Low Phonon Energy Research Articles

Dual Photosensitizers Material for Photodynamic Theraphy

Abstract Fluoride-based upconversion luminescent materials have the advantage of low phonon energy, which can effectively reduce the non-radiative transition process, so that materials have higher luminous efficiency than other matrix materials. The core-shell NaGdF4:Er3+,Yb3+ @NaGdF4:Tm3+,Yb3+ nanoparticals were synthesized by thermal decomposition method. The core-shell structure can effectively avoid the surface quenching effect, meanwhile, Tm3+ in the shell transmits part of the photons in its excited state to Er3+, effectively enhancing the red emission of Er3+ and improving the luminous efficiency of the samples as a whole. The samples were further coated with a layer of mesoporous silica(mSiO2), where the photosensitizer(PS) Ce6 (red light activated) and MC540 (blue-green light activated) were compounded on through covalent bonds and electrostatic forces, respectively. So that three visable lights include red, green,and blue are all emitted from the sample to activate the PSs to produce reactive oxygen species (ROS) under 980nm laser irradiation. In cells experiments, the samples were modified with folic acid (FA), which can mediated the cancer cells to target endocytosis. Notable photodynamic therapy (PDT) efficiency was observed under this dual-photosensitizers composite samples for its ROS generation.

Multimode vibrational coupling across the insulator-to-metal transition in 1T-TaS2 in THz cavities.

The use of optical cavities on resonance with material excitations allows controlling light-matter interaction in both the regimes of weak and strong coupling. We study here the multimode vibrational coupling of low energy phonons in the charge-density-wave material 1T-TaS2 across its insulator-to-metal phase transition. For this purpose, we embed 1T-TaS2 into THz Fabry-Pérot cryogenic cavities tunable in frequency within the spectral range of the vibrational modes of the insulating phase and track the linear response of the coupled phonons across the insulator-to-metal transition. In the low temperature dielectric state, we reveal the signatures of a multimode vibrational strong collective coupling. The observed polariton modes inherit character from all the vibrational resonances as a consequence of the cavity-mediated hybridization. We reveal that the vibrational strong collective coupling is suppressed across the insulator-to-metal transition as a consequence of the phonon-screening induced by the free charges. Our findings emphasize how the response of cavity-coupled vibrations can be modified by the presence of free charges, uncovering a new direction toward the tuning of coherent light-matter interaction in cavity-confined correlated materials.

Temperature dependent upconversion luminescence of GdScO3 phosphors with low phonon energy for optical thermometry

Temperature dependent upconversion luminescence of GdScO3 phosphors with low phonon energy for optical thermometry

Superconductivity in LaO: a density functional theory study with local, semilocal, and nonlocal exchange-correlation functionals

We studied the dynamical, electronic, and superconducting properties of LaO using a local (PZ), a semilocal (PBE), and three nonlocal correlation functionals (rVV10, vdW-DF2, and vdW-DF3) of the density-functional theory. We concluded that the nonlocal correlations have a marginal effect on the electronic band energies near the Fermi surface. However, the corresponding shifts in the density of states are relatively significant. In contrast, the phonon energies get modified by larger amounts, particularly for optical phonons. These variations in energies of optical phonons do not get reflected to the same degree in electron-phonon coupling constant, λ, from different functionals as their contribution in λ is minor that ranges from 21% to 33%. Moreover, the imperative role of Kohn anomalies and Fermi surface nesting for the electron-phonon coupling is reconfirmed. We also highlighted the role of the matrix elements that surpasses, in certain parts of the Brillouin Zone, all other factors including the Fermi surface nesting. The nonlocal correlation functional, vdW-DF2, gives significantly different results than other nonlocal as well as local/semilocal functionals due to excessive low energy phonons and larger phonon linewidth.

Achieving Near-Infrared Highly Sensitive Temperature Sensing in Lanthanide-Doped Lead-Free Double Perovskite NaLaMgWO6 with Significant Thermal Enhancement.

The significant temperature response of lanthanide-doped up-conversion luminescent materials is typically characterized by a severe thermal quenching of the luminescence intensity at elevated ambient temperatures, which severely restricts materials' capability in temperature sensing. Herein, the influence of matrix phonon properties on the remarkable thermal enhancement effect in the thermosensitive material NaLaMgWO6:Yb3+/Nd3+ is reported. It is elucidated that achieving a significant thermal enhancement of Nd3+ with a higher phonon energy oxide matrix is easier than a halide matrix, which has lower phonon energy by comparison with previous findings. Interestingly, the emission of thermally related levels gets enhanced to various extents through phonon-assisted thermal population. In light of this, a three-model thermometer is constructed based on luminescence intensity ratio (LIR) technology. Given that Sr and ΔE possess a positive correlation, it is feasible to acquire greater temperature monitoring sensitivity Sr in Nd3+, which has a larger ΔE. At 313 K, this thermometry model may achieve a maximum sensitivity of 2.84%·K-1. This work not only provides guidance for the selection of efficient near-infrared up-conversion material but also opens up a prospect for the realization of ultrasensitive thermally coupled luminescent thermometers.

Highly efficiency up and down -conversion photoluminescence in Er/Tm/Yb co-doped lutecia-stabilized zirconia single crystals

High-quality transparent cubic lutecia-stabilized zirconia and LSZ:Yb1Er0.05Tm0.5 single crystals were grown by the optical floating zone method for the first time. For comparison, YSZ and YSZ:Yb1Er0.05Tm0.5 single crystals were also grown. No absorption peaks were observed in the 200 ∼1100 nm range in the transmission and absorption spectra of LSZ and YSZ, indicating that both crystals are excellent matrix crystals. The absorption spectra of LSZ:Yb1Er0.05Tm0.5 and YSZ:Yb1Er0.05Tm0.5 crystals exhibit several absorption peaks at 377, 408, 462, 488, 516, 679, 785 nm and a strong broad absorption band in the 836 ∼ 1050 nm range. The up-conversion photoluminescence of the LSZ:Yb1Er0.05Tm0.5 crystal excited by a 980 nm laser exhibited several distinct emission peaks at 300, 372, 476, 531, 548, 642 and 798 nm; similar emission peaks were observed in the up-conversion photoluminescence spectrum of the YSZ:Yb1Er0.05Tm0.5 crystal, except for the absence of the 300 nm peak. The intensity of the emission peaks of the former was higher than that of the corresponding peaks of the latter. Power curves indicated that the 300 nm emission is a four-photon up-conversion process, the 372 nm and 476 nm emissions are three-photon processes, and the 548 nm and 642 nm emissions are two-photon processes. Under excitation at 379 nm, the down-conversion photoluminescence spectra of the LSZ:Yb1Er0.05Tm0.5 and YSZ:Yb1Er0.05Tm0.5 crystals showed emission peaks at 450, 457, 511, 531 and 637 nm, the peak intensities of the former are higher than those of the latter, which is due to the former with higher density and lower phonon energy as compare to the latter. These results indicate that LSZ:Yb1Er0.05Tm0.5 single crystal has advantages over YSZ:Yb1Er0.05Tm0.5 single crystal for luminescence in photonic devices.

Influence of Host Lattice Ions on the Dynamics of Transient Multiband Upconversion in Yb-Er Codoped NaLnF4 and LiLnF4 Microcrystals (Ln: Y, Lu, Gd).

Inorganic host matrices provide a tunable luminescence environment for lanthanide ions, allowing for the modulation of upconversion luminescence (UCL) properties. AREF4 (A = alkali metal, RE = rare earth) have a low phonon energy and a high optical damage threshold, making them widely used as the host matrix for UCL materials. However, the impact mechanism of alkali metal ions and lanthanide lattice ions on transient UCL dynamics in AREF4 remains unclear. This study utilized a high-power nanosecond-pulsed laser at 976 nm to excite Yb-Er codoped NaLnF4 and LiLnF4 (Ln: Y, Lu, and Gd) microcrystals (MCs). All samples exhibit multiband emission, and the transient UC dynamics are discussed in detail. Compared with LiLnF4, NaLnF4 has higher UC efficiency and red to green (R/G) ratio. Lanthanide ions (Y, Lu, and Gd) affect the energy transfer (ET) distance in Yb-Er codoped systems, thereby altering UC efficiency and the R/G ratio. The energy level coupling between Gd3+ and Er3+ prolongs the duration of the UC emission. Specifically, the red emission lifetime of NaGdF4 is five times longer than that of NaYF4. Our research contributes to exploring excellent alternative host matrices for NaYF4 in the fields of rapid-response optoelectronic devices, micro-nano lasers, and stimulated emission depletion (STED) microscopy.

Prediction of novel layered indium halide superconductors

Abstract We design two new layered indium halide compounds LaOInF2 and LaOInCl2 by means of first-principles calculations and evolutionary crystal structure prediction. We find both compounds crystallize in a tetragonal structure with P4/nmm space group and have indirect band gaps of 2.58 eV and 3.21 eV, respectively. By substituting O with F, both of them become metallic and superconducting at low temperature. The F-doping leads to strong electron–phonon coupling in the low-energy acoustic phonon modes which is mainly responsible for the induced superconductivity. The total electron–phonon coupling strength are 1.86 and 1.48, while the superconducting transition temperature (T c) are about 7.2 K and 6.5 K with 10% and 5% F doping for LaOInF2 and LaOInCl2, respectively.

The physical properties of crystalline iron-rich silicides

The formation enthalpy, electronic structure, lattice dynamics and elasticity of several complex ordered iron-rich silicides (Fe11Si5, Fe13Si3, Fe17Si12 and Fe24Si5) are calculated from the first-principles calculations. It is found that the Debye temperature ΘD of the system decreases with the increase of the ratio of the number of iron atoms to the number of silicon atoms in the same structure. The softening of low-energy acoustic phonons is more obvious with the increase of iron atoms. The elastic constants C11 and C44, Young's modulus E and shear modulus G of the system decrease with the increase of iron atoms. An anomalous phenomenon occurs in the high frequency region of Fe24Si5. The contribution of Fe1 atoms with smaller magnetic moment to the phonon density of states is much larger than that of the Si and other Fe atoms. This indicates that the local metal bond strength between Fe1-Fe1 atoms is stronger.

Optimization of Yb:CaF2 Transparent Ceramics by Air Pre-Sintering and Hot Isostatic Pressing

Yb:CaF2 transparent ceramics represent a promising laser gain medium for ultra-short lasers due to their characteristics: low phonon energy, relatively high thermal conductivity, negative thermo-optical coefficient, and low refractive index. Compared to single crystals, Yb:CaF2 ceramics offer superior mechanical properties, lower cost, and it is easier to obtain large-sized samples with proper shape and uniform Yb3+ doping at high concentrations. The combination of air pre-sintering and Hot Isostatic Pressing (HIP) emerges as a viable strategy for achieving high optical quality and fine-grained structure of ceramics at lower sintering temperatures. The properties of the powders used in ceramic fabrication critically influence both optical quality and laser performance of Yb:CaF2 ceramics. In this study, the 5 atomic percentage (at.%) Yb:CaF2 transparent ceramics were fabricated by air pre-sintering and hot isostatic pressing (HIP) using nano-powders synthesized through the co-precipitation method. The co-precipitated powders were optimized by studying air calcination temperature (from 350 to 550 °C). The influence of calcination temperature on the microstructure and laser performance of Yb:CaF2 ceramics was studied in detail. The 5 at.% Yb:CaF2 transparent ceramics air pre-sintered at 625 °C from powders air calcined at 400 °C and HIP post-treated at 600 °C exhibited the highest in-line transmittance of 91.5% at 1200 nm (3.0 mm thickness) and the best laser performance. Specifically, a maximum output power of 0.47 W with a maximum slope efficiency of 9.2% at 1029 nm under quasi-CW (QCW) pumping was measured.

Contrasting Ultra-Low Frequency Raman and Infrared Modes in Emerging Metal Halides for Photovoltaics.

Lattice dynamics are critical to photovoltaic material performance, governing dynamic disorder, hot-carrier cooling, charge-carrier recombination, and transport. Soft metal-halide perovskites exhibit particularly intriguing dynamics, with Raman spectra exhibiting an unusually broad low-frequency response whose origin is still much debated. Here, we utilize ultra-low frequency Raman and infrared terahertz time-domain spectroscopies to provide a systematic examination of the vibrational response for a wide range of metal-halide semiconductors: FAPbI3, MAPbI x Br3-x , CsPbBr3, PbI2, Cs2AgBiBr6, Cu2AgBiI6, and AgI. We rule out extrinsic defects, octahedral tilting, cation lone pairs, and "liquid-like" Boson peaks as causes of the debated central Raman peak. Instead, we propose that the central Raman response results from an interplay of the significant broadening of Raman-active, low-energy phonon modes that are strongly amplified by a population component from Bose-Einstein statistics toward low frequency. These findings elucidate the complexities of light interactions with low-energy lattice vibrations in soft metal-halide semiconductors emerging for photovoltaic applications.

Nanoparticle doping and molten-core methods towards highly thulium-doped silica fibers for 0.79 μm-pumped 2 μm fiber lasers – A fluorescence lifetime study

We study the fluorescence lifetime of Thulium-doped silica fibers for efficient laser operation in the 2 μm “eye-safe” wavelength range pumped by 0.79 μm radiation. A large set of optical fibers prepared by Modified Chemical Vapor Deposition combined with solution doping or nanoparticle doping, and Molten-core method is investigated in terms of fluorescence lifetimes of the 3F4 and 3H4 excited levels, which contain information about the Tm3+ ion environment, the rate of unwanted processes, such as concentration quenching or multiphonon relaxation, as well as the inter-ionic energy-transfer processes, including the cross-relaxation. Maximum evaluated lifetime values are 778 μs for the 3F4 level and 56 μs for the 3H4 level. From the lifetime study, we conclude that for Tm3+ concentrations above 10,000 ppm and enhanced aluminum concentrations above 5 mol. % Al2O3, the cross-relaxation efficiency is enhanced and multiphonon relaxation is remarkably reduced due to the lower phonon energy of the resulting alumino-silicate glass.

Heterointerface-engineered SnO2@SnO nanoparticle@foamed C composites for prominent microwave absorption and thermal conduction performance

The development of multifunctional materials with wide-band microwave absorption properties (MWAPs), high thermal conductivity (TC), and excellent electrical isolation is rather challenging due to the performance incompatibility. To resolve this challenge, SnO2@SnO nanoparticle(NP)@foamed C composites are synthesized as an electrically insulated filler with low loads, excellent MWAPs, and high TC via a facile salt-template-assisted freeze-drying-annealing route. By controlling the annealing temperature (Ta) and the amount of SnCl2·2H2O (n), their heterointerfaces, textures, and defects were finely modulated. Our results show that the SnO2@SnO NP@foamed C composites have a large TC (3.48 W/(m·K); 1.5 wt% load), a minimal reflection loss (RLmin) of −40.75 dB, and an effective absorption bandwidth (EAB) of 6.88 GHz at a low load of 25 wt%. The composites exhibit an 8.0 % increase in TC, a 9.4 % increase in EAB, and an 11.0 % increase in RLmin compared with pure foamed C. Besides, the mechanism of dielectric loss and thermal transfer at the atomic level was revealed by the calculations of the density of states (DOS) and the phonon density of states (PDOS). The boosted MWAPs could be ascribed to the breakdown of local microstructural symmetry and the formation of extra electric dipoles at the interfaces of SnO/C, SnO/SnO2, and SnO2/C. The improved TC mainly results from the combined effect of the low-energy phonons from SnOx and the high-energy phonons from C. This study provides theoretical guidance for designing integrated materials with effective microwave absorption and thermal conduction in the electronic industry.

Ultralow Thermal Conductivity in Vacancy-Ordered Halide Perovskite Cs3Bi2Br9 with Strong Anharmonicity and Wave-Like Tunneling of Low-Energy Phonons.

Halide perovskites are of great interest due to their exceptional optical and optoelectronic properties. However, thermal conductivity of many halide perovskites remains unexplored. In this study, an ultralow lattice thermal conductivity κL (0.24W m-1 K-1 at 300 K) is reported and its weak temperature dependence (≈T-0.27) in an all-inorganic vacancy-ordered halide perovskite, Cs3Bi2Br9. The intrinsically ultralow κL can be attributed to the soft low-lying phonon modes with strong anharmonicity, which have been revealed by combining experimental heat capacity and Raman spectroscopy measurements, and first-principles calculations. It is shown that the highly anharmonic phonons originate from the Bi 6s2 lone pair expression with antibonding states of Bi 6s and Br 4p orbitals driven by the dynamic BiBr6 octahedral distortion. Theoretical calculations reveal that these low-energy phonons are mostly contributed by large Br motions induced dynamic distortion of BiBr6 octahedra and large Cs rattling motions, verified by the synchrotron X-ray pair distribution function analysis. In addition, the weak temperature dependence of κL can be traced to the wave-like tunneling of phonons, induced by the low-lying phonon modes. This work reveals the strong anharmonicity and wave-like tunneling of low-energy phonons for designing efficient vacancy-ordered halide perovskites with intrinsically low κL.

Structural insight of fluorophosphate glasses through F/O ratio: case study of Raman and NMR spectra

Fluorophosphate glass has excellent characteristics such as low nonlinear refractive index, anomalous partial dispersion, low phonon energy, high UV transparency and high rare earth doping concentration, etc. The two anion ions of fluorine (F) and oxygen (O) and their F/O ratio in fluorophosphate glasses provide important structural characteristics of the specific glass. To explore this, a series of fluorophosphate glass samples with theoretical F/O ratios ranging from 1 to 7 were prepared, Raman spectroscopy and 31P nuclear magnetic resonance (NMR) spectroscopy were mainly employed to elucidate the structural polyhedrons made of the network chain. The underlying correlation between the Qn units and F/O ratio was explored, i.e., the Q2 unit dominate when the F/O ratio is less than 0.3, and predominantly Q2 or Q1 unit is predominant as F/O ratio ranges from 0.3 to 1, it comes to be Q1 or Q0 unit as F/O ratio further increase to 4, while it becomes Q0 when the F/O ratio is greater than 4. The applicability of this interval estimation was verified by comprehensive analyzing a variety of structural results of fluorophosphate glasses with various glass compositions. The explored interrelation between the F/O ratio and structural property is of great significance for developing low nonlinear and UV transparent fluorophosphate glasses.

2.7μm luminescence and structural properties of Er3+-doped fluorotellurate glass

In this paper, the thermal properties and internal structures of fluorotellurate glasses with different concentrations of TeO2 were studied. Glass samples with a concentration of 30mol% TeO2 were doped with different concentrations of Er3+ (1,2, 3,3.5,4,4.5,5mol%) and their luminescence characteristics were analyzed. The fluorotellurate glass possess high infrared transmittance (93 %), thermal stability (ΔT>110 °C), and low phonon energy (821 cm−1). Er3+ doped fluorotellurate glass exhibits high fluorescence lifetime of 4I11/2 level (1.59 ms), large emission cross-section (5.98 × 10−21cm2), and achieves a quantum efficiency of up to 30 %. These experimental findings suggest promising prospects for the utilization of Er3+ doped fluorotellurate glass in 2.7 μm laser applications.

A stress-induced source of phonon bursts and quasiparticle poisoning

The performance of superconducting qubits is degraded by a poorly characterized set of energy sources breaking the Cooper pairs responsible for superconductivity, creating a condition often called “quasiparticle poisoning”. Both superconducting qubits and low threshold dark matter calorimeters have observed excess bursts of quasiparticles or phonons that decrease in rate with time. Here, we show that a silicon crystal glued to its holder exhibits a rate of low-energy phonon events that is more than two orders of magnitude larger than in a functionally identical crystal suspended from its holder in a low-stress state. The excess phonon event rate in the glued crystal decreases with time since cooldown, consistent with a source of phonon bursts which contributes to quasiparticle poisoning in quantum circuits and the low-energy events observed in cryogenic calorimeters. We argue that relaxation of thermally induced stress between the glue and crystal is the source of these events.

Lattice Dynamics of Quasi-2D Perovskites from First Principles.

We present the vibrational properties and phonon dispersion for quasi-2D hybrid organic-inorganic perovskites (BA)2CsPb2I7, (HA)2CsPb2I7, (BA)2(MA)Pb2I7, and (HA)2(MA)Pb2I7 calculated from first principles. Given the highly complex nature of these compounds, we first perform careful benchmarking and convergence testing to identify suitable parameters to describe their structural features and vibrational properties. We find that the inclusion of van der Waals corrections on top of generalized gradient approximation (GGA) exchange-correlation functionals provides the best agreement for the equilibrium structure relative to experimental data. We also investigate the impact of the molecular orientation on the equilibrium structure of these layered perovskite systems. Our results suggest ground state ferroelectric alignment of molecular dipoles in the out-of-plane direction is unlikely and support the assignment of the centrosymmetric space group for the low-temperature phase of (HA)2(MA)Pb2I7. Finally, we compute vibrational properties under the harmonic approximation. We find that stringent energy cut-offs are required to obtain well-converged phonon properties, and once converged, the harmonic approximation can capture key physics for such a large, hybrid inorganic-organic system with vastly different atom types, masses, and interatomic interactions. We discuss the obtained phonon modes and dispersion behavior in the context of known properties for bulk 3D perovskites and ligand molecular crystals. While many vibrational properties are inherited from the parent systems, we also observe unique coupled vibrations that cannot be associated with vibrations of the pure constituent perovskite and ligand subphases. Energy dispersion of the low energy phonon branches primarily occurs in the in-plane direction and within the perovskite subphase and arises from bending and breathing modes of the equatorial Pb-I network within the perovskite octahedral plane. The analysis herein provides the foundation for future investigations on this class of materials, such as exciton-phonon coupling, phase transitions, and general temperature-dependent properties.

New Lead-free Hybrid Layered Double Perovskite Halides: Synthesis, Structural Transition and Ultralow Thermal Conductivity.

Hybrid layered double perovskites (HLDPs), representing the two-dimensional manifestation of halide double perovskites, have elicited considerable interest owing to their intricate chemical bonding hierarchy and structural diversity. This intensified interest stems from the diverse options available for selecting alternating octahedral coordinated trivalent [M(III)] and monovalent metal centers [M(I)], along with the distinctive nature of the cationic organic amine located between the layers. Here, we have synthesized three new compounds with general formula (R'/R'')4/2M(III)M(I)Cl8; where R'=C3H7NH3 (i.e. 3N) and R''=NH3C4H8NH3 (i.e. 4N4); M(III)=In3+ or Ru3+; M(I)=Cu+ by simple solution-based acid precipitation method. The structural analysis reveals that (4N4)2CuInCl8 and (4N4)2CuRuCl8 adopt the layered Dion Jacobson (DJ) structure, whereas (3N)4CuInCl8 exhibits layered Ruddlesden Popper (RP) structure. The alternative octahedra within the inorganic layer display distortions and tilting. Three compounds show temperature-dependent structural phase transitions where changes in the staking of inorganic layer, extent of octahedral tilting and reorientation of organic spacers with temperature have been noticed. We have achieved ultralow lattice thermal conductivity (κL) in the HLDPs in the 2 to 300 K range, marking a distinctive feature within the realm of HLDP systems. The RP-HLDP compound, (3N)4CuInCl8, demonstrates anisotropy in κL while measured parallel and perpendicular to layer stacking, showcasing ultralow κL of 0.15 Wm-1K-1 at room temperature, which is one of the lowest values obtained among Pb-free metal halide perovskite. The observed ultralow κL in three new HLDPs is attributed to significant lattice anharmonicity arising from the chemical bonding heterogeneity and soft crystal structure, which resulted in low-energy localized optical phonon modes that suppress heat-carrying acoustic phonons.

Structure and Spectral Properties of Er3+-Doped Bismuth Telluride Near-Infrared Laser Glasses.

TeO2-Bi2O3-B2O3-ZnO laser glasses doped with Er3+ were synthesized through an optimized melt-quenching method. The absorption spectra at 808 nm LD pumping were studied. Various spectral tests and data analyses indicate that the maximum fluorescence emission intensity can be obtained when the Er3+ doping concentration reaches 2%. In this case, the emission cross-section can reach up to 9.12 × 10-21 cm2 and the gain coefficient at 1.55 μm is 6.17 cm-1. Simultaneously, the sample has a lower phonon energy in the high-frequency band at 1077 cm-1, which reduces the probability of non-radiative relaxation. The calculated energy transfer coefficient CD-A is 13.8 × 10-40 cm6/s, reflecting the high cross-relaxation probability of Er3+ in the sample, which promotes the luminescence of 1.55 μm and favors the emission in the near-infrared region. The comprehensive results demonstrate that the prepared Er3+-doped bismuth telluride laser glass can be used as a promising and high-quality gain material for near-infrared lasers.