Search

Luminescent ns2 centers have shown great potential for applications as phosphors and scintillators and intervalent charge transfer transitions are explored.

A striking UV-NIR downshifting occurs in the Cs2NaBiCl6:Er3+ host, and the 4I13/2 emitting level is populated by at least two channels.

The Cr

The abundant site occupancy and optical transitions of multivalence Mn dopants in luminescent materials have attracted much attention. Here, detailed first-principles calculations based on density functional theory have been carried out to clarify the multisite and multivalence nature of Mn ions in solids and predict their optical transition properties by using garnets as prototype systems. The formation energies of dodecahedral, octahedral, and tetrahedral coordinated Mn dopants are evaluated with chemical potential environments, and the preferable site occupancy and valence state of Mn ions in three garnet systems are clarified. The results show that even in a fixed atmosphere, taking Ca

We report an experimental investigation of quantum correlations in a two-qutrit spin system in a single nitrogen-vacancy center in diamond at room temperatures. Quantum entanglement between two qutrits was observed at room temperature, and the existence of nonclassical correlations beyond entanglement in the qutrit case has been revealed. Our work demonstrates the potential of the NV centers as the multiqutrit system to execute quantum information tasks and provides a powerful experimental platform for studying the fundamental physics of high-dimensional quantum systems in the future.

Bismuth ion-doped phosphate crystals have shown rich luminescence phenomena. However, the complexity and variety of Bi3+-related transitions bring great challenges to the understanding of the under...

Ce3+ and Eu2+ single- and double-doped CaMgSi2O6 phosphors have been prepared by a high-temperature solid-state reaction approach. The VUV–UV–vis luminescence properties are investigated at cryogen...

High quality nanomechanical oscillators are promising platforms for quantum entanglement and quantum technology with phonons. Realizing coherent transfer of phonons between distant oscillators is a key challenge in phononic quantum information processing. Here, we report on the realization of robust unidirectional adiabatic pumping of phonons in a parametrically coupled nanomechanical system engineered as a one-dimensional phononic topological insulator. By exploiting three nearly degenerate local modes-two edge states and an interface state between them-and the dynamic modulation of their mutual couplings, we achieve nonreciprocal adiabatic transfer of phononic excitations from one edge to the other with near unit fidelity. We further demonstrate the robustness of such adiabatic transfer of phonons in the presence of various noises in the control signals. Our experiment paves the way toward nonreciprocal phonon dynamics via adiabatic pumping and is valuable for phononic quantum information processing.

Ce

Topological soliton states, existing in the topological structures with edge defect or interface defect, are usually studied under steady state. Here, we experimentally observe the dynamic processes of the generation and the extinction of such soliton states in the Su-Schrieffer-Heeger model. The different topological structures are implemented on a programmable nanomechanical lattice, consisting of eight adjacent string resonators which are parametrically coupled by manipulation voltages. Moreover, the beating and localization behaviors at different topological interfaces are also observed in the same device. These results explicitly exhibit the dynamic processes of topological soliton states, which reveal real potential toward integrated multifunctional topological materials.

Luminescent materials with controllable colour evolution features are demanded for the development of multi-level anti-counterfeiting technologies. Here we report the structural and luminescence properties of CaMgSi2O6:Ln (Ln = Eu2+, Eu3+, Eu2+/3+) samples in detail and reveal their excitation-wavelength/temperature driven colour evolution characteristics. By tuning either the excitation-wavelength (276, 304, 343, 394 nm) or temperature (in the 330-505 K range), the designed samples with co-existing Eu2+/Eu3+ ions can achieve diverse and controllable colour evolution from red, to pink, purple and blue. This shows their potential application in anti-counterfeiting with the help of sophisticated pattern design. In addition, the underlying mechanism of the Stokes shift of the Eu2+ emission and valence stability of both Eu2+/Eu3+ ions in CaMgSi2O6 are also studied in depth. These results are valuable for designing colour-controllable luminescent materials based on the co-existence of the Eu2+/Eu3+ ions for anti-counterfeiting applications.

Bismuth dopants have attracted intensive studies experimentally for their extremely broad near-infrared luminescence. Here we performed first-principles calculations to investigate the site occupancy and valence state by taking the condition of synthesis into consideration, and then calculated the excited states and various transitions of the bismuth ions by focusing on the targeted valent state Bi+ in a variety of ternary chloride MXCl3 (M = K, Rb, Cs; X = Mg, Cd) hosts. The results on formation energies and charge transition levels show that vacant defects play an important role in the charge compensation for the bismuth dopants, and a lower chemical potential of chlorine benefits the stabilization of Bi+ at monovalent M sites. The multi-configurational quantum-chemical method and the constrained occupancy approach together confirm the near-infrared photoluminescence of Bi+, and the spontaneous emission rates due to electric-dipole and magnetic-dipole contributions are evaluated and analyzed in terms of transition selection rules, to affirm the Bi+ nature of the long lifetime luminescence. Our results show that the mechanisms revealed in this study, and the combination of density-functional calculations for defect formation energies with the wave-function based calculations for optical transitions, are effective in exploring the luminescence of bismuth dopants in solids.

Detecting magnetic field is of great importance for many applications, such as magnetoencephalography and underground prospecting. There have been many magnetometers being widely used since the age of Hall magnetometer. One of the magnetometers, the superconducting quantum interference device, is capable of measuring femtotesla magnetic fields at cryogenic temperature. However, a solid-state magnetometer with femtotesla sensitivity under ambient conditions remains elusive. Here we present a hybrid magnetometer based on the ensemble nitrogen-vacancy centers in diamond with the sensitivity of ( 195 ± 60 ) fT / Hz 1 / 2 under ambient conditions, which can be further advanced to 11 fT / Hz 1 / 2 at 100 Hz with cutting-edge fabrication technologies. Our method will find potential applications in biomagnetism and geomagnetism.

The origin of the self-activated luminescence in the apatite-type M5(PO4)3X (MPOX; M = Sr or Ba; X = Cl or Br) samples and the spectral assignment for cerium-doped Sr5(PO4)3Cl (SPOC) phosphors are ...

Ce3+-doped LiSr4(BO3)3 phosphors have been prepared by a high-temperature solid-state reaction method, and structural refinement of the host compound has been performed. The excitation and emission spectra in the vacuum ultraviolet-ultraviolet-visible range at cryogenic temperatures reveal that Ce3+ ions preferentially occupy eight-coordinated Sr2+ sites in LiSr4(BO3)3. Such experimental attribution is well corroborated by the calculated 4f-5d transition energies and defect formation energies of Ce3+ ions at two distinct Sr2+ sites in the first-principles framework. In addition, the doping concentration-dependent luminescence and the temperature-dependent luminescence are systematically investigated by luminescence intensity and lifetime measurements, respectively. This shows that concentration quenching does not occur in the investigated doping range, but inhomogeneous broadening exists in the concentrated samples. With the estimated thermal quenching activation energy, the discussions on the thermal quenching mechanisms suggest that the thermal-ionization process of the 5d electron is a dominant channel for thermal quenching of Ce3+ luminescence, despite the fact that thermally activated concentration quenching cannot be excluded for the highly doped samples. Finally, the X-ray excited luminescence measurement demonstrates the promising applications of the phosphors in X-ray detection.

Titanium sapphire is one of the most important laser crystals suitable for widely tunable and ultrashort pulsed lasers with high gain and high power outputs, but its performance is limited by the residual infrared absorption at the operation wavelength region of the laser. Although studies have been made over decades in improving the laser performance and the solutions to eliminate this residual absorption, there still remain some controversies for the binding tendency and charge-transfer transition energy of Ti related pairs, which is supposed to be the culprit of this residual absorption. In this paper, we clarify that previously predicted strong binding tendencies in ${\mathrm{Ti}}^{3+}\text{\ensuremath{-}}{\mathrm{Ti}}^{3+}$ and ${\mathrm{Ti}}^{3+}\text{\ensuremath{-}}{\mathrm{Ti}}^{4+}$ pairs should be artificial and are blamed on the intrinsic delocalization error in general approximate density functionals. We show that such errors can be eliminated by Hubbard $U$ corrected generalized-gradient-approximation method with $4\ensuremath{\le}U\ensuremath{\le}5\phantom{\rule{0.16em}{0ex}}\mathrm{eV}$ or hybrid density functionals such like HSE06 and PBE0, which approximately satisfy the generalized Koopmans' condition. Our calculations reveal that the equilibrium geometry and electronic structure of ${\mathrm{Ti}}^{3+}\text{\ensuremath{-}}{\mathrm{Ti}}^{4+}$ pairs can be ${\mathrm{Ti}}^{3+}\text{\ensuremath{-}}{\mathrm{Ti}}^{4+}$-type or ${\mathrm{Ti}}^{3.5+}\text{\ensuremath{-}}{\mathrm{Ti}}^{3.5+}$-type configurations with very small energy differences ($\ensuremath{\lesssim}0.1\phantom{\rule{0.16em}{0ex}}\mathrm{eV}$), and both of them have residual infrared absorption, which are predicted to be about three orders of magnitude stronger in oscillator strength per defect than the pump absorption of ${\mathrm{Ti}}^{3+}$ dopants. Regarding ${\mathrm{Ti}}^{3+}\text{\ensuremath{-}}{\mathrm{Ti}}^{3+}$ pairs, it is shown that they do not contribute to the residual infrared absorption in the wavelength range of laser operation, but their charge-transfer transitions can explain the residual UV band at 270 nm and $E$ band at 400 nm in the absorption spectra of Ti:${\mathrm{Al}}_{2}{\mathrm{O}}_{3}$ crystals. Furthermore, the charge-transfer transition energies and Stokes shift of ${\mathrm{Ti}}^{4+}$ and ionization energies for ${\mathrm{Ti}}^{3+}$ are also well interpreted by our calculations. The calculation method developed together with the predicted optical properties forms the basis for exploration on eliminating the residual infrared absorption in titanium sapphire.

First-principles calculations using the hybrid density functional are carried out to study the defect levels and photoluminescence of bismuth doped in perovskites $R{\mathrm{AlO}}_{3}$ ($R=\mathrm{Y}$, Gd, La) and $\mathrm{La}B{\mathrm{O}}_{3}$ ($B=\mathrm{Al}$, Ga, In). Bismuth dopants are confirmed to be predominantly ${\mathrm{Bi}}^{3+}$ occupying the $R$ site, i.e., ${\mathrm{Bi}}_{R}^{0}$ ($R=\mathrm{Y}$, Gd, La). The variation of the electron trap depth ${\mathrm{Bi}}_{R}(0/\ensuremath{-}1)$ is shown mainly due to the shift of the conduction band, while the hole trap level ${\mathrm{Bi}}_{R}(+1/0)$ shows the correlation with the shortest $R\text{--}\mathrm{O}$ bond length in hosts. Based on the defect level diagram from the first-principles calculation, the transition types of excitation and emission are predicted. Among the systems considered, the lowest excited level that produces the photoluminescence is the $^{3}P_{0,1}$ levels of the $6{s}^{1}6{p}^{1}$ configuration of ${\mathrm{Bi}}^{3+}$, except for ${\mathrm{Bi}}^{3+}$-doped ${\mathrm{LaAlO}}_{3}$, which is the valence band to ${\mathrm{Bi}}^{3+}$ charge transfer state. The photoluminescence involving $^{3}P_{0,1}$ states shows similar Stokes shift in the series, and the excitation and emission energies exhibit almost linear correlation with the band gaps of hosts of a slope $\ensuremath{\sim}0.22$. Furthermore, our calculations show that there is no tendency of forming excessive ${\mathrm{Bi}}^{3+}$ pairs in all the five $RB{\mathrm{O}}_{3}$:${\mathrm{Bi}}^{3+}$, while the ${\mathrm{Gd}}^{3+}\text{\ensuremath{-}}{\mathrm{Gd}}^{3+}$ coupling in ${\mathrm{GdAlO}}_{3}$ provides a ``bridge'' for energy migration from an excited isolated ${\mathrm{Bi}}^{3+}$ ion to the ${\mathrm{Bi}}^{3+}$ pairs that are naturally present due to random distribution, leading to the 495-nm emission being observed uniquely in bismuth-doped ${\mathrm{GdAlO}}_{3}$ among the series of systems considered. The results lay the basis for manipulating the trap levels and excitation and emission wavelengths in ${\mathrm{Bi}}^{3+}$-doped perovskite oxides.

Bismuth dopants have attracted intensive studies experimentally for their extremely broad near-infrared luminescence. Here we performed first-principles calculations to investigate the site occupancy and valence state by taking the condition of synthesis into consideration, and then calculated the excited states and various transitions of the bismuth ions by focusing on the targeted valent state Bi

By studying the temperature-induced red-shift of the V O charge transfer band (CTB) edge in YVO4:10% Eu3+, we demonstrate a high-sensitive strategy for optical temperature sensing using the combination of the temperature-induced enhancement of the excitation in the tail of the CTB and the thermal population of 5D1 state of Eu3+. Under a constant 358 nm excitation, the integrated emission intensity corresponding to 5D1 → 7F1 transition of Eu3+ exhibits drastic temperature dependence ranging from 300 to 480 K. A high relative sensitivity SR was obtained to be 3923/T2. Temperature cycling tests were performed to evaluate the reusability and feasibility as temperature sensors. Our results indicate the potential use of the proposed strategy for high performance optical thermometry.

Luminescent materials with controllable colour evolution features are demanded for the development of multi-level anti-counterfeiting technologies. Here we report the structural and luminescence properties of CaMgSi2O6:Ln (Ln = Eu2+, Eu3+, Eu2+/3+) samples in detail and reveal their excitation-wavelength/temperature driven colour evolution characteristics. By tuning either the excitation-wavelength (276, 304, 343, 394 nm) or temperature (in the 330-505 K range), the designed samples with co-existing Eu2+/Eu3+ ions can achieve diverse and controllable colour evolution from red, to pink, purple and blue. This shows their potential application in anti-counterfeiting with the help of sophisticated pattern design. In addition, the underlying mechanism of the Stokes shift of the Eu2+ emission and valence stability of both Eu2+/Eu3+ ions in CaMgSi2O6 are also studied in depth. These results are valuable for designing colour-controllable luminescent materials based on the co-existence of the Eu2+/Eu3+ ions for anti-counterfeiting applications.

Bismuth ion-doped phosphate crystals have shown rich luminescence phenomena. However, the complexity and variety of Bi

Ultralow-dissipation mechanical systems play an important role in metrology and exploring macroscopic quantum phenomena. Here we report a diamagnetic levitated micromechanical oscillator operating at 3 K with measured dissipation down to $0.59\phantom{\rule{0.2em}{0ex}}\ensuremath{\mu}\mathrm{Hz}$ and a quality factor up to $2\ifmmode\times\else\texttimes\fi{}{10}^{7}$. This mechanical system achieves the lowest dissipation among the state-of-the-art microscale and nanoscale mechanical systems reported to date, with orders-of-magnitude reduction over other systems based on different principles. The cryogenic diamagnetic levitated oscillator is applicable on a wide range of mass, making it a good candidate system for ultrasensitive measurements of both force and acceleration. By virtue of the strong magnetic gradient, this system is potentially capable of studying quantum spin mechanics.

The ${\mathrm{Bi}}^{3+}$ ion is an excellent activator and sensitizer for luminescent materials. However, the complexity and variety of the ${\mathrm{Bi}}^{3+}$-related transitions bring a great challenge to the study of luminescence processes of ${\mathrm{Bi}}^{3+}$ doped materials. Here, we presented first-principles calculations to determine the excitation, relaxation, and emission processes of ${\mathrm{Bi}}^{3+}$ activated materials by using $\mathrm{Ca}M{\mathrm{O}}_{3}:{\mathrm{Bi}}^{3+}(M=\mathrm{Zr},\phantom{\rule{0.28em}{0ex}}\mathrm{Sn},\phantom{\rule{0.28em}{0ex}}\mathrm{Ti})$ as prototype systems, where ${\mathrm{Bi}}^{3+}$ substitutes ${\mathrm{Ca}}^{2+}$ in similar coordinate environments but presents tremendously different excitation and emission spectra. The equilibrium geometric structures of excited states were calculated based on density-functional theory (DFT), with appropriately constraining the electron occupation and including the spin-orbit couplings. Then the hybrid DFT calculations were carried out to obtain the electronic structures and defect levels. Different metastable excited states and Stokes shift were obtained for $M=\mathrm{Zr}$, Sn, and Ti, which explain the remarkable differences in the measured emission spectra. The energies of three types of transitions are obtained from the calculations, including intra-${\mathrm{Bi}}^{3+}$ bands transition and charge transfer between ${\mathrm{Bi}}^{3+}$ ions and the band edges. This leads to a clear and reliable interpretation of all the excitation spectra in the series. The method and its applications to $\mathrm{Ca}M{\mathrm{O}}_{3}:{\mathrm{Bi}}^{3+}$ show the potential of first-principles calculations in analyzing and predicting luminescent properties of ${\mathrm{Bi}}^{3+}$ activated materials.

Levitated oscillators with millimeter or sub-millimeter size are particularly attractive due to their potential role in studying various fundamental problems and practical applications. One of the crucial issues towards these goals is to achieve efficient measurements of oscillator motion, while this remains a challenge. Here we theoretically propose a lens-free optical detection scheme, which can be used to detect the motion of a millimeter or sub-millimeter levitated oscillator with a measurement efficiency close to the standard quantum limit with a modest optical power. We demonstrate experimentally this scheme on a 0.5 mm diameter micro-sphere that is diamagnetically levitated under high vacuum and room temperature, and the thermal motion is detected with high precision. Based on this system, an estimated acceleration sensitivity of $9.7 \times 10^{-10}\rm g/\sqrt{Hz}$ is achieved, which is more than one order improvement over the best value reported by the levitated mechanical system. Due to the stability of the system, the minimum resolved acceleration of $3.5\times 10^{-12}\rm g$ is reached with measurement times of $10^5$ s. This result is expected to have potential applications in the study of exotic interactions in the millimeter or sub-millimeter range and the realization of compact gravimeter and accelerometer., Comment: Physical Review Applied (to be published)

Physical systems with gain and loss can be described by a non-Hermitian Hamiltonian, which is degenerated at the exceptional points (EPs). Many new and unexpected features have been explored in the non-Hermitian systems with a great deal of recent interest. One of the most fascinating features is that, chiral state conversion appears when one EP is encircled dynamically. Here, we propose an easy-controllable levitated microparticle system that carries a pair of EPs and realize slow evolution of the Hamiltonian along loops in the parameter plane. Utilizing the controllable rotation angle, gain and loss coefficients, we can control the structure, size and location of the loops in situ. We demonstrate that, under the joint action of topological structure of energy surfaces and nonadiabatic transitions (NATs), the chiral behavior emerges both along a loop encircling an EP and even along a straight path away from the EP. This work broadens the range of parameter space for the chiral state conversion, and proposes a useful platform to explore the interesting properties of exceptional points physics., 7pages,6 figures

We demonstrate the super-resolution localization of the nitrogen vacancy centers in diamond by a novel fluorescence photoswitching technique based on coherent quantum control. The photoswitching is realized by the quantum phase encoding based on pulsed magnetic field gradient. Then we perform super-resolution imaging and achieve a localizing accuracy better than 1.4 nm under a scanning confocal microscope. Finally, we show that the quantum phase encoding plays a dominant role on the resolution, and a resolution of 0.15 nm is achievable under our current experimental condition. This method can be applied in subnanometer scale addressing and control of qubits based on multiple coupled defect spins., Comment: 5 pages, 4 figures

Realizing a controllable network with multiple degrees of interaction is a challenge to physics and engineering. Here, we experimentally report an on-chip reconfigurable network based on nanoelectromechanical resonators with nearest-neighbor (NN) and next-nearest-neighbor (NNN) strong couplings. By applying different parametric voltages on the same on-chip device, we carry out perfect coherent transfer in NN and NNN coupled array networks. Moreover, the low-loss resonators ensure the desired evolution to achieve perfect transfer and the demonstration of the parity-dependent phase relation at transmission cycles. The realization of NNN couplings demonstrates the capability of engineering coherent coupling beyond a simple model of a NN coupled array of doubly clamped resonators. Our reconfigurable nanoelectromechanical network provides a highly tunable physical platform and offers the possibilities of investigating various interesting phenomena, such as topological transport, synchronization of networks, as well as metamaterials., 7 pages, 4 figures

Cr3+ activated persistent luminescent phosphors with the spinel structure are emerging materials in bio-imaging applications for their distinctive features of deep bio-tissues penetration and recha...