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In this study, emissions between 350 nm and 2.8 μm are produced from molten-salt-synthesized LaF3:Yb3+,Er3+ (LFYE) nanocrystals (NCs) under 980 nm excitation. In fact, such wide spectral emissions ...

High pressure spectroscopy is of immense importance in understanding materials with respect to their high pressure phases, structural phase transitions, designing pressure sensors, etc. With this objective in mind, we have carried out time resolved photoluminescence and Raman spectroscopy on La2Hf2O7:Eu3+ (LHOE) nanoparticles (NPs) under applied high pressure. High pressure Raman spectra of the LHOE NPs suggest enhanced disordering at high pressure and shifting of the most intense F2g Raman band to higher wavenumber. High pressure excitation photoluminescence spectra of the LHOE NPs demonstrate that the O2− → Eu3+ charge transfer band quenches beyond 2.7 GPa whereas not many changes could be observed from the intra-configurational f–f excitation bands of Eu3+ ion. High pressure emission photoluminescence spectra of the LHOE NPs show gradual lowering of asymmetry ratio value, reduced Stark component in magnetic dipole transition, and the disappearance of the 5D0 → 7F0 transition of Eu3+ ion at high pressure. These observations suggest significant improvement in Eu3+ symmetry. These results are further corroborated with lifetime spectroscopy, which indicates high pressure induced tunneling of Eu3+ ion from La3+ to Hf4+ sites. These changes are visualized by beautiful color tunability of the LHOE NPs from red to orange to yellow and correlated color temperature from 1900 to 2600 K. This work demonstrates a new mode of designing optically tunable luminescent nanomaterials and understanding high pressure induced changes in photonic materials.

A proposed method for treating nuclear high level radioactive (NHLW) is to encapsulate it in a matrix made of complex oxide materials, such as pyrochlores with the general formula A2B2O7. Rare-earth hafnate pyrochlores have the potential to advance the current methods of NHLW disposal due to their robust chemical stability in radioactive environments, their high thermal stability, and their natural structural compatibility with radionuclide species. In this study, RE2Hf2O7:Eu3+ (RE = Y, La, Pr, Gd, Er, Lu) nanoparticles synthesized by a molten salt method were exposed to highly energetic gamma-ray irradiation. La2Hf2O7:Eu3+ and Lu2Hf2O7:Eu3+ underwent the order pyrochlore-disorder fluorite structural phase transition after exposure to gamma-ray irradiation. There was a change in the O-Eu charge transfer band (CTB) position as a function of gamma-ray dose. There was no change in the local symmetry of the Eu3+ dopant in Y2Hf2O7, Gd2Hf2O7 and Lu2Hf2O7, but in La2Hf2O7:Eu3+ gamma-ray dose reduced the symmetry around the Eu3+. For Y2Hf2O7:Eu3+ and La2Hf2O7:Eu3+, the lifetime and emission intensity were found to degrade possibly due to creation of gamma ray-induced defects which provides non-radiative pathways. Regarding Gd2Hf2O7:Eu3+, the concentration of oxygen vacancy defects predominated over other defects leading to enhanced emission and lifetime after gamma-ray irradiation. This study is of utmost importance for the design of a robust rare earth hafnate pyrochlore to be used as a nuclear waste host or gamma-ray based scintillator material.

In this work, we designed a two-step method to prepare carbon-incorporated silica from rice husk biomass. This two-step method could promote the chemical bonding between carbon and silica that is responsible for the generation of photoluminescence and effectively remove free carbon in the final product that is responsible for the quenching of photoluminescence. Such a structural optimization of the carbon-incorporated silica derived from rice husks led to a significant improvement in its photoluminescence with the emission band covering the entire visible spectrum. The toxicity of the carbon-incorporated silica from rice husks was 2-fold lower compared to commercial crystalline and amorphous spherical silica. Therefore, such rice husk-derived carbon-incorporated silica by the two-step method is promising for widespread application.

Complex oxides of the RE2Hf2O7 series are functional materials that exist in the fluorite or pyrochlore phase depending on synthesis method and calcination temperature. In this study, we investigate the process of synthesis, crystal structure stabilization, and phase transition in a series of RE hafnate compounds, synthesized by the coprecipitation process of a single-source complex hydroxide precursor followed with direct calcination or molten-salt synthesis (MSS) method. Phase pure RE2Hf2O7 (RE = Y, La, Pr, Gd, Er, and Lu) ultrafine nanostructured powders were obtained after calcinating the precursor in a molten salt at 650 °C for 6 h. Moreover, we demonstrate that the MSS method can successfully stabilize ideal pyrochlore structures for La2Hf2O7 and Pr2Hf2O7 in the nanodomain, which is not possible to achieve by direct calcination of the coprecipitated precursor at 650 °C. We propose mechanisms to elucidate the differences in these two synthesis methods and highlight the superiority of the MSS method for the production of RE hafnate nanoparticles.

Here we report the successful preparation of upconversion (UC) gadolinium oxysulfate (Gd2O2SO4) hollow nanoparticles with sensitizer Yb3+ and activator Er3+ co-doped through a biomolecule-assisted hydrothermal route and followed by calcination. By changing the experimnetal parameters, including the reaction temperature and surfactant type and concentration, the particle size and morphology can be regulated. Under the excitation of 980 nm laser, the red-to-green (R:G) emission intensity ratio is about 21:1, indicating the red emission color of 90%Gd2O2SO4:9%Yb3+,1%Er3+ hollow nanoparticles. The influence of the low temperature on luminescence is interpretated with enegy transfer mechanism. The red emission color and long lifetime at red emission regions enable their promising advanced luminescence microscopy applications.

New optical materials with efficient luminescence and scintillation properties have drawn a great deal of attention due to the demand for optoelectronic devices and medical theranostics. Their nanomaterials are expected to reduce the cost while incrementing the efficiency for potential lighting and scintillator applications. In this study, we have developed praseodymium-doped lanthanum hafnate (La2Hf2O7:Pr3+) pyrochlore nanoparticles (NPs) using a combined co-precipitation and relatively low-temperature molten salt synthesis procedure. XRD and Raman investigations confirmed ordered pyrochlore phase for the as-synthesized undoped and Pr3+-doped La2Hf2O7 NPs. The emission profile displayed the involvement of both the 3P0 and 1D2 states in the photoluminescence process, however, the intensity of the emission from the 1D2 states was found to be higher than that from the 3P0 states. This can have a huge implication on the design of novel red phosphors for possible application in solid-state lighting. As a function of the Pr3+ concentration, we found that the 0.1%Pr3+ doped La2Hf2O7 NPs possessed the strongest emission intensity with a quantum yield of 20.54 ± 0.1%. The concentration quenching, in this case, is mainly induced by the cross-relaxation process 3P0 + 3H4 → 1D2 + 3H6. Emission kinetics studies showed that the fast decaying species arise because of the Pr3+ ions occupying the Hf4+ sites, whereas the slow decaying species can be attributed to the Pr3+ ions occupying the La3+ sites in the pyrochlore structure of La2Hf2O7. X-ray excited luminescence (XEL) showed a strong red-light emission, which showed that the material is a promising scintillator for radiation detection. In addition, the photon counts were found to be much higher when the NPs are exposed to X-rays when compared to ultraviolet light. Altogether, these La2Hf2O7:Pr3+ NPs have great potential as a good down-conversion phosphor as well as scintillator material.

In this work, high purity amorphous silica derived from rice husk (RH) biomass was used to prepare green phosphor (Zn2SiO4:Mn2+). Based on the solid phase reaction under high temperature, the optimum doping concentration and reaction temperature were identified. The overall performance in terms of photoluminescence intensity and quantum yield of the RH-derived phosphor was superior to the one derived from commercial silica and close to the one made from silicic acid. The results showed that the phosphor derived from RH silica could serve as an alternative to commercial phosphor because of its decent properties and inexpensive green resource.

We report the generation of La2Zr2O7:5%Eu3+@Y2O3 (LZO5E@YO) core@shell crystalline inorganic-inorganic heterogeneous nanoparticles (NPs). The Y2O3 (YO) shell coating process based on a chemical sol-gel method led to the growth of a thin YO shell on the ordered pyrochlore La2Zr2O7:5%Eu3+ (LZO5E) core NPs. Photoluminescence (PL) analyses demonstrated a blue shift of 15 nm on charge transfer (CT) excitation band of the core@shell NPs from that of the core NPs. Scanning electron microscopy (SEM) and transmission electron microscopy (TEM) along x-ray diffraction (XRD), Fourier-transform Infrared spectroscopy (FTIR) and x-ray photoelectron spectroscopy (XPS) studies confirmed the formation of the thin YO layer over the LZO5E core NPs. The PL intensity of the LZO5E@YO core@shell NPs was enhanced by three fold compared to that of the LZO5E core NPs, and higher quantum yield (QY) was observed for the former compared to the original NPs by more than 70%. Higher radioluminescence (RL) emission was also observed for the core@shell NPs compared to the core NPs. Our ability of obtaining near-perfect core@shell heterostructure with enhanced luminescence performance opens the door for the development of efficient La2Zr2O7:5%Eu3+@Y2O3 NPs for both optical and x-ray scintillation applications.

Nanocrystalline complex oxide scintillators have emerged for use in X-ray and gamma-ray detection in recent years. Here the doping concentration dependence of europium-doped lanthanum zirconate (La2Zr2O7:xmol%Eu3+, x = 1 to 35) nanoparticles (NPs) were investigated by using X-ray diffraction (XRD), X-ray photoelectron spectroscopy (XPS), Raman spectroscopy, scanning electron microscopy (SEM), and optically and X-ray excited luminescence. Spectroscopic methods revealed a gradual increase in disorder from the ordered pyrochlore structure to the defect fluorite structure as the Eu3+ concentration increases. They showed red luminescence under charge transfer band (258 nm), and Eu3+ 4f-4f bands (322, 394 and 465 nm) excitation with optical intensity dependent on the Eu3+ doping concentration and not quenching up to 5% Eu3+ doping concentration. The quantum yield of the red emission was found to depend on the Eu3+ doping concentration and excitation wavelength. Moreover, these La2Zr2O7:x%Eu3+ NPs demonstrated an atypical Eu3+ related scintillating response with a red emission under high-energy X-ray excitation with the scintillation intensity also depending on the Eu3+ doping concentration. Finally, the irradiation damage behavior induced by the excitation source was representatively examined for the La2Zr2O7:5%Eu3+ NPs. It is expected that the current study will pave the way for future research of nanoscintillators.

This study presents the structural, optical, and radioluminescent characterization of newly synthesized europium-doped lanthanum hafnate (La 2 Hf 2 O 7 :xmol%Eu 3+ , x=0 to 35) nanoparticles (NPs) for use as phosphors and scintillation materials. Samples prepared through a combined co-precipitation and molten salt synthetic process were found to crystalize in the pyrochlore phase, a radiation tolerant structure related to the fluorite structure. These samples exhibit red luminescence under ultraviolet and X-ray excitation. Under these excitations, the optical intensity and quantum yield of the La 2 Hf 2 O 7 :xmol%Eu 3+ NPs depend on the Eu 3+ concentration and are maximized at 5%. It is proposed that there is a trade-off between the quenching due to defect states/cross-relaxation and dopant concentration. An optimal dopant concentration allows the La 2 Hf 2 O 7 :5 mol%Eu 3+ NPs to show the best luminescent properties of all the samples.

Upconversion (UC) particles are currently under intensive investigation, normally for their visible instead of ultraviolet (UV) light luminescence under near-infrared (NIR) irradiation. As a commonly studied host, NaYF4 in particular is known to have low phonon energy and high UC efficiency. Here, we present our work on enhancing UC luminescence in the UV region by adding a third dopant into a binary-doped NaYF4:Yb3+,Tm3+ host. More specifically, neodymium (Nd3+) or gadolinium (Gd3+) ions was co-doped into parent NaYF4:20mol%Yb3+,0.5mol%Tm3+ UC particles to enhance their UV UC luminescence. Experimental results demonstrated that these particles exhibited the highest degree of UV UC enhancements when co-doped with 0.05mol% Nd3+ or 2.0mol% Gd3+, expanding the potential of this type of materials into many possible applications by directly converting NIR irradiation into UV light. Fundamentally, the UV UC emission dependence of these triply doped NaYF4:Yb3+,Tm3+ particles with different Nd3+ and Gd3+ doping concentrations was investigated in terms of ground state absorption, excited state absorption and energy transfer UC mechanisms.

A series of 5 mol % Eu3+-doped rare earth (RE) hafnium oxide RE2Hf2O7 (RE = Y, La, Pr, Gd, Er, and Lu) nanoparticles (NPs) have been synthesized, calcinated, and systematically investigated using X-ray diffraction (XRD), Raman spectroscopy, X-ray photoelectron spectroscopy, scanning electron microscopy, Fourier transform infrared spectroscopy, and optically excited luminescence. Effects of the A-site RE3+ cation and calcination on the crystal structure of the RE2Hf2O7:5%Eu NPs were distinguished using XRD and Raman studies. Spectroscopic analysis showed that the La2Hf2O7:5%Eu3+ and Pr2Hf2O7:5%Eu3+ possessed ordered pyrochlore structures while the RE2Hf2O7:5%Eu3+ compositions (RE = Y, Er, and Lu) possessed disordered fluorite structure and were thermodynamically stable up to the highest calcination temperature employed in this study (1500 °C); however, a disordered–ordered transition observed in the Gd2Hf2O7:5%Eu3+ composition indicated that it was not thermodynamically stable. Detailed photoluminescence (...

The development of nanostructured anode materials for rechargeable Lithium-ion Batteries has seen a growing interest. We herein report the use of a new scalable technique, Forcespinning (FS) to produce binder-free porous Sn/C composite nanofibers with different Sn particle size loading. The preparation process involves the FS of Sn/PAN precursor nanofibers and subsequently stabilizing in air at 280 °C followed by carbonization at 800 °C under an inert atmosphere. The Sn/C composite nanofibers are highly flexible and were directly used as binder-free anodes for lithium-ion batteries. The produced Sn/C composite nanofibers showed an improved discharge capacity of about 724 mA h g− 1 at a current density of 100 mA g− 1 for over 50 cycles compared to most nanofiber electrodes prepared by electrospinning and centrifugal spinning. The FS method clearly produces Sn/C nanofiber composite electrodes that have a high specific capacity and excellent cyclic performance, owing to the unique structure and properties of the nanofibers. The FS technology is thus a viable method for the large scale production of nano/micro fibers for battery electrodes, separators, and other applications. To the best of our knowledge, this is the first time to report results on the use of Forcespinning technology to produce composite nanofiber anodes for lithium-ion batteries.

Complex oxides of the RE

Herein, La2Zr2O7:5% Eu3+ nanoparticles (NPs) with different sizes have been synthesized for the first time through a modified facile molten salt process using a single-source complex precursor of La(OH)3·ZrO(OH)2:Eu(OH)3·nH2O. It was found that the concentration of the added ammonia to co-precipitate the corresponding metallic ions to form the precursor can influence the final particle size of the fluorite La2Zr2O7:5%Eu3+ NPs. Furthermore, the crystal phase of the La2Zr2O7:5%Eu3+ NPs was transferred from fluorite to pyrochlore after thermal treatment at 1000°C. The relationship between photoluminescence (PL), quantum yield (QY), particles size and crystal phase has been further investigated through fluorescence decay, site symmetry, and Judd–Ofelt (J–O) analysis. Specifically, PLQY and lifetime increase with increasing particle size of the fluorite La2Zr2O7:5%Eu3+ NPs. Additionally, crystal phase transfer from fluorite to pyrochlore resulted in large PLQY decrease and moderate lifetime increase in the La2Zr2O7:5%Eu3+ NPs.

In this paper, we report a detailed computational and experimental investigation of the structural, electronic and dynamic properties of undoped and Er3+-doped Y2O2S phosphors by using computational crystal field (CF) calculations and electronic density of states by density functional theory (DFT), combined with optical measurements including excitation spectra, emission spectra from X-ray, ultraviolet and near infrared (NIR) excitations, and quantum yield determination under ultraviolet and NIR excitations. Emission decays and quantum yields of the visible and NIR bands were measured for different Er3+ doping concentrations in the Er3+-doped Y2O2S phosphors. Results show that green (550 nm) and red (667 nm) emission intensity and the respective ratio of these emission intensities depend on both the excitation wavelength and the Er3+ doping concentration. Although the total emission efficiency does not appreciably depend on the excitation wavelength, the excitation wavelength that provided the highest efficiency was found to be 250 nm in these Er3+-doped Y2O2S phosphors with both 1% and 10% Er doping concentrations.

There is increasing interest in rare earth (RE) doped nanoparticles (NPs) due to their sharp absorption and photoluminescence (PL) in the near infrared (NIR) spectral region. These NIR based nanoparticles (NPs) could allow biological imaging at substantial depths with enhanced contrast and high spatial resolution due to the absence of auto fluorescence in biological samples under infrared excitation. Here, we present the highly efficient infrared photoluminescence in GdF₃:Nd(3+) nanoparticles under 800 nm excitation within the hydrodynamic size limitations for bio-applications. The downconversion (Stokes emission) absolute quantum yields (QY) in powder, polymaleic anhydride-alt-1-octadicene (PMAO) coated powder and colloidal solutions have been investigated. QY measurements have revealed that downconversion (Stokes emission) QYs of approximately 5 ± 2 nm sized GdF₃:1% Nd(3+) colloidal NPs are 2000 times higher than those of efficient upconversion (UC) particles NaYF₄:20% Er/2% Yb of the same size. Furthermore, the utility of these NIR emitting nanoparticles for bioimaging probes has been demonstrated by confocal imaging and spectroscopic study.

In this letter, we report the absolute upconversion quantum yields (QY) for 9% Yb3+ and 1% Er3+ co-doped La2O2S and its comparison with NaYF4 doped with 20% Yb3+, 2% Er3+ for all the upconversion emissions centered at 410, 550, 667, and 822 nm at various excitation power densities at 977 nm excitation. The maximum upconversion QY for 9% Yb3+ and 1% Er3+ co-doped La2O2S was measured to be 5.83±0.87% at the excitation power density of 13 W/cm2. An excitation power dependent study revealed that although absolute upconversion QY measured for NaYF4: 20% Yb, 2% Er is higher at higher excitation power densities, La2O2S: 9% Yb, 1% Er possesses higher QYs at the lower excitation power densities.

Using the integrating sphere technique the absolute quantum yield measurements of the visible emission bands at 550, 650 and 750 nm in Yb/Ho doped M2O2 S( M¼Y, Gd, La) upconversion phosphor have been reported for the first time. Observations show that the 750 nm emission in La2O2S doped with 1 mol% each of Yb and Ho yield the highest efficiency of 0.12% followed by green emission which is 0.065% with 9.5% Yb and 0.5% Ho in the same host. The red emission in La2O2S, Y2O2S are nearly 6 times weaker than green emission, whereas in Gd2O2S it is 14 times less efficient making Gd2O2S doped with 4.5 mol% Yb and 0.5 mol% Ho as the most efficient single color green upconvertor among all three host compositions studied.

Polycaprolactone (PCL) fibers were produced using Forcespinning® (FS). The effects of PCL concentration, solvent mixture, and the spinneret rotational speed on fiber formation were evaluated. The concentration of the polymer in the solvents was a critical determinant of the solution viscosity. Lower PCL concentrations resulted in low solution viscosities with a correspondingly low fiber production rate with many beads. Bead-free fibers with high production rate and uniform fiber diameter distribution were obtained from the optimum PCL concentration (i.e., 12.5 wt%) with tetrahydrofuran (THF) as the solvent. The addition of N, N-dimethylformamide (DMF) to the THF solvent promoted the gradual formation of beads, split fibers, and generally affected the distribution of fiber diameters. The crystallinity of PCL fibers was also affected by the processing conditions, spinning speed, and solvent mixture.

Spectroscopic studies of Er 3 þ /Yb 3 þ co-doped (Ba,La)-fluorotellurite glass composition have been carried out using standard experimental and theoretical methods. Quantitative analyses of the room temperature absorption and emission spectra as well as the emission lifetimes yield various important spectroscopic parameters such as the radiative decay rates, fluorescence branching ratios, and emission/absorption cross sections. In addition, internal radiative quantum yields have been determined for the infrared emission at 1571 nm and for the upconversion emission at 547 nm. The influence of various non-radiative properties such as multiphonon relaxation, concentration quenching, and quenching by hydroxyl radicals have also been quantitatively estimated and correlated with the observed spectral properties. The comparative studies with the other composition of tellurite and different glasses showed that present glass composition could be a potential candidate for the broadband amplifier.

Highly transparent Tm:Ho:YAG transparent ceramics were prepared using advanced ceramic technology and their spectroscopic properties were studied for infrared laser applications. Following the Judd-Ofelt procedure several spectroscopic properties such as the radiative transition probability (Arad), radiative decay time (� rad) and fluorescence branching ratio (� ) are quantitatively obtained from the absorption spectrum. The absorption and emission cross sections corresponding to the 5I7 → 5 I8 transition of Ho 3+ at 2.1 � m have been evaluated following Mc Cumber theory and found that the obtained emission spectrum very well correlates to the simulated emission spectral data. The optical gain spectrum spread from 1800 nm to 2150 nm with a spectral width of over 107 nm and maximum gain coefficient of 0.44 cm −1 . Thus it is expected that the Tm 3+ :Ho 3+ :YAG ceramics

Trivalent ytterbium and erbium doped in yttrium oxysulfide (Y2O2S:Yb3+,Er3+) phosphors were synthesized by solid state flux fusion method and their upconversion spectral properties were studied as a function of different Yb3+ concentrations. The solid state flux fusion results in well crystallized hexagonal shaped phosphor particles with an average size of 3.8 μm. The detailed optical characterizations such as absorption, emission, and fluorescence decay were performed to explore the emission processes in the UV–VIS–NIR as well as to quantitatively estimate the fluorescence quantum yield. Upconversion spectral studies show that for all the compositions, green emissions are stronger; in particular the green emission intensity is 1.7 times stronger than the red intensity with composition of 9 mol% Yb3+ and 1 mol% Er3+. Mechanisms of upconversion by two-photon and energy transfer processes are interpreted and explained. The color coordinates are measured and the color tunability was analyzed as a function of the 980 nm excitation power. Results show that the Y2O2S:Yb3+,Er3+ phosphor offers power dependent color tuning properties where the emission color can be tuned from 490 to 550 nm by simply changing the 980 nm excitation power from 10 to 50 mW.

The 1550 nm excited upconversion spectral studies of Yb 3 + and Er 3 + co doped M 2 O 2 S (M = La, Gd, Y) phosphors were reported for the first time. Studies show that all the compositions are stronger in red emission with the highest intensity in Gd 2 O 2 S and lowest in Y 2 O 2 S.The red to green emission intensity ratios are 2.7, 3.6 and 3 in Gd 2 O 2 S, La 2 O 2 S and Y 2 O 2 S respectively. Mechanisms of up conversion by multiphoton absorption and energy transfer processes are interpreted and explained.

In this paper, we study the computational modeling of the localized surface plasmonic and scattering field effect arising from of gold nanorods. We also report the synthesis and optical characterization of core-spacer-shell nanocomposites composed of gold nanorods coated with SiO2 and finally coated with Y2O3:Er3+/Yb3+ (Aunanorods@mSiO2@Y2O3:Er3+/Yb) through a layer-by-layer method. Preliminary upconversion analysis of singly (Aunanorods@mSiO2@Y2O3:Er3+/Yb) at 980 excitation indicates that the composition has to be optimized to understand the role of silica as a spacer and near field enhancer (gold nanorod) in the system.

Yb and Er-doped Y2O2S phosphor was synthesized by solid state flux fusion method and their upconversion spectral properties were studied as a function of different Yb concentrations. The solid state flux fusion results in well crystallized hexagonal shaped phosphor particles of average size 3.8 μm. The detailed optical characterizations such as absorption, emission, and fluorescence decay were performed to explore the emission processes in the UV-VIS-NIR as well as to quantitatively estimate the fluorescence quantum yield. Upconversion spectral studies show that for all the compositions, green emissions are stronger, particularly; the green emission intensity is 1.7 times stronger than the red one with composition of 8 mol% Yb and 1 mol% Er. Mechanisms of upconversion by two photon and energy transfer processes are interpreted and explained. The color coordinates are measured and the color tunability was analyzed as a function of the 980 nm excitation power. Results show that the Y2O2S:Yb,Er phosphor offers power dependent color tuning properties where the emission color can be tuned from 490 to 550 nm by simply changing the 980 nm excitation power from 10 to 50 mW.

In this paper, we discuss the concept of an efficient infrared upconverting phosphor as an energy converting material that could potentially improve the efficiency of Si solar cells in bifacial configuration. Basic spectroscopic studies of Yb and Er-doped La2O2S phosphor was reported with particular attention to its upconversion properties under 1550 nm excitation. Different concentrations of phosphors were synthesized by solid state flux fusion method. The phosphor powders were well crystallized in a hexagonal shape with an average size 300-400 nm. The most efficient upconverting sample (1%Yb: 9% Er doped La2O2S) was also studied under the illumination with infrared (IR) broad band spectrum above 1000 nm. Our measurements show that even with an excitation power density of 0.159 W/cm2 using a tungsten halogen lamp the material shows efficient upconversion corroborating the fact that the present phosphors could be potential candidates for improving the efficiency of the present Si solar cells.

Basic spectroscopic studies of Yb and Er-doped M2O2S (M= Gd, La,Y) phosphor was reported with particular attention to its upconversion properties under 1550 nm excitation. Since the absorption spectra of Co2+overlaps with Er3+(4I13/2→4I15/2) at near infrared (NIR) region, we are proposing the concept of an efficiency enhancement of infrared upconverting phosphors as an energy converting material that could potentially improve the efficiency of Si solar cells in bifacial configuration. Different concentrations of Er3+/Co2+ phosphors were synthesized by solid state flux fusion method. The phosphor powders were well crystallized in a hexagonal shape with an average size 4 mm. Preliminary upconversion analysis of singly Er3+ and doubly Co2+/Er3+ doped Y2O2S under 980 and 1550 nm excitation indicates that the composition has to be optimized to understand the role of Co2+ in the system.

Optical damage experiments were carried out in a series of Holmium doped congruent lithium niobate (Ho:cLN) crystals as a function of dopant concentration and laser intensity. The light induced beam distortion was recorded with a camera and a detector under the pseudo-Z-scan configuration. At 532 nm, strong suppression of the optical damage was observed for the 0.94 mol. % doped crystal. Increased resistance to optical damage was also observed at 488 nm. The suppression of the optical damage is predominantly attributed to the reduction of the Nb antisites due to the holmium doping.

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Efficient photon upconversion (UC) is a promising way to utilize the infrared photons, where upconversion quantum yield (QY) is a key parameter to find the potential application of these UC materials for many applications. Here we are reporting the absolute upconversion QYs for different concentrations of M2O2S:Yb3+/Er3+ (M = Gd, Y, La) in comparison with β-NaYF4:20%Yb3+/2%Er3+ for the UC emissions centered at 410, 550, 667 and 822 nm at varying excitation power densities under 980 nm excitation. Concentration dependent upconversion QY analysis has revealed that La2O2S:1%Yb3+/1%Er3+ and Y2O2S:1%Yb3+/1%Er3+ possess almost similar upconversion QY compared to that of 9%Yb3+/1%Er3+:La2O2S. Measurements under identical conditions with respect to the reported most efficient upconverting phosphor NaYF4:20%Yb3+/2%Er3+ show that M2O2S:Yb3+/Er3+ yields a higher absolute upconversion QY at lower excitation power densities compared to that of β-NaYF4:20%Yb3+/2%Er3+. Furthermore, UC spectral studies and lifetime measurements were performed for a series of M2O2S:Yb3+/Er3+ phosphors to analyze the UC mechanisms in these phosphors. We show that upconversion emission from 4F9/2 is mainly influenced by the longer lifetime of metastable state 4I13/2.

Here we report the synthesis, characterization and application of a multifunctional surface functionalized GdF3:Nd3+ nanophosphor that exhibits efficient near infrared (NIR) fluorescence as well as magnetic properties, which can be utilized for bimodal imaging in medical applications. The nanoparticles are small with an average size of 5 nm and form stable colloids that last for several weeks without settling, enabling the use for several biomedical and photonic applications. Their excellent NIR properties, such as nearly 11% quantum yield of the 1064 nm emission, make them ideal contrast agents and biomarkers for in vitro and in vivo NIR optical bioimaging. The nanophosphors which were coated with poly(maleic anhydride-alt-1-octadicene) (PMAO) were implemented in cellular imaging, showing no significant cellular toxicity for concentrations up to 200 μg ml−1. Furthermore, the incorporation of Gd into the nanocrystalline structure renders them with exceptional magnetic properties, making them ideal for use as magnetic resonance imaging (MRI) contrast agents. The utility of these NIR emitting nanoparticles in infrared bioimaging and as contrast agents in magnetic resonance imaging was demonstrated by confocal imaging, magnetic resonance and tissue experiments.

In this article, we report the detailed spectroscopic studies of high Er3+content (50%) transparent YAG ceramic co-doped with nominal Cr3+ content (0.1 mol %). Various radiative and non-radiative spectroscopic properties such as radiative decay time, fluorescence branching ratio, emission/absorption cross sections, internal radiative quantum yields of the infrared and the upconverted emission bands are explored using standard experimental and theoretical methods and compared with YAG single crystal. Results show that although the non-radiative losses are high for 50% Er doped ceramic; several radiative spectral properties are almost in agreement with those for the single crystal YAG. Furthermore, because of the low dopant concentration of Cr3+, the sensitizing effect of Cr3+ was not observed.