Phonon Intensity Research Articles

Singular Continuous and Nonreciprocal Phonons in Quasicrystal AlPdMn.

In quasicrystals lacking translational symmetry but having highly ordered structures, understanding how phonons propagate in their aperiodic lattices remains an unsolved issue. We present an inelastic neutron scattering study on acoustic phonon modes of icosahedral quasicrystal AlPdMn, revealing hierarchical pseudo-gap structure in low-energy acoustic modes. Additionally, phonon intensities are asymmetric in energy and wave vectors with respect to the Bragg peak, indicating characteristic nonreciprocal phonon propagation in quasicrystals.

Influence of the Bias Voltage on Effective Electron Velocity in AlGaN/GaN High Electron Mobility Transistors.

The small-signal S parameters of the fabricated double-finger gate AlGaN/GaN high electron mobility transistors (HEMTs) were measured at various direct current quiescent operating points (DCQOPs). Under active bias conditions, small-signal equivalent circuit (SSEC) parameters such as Rs and Rd, and intrinsic parameters were extracted. Utilizing fT and the SSEC parameters, the effective electron velocity (νe-eff) and intrinsic electron velocity (νe-int) corresponding to each gate bias (VGS) were obtained. Under active bias conditions, the influence mechanism of VGS on νe-eff was systematically studied, and an expression was established that correlates νe-eff, νe-int, and bias-dependent parasitic resistances. Through the analysis of the main scattering mechanisms in AlGaN/GaN HEMTs, it has been discovered that the impact of VGS on νe-eff should be comprehensively analyzed from the aspects of νe-int and parasitic resistances. On the one hand, changes in VGS influence the intensity of polar optical phonon (POP) scattering and polarization Coulomb field (PCF) scattering, which lead to changes in νe-int dependent on VGS. The trend of νe-int with changes in VGS plays a dominant role in determining the trend of νe-eff with changes in VGS. On the other hand, both POP scattering and PCF scattering affect νe-eff through their impact on parasitic resistance. Since there is a difference in the additional scattering potential corresponding to the additional polarization charges (APC) between the gate-source/drain regions and the region under the gate, the mutual effects of PCF scattering on the under-gate electron system and the gate-source/drain electron system should be considered when adjusting the PCF scattering intensity through device structure optimization to improve linearity. This study contributes to a new understanding of the electron transport mechanisms in AlGaN/GaN HEMTs and provides a novel theoretical basis for improving device performance.

Impact of material-dependent radiation – longitudinal optical phonon interaction on thermal electric-dipole radiation from surface metal − semiconductor grating structures

Infrared thermal radiation emission in the 8.5 – 28 THz frequency region is obtained using surface metal–semiconductor grating structures on undoped (u-) GaAs, u-GaP, u-ZnO, u-GaN, and n-type SiC in a temperature range of 430 – 630 K. These emissions resonate with longitudinal optical (LO) phonon or LO-like lattice vibration energies determined by the zero points of the real parts of the dielectric functions in the surface structures. The emissions of materials with Reststrahlen bandwidths of a few tens of cm−1 show the emissions resonating with their LO phonon modes, while materials with bandwidth of more than 170 cm−1 show peak energies significantly lower than the LO phonon: LO-like phonon resonance. The emission intensity is found to be dominated by the balance of radiative and nonradiative LO or LO-like phonon annihilation rates. The radiative rate is dominated by the LO-phonon–radiation interaction Hamiltonian and the Bose-Einstein factor. High emission intensity is obtained for the structure on u-ZnO with intense LO-like phonon–radiation interaction. The dependence of the emission intensity on temperature and emission window width for various materials shows the effect of material-dependent metal/semiconductor interface conditions on the emission efficiency.

Enhanced thermoelectric properties for eco-friendly CaTiO3 by band sharpening and atomic-scale defect phonon scattering

CaTiO3-based compounds have emerged as a promising thermoelectric material, renowned for their environmentally benign, thermally stable, and cost-efficient merits. Non-etheless, the pristine CaTiO3 manifests inherently low electronic transport properties. Herein, the thermoelectric properties of Ca1-xDyxTiO3 (x = 0, 0.05, 0.10, 0.15, 0.20) compounds are systematically investigated. The electrical transport properties are markedly enhanced by synergistic optimization of the carrier concentration, mobility, and density-of-states effective mass. Density functional theory results demonstrate that the conduction band tends to be sharper and that the lighter band participates in carrier transport after Dy doping. The large discrepancy in atomic mass results in considerable mass fluctuations, which give rise to intense phonon scattering. Benefitting from the modulated band structure and reduced thermal conductivity, the highest thermoelectric figure of merit (ZT) of 0.31 is achieved at 1073 K, enhanced by 287.5% in contrast with pristine CaTiO3 (ZTmax = 0.08). The defect and energy band modulation strategies proposed to optimize thermoelectric performance are applicable to other thermoelectric materials. This investigation inspires the exploration of high-performance and eco-friendly high-temperature thermoelectric material.

Chalcogenide perovskite BaZrS3 bulks for thermoelectric conversion with ultra-high carrier mobility and low thermal conductivity

Chalcogenide perovskites are expected to be promising thermoelectric materials, since they not only possess efficient carrier transport and defect tolerance, but also demonstrate unique advantages of high thermodynamic stability, eco-friendly and earth-abundant constituents. Especially, theoretical reports have predicted their “glass-like” thermal conductivities. However, experimental investigation on thermoelectric performances of chalcogenide perovskite BaZrS3 is extremely scarce due to the difficulty in preparing high-quality bulk samples, which originates from the brittle nature, high melting point, and the large difference in melting points between Ba/S and Zr. In this work, pure phase BaZrS3 bulks with high relative density reaching 100 % are realized by optimized sulfurization from low-cost BaZrO3 powders combined with fast spark plasma sintering. A maximum zT value of 0.37 at 623 K in BaZrS3 bulks is achieved, which is the record-high value among the reported sulfide, halide, and hybrid perovskite materials. A room-temperature electron mobility up to 385 cm2V−1s−1 is among the highest values for perovskites due to the high phase purity, dense morphology and corner-sharing ZrS6 octahedral three-dimensional network as effective carrier channels. Meanwhile, a measured low lattice thermal conductivity of 1.11 Wm−1K−1 at 623 K is attributed to the intense phonon scattering from the intrinsic distorted-perovskite structure and the lattice defects by sulfur deficiency. Moreover, the BaZrS3 bulks in this work are stable against moisture/air and high temperature test. This work provides new insights into the fundamental electrical and thermal properties of chalcogenide perovskites, and highlights their great potential in the practical thermoelectric applications.

Adjustment in phonon scattering through doping to boosting the Near-IR photoresponse performance of p-type SnSe nanosheets

As a p-type semiconductor, layered SnSe has attracted more and more attention because of its great potential application in the field of optoelectronics. However, the strong phonon scattering caused by abundant intrinsic vacancy defects dramatically reduces the performance of carrier transport. It is significant to effectively compensate for the intrinsic defects and reduce the phonon scattering for photodetection materials. In this letter, a novel and simple method is used to reduce the scattering and thus improve the detector performance. The inhibition effect of doping on phonon scattering is systematically studied by experiments and theoretical calculations. The Bi-doped SnSe photodetector exhibits great responsivities of 2.13 A W−1 (447 nm), 1.35 A W−1 (655 nm) and 1.91 A W−1 (980 nm) at 5 V, which are about 2∼3 folds better than those of the undoped device. Furthermore, for the Bi-doped SnSe photodetector, the Ion/Ioff are about 46.7, 20.3 and 30.3 for 447 nm, 655 nm and 980 nm, respectively, which are much higher than those of the SnSe photodetector. The photoluminescence and absorption are performed to confirm the bandgap and defects energy level. Meanwhile, the temperature-dependent current-voltage curves measurement is utilized to prove that the enhancement in response performance is because of the decrease in intensity of phonon scattering, which is attributed to the reduction of scattering centers and the weakening of the effect of vacancy defects on the structural translational asymmetry. All these results evidently illustrate that adjustment in phonon scattering is an effective way to achieve high-performance SnSe photodetectors.

Ultrafast reversible phase engineering in MoTe2 thin film via polaron formation

The emergence of various polymorphs in two-dimensional transition metal dichalcogenides provides an opportunity for robust phase engineering by temperature, strain, laser irradiation, and external charge doping (Keum in Nat. Phys. 11:482, 2015; Song in Nano Lett. 16:188, 2016; Cho in Science 349:625, 2015; Kim in Nano Lett. 17:3363, 2017). This provides means to develop homojunction of metal–semiconductor, enhance mobility, reduce contact resistance, and observe novel quantum critical phenomena in mesoscopic systems. The rich physics paves the way for ultrafast light-induced switching/memory devices and optical data processing in optoelectronics. However, the fundamental temporal evolution of the laser-driven phase transformation, in particular regarding heat and charge carriers, remains elusive. We report an ultrafast reversible structural transformation in MoTe2 by coherent phonon dynamics through polaron formation at room temperature. At a high photon density, the generated coherent phonons are coupled with excitons to form polarons. The strong exciton–phonon coupling disturbs and dephases the coherent phonons of the semiconducting 2H phase in MoTe2, and generates lattice distortions to further stabilize new coherent phonons of the metallic 1T’-phase, manifested by the emergence of the corresponding phonons in each phase. This structural transformation is fully reversible within a few picoseconds by switching on/off the laser. The nonlinear response of the phonon intensity to the excited carrier density in the intermediate region indicates a gradual structural transformation through coexisting 2H and 1T’ phases.

Defect induced crystal lattice disorder and its effect on the electron-phonon coupling in Fe doped ZnO thin films

We established a strong correlation between the crystal lattice disorder in Fe doped ZnO (FexZn1-xO) thin films and its effect on the electron phonon (e-p) coupling strength (I2LO/I1LO) which decreased with Fe doping concentration, improved with annealing temperature and showed a mixed increasing/decreasing trend by the variation of the argon (Ar) to oxygen (O2) gas ratio (Ar + O2, Ar) in the deposition chamber. Fe doping raised the number of phonon modes, intensity and full width at half maximum (FWHM) of the 1LO phonon modes suggesting the confinement of phonons due to the increased crystal lattice disorder in the FexZn1-xO films. High temperature annealing enhanced the e-p coupling strength reaching a maximum at 500 °C indicating better crystal quality at high temperature. Furthermore, the e-p coupling strength dropped with the doping concentration for the films prepared in Ar + O2 atmosphere and that showed a mixed increasing/decreasing trend for films prepared in Ar atmosphere. This unique physical phenomena confirmed that the coupling strength not only depend on the dopant concentration but also the dopant induced micro/nano defects that modulate the crystal lattice disorder and the coupling strength in doped ZnO. The as prepared FexZn1-xO thin films were highly oriented along the c-axis displaying columnar nanorod (film) like morphology at low (high) Fe doping concentration with the co-existence of both Fe2+ and Fe3+ ions. Fe doping increased the band gap from 3.28 eV for un-doped ZnO to 3.35 eV (1.40 at.% of Fe) and 3.42 eV (3.5 at.% of Fe). Nearly forty (40) thin films were used for a detailed investigation.

Enhanced Thermoelectric Performance of MnTe by Decoupling of Electrical and Thermal Transports

AbstractLead‐free polycrystalline manganese telluride holds great potential in the development of waste heat recovery due to its fascinating physical properties. However, the poor thermoelectric (TE) performance in the p‐type MnTe alloys always results from their inferior carrier concentration, leading to low power factor and high thermal conductivity which restrict the overall thermoelectric performance. In this work, the problem is solved by decoupling its electrical and thermal transports through the hole donor Ge‐deficiency in MnTe + x mol.% GeTe (0 ≤ x ≤ 4) compounds. Intrinsically, extra GeTe in MnTe + x mol.% GeTe compound offers free charge carriers due to a narrow bandgap comparatively, realizing not only a full assessment of stimulated electrical performance but also an enhanced power factor. Moreover, benefiting from the nano‐precipitates and tweed microstructures, the lattice thermal conductivity effectively reduces due to the intensive phonon scattering accordingly. Ultimately, a maximum ZT of ≈1.2 at 873 K in the 3 mol.% GeTe doped MnTe sample is realized.

Microstructure Optimization in the Shear‐Exfoliated Bi6Cu2Se4O6 through Introducing Reduced Graphene Oxide Leads to Wide‐Ranged Thermoelectric Performance

AbstractBi6Cu2Se4O6 is considered as an ideal n‐type thermoelectric material to pair with p‐type BiCuSeO for preparing oxyselenide‐based thermoelectric devices, but its thermoelectric performance is limited by poor electrical conductivity. In this research, the reduced graphene oxide (rGO) nanosheets are introduced into Bi6Cu2Se3.6Cl0.4O6 matrix through liquid‐phase shear exfoliation to modify the microstructure. rGO can insert into matrix grains as intercalations, or embed into grain boundaries as wetting phase, and prompt grain alignment, which contributes to the significantly enhanced carrier mobility, thus leading to an improvement in electrical conductivity from ≈15 S cm−1 to ≈230 S cm−1 at 303 K. Whereafter, the effective donor dopant Nb is chosen to substitute Bi. The carrier concentration is increased without damaging the carrier mobility, resulting in a further improved electrical conductivity of ≈840 S cm−1 at 303 K. Lattice thermal conductivity is also suppressed owing to the intensive phonon scattering by point defects and grain boundaries. Ultimately, a record‐breaking peak ZT ≈0.5 (873 K) and average ZT ≈0.3 (303–873 K) can be achieved in Bi5.91Nb0.09Cu2Se3.6Cl0.4O6 + 0.5% rGO. The microstructure optimization method in this research effectively improves thermoelectric performance, and is anticipated to be applied in other thermoelectrics.

Synthesis, crystal structure and photoluminescence properties of Mn4+ activated K2WO2F4·H2O

Oxyfluorides activated with Mn4+ have great potential in phosphors converted LED. Phosphors with intensive zero phonon line (ZPL) emission are expected to improve the performance of the light sources. Microcrystalline powders of oxyfluoride K2WO2F4·H2O activated with Mn4+ were synthesized by using a coprecipitation method. The structural parameters and atomic coordinations of K2WO2F4·H2O were determined by both refinement and calculation. K2WO2F4·H2O crystallizes in the monoclinic crystal system with C2/m group space. The unit cell could be considered as a stack of KWO2F4 slices with another K+ ion and H2O molecule in the interstitial. The morphology and photoluminescence properties of K2WO2F4·H2O: Mn4+ were studied as a function of Mn4+ concentration. It is revealed that the microcrystalline shows highly orientational preferred growth. Mn4+ shows bright red emission upon the excitation of blue light. The emission is due to the 2Eg→4A2g transition. Furthermore, the photoluminescence features intensive ZPL emission and short excitation state lifetime, which is ascribed to the highly distorted coordination environment. The effects of octahedron distortion and the second coordination sphere on the ZPL emission intensity are discussed.

Non-equivalent Mn4+ doping in mixed-anion host of K3Na(MoO2F4)2·H2O achieving short fluorescence lifetime and intense zero phonon line

The parity-selection rule for the Mn4+ d → d intra-configurational transition becomes relaxed after placing it into Mo6+-based distorted octahedra, which induced an oxyfluoride phosphor with fast decay and intense zero phonon line emission.

Phonon Mediated Collective Dynamics of Coherently Pumped Two-Level Emitters

"We investigate the collective quantum dynamics of an ensemble of two-level emitters, embedded in a crystal, and coherently pumped by a moderately intense, and externally applied coherent electromagnetic field. The ensemble is damped preponderantly via the surrounding phonon reservoir which mediates the inter-particle collective interactions. We have found that generally phonon transitions among the corresponding dressed states are taking place involving simultaneously many single emitters or pairs of two-level emitters, respectively. In both cases the phonon intensity can be proportional to the squared number of involved two-level emitters."

Influence of Lu3+ addition on the structure, mechanical and thermophysical properties of Gd3TaO7 oxide

To optimise the mechanical and thermophysical properties of Gd3TaO7, Lu3+ doped Gd3TaO7 oxides were synthesised using sol-gel and high-temperature sintering methods. The results show that nanopowders with uniform particle sizes and bulk samples with compact microstructures were successfully obtained. Owing to the decreased order degree of lattice with increasing fraction of Lu3+, the lattice of (Gd1‒xLux)3TaO7 transforms gradually from an ordered pyrochlore (x ≤ 0.5) into a disordered fluorite (x ≥ 0.7). The Young's modulus (174–192 GPa), Vickers hardness (9.9–10.9 GPa), and fracture toughness (2.61–3.68 MPa m0.5) of the bulk samples are superior or comparable to those of Y2O3-stabilised zirconia (YSZ), which can prolong the service life of thermal barrier coating. The thermal conductivity of (Gd1‒xLux)3TaO7 (0.976–1.628 W m‒1 K‒1, 50–1000 °C), first decreases and then elevates with increasing fraction of Lu3+. Owing to the intensive phonon scattering caused by high-concentration point defects, the thermal conductivity of (Gd1‒xLux)3TaO7 is approximately half that of YSZ. Additionally, the excellent lattice steadiness up to 1400 °C and high average thermal expansion coefficient (≥10.71 × 10‒6 K‒1, 1000–1400 °C) of (Gd1‒xLux)3TaO7 oxides will assist in preventing the premature failure of thermal barrier coating.

Performance limit of all-wrapped monolayer MoS2 transistors

All-wrapped transistors consisting of two-dimensional transition-metal dichalcogenide channels are appealing candidates for post-silicon electronics. Based on the Boltzmann transport theory, here we report a comprehensive theoretical survey on the performance limits for monolayer MoS2 transistors with three prototypical gate dielectrics (Al2O3, HfO2 and BN), by including primary extrinsic charge scattering mechanisms present in practical devices. A concept of “dead space” between the dielectrics and channels is proposed and used in calculation to ameliorate the general overestimation in scattering intensity of surface optical phonons, which enables an accurate description of electronic transport behavior. Crucial device indices, including charge mobility and current density, are thoroughly analyzed for transistors at post-silicon technological nodes beyond 1 nm. The on-state current is estimated to be generally greater than 2 mA μm−1 at channel lengths below 10 nm. The results clarify the potential benefits in performance from extremely miniaturized monolayer-channel transistors for More-Moore electronics.

Infrared photoluminescence and dynamic properties of ZnGa2Se4

The optical properties of the ZnGa2Se4 are investigated by infrared (IR) reflectivity, Raman scattering, photoluminescence and DFT simulations. We have analyzed pairs of lines of FL corresponding to 1.24[Formula: see text]eV and 1.22[Formula: see text]eV at low energy excitations, about these FL maxima haven’t any information in other works. Studies show that depending on the temperature, the intensity of luminescence decreases and formed new third maximum. The energy difference between each of these peaks is 0.02[Formula: see text]eV, which corresponds to the energy of the most intense phonon in the Raman spectrum.

Selective coupling of coherent optical phonons in YBa2Cu3O7−δ with electronic transitions

We investigate coherent lattice dynamics in optimally doped ${\mathrm{YBa}}_{2}{\mathrm{Cu}}_{3}{\mathrm{O}}_{7\ensuremath{-}\ensuremath{\delta}}$ driven by ultrashort ($\ensuremath{\sim}12$ fs) near-infrared and near-ultraviolet pulses. Transient reflectivity experiments, performed at room temperature and under moderate ($<0.1$ mJ/${\mathrm{cm}}^{2}$) excitation fluence, reveal ${A}_{g}$-symmetry phonon modes related to the O(2,3) bending in the ${\mathrm{CuO}}_{2}$ planes and to the apical O(4) stretching at frequencies between 10 and 15 THz, in addition to the previously reported Ba and Cu(2) vibrations at 3.5 and 4.5 THz. The relative coherent phonon amplitudes are in stark contrast to the relative phonon intensities in the spontaneous Raman scattering spectrum excited at the same wavelength. This contrast indicates mode-dependent contributions of the Raman and non-Raman mechanisms to the coherent phonon generation. We show that the particularly intense coherent Cu(2) phonon, together with its initial phase, supports its generation predominately via a displacive mechanism, possibly involving the charge transfer within the ${\mathrm{CuO}}_{2}$ planes. The small amplitude of the coherent out-of-phase O(2,3) bending mode at 10 THz also suggests the involvement of non-Raman generation mechanism. The generation of the other coherent phonons can in principle be explained within the framework of Raman mechanism. When the pump light has the polarization component perpendicular to the ${\mathrm{CuO}}_{2}$ plane, the coherent O(4) mode at 15 THz is strongly enhanced compared to the in-plane excitation, corresponding to the large polarizability component associated with the hopping between the apical and the chain oxygens, O(4) and O(1).

Raman spectroscopy study of CdS nanorods and strain induced by the adsorption of 4-mercaptobenzoic acid.

In this study, near- and off-resonance Raman spectra of cadmium sulfide (CdS) quantum rods (NRs) and 4-mercaptobenzoic acid (4-MBA) adsorbed CdS NRs are reported. The envelopes of characteristic optical phonon modes in the near-resonance Raman spectrum of CdS NRs are deconvoluted by following the phonon confinement model. As compared with off-resonant Raman spectra, optical phonon modes scattering cross section is amplified significantly in near-resonance Raman spectra through the Fröhlich interaction. The Huang-Rhys factor defining the strength of the Fröhlich interaction is estimated (∼0.468). Moreover, the adsorption of different concentrations of 4-mercaptobenzoic acid (4-MBA) onto CdS NRs produces surface strain in CdS NRs originating due to surface reconstruction and consequently blue and red shifts in off-resonance (514.5nm) Raman spectra depending on the concentration of 4-MBA. These consequences are attributed to compressive and tensile strains, respectively. Relative to bulk CdS powder as the reference, strain in CdS NRs increases with decreasing 4-MBA concentrations. In off-resonance Raman spectra of 4-MBA adsorbed CdS NRs, the full width at half maxima of phonon modes (1-LO and 2-LO) and intensity ratio I2-LO/I1-LO increase with decreasing 4-MBA concentration.

On-the-fly machine learning potential accelerated accurate prediction of lattice thermal conductivity of metastable silicon crystals

In this paper, we propose a convenient strategy to accelerate the evaluation of lattice thermal conductivity through combining phonon Boltzmann transport equation (PBTE) and on-the-fly machine learning potential (FMLP). The thermal conductivity of diamond silicon ($d\text{\ensuremath{-}}\mathrm{Si}$) is evaluated firstly by density functional theory (DFT), FMLP, and empirical potential with PBTE, respectively. The results demonstrate the proposed strategy integrates the prediction accuracy of DFT and computational speed of empirical potential, breaking the dilemma of traditional thermal conductivity assessment schemes. Based on this, the efficient strategy is applied to predict thermal conductivity of 102 low-energy metastable silicon crystals with energies between $d\text{\ensuremath{-}}\mathrm{Si}$ and experimentally ${\mathrm{Si}}_{24}$. Among them, the $Cmcm\text{\ensuremath{-}}{\mathrm{Si}}_{16}, P6/mmm\text{\ensuremath{-}}{\mathrm{Si}}_{36}$-2, $Pnma\text{\ensuremath{-}}{\mathrm{Si}}_{32}$-2 are predicted to host lowest lattice thermal conductivity in $xx$ (8.213 ${\mathrm{Wm}}^{\ensuremath{-}1}{\mathrm{K}}^{\ensuremath{-}1}$), $yy$ (10.917 ${\mathrm{Wm}}^{\ensuremath{-}1}{\mathrm{K}}^{\ensuremath{-}1}$), and $zz$ (11.807 ${\mathrm{Wm}}^{\ensuremath{-}1}{\mathrm{K}}^{\ensuremath{-}1}$) directions, respectively. Such low lattice thermal conductivity benefits from the combined effect of low phonon group velocity and intense phonon scattering caused by distorted $s{p}^{3}$ hybrid states in these metastable silicon crystals. The findings presented in this work provide new candidates and insights of silicon-based materials with ultra-low thermal conductivity, which will greatly expand the applications in thermoelectric and thermal insulation fields.

Intense blue-emitting Yb/Tm-CaSiO3 wollastonite upconversion phosphors

Wollastonite is a naturally occurring mineral with a chemical formula of CaSiO3. Owing to outstanding mechanical, chemical, and thermal stabilities, wollastonites have become one of the most versatile industry minerals for applications in construction materials, cement, plastics, paints and coatings, friction, automobile brakes, ceramic and metallurgical applications to name a few. Despite technological importance, research on functional properties such as photon upconversion in wollastonites is still lacking. In this report, an initiative has been taken to demonstrate ultra-violet, blue, and near-infrared photon upconversion in CaSiO3 wollastonite via Yb and Tm doping. The wollastonite ceramics are synthesized via microwave hydrothermal technique followed up by heat-treatment in air. β-wollastonite (2M) phase in the synthesized samples has been confirmed by X-ray diffraction and a successful doping of Yb3+ and Tm3+ ions in the CaSiO3 lattice has been confirmed by X-ray photoelectron spectroscopy. The most intense phonon band has been observed at 872 cm−1. Upon 980 nm excitation, ultraviolet, intense blue, and near-infrared upconversion emissions as well as downshifting infrared emissions are observed from Tm3+ ions as a result of sensitization by Yb3+. The temporal evolution of the emitting states is studied to understand the emission mechanism. An absolute upconversion quantum yield of the 20Yb/0.5Tm–CaSiO3 sample in the 400–850 nm range is 0.79%.