Stark Energy Research Articles

Near‐Infrared Thermometer Based on Stark Energy Levels of Yb3+ in Garnet

A Yb3+‐doped Gd3Al2Ga3O12 garnet (GAGG) Boltzmann thermometer is prepared and studied in this work. Due to the Boltzmann distribution of the population of Stark sublevels of Yb3+, the photoluminescence peaks of Yb3+ in the wavelength range of 950–1000 and 1000–1050 nm exhibit opposite temperature dependencies, which makes the luminescence intensity ratio (LIR) of two Yb3+ peaks work as a luminescence thermometer with a relative sensitivity of 1.6% K−1 at 200 K. It is worth nothing that this LIR value still follows the Arrhenius model at temperatures as low as 200 K. In these results, it is suggested that Yb3+‐doped GAGG thermometer can achieve high sensitivity for accurate temperature measurements. In addition, the accurate position of various Stark sublevels of Yb3+ in GAGG is obtained for the first time. In this work, it is confirmed that the Yb3+‐doped GAGG thermometer exhibits potential applications in the fields of microelectronics and biology.

Crystal field effects of Al doping on the Stark splitting and gain bandwidth of erbium doped silica fibers

In this study, erbium-doped silica fibers (EDFs) with different Al/Er ratios were prepared by high-temperature source combined with the modified chemical vapor deposition (MCVD) method. The effects of different Al/Er ratios on the gain performance of erbium-doped silica fiber amplifiers (EDFA) were investigated. The EDFA demonstrated in this paper achieves a maximum gain of 45 dB at 1560 nm when the signal power is −20 dB, while the bandwidth of 20 dB gain is up to 68 nm (1532∼1600 nm). Additionally, the effect of Al doping on the crystal field around the Er ion was analyzed and the Stark energy level distribution of the Er ions was further derived. Our approach offers a feasible solution for C + L band amplification from the perspective of Stark effect and crystal field analysis.

Erbium-based hydrothermal YOF with stark sublevels for in vivo NIR II luminescence nanothermometer

Rare earth luminescent materials have attracted extensive attention in the biomedical field as noncontact temperature monitoring devices with microscopic resolution due to their properties in the visible and near-infrared regions. At the application level, it is required to have a certain temperature monitoring capability in the near-infrared region II window to enhance the tissue penetration depth. Here, two kinds of YOFs: Er[Formula: see text], Yb[Formula: see text] were prepared by co-precipitation and hydrothermal method, and the luminescence was enhanced by ion doping. An Er[Formula: see text]-based ratiometric nanothermometer of 4F[Formula: see text]I[Formula: see text] (672[Formula: see text]nm, upconversion luminescence) to 4I[Formula: see text]I[Formula: see text] (1580[Formula: see text]nm/1566[Formula: see text]nm, NIR II downshifting luminescence) were designed with the Stark energy level. When doped with 2% Zn[Formula: see text], the relative temperature sensitivity of YOF prepared by co-precipitation method was improved from 0.30% [Formula: see text] (30∘C) to 0.59% [Formula: see text] (30∘C), expanding its use as a temperature monitoring device possibility. The temperature sensitivity of YOF prepared by hydrothermal method was 1.01% [Formula: see text] (30∘C). Finally, the NIR II luminescence of the prepared nanothermometer was used as a control for temperature monitoring of heating sites in mice. The results showed that it can distinguish heating site from control site and no significant cytotoxicity or damage to the tissues was revealed, indicating its broad prospects in the biomedical field and other temperature monitoring scenarios in the future.

Site‐selective fluorescence and spectroscopic properties of Yb‐doped lanthanum titanate glasses

AbstractYtterbium‐doped lanthanum titanate glasses were prepared by levitation melting for the detailed characterization of the spectroscopic properties in the rare‐earth titanate glass host. Low‐temperature fluorescence spectroscopy reveals distinct site‐selectivity in both static and lifetime fluorescence measurements suggesting an absence of clustering as well as significant variation of local ytterbium environments. Typical site‐selectivity behavior of a shrinking Stark manifold with lower excitation energy is observed. At 77 K, both the mean emission frequency and the fluorescence lifetime initially increase as the excitation energy decreases from about 11100 to 10750 and then slightly decrease at lower excitation energy. Temperature‐dependent lifetime measurements between 77 and 420 K show a decreasing lifetime with increasing temperature and are well described by a two‐level thermal activation model. The temperature‐dependent fluorescence spectroscopy coupled with a room temperature white light absorption measurement allow the determination of the Stark energy levels of in lanthanum titanate glass as well as the calculation of the laser cross‐sections.

Sensitivity of radio-frequency electric field sensor based on Rydberg Stark effect

Rydberg atoms hold special attraction in electric applications due to their large transition electric dipole moments and huge polarization, which leads to a strong response of atom to electric fields. In radio-frequency (RF) fields, the Rydberg levels are AC Stark shift and splitting, which can realize the study of high-sensitivity electric field sensor of Rydberg atoms. In this work, we use the simpler Shirley’s time-independent Floquet Hamiltonian model to calculate the AC Stark energy spectrum of Cs Rydberg atoms. This model can reduce the basic Hamiltonian into such a Hamiltonian that includes only those Rydberg states that have direct dipole-allowed transitions with the target state, thereby significantly improving the speed of computation. The accuracy of the calculation is proved by fitting with the calculated frequency shift of DC Stark energy levels in the weak fields, and the polarizability of 60D<sub>5/2</sub> and 70D<sub>5/2</sub> Rydberg atomic states are obtained by fitting with the measured ion spectra of DC Stark Cs ultra-cold Rydberg atoms in magneto-optical trap. In addition, we calculate the AC Stark shift of Cs Rydberg atom <inline-formula><tex-math id="M2">\begin{document}$ \left| {60{{\text{D}}_{5/2}},{m_j} = 1/2} \right\rangle $\end{document}</tex-math><alternatives><graphic specific-use="online" xmlns:xlink="http://www.w3.org/1999/xlink" xlink:href="9-20240162_M2.jpg"/><graphic specific-use="print" xmlns:xlink="http://www.w3.org/1999/xlink" xlink:href="9-20240162_M2.png"/></alternatives></inline-formula> state in electric fields with different frequencies with <i>ε</i> = 100 mV/m. Rydberg atoms provide a structured spectrum of sensitivity to electric fields due to strong resonant interaction and off-resonant interaction with many dipole-allowed transitions to nearby Rydberg states. This kind of the frequency response structure is of significance to a broadband sensor. And we calculate the sensitivity and the scaling of the signal-to-noise ratio (SNR), <i>β</i>, varying with detuning from the <inline-formula><tex-math id="M3">\begin{document}$ \left| {60{{\text{D}}_{5/2}}} \right\rangle \to \left| {61{{\text{P}}_{3/2}}} \right\rangle $\end{document}</tex-math><alternatives><graphic specific-use="online" xmlns:xlink="http://www.w3.org/1999/xlink" xlink:href="9-20240162_M3.jpg"/><graphic specific-use="print" xmlns:xlink="http://www.w3.org/1999/xlink" xlink:href="9-20240162_M3.png"/></alternatives></inline-formula> transition. The value of <i>β</i> allows one to use the result for any Rydberg state sensor to determine the SNR for any <i>Ε</i> in a 1 s measurement. Therefrom, Rydberg sensor can preferentially detect many RF frequencies spreading across its carrier spectral range without modification while effectively rejecting large portions where the atom response is significantly weaker, and the signal depends primarily on the detuning of the RF field to the nearest resonance which does not convey the RF frequency directly.

Electromagnetically induced transparency spectra of cesium Rydberg atoms decorated by radio-frequency fields

<sec>The large electric dipole moment of the Rydberg atom allows for strong coupling with weak electric fields, and is widely used in electric field measurements because of its reproducibility, precision and stability. The combination of Rydberg atoms and electromagnetically induced transparency (EIT) technology has been used for detecting and characterizing radio-frequency (RF) electric fields. </sec><sec>In this work, by selecting probe light (852 nm), dressed light (1470 nm), and coupled light (780 nm), the Rydberg state (49<i>P</i><sub>3/2</sub>) of Cs atom is prepared by using a three-photon excitation scheme through using all-infrared light excitation of Rydberg atoms. We experimentally observe the EIT spectra of the Rydberg states decorated by radio-frequency electric fields, which optically detects Rydberg atoms. The effect of the amplitude and frequency of the RF electric field on the spectrum is explored in light of changes in the EIT spectrum. The results show that in the region of weak electric field, only the ac Stark energy shift and spectral broadening occur. As the electric field is further enhanced, the sideband phenomenon occurs in both the primary peak and secondary peak of the EIT. In the region of strong field, the Rydberg energy level produces a series of Floquet states with higher-order terms, as well as state shifting and mixing, resulting in asymmetry in the spectra of the EIT sideband peaks. The effect of frequency on the shielding effect of the Cs vapor cell is further discussed based on the shift of the main peak of the EIT.</sec><sec>The demodulation of the electric field in a range of 50 Hz–1 kHz with a fidelity of 95% is achieved by modulating the low-frequency electric field to the RF electric field. The results can provide valuable references for spectral detection and traceable measurements of low-frequency electric fields.</sec>

Novel Sm3+ doped YCa4O(BO3)3 phosphors: Structural and, low and room temperature luminescent insights

Inorganic phosphors, known for their ability to capture energy from various sources and emit visible light, have become essential in the development of advanced lighting and display technologies. This study explores YCa4O(BO3)3 (YCOB) as a potential host material for phosphors, focusing on the luminescent properties of YCOB phosphors doped with Sm3+ ions. The successful integration of Sm3+ ions into the YCOB host lattice is confirmed through structural characterization using X-ray diffraction (XRD), Fourier-Transform Infrared Spectroscopy (FTIR), and Energy-Dispersive X-ray Spectroscopy (EDS). Photoluminescence (PL) studies reveal distinct emission spectra with Stark energy level splitting, indicating a cooperative effect between Y3+ and Sm3+ ions. Concentration quenching, mainly attributed to dipole-dipole (d-q) interactions, is observed at higher Sm3+ concentrations. Temperature-dependent PL measurements demonstrate thermal quenching at lower temperatures and increased emission intensity with higher laser power. Thermal quenching is explained by reduced lattice vibrations and electron-phonon interactions, leading to decreased radiative recombination of charge carriers. The CIE chromaticity data position the samples in the orange-red region, emitting vibrant orange-red light. This comprehensive investigation provides insights into the synthesis and luminescent properties of YCOB:Sm3+ phosphors, highlighting their potential applications in luminescent devices.

Calculations of Relativistic Stark Energies and Widths in Hydrogen-Like Ions Using the Complex-Scaling Method

Calculations of Relativistic Stark Energies and Widths in Hydrogen-Like Ions Using the Complex-Scaling Method

Cooling access and energy requirements for adaptation to heat stress in megacities

As urban areas are increasingly exposed to high temperatures, lack of access to residential thermal comfort is a challenge with dramatic consequences for human health and well-being. Air-conditioning (AC) can provide relief against heat stress, but a massive AC uptake could entail stark energy demand growth and mitigation challenges. Slums pose additional risks due to poor building quality, failing to provide adequate shelter from severe climatic conditions. Thus, it is unclear how many people in the Global South will still lack access to basic cooling under different future climate and socioeconomic developments. We assess the impact of different shared socioeconomic pathways (SSPs) and climate futures on the extent of population lacking access to cooling where needed—the cooling gap—and energy requirements for basic comfort for a set of 22 megacities in the Global South. We find that different SSPs greatly influence the extent of future cooling gaps, generally larger in SSP3 due low income levels, and consequent limited access to AC and durable housing. Megacities in Sub-Saharan Africa and South Asia have the largest share of population affected, ranging from 33% (SSP1) to 86% (SSP3) by mid-century. Energy requirements to provide basic cooling for all are higher in SSP1 for most megacities, driven by urbanization, and can increase by 7 to 23% moving from 2.0 to 3.0 °C temperature rise levels. Strategies combining improved building design and efficient cooling systems can improve adaptation to heat stress in cities while reducing energy and emission requirements to reach climate and sustainability goals.

Roles of the transition amplitude phases in photoelectron asymmetry of single strong attosecond pulse

The angular distributions of the photoelectrons in ionization of hydrogen atom by both circularly and linearly polarized intense extreme ultraviolet (XUV) attosecond pulse are investigated by numerically solving the time-dependent Schrödinger equation. We clearly identify nonperturbative features in studying the asymmetrical photoelectron angular distributions in the polarization plane for the XUV photon energy (16.3 eV) close to the ionization threshold, while such nonperturbative features are absent for higher photon energy (36 eV) in the same pulse intensity region. In addition to the carrier-envelope phase (CEP) dependence, the ejection asymmetry of the photoelectron is also sensitive to the relative phases of transition amplitudes in absorbing one photon and two photons. As a consequence, the CEPs corresponding to the maximal (or zero) asymmetry obviously vary as the pulse intensity increases in a moderately large region from 1 × 1015 W cm−2 to 30 × 1015 W cm−2. We attribute the intensity dependence of the transition amplitude phases to a consequence of the depletion of population as well as the Stark energy shift of the initial state. We show that the relative phases of transition amplitudes can be precisely decoded from the pulse intensity dependence of the ejection asymmetry and those phases are insensitive to the ellipticity of the laser pulse.

Temperature sensing properties of NaYTiO4: Yb/Tm phosphors based on near-infrared up-conversion luminescence

In this study, NaYTiO4: Yb/Tm phosphors with different concentrations of Yb3+ and Tm3+ ions were synthesized by conventional solid-state reaction. Upon a 980 nm laser excitation, the up-conversion luminescence properties in a wide temperature range (303–823 K) were investigated. By employing the fluorescence intensity ratio (FIR) techniques based on the robust near-infrared emissions of thermally coupled 3F2,3/3H4 energy levels and 3H4(1)/3H4(2) Stark energy levels, the calculated absolute sensitivity (Sa), relative sensitivity (Sr), and temperature uncertainty (δT) values demonstrated good temperature sensing properties. For the 3F2,3/3H4 energy levels, the maximum Sr and minimum δT values are 1.04% K−1 and 0.010 K at 463 K, respectively. Moreover, the maximum Sa is 0.32 × 10−3 K−1 at 823 K. In addition, the thermally coupled 3H4 Stark energy levels present the maximum Sa, Sr and the minimum δT are 0.88 × 10−3 K−1, 0.60% K−1 and 3.17 K at 303 K, respectively. Besides, due to the ratio of blue to red emission varying with elevated temperature, the NaYTiO4: Yb/Tm phosphors are expected to be applied as an intuitive high-temperature indicator.

Calculations of relativistic Stark energies and widths in hydrogen-like ions using the complex-scaling method

The relativistic calculations of energies and widths are performed for the lowest states of hydrogen and hydrogen-like neon. The calculations are carried out using the finite-basis technique combined with the complex-scaling method. The obtained results are compared with the available nonrelativistic and relativistic data. Keywords: Stark effect, complex scaling.

Absorption and emission cross-sections, Stark energy levels, and temperature dependent gain of Yb:QX phosphate glass.

We have obtained the absolute absorption cross-sections of Yb-doped phosphate QX laser glass at 300 K from 800-1100 nm, and generated the emission cross-sections via the standard method of reciprocity. By generating nine detailed high-confidence fitting functions for the absorption cross-sections, we then applied reciprocity to the individual absorption functions and obtain, for the first time to our knowledge, nine corresponding detailed emission functions that when summed, display a more accurate representation of the emission cross-sections as a function of wavelength than the standard method. A deeper mathematical understanding of reciprocity is also presented, along with derived Yb:QX Stark levels.

Luminescent Er3+ centers in CaSc2O4:Er3+:Yb3+ upconversion phosphor

The structure of luminescent centers in the upconversion material Er:Yb:CaSc2O4 is investigated using high-resolution optical spectroscopy methods at low temperature (10K). Two luminescent centers were identified in Er(2 at%):CaSc2O4: one corresponding to Er3+ on Ca2+ positions (center I) and one corresponding to Er3+ on Sc3+ positions (center II). Both X-ray diffraction and optical spectroscopy indicate an increase in the population of center II with the increase of doping concentrations. The Stark energy levels corresponding to multiplets 4I15/2, 4I13/2, 4F9/2 and 4S3/2 were obtained for the two luminescent centers, using selectively-excited luminescence. Upconversion measurements performed at low temperatures (10K) showed that the contribution of center I is dominant. The temperature dependence of the upconversion intensity and of the red to green ratio is discussed.

Determination of charge-compensated C 3υ (II) centers for Er3+ ions in CdF2 and CaF2 crystals* *Project supported by the National Natural Science Foundation of China (Grant No. 1170513), the Natural Science Foundation of Shaanxi Province, China (Grant No. Z20200051), the Foundation of the Education Department of Shaanxi Provincial Government, China (Grant No. 16JK1461), and the Scientific Research Foundation of Xi’an

A unified theoretical method is established to determine the charge-compensated C 3v (II) centers of Er3+ ions in CdF2 and CaF2 crystals by simulating the electron paramagnetic resonance (EPR) parameters and Stark energy levels. The potential (Er3+–F−–) and (Er3+––O2–) structures for the C 3v (II) centers of Er3+ ions in CdF2 and CaF2 crystals are checked by diagonalizing 364 × 364 complete energy matrices in the scheme of superposition model. Our studies indicate that the C 3v (II) centers of Er3+ ions in CdF2 and CaF2 may be ascribed to the local (Er3+–F−–) structure, where the upper ligand ion F− undergoes an off-center displacement by ΔZ ≈ 0.3 Å for CdF2 and ΔZ ≈ 0.29 Å for the CaF2 along the C 3 axis. Meanwhile, a local compressed distortion of the cluster is expected to be ΔR ≈ 0.07 Å for CdF2:Er3+ and ΔR ≈ 0.079 Å for CaF2:Er3+. The considerable g-factor anisotropy for Er3+ ions in each of both crystals is explained reasonably by the obtained local parameters. Furthermore, our studies show that a stronger covalent effect exists in the C 3v (II) center for Er3+ in CaF2 or CaF2, which may be due to the stronger electrostatic interaction and closer distance between the central Er3+ ion and ligand O2– with the (Er3+–F−–) structure.

Conjoint influence of quantum interference and Freeman resonance on substructures of the photoelectron spectra in above-threshold ionization

Based on the numerical solution of the full-dimensional time-dependent Schr\odinger equation, we study the above-threshold ionization of atomic hydrogen by subpicosecond laser pulses at wavelengths ranging from 300 nm to 800 nm, in which regime substructures of the photoelectron energy spectra resulting from quantum interference are entangled with those induced by the Freeman resonance. By analyzing the time-dependent populations and ac Stark energy shifts of the relevant atomic levels, and observing the pulse intensity dependence and the pulse length evolution of the spectra, we clearly identify the origins of the substructures exhibited in the spectra.

A continuous 1 052 nm and 1 061 nm dual-wavelength Nd:YAG laser

Exploiting a specially designed Fabry-Perot filter as output coupler, a continuous 1 052 nm and 1 061 nm dual-wavelength laser is realized. The threshold, slope efficiency and maximum power of the 1 052 nm and 1 061 nm dual-wavelength laser are 2.55 W, 17.5% and 571 mW, respectively. The competition and coexistent relationships between 1 052 nm, 1 061 nm and 1 064 nm are analyzed. Involved non-degenerate Stark energy level structures are used to classify dual-wavelength lasers. According to this method, dual-wavelength lasers can be classified as different upper and lower non-degenerate Stark energy levels, the same upper but different lower Stark energy levels, different upper but the same lower Stark energy levels. Representative Nd:YAG dual-wavelength lasers are classified according to this criterion. It is found that the realization of front two type lasers is easy and that of third type lasers is challenging. This method can be used as a level of difficulty reference for the realization of dual-wavelength lasers.

Unraveling the local structure and luminescence evolution in Nd3+-doped LiYF4: a new theoretical approach.

Neodymium ion (Nd3+)-doped yttrium lithium fluoride (LiYF4, YLF) laser crystals have shown significant prospects as excellent laser materials in many kinds of solid-state laser systems. However, the origins of the detailed information of their local structure and luminescence evolution are still poorly understood. Herein, we use an unbiased CALYPSO structure searching technique and density functional theory to study the local structure of Nd3+-doped YLF. Our results reveal a new stable phase with the P4[combining macron] (No. 81) space group for Nd3+-doped YLF, indicating that the host Y3+ ion site was naturally occupied by the Nd3+ ion impurity. On the basis of our newly developed WEPMD method, we adopt a specific type of orthogonal correlation crystal field to obtain a new set of crystal-field parameters as well as 182 complete Stark energy levels. Many absorption and emission lines for Nd3+-doped YLF are calculated and discussed based on Judd-Ofelt theory, and our results indicate that some of the observed absorption and emission lines are perfectly reproduced by our theoretical calculations. Additionally, we predict several promising transition lines in the visible and near-infrared spectral regions, including the electronic dipole emission lines 4F5/2 → 4I9/2 at 808 nm and 2H9/2 → 4I9/2 at 799 nm, as well as the magnetic dipole emission lines 4F3/2(27) → 4I11/2(6) at 1047 nm and 4F3/2(27) → 4I11/2(8) at 1052 nm. These transition channels indicate that Nd3+-doped YLF laser crystals have greatly promising laser actions for serving as a solid-state laser material.

Investigation of the Structure and Luminescence Mechanism of Tm3+-Doped LiYF4: New Theoretical Perspectives.

The absorption and emission transitions of Tm3+-doped LiYF4 have been extensively investigated due to the excellent properties and enormous applications of these materials as laser materials. However, the challenging issues regarding the local structure and luminescence mechanism have not been conclusively established to date. To address these challenges, the CALYPSO structure search method is employed, and the results first reveal the ground-state structure of Tm3+-doped LiYF4, which crystallizes in the space group P4̅ (No. 81) of the tetragonal system. The Y3+ ions are replaced by Tm3+ ions, forming a local configuration of [TmF8]5-. Furthermore, the complete Stark energy levels of Tm3+-doped LiYF4 are predicted by using our newly developed WEPMD method, which provides preliminary preparation for further spectral exploration. Judd-Ofelt analysis is performed to evaluate the electric dipole transition intensities. Two prominent transitions, 3H5 → 3H6 (1223 nm) and 3H4 → 3H6 (801 nm), are predicted to be good candidates for near-infrared lasers. This study not only is useful for determining the luminescence properties of Tm3+-doped LiYF4 but also offers an effective way to search for other rare-earth-doped lasing crystals for the future design of lasing materials.

Purely long-range polar molecules composed of identical lanthanide atoms

Doubly polar molecules, possessing an electric dipole moment and a magnetic dipole moment, can strongly couple to both an external electric field and a magnetic field, providing unique opportunities to exert full control of the system quantum state at ultracold temperatures. We propose a method for creating a purely long-range doubly polar homonuclear molecule from a pair of strongly magnetic lanthanide atoms, one atom being in its ground level and the other in a superposition of quasi-degenerate opposite-parity excited levels [Phys.~Rev.~Lett.~\textbf{121}, 063201 (2018)]. The electric dipole moment is induced by coupling the excited levels with an external electric field. We derive the general expression of the long-range, Stark, and Zeeman interaction energies in the properly symmetrized and fully-coupled basis describing the diatomic complex. Taking the example of holmium, our calculations predict shallow long-range wells in the potential energy curves that may support vibrational levels accessible by direct photoassociation from pairs of ground-level atoms.