples follows the single exponential nature. The average decay time varies in the same manner as the emission intensity with Pr3+ concentration. The color purities of the lights emitted from all the materials under 242 nm and 448 nm excitations are low (close to 10%) and hence suitable for white light. A bright white LED is successfully fabricated by coating the optimised phosphor SrWO4: 3 mol% Pr3+ on a 460 nm blue LED chip. The interesting results recommend that the proposed material can be used in developing single phase white-LED.

Scattering amplitude and two-body loss of ultracold alkaline-earth atoms in a shaking synthetic magnetic field

The idea of manipulating the interaction between ultracold fermionic alkaline-earth (like) atoms via a laser-induced periodical synthetic magnetic field was proposed in Kanász-Nagy et al (2018 Phys. Rev. B 97, 155156). In that work, it was shown that in the presence of the shaking synthetic magnetic field, two atoms in 1S0 and 3P0 states experience a periodical interaction in a rotated frame, and the effective inter-atomic interaction was approximated as the time-averaged operator of this time-dependent interaction. This technique is supposed to be efficient for 173Yb atoms which have a large natural scattering length. Here we examine this time-averaging approximation and derive the rate of the two-body loss induced by the shaking of the synthetic magnetic field, by calculating the zero-energy inter-atomic scattering amplitude corresponding to the explicit periodical interaction. We find that for the typical cases with shaking angular frequency λ of the synthetic magnetic field being of the order of (2π) kHz, the time-averaging approximation is applicable only when the shaking amplitude is small enough. Moreover, the two-body loss rate increases with the shaking amplitude, and is of the order of 10−10 cm3 · s−1 or even larger when the time-averaging approximation is not applicable. Our results are helpful for the quantum simulations with ultracold gases of fermionic alkaline-earth (like) atoms.

A field ionizer for photodetachment studies of negative ions.

In this paper, we present an apparatus for studies into the photodetachment process of atomic negative ions. State-selective detection of the residual atom following the initial photodetachment step is achieved by combining resonant laser excitation of the photo-detached atom with electric field ionization. The resonance ionization technique in combination with a co-linear ion-laser beam geometry gives an experimental apparatus that has both high selectivity and sensitivity. In addition to measurements of a single selected partial photodetachment channel, the apparatus also can be used to study a manifold of photodetachment channels in which the residual atom is left in a high-lying Rydberg state and for investigation of the double electron-detachment process. Ion-optical simulations in SIMION are used to illustrate the operation of the apparatus for studying such processes. Successful performance of the apparatus against the simulation is demonstrated by a high resolution study of the photodetachment of cesium, where the sharp s-wave threshold of the photodetachment processes leaving the residual atom in the excited 6p state was investigated.

Photoionization cross sections of ultracold 88Sr in 1P1 and 3S1 states at 390 nm and the resulting blue-detuned magic wavelength optical lattice clock constraints.

We present the measurements of the photoionization cross sections of the excited 1P1 and 3S1 states of ultracold 88Sr atoms at 389.889 nm wavelength, which is the magic wavelength of the 1S0-3P0 clock transition. The photoionization cross section of the 1P1 state is determined from the measured ionization rates of 88Sr in the magneto-optical trap in the 1P1 state to be 2.20(50)×10-20 m2, while the photoionization cross section of 88Sr in the 3S1 state is inferred from the photoionization-induced reduction in the number of atoms transferred through the 3S1 state in an operating optical lattice clock to be 1.38(66) ×10-18 m2. Furthermore, the resulting limitations of employing a blue-detuned magic wavelength optical lattice in strontium optical lattice clocks are evaluated. We estimated photoionization induced loss rates of atoms at 389.889 nm wavelength under typical experimental conditions and made several suggestions on how to mitigate these losses. In particular, the large photoionization induced losses for the 3S1 state would make the use of the 3S1 state in the optical cycle in a blue-detuned optical lattice unfeasible and would instead require the less commonly used 3D1,2 states during the detection part of the optical clock cycle.

Tailoring Photophysical Dynamics in a Hybrid Gallium-Bismuth Heterometallic Halide by Transferring from an Indirect to a Direct Band Structure.

Low-dimensional lead-free metal halides have emerged as novel luminous materials for solid-state lighting, remote thermal imaging, X-ray scintillation, and anticounterfeiting labeling applications. However, the influence of band structure on the intriguing optical property has rarely been explored, especially for low-dimensional hybrid heterometallic halides. In this study, we have developed a lead-free zero-dimensional gallium-bismuth hybrid heterometallic halide, A8(GaCl4)4(BiCl6)4 (A = C8H22N2), that is photoluminescence (PL)-inert because of its indirect-band-gap character. Upon rational composition engineering, parity-forbidden transitions associated with the indirect band gap have been broken by replacing partial Ga3+ with Sb3+, which contains an active outer-shell 5s2 lone pair, resulting in a transition from an indirect to a direct band gap. As a result, broadband yellow PL centered at 580 nm with a large Stokes shift over 200 nm is recorded. Such an emission is attributed to the radiative recombination of an allowed direct transition from triplet 3P1 states of Sb3+ based on experimental characterizations and theoretical calculations. This study provides not only important insights into the effect of the band structure on the photophysical properties but a guidance for the design of new hybrid heterometallic halides for optoelectronic applications.

Inner mechanism of Pr3+ luminescence thermometers based on the intervalence charge transfer state

Owing to their ultra-high temperature sensitivity, luminescence thermometers based on the intervalence charge transfer state of Pr3+ have drawn more and more attention. But the inner mechanism of Pr3+ luminescence thermometers, especially which parameters could affect the value of relative sensitivity, is still not fully revealed. In this paper, the luminescence thermometer properties of Ba1-xCaxTiO3:1%Pr3+ (x=0-0.7) with variation temperature have been systematically studied. The process of electrons in the 3P0 state passed through the intervalence charge-transfer state to the 1D2 state has been found to be sensitive to temperature variation. Through the intervalence charge transfer state engineering, we successfully realized the effective regulation of the intervalence charge transfer state energy position by replacing Ba2+ with Ca2+ and find that the effective energy gap between the 3P0 state and the intervalence charge transfer state is the key parameter that affects the relative sensitivity of luminescence thermometers. Moreover, the maximum relative sensitivity of Pr3+-doped BaTiO3, evaluated to be 2.26% K−1 at 413K under 450 nm excitation, is the one of the best performances among the Pr3+-based luminescence thermometers. This research could lead to the novel development of an efficient and high-performance optical thermometer.

Bright luminescence of Sb doping in all-inorganic zinc halide perovskite variant

Halide lead perovskites are considered as one of the most promising optoelectronic materials in decades, but the toxicity and bio-accumulation of lead retard the commercialization. Therefore, seeking suitable lead-free perovskites and their variants are of vital importance. In this work, all-inorganic zinc halide perovskite variant Cs2ZnCl4 crystals with Sb3+ doping are synthesized via hydrothermal method. Transparent millimeter-sized crystals exhibit bright red photoluminescence (PL) under room temperature (RT) on account of self-trapped exciton (STE) emission of Sb3+, from 3P1 to 1S0 states. Temperature-dependent PL and time-resolved PL exhibit bimodality and intensity variations, revealing that Jahn-Teller effect of 3P1 state results two energy minima, and thermal activation may contribute to the spectrum change. Further, DFT calculations are carried out and the influences of Sb3+ doping are revealed. A bandgap reduction is achieved via doping, and the band edges are localized at Sb3+. A combination of experimental and theoretical studies demonstrates well that the soft lattice structure and the 5s2 lone pairs of Sb are vital for the STE emission.

(INVITED) Reduced low temperature lifetimes of Bi3+ luminescence in magnetically ordered host lattices

This paper is specifically concerned with the radiative lifetime of the spin and orbitally forbidden Bi3+3P0 →1S0 emission transition. In diamagnetic host lattices, the lifetime of this strongly forbidden transition is long (∼1 ms). Experimental data in the literature show a drastic lifetime shortening in lattices containing Gd3+ compared to the diamagnetic lattices. Here, we propose that the lifetime shortenings have their origin in an internal magnetic field, the so-called molecular field, which is created at the Bi3+ site by the magnetically ordered Gd3+ sublattice. This molecular field mixes the 3P0 and 3P1 states to break the selection rule forbidding the 3P0 →1S0 emission transition.