We show theoretically with the simplest possible model that intensity of an upconversion luminescence is excited by sequential absorption n photons has a dependence on absorbed pump power P, which may range from limit ${P}^{n}$ down to ${P}^{1}$ for upper state and less than intermediate states. The two limits are identified as cases infinitely small large rates, respectively. In latter case, intensities states changes underlying decay mechanisms. certain situations, energy-transfer...

Hexagonal sodium yttrium fluoride, NaYF4, is the most efficient host material to date for green (Yb3+/Er3+ doped) and blue (Yb3+/Tm3+ upconversion (UC) phosphors, i.e., phosphors which emit visible light upon infrared (IR) excitation. The structure of hexagonal phase gives rise controversy about cation sites distribution. X-ray diffraction patterns our do not fit well with crystal reported NaNdF4 (space group P6̄, Z = 1.5). Na:M ratio (M Y, Nd, Er, Tm, Yb) deviates significantly from 1:1, it...

Since the first demonstration of net cooling twenty years ago, optical refrigeration solids has progressed to outperform all other solid-state processes. It become and only refrigerator capable reaching cryogenic temperatures, now below 100 K. Such substantial progress required a multi-disciplinary approach pump laser absorption enhancement, material characterization purification, thermal management. Here we present culmination two decades progress, record ≈ 91 K from room temperature.

A spectroscopic investigation of an extensive series ${\mathrm{Er}}^{3+}$-doped and ${\mathrm{Er}}^{3+}{,\mathrm{Y}\mathrm{b}}^{3+}$-codoped soda-lime-silicate (SL) aluminosilicate (AS) glasses is presented. Compared to SL glasses, $4f$ transitions in AS show higher oscillator strengths, larger inhomogeneous broadening, smaller crystal-field splittings the respective excited-state multiplets. The ${\mathrm{Er}}^{3+}$ relaxation dynamics adequately described by a combination Judd-Ofelt model...

We describe a novel approach to directly measure the energy of narrow, low-lying isomeric state in 229Th. Since nuclear transitions are far less sensitive environmental conditions than atomic transitions, we argue that 229Th optical transition may be driven inside host crystal with high Q. This technique might also allow for construction solid-state frequency reference surpasses short-term stability current clocks, as well improved limits on variability fundamental constants. Based analysis...

We report a new mechanism of intrinsic bistability, operative in excited atomic systems with substantial atom-atom coupling. Predictions and observations bistable luminescence from ${\mathrm{Yb}}^{3+}$ pairs crystalline ${\mathrm{Cs}}_{3}$${\mathrm{Y}}_{2}$${\mathrm{Br}}_{9}$: are good agreement have interesting implications for local field effects solids dense, ultracold gases.

Relaxor ferroelectricity is observed in many strongly disordered ferroelectric solids. However, the atomistic mechanism of phenomenon, particularly at high temperatures, not well understood. In this Letter we show local lattice dynamics as origin relaxor through first use dynamic pair-density function determined by pulsed neutron inelastic scattering. For a prototypical ferroelectric, $\mathrm{Pb}({\mathrm{Mg}}_{1/3}{\mathrm{Nb}}_{2/3}){\mathrm{O}}_{3}$, demonstrate that polarization sets...

We review the field of laser cooling solids, focusing our attention on recent advances in cryogenic an ytterbium-doped fluoride crystal (Yb3+:YLiF4). Recently, bulk this material to 155 K has been observed upon excitation near lowest-energy (E4–E5) crystal-field resonance Yb3+. Furthermore, local same a minimum achievable temperature 110 measured, agreement with predictions model. This value is limited only by current purity. Advanced synthesis approaches reviewed here would allow reaching...

Abstract Solid-state optical refrigeration uses anti-Stokes fluorescence to cool macroscopic objects cryogenic temperatures without vibrations. Crystals such as Yb 3+ -doped YLiF 4 (YLF:Yb) have previously been laser-cooled 91 K. In this study, we show for the first time laser cooling of a payload connected crystal. A YLF:Yb crystal was placed inside Herriott cell and pumped with 1020-nm (47 W) HgCdTe sensor that is part working Fourier Transform Infrared (FTIR) spectrometer 135 This...

Single crystals of ${\mathrm{Cs}}_{3}$${\mathrm{Lu}}_{2}$${\mathrm{Br}}_{9}$:1%${\mathrm{Er}}^{3+}$ were grown using the Bridgman technique. The low phonon energy \ensuremath{\le}190 ${\mathrm{cm}}^{\mathrm{\ensuremath{-}}1}$ strongly suppresses multiphonon relaxation in this host. For a series excited states radiative is found to be dominant. As consequence, shows strong visible upconversion luminescence from $^{2}$${\mathit{H}}_{9/2}$ and $^{4}$${\mathit{F}}_{7/2}$ when into...

A quantitative description of optical refrigeration in ${\mathrm{Yb}}^{3+}$-doped ZBLAN glass the presence transition-metal and $\mathrm{OH}$ impurities is presented. The model includes competition radiative processes with energy migration, transfer to ions, multiphonon relaxation. Molecular dynamics calculations pure doped ions provide structural information that, when combined spectroscopic data, allows for calculation electric-dipole energy-transfer rates framework Dexter theory. data...

Persistent phosphors can emit light long after the excitation has ended.The field of persistent luminescence strongly matured during past decade, with considerable progress having been made in synthesis and characterization methods, understanding trapping de-trapping mechanisms, application these materials.This focus issue "Persistent Phosphors," within April

Neutron detectors are crucial in fundamental science, nuclear security, safeguards, and civil applications. 3He-filled gas proportional counters the gold standard for thermal neutron detection, prized their efficiency, neutron/gamma discrimination, stability; however, scarcity of 3He has prompted search alternatives. Here, we introduce a detector design based on scintillating composite consisting 6Li glass scintillator particles dispersed an organic matrix. A this composite, photomultiplier...

A detailed study of upconversion processes in ${\mathrm{Cs}}_{3}{\mathrm{Er}}_{2}{X}_{9}$ $(X=\mathrm{C}\mathrm{l},\mathrm{}\mathrm{B}\mathrm{r},\mathrm{}\mathrm{I})$ crystals and the diluted systems ${\mathrm{Cs}}_{3}{\mathrm{Lu}}_{2}{\mathrm{Cl}}_{9}:1%$ ${\mathrm{Er}}^{3+},$ ${\mathrm{Cs}}_{3}{\mathrm{Lu}}_{2}{\mathrm{Br}}_{9}:1%$ ${\mathrm{Cs}}_{3}{\mathrm{Y}}_{2}{\mathrm{I}}_{9}:1%$ ${\mathrm{Er}}^{3+}$ is presented. Efficient two-, three-, four-step excitation along sequence...

The dimer compounds ${\mathrm{Cs}}_{3}$${\mathrm{Er}}_{2}$${\mathit{X}}_{9}$ (X=Cl,Br,I) were synthesized and grown as crystals. Their f-f absorption spectra measured their upconversion luminescence behavior was studied a function of temperature. Both $^{4}$${\mathit{I}}_{15/2}$${\ensuremath{\rightarrow}}^{4}$${\mathit{I}}_{11/2}$ $^{4}$${\mathit{I}}_{15/2}$${\ensuremath{\rightarrow}}^{4}$${\mathit{I}}_{9/2}$ excitations used. highest-energy phonons found by Raman spectroscopy at 285, 190,...

Uniform upconversion in erbium-doped silicate glasses is investigated as a function of glass composition, concentration, and fabrication method. Comparisons coefficients are made among soda lime aluminosilicate bulk waveguides. also with studies performed by other researchers. The results indicate that both the composition preparation method affect value coefficient, much factor-of-4 variation observed at fixed Er(3+) concentration. Values coefficient found to be consistent Förster-Dexter...

Single crystals of Cs3Yb2Br9 were grown using the Bridgman technique. Well-resolved absorption, luminescence, excitation, and Raman measurements down to 5 K are reported analyzed. The crystal-field splitting Yb3+ in was determined can be rationalized terms a trigonally distorted YbBr63− octahedron. Under near-infrared (NIR) cw-laser excitation 2F7/2→2F5/2 transitions, shows up-conversion luminescence green spectral region. Conversely, NIR 2F5/2→2F7/2 excited at twice energy transitions These...

In single crystals of the dimer compound Cs3Y2Br9:10% Yb3+ below 31 K, both visible (VIS) and near-infrared (NIR) luminescence intensities were found to exhibit hysteresis as a function incident NIR intensity temperature. The optical bistability is intrinsic not result an external feedback. Lowering temperature 11 K strongly enhances all-optical switching behavior. on VIS cooperative upconversion transitions occurs simultaneously with opposite polarity reflecting competition emission...

Optical cooling of a YLF:Yb single crystal to 87 K, well below the minimum achievable temperature predicted from existing theory, has been observed. This discrepancy between theory and data motivated us revisit current model optical refrigeration, in particular critical role parasitic background absorption. Challenging experiments that measured efficiency as function reveal absorption coefficient decreases with temperature, resulting significant enhancement at cryogenic temperatures. These...

We report the first observation of intrinsic optical bistability in ${\mathrm{CsCdBr}}_{3}:1%$ ${\mathrm{Yb}}^{3+}$ and show, using site-selective spectroscopy, that only asymmetric, strongly coupled ion-pair minority site gives rise to hysteresis near-infrared cooperative up-conversion luminescence as a function incident laser intensity below 15 K.

We have measured the crystalline electric field (CEF) excitations of CeMIn5 (M = Co, Rh, Ir) series heavy fermion superconductors by means inelastic neutron scattering. Fits to a CEF model reproduce scattering spectra and high temperature magnetic susceptibility. The parameters, energy level splittings, wavefunctions are tabulated for each member compared other as well results previous measurements. Our indicate that splitting in all three materials is similar, can be thought being derived...