Infrared Laser Pumped Green and Blue Laser Emissions from a Single Solid State Material Doped by Rare Earth ions

The possible ways and progress of infrared or red laser pumped green and blue laser emissions from a single solid state material doped by rare earth ions are outlined. The green and blue lasers realized from infrared laser pumped rare earth doped nonlinear laser crystals by means of self-frequency-conversion and from infrared laser pumped rare earth-doped bulk, fiber and microsphere materials by means of frequency upconversion are introduced in detail. Other kinds of devices and methods are also compared. The typical nonlinear laser crystals such as YA13(BO3)4, GdA13(BO3)4, YCa4O(BO3)3,GdCa4O(BO3)3, and the typical upconversion fluoride fibers are compared and analyzed. The major problems remaining to be solved and the developing trends in the area are also discussed.     

Recent progress of energy transfer and luminescence intensity boosting mechanism in Nd~(3+)-sensitized upconversion nanoparticles

Rare earth doped upconversion nanoparticles can be considered as the spice of research in the field of luminescence nanomaterials due to their unique optical properties such as near-infrared excitation.Enormous works have been reported about biomedical applications of 980 nm excited and Yb~(3+)-sensitized upconversion nanoparticles.However,980 nm excitation wavelength overlaps with the absorption band of water molecules in the biological environment,leading to overheating effect that can induce thermal damages of normal cells and tissues.Recently,Nd~(3+)-sensitized upconversion nanoparticles which can be excited with 808 nm has been widely investigated as alternative nanoparticles that can surmount this issue of overheating effect.Even though Nd~(3+)-sensitized upconversion nanoparticles can reduce the overheating effect by 20 fold as compared to Yb~(3+)-sensitized counterpart,there are several factors that reduce the upconversion luminescence intensity.In this review article,photon energy harvesting and transferring mechanisms in Nd~(3+),Yb~(3+)and emitter ions co-doped upconversion nanoparticles under 808 nm excitation are briefly discussed.Factors that affect upconversion luminescence intensity and quantum yield of Nd~(3+)-sensitized upconversion nanoparticles are also addressed.Besides,some of the important strategies that have been recently utilized to boost upconversion luminescence intensity of Nd~(3+)sensitized upco nversion nanoparticles are tho roughly summarized.Lastly,the future challenges in the area and our perspectives are in sight.     

Recent progress on upconversion luminescence enhancement in rare-earth doped transparent glass-ceramics

The upconversion(UC) of the rare earth doped glass-ceramics has been extensively investigated due to their potential applications in many fields, such as color display, high density memories, optical data storage, sensor and energy solar cell, etc. Many series of them, especially the oxyfluorides glasses containing Ba2 LaF 7 nanocrystals were studied in this review work, due to the thermal and mechanical toughness, high optical transmittance from the ultraviolet to the infrared regions, and a low nonlinear refractive index compared to the other commercial laser glasses. Moreover, the energy transfer(ET) between the rare earth ions and transition metals plays an important role in the upconversion process. The cooperative ET has been researched very activly in UC glasses due to applications in the fields of solar cells, such as in the Er/Yb, Tm/Yb, Tb/Yb, Tb/Er/Yb and Tm/Er/Yb couples. The present article reviews on the recent progress made on:(i) upconversion materials with fluoride microcrystals in glasses and the mechanisms involved, including the UC in double and tri-dopant RE ions activated fluoride microcrystal, energy transfer process; and(ii) the effect of the metal Mn and nanoparticles of Au, Ag, Cu on the enhancement of UC emissions. Discussions have also been made on materials, material synthesis, the structural and emission properties of glass-ceramics. Additionally, the conversion efficiency is still a challenge for the spectra conversion materials and application; challenge and future advances have also been demonstrated.     

通讯用稀土掺杂光学材料

本文根据文献报道 ,简要介绍了稀土掺杂的光学材料、光学放大器、光纤激光器等在通讯产业的应用 ,这些应用促使通讯产业发生了革命性的变化和飞速的发展。     

Recent development in upconversion nanoparticles and their application in optogenetics: A review

Ion channels present in the plasma membrane are responsible for integration and propagation of electric signals, which transmit information in nerve cells. Malfunction of these ion channels leads to many neurological diseases. Recently, optogenetic technology has gained a lot of attention for the manipulation of neuronal circuits. Optogenetics is a neuromodulation approach that has been developed to control neuronal functions and activities using light. The lanthanide-doped upconversion nanoparticles (UCNPs) absorb low energy photons in near-infrared (NIR) window and emit high energy photons in the visible spectrum region via nonlinear processes. In the last few decades, UCNPs have gained great attention in various bio-medical applications such as bio-imaging, drug delivery and optogenetics. The near-infrared illumination is considered more suitable for optogenetics application, due to its lower degree of light attenuation and higher tissue penetration compared to visible light. Therefore, UCNPs have been considered as the new promising candidates for optogenetics applications. Upconversion nanoparticle-mediated optogenetic systems provide a great opportunity to manipulate the ion channel in deep tissue. Herein, we summarize the upconversion photoluminescence in lanthanide doped nanomaterials and its mechanisms and several approaches adopted to tune emission color or enhance upconversion efficiency. Recent advances of lanthanide-doped UCNPs design strategy and their mechanism are reviewed. Then, we discuss the neural circuitry modulation using upconversion nanoparticles mediated optogenetics. Moreover, the future perspectives towards optogenetics are also included.     

Controlling upconversion through interfacial energy transfer(IET):Fundamentals and applications

Photon upconversion has received substantial attention owing to its great promise in broad applications from bioimaging to other frontier fields like display,upconversion laser,information security and anticounterfeiting.A smart control and manipulation of the upconversion luminescence has always been a key topic,however,to date the most efficient mechanism for upconversion nanoparticles remains the energy transfer upconversion and recently reported energy migration mediated upconversion.Recently,we found that the interfacial energy transfer(IET) is also an efficient approach for enabling and tuning photon upconversion of lanthanide ions.Moreover,it can be used for the mechanistic understanding of the interionic interactions such as energy transfer and energy migration on the nanoscale.In this review,the recent advances of the research on the IET are summarized,the principles for designing IET process and typical examples are discussed together with its applications in both mechanistic research and frontier information security.The challenges and perspectives for future research are also commented.     

Theory of intergranular creep cavity nucleation,growth and interaction

Creep cavitation is modeled assuming random continuous cavity nucleation, coupled growth by diffusion and plastic deformation, diffusive cavity interactions and cavity interconnection and finally, failure at a critical a real damage fraction. Nucleation is simulated by Monte-Carlo techniques using an empirically-derived nucleation law for copper that depends on the steady-state creep strain. For initially fully-dense materials, cavity nucleation dominates the cavity number density until interconnection and coarsening become important late in rupture life. In this situation, Monkman-Grant behavior is obtained and cavity sizes approach stable log-normal distributions. However, when a small fraction of cavities pre-exist, the cavity density is dominated by cavity interactions and the density remains relatively constant despite continuous nucleation. In this case, cavity growth controls the rupture time and cavity size distributions tend to approach log-normal distribution more slowly. These diffusive interactions diminish for larger but more widely-spaced pre-existing cavities because of limited interactions between the pre-existing and nucleating cavities. The sensitivity of the rupture life on dihederal angle and nucleation rate are also examined, and the statistics of failure are quantified.     

Infrared to near-infrared and visible upconversion photoluminescence of LiYbF4：Er3＋ nanorods

Colloidal LiYbF4:Er3+ nanorods were synthesized in an aqueous system which had the ratio of length to diameter of～2.These LiYbF4:Er3+ nanorods emitted intense upconversion light under excitation of infrared at 1488 nm.Importantly,the intensities of two-and three-photon anti-Stokes upconversion PL bands were observed which were comparable to that of the Stokes emission under excitation with low power density.The plots of excitation power density versus emission intensity indicated that all the emissions centered at 549,668,and 978 nm took a two-photon upconversion process.However,it could be simply deduced that the energy of two photons of 1488 nm were inadequate to produce a photon of 668 or 549 nm.For this conflict,the shape and saturation effects in the intermediate energy states were introduced to demonstrate the corresponding upconversion processes.     

High value-added fluorescence upconversion agents-assisted nanosemiconductors for efficient wide spectral response photocatalysis:Exerting energy transfer effect and applications

The design of the photocatalytic materials has made a great of remarkable progress in the area of the enhancement photocatalytic activity,but there are still lots of problems such as wide band gap,low utilization of sunlight,low quantum efficiency and poor stability,which further limit the extensive practical applications.Thus,it is a hot research topic and key scientific problem to be solved that how to design and prepare the catalysts,which can respond to visible and near-infrared light in sunlight.Inspired by efficient nonlinear optical upconversion materials,upconversion-based nanocomposites can indirectly broaden the absorption ranges of semiconductors by co nverting the captured long-band visible and near-infrared incident light into high-energy short-band visible or ultraviolet light,which can be adopted as the promising candidate in wide-spectral-light-activating photocatalytic materials coupling with conventional semiconductors.According to our recent works and literature reports,recent review summarizes the research progress of photocatalytic materials with upconversion effect on photolysis of water for hydrogen production,degradation of organic and inorganic pollutants,reduction of CO₂ and photodynamic therapy.The prepared nanocomposites can suppress the recombination of electrons and holes,and greatly improve the photocatalytic efficiency by the synergistic effect.It maybe stimulates a great interest in rational design and preparation of efficient full-spectrum photocatalytic systems and their wide application in solar energy conversion.     

On the evolution of some endoscopic light delivery systems for photodynamic therapy

Progress in photodynamic therapy (PDT) depends on the development of: (1) photosensitizers, (2) optical devices among which are lasers and light delivery systems, and (3) clinical procedure. The light delivery systems which are the focus of this article are fiberoptic devices developed in Lausanne, Switzerland for use in the endoscopic treatment of cancer or precancerous lesions in the bronchi, the esophagus, the uterus, the cervix, the upper aerodigestive tract and thoracic cavity. Light delivery systems for both surface and interstitial application are presented, together with some of the physical principles on which they are based. Incorporation in these devices of the possibility for in-situ measurement of reflected therapeutic light and/or fluorescence emitted by endogenous and/or exogenous dyes allows for improved light and drug dosimetry, as well as the measurement of photobleaching, local oxygenation and other tissue properties. The necessity of information on tissue optical parameters, as well as the use of simple mathematical models and tissue phantoms, for optimizing light distributing devices is underlined. The devices are optimized for delivering the desired light intensity distribution to the targeted region with minimal losses. In some cases this implies using the device to modify the shape of the hollow organ during PDT, an example of which is given for the case of the esophagus. In another strategy, one adapts the shape of the device to that of the organ, using an elastic balloon catheter. Here examples are given for the uterus, the bronchi and the thoracic cavity. The mechanical properties, the sizes, shapes and materials of the light delivery systems must be optimized for safe use while retaining low cost. Furthermore, the devices must whenever possible be rendered compatible with existing medical technology. A significant improvement in clinical efficacy has been demonstrated in the testing of some of these new fiberoptic light delivery systems. For endoscopic PDT in the hollow organs, the design and optimalization of multiple new approaches to light distribution will continue to lead to improved clinical results.     

Suppression of inner energy dissipation in Yb-doped NaErF4 upconversion nanocrystals through an energy cycling strategy

Suppression of the inner energy dissipation,related to the lattice phonons and inner defects,in lanthanide doped upco nversion luminescent materials remains a formidable challenge.Herein,we reveal an energy cycling strategy capable of suppressing the inner energy dissipation in lanthanide doped upconversion nanocrystals.Yb³⁺ ions were introduced in Er³⁺ heavily doped nanocrystals as an energy reservoir to compete with the inner energy dissipation.The detailed energy cycling...     

Preparation and upconversion luminescence modification of YbPO_4:Er~(3+) inverse opal heterostructure

Photonic crystal heterostructures composed of YbPO_4:Er~(3+) inverse opal and polystyrene opal were prepared via a template-assisted process, which exhibited two photonic band gaps. The microstructure,phase and optical properties of photonic crystal heterostructures were investigated by x-ray diffraction,scanning electron microscopy, fluorescence spectroscopy, absorption spectroscopy, fluorescence lifetime,etc. The upconversion emission suppression caused by single photonic band gap from the following YbPO_4:Er~(3+) inverse opal or the upper opal was observed. The upconversion luminescence was strongly suppressed due to the two photonic band gap overlapping effect caused by the following YbPO_4:Er~(3+) inverse opal or the upper opal. The modified mechanisms of upconversion luminescence were discussed by the upconversion luminescence lifetime of YbPO_4:Er~(3+) photonic crystal heterostructures. The results demonstrated the modified upconversion luminescence is attributed to the photon trapping caused by Bragg reflection of photonic crystal heterostructures.     

A homogeneous DNA assay by recovering inhibited emission of rare earth ions-doped upconversion nanoparticles

Robust and easy-to-use kits specific for a particular DNA sequence are desirable for early detection of diseases. However, the major challenge with these tests is often the background fluorescence artifacts arising from biological species due to employing UV and visible range of light. Here, we have reported a near-infrared (NIR) fluorescence “turn-on” kit based on rare earth ions doped nanoparticles, upconversion nanoparticles (UCNPs), and gold nanoparticles (AuNPs), which forms a fluorescence-quencher pair, brought together by a hairpin structure through the formation of double-stranded DNA (dsDNA), with quenched upconversion luminescence. In the presence of analytes, the molecular beacon opens to push AuNPs away from UCNPs, with a distance longer than the efficient quenching distance, so that the inhibited upconversion emission will be restored. We demonstrated that this assay provides a homogeneous, facile, simple and highly selective HIV-1 based DNA detection system with restore efficiency up to 85%, and the detection limit of 5 nm.     

The effect of the nasopharyngeal air cavity on x-ray interface doses

We investigated the impact of air cavities in head and neck cancer patients treated by photon beams based on clinical set-ups. The phantom for investigation was constructed with a cubic air cavity of 4 x 4 x 4 cm3 located at the centre of a 30 x 30 x 16 cm3 solid water slab. The cavity cube was used to resemble an extreme case for the nasal cavity. Apart from measuring the dose profiles and central axis percentage depth dose distribution, the dose values in 0.25 x 0.25 x 0.25 cm3 voxels at regions around the air cavity were obtained by Monte Carlo simulations. A mean dose value was taken over the voxels of interest at each depth for evaluation. Single-field results were added to study parallel opposed field effects. For 10 x 10 cm2 parallel opposed fields at 4, 6 and 8 MV, the mean dose at regions near the lateral interfaces of the cavity cube were decreased by 1 to 2% due to the lack of lateral scatter, while the mean dose near the proximal and distal interfaces was increased by 2 to 4% due to the greater transmission through air. Secondary build-up effects at points immediately beyond the air cavity cube are negligible using field sizes greater than 4 x 4 cm2. For most head and neck treatment, the field sizes are usually 6 x 6 cm2 or greater, and most cavity volumes are smaller than our chosen dimensions. Therefore, the influence of closed air cavities on photon interface doses is not significant in clinical treatment set-ups.     

Cavity distribution pattern in a superplastically deformed aluminum alloy

Cavitation in superplastically formed AA7475 aluminum alloy by gas pressure has been investigated. Two systems of cavity stringers on the diametrical section of the pressure-formed domes were observed by using optical microscopy under normal light, polarized light, and dark field. Qualitative analyses have shown that the cavity stringers are oriented 35 ∼ 60 deg to the midplane of the sheet, and the spacing of the cavity stringers decreases with increasing strain. The explanation of this new observation of cavity morphology is given from a viewpoint of cooperative grain boundary sliding (CGBS). Formerly Associate Professor with the Department of Materials Science, Ufa Aviation Institute     

An analysis of cavity growth during superplasticity

Cavity growth at high temperatures may be controlled by vacancy diffusion, giving cavities which are approximately spherical and randomly distributed, or by power-law creep, giving cavities which are elongated and aligned in the direction of the tensile stress. In general, diffusion growth is favored at low total strains, and there is a transition to power-law growth at a critical cavity radius,r _c. The value ofr _c increases with decreasing strain-rate, so that there is also a transition from predominanly power-law growth at high stress levels to predominantly diffusion growth at low stress levels. Both types of cavities have been observed in superplastic materials, but the diffusion growth rate may be enhanced if the cavity intersects a number of grain boundaries. The analysis is in good agreement with experimental results reported for three diffent superplastic materials. DAVID A. MILLER, formerly Research Associate, Department of Materials Science, University of Southern California.     

Effect of surface diffusion on creep fracture

The effect of surface diffusion on the growth of intergranular cavities under creep conditions is investigated considering its influence on the shape of the cavities. First, general equations relating the rate of cavity growth and the applied stress are given for the case of isolated cavities and an array of interacting cavities. The conditions for cavities to grow in an equilibrium and crack-like forms, respectively, are established. The transition from equilibrium to crack-like forms is discussed and an estimate for the lower and upper limit of the rate of cavity growth during this transition suggested. Expressions for the growth rates of crack-like cavities which grow independently of each other as well as those in an array of interacting cavities are then derived. Several different regimes in which stress dependence of the rate of cavity growth vary are found. Conditions under which these regimes can occur are discussed. A comparison of the theory with several recent experimental studies is made and an excellent agreement between the theory and experiment is obtained assuming that different regimes of cavitation occur in different materials and at different stress levels in the same material. T. Takasugi is on leave from The Institute for Iron Steel and Other Metals, Tohoku University, Sendai, Japan.     

Mechanisms of intergranular cavity growth in Ni3Al (Zr,B)

A technique based on hydrogen embrittlement has been used to study the morphology and growth characteristics of grain boundary cavities in a Ni₃Al alloy. The technique facilitates brittle intergranular fracture of specimens previously tested at elevated temperatures. This capability makes it possible to distinguish cavities that have formed by cavity coalescence and also determine cavity shape in three dimensions. Contrary to earlier reports of crack-like cavity growth, the results indicate that the shapes of individually growing cavities in Ni₃Al are consistent with quasi-equilibrium cavity growth theory. Cavity size measurements have also been compared with predictions of both quasi-equilibrium and crack-like cavity growth models. These results also support the finding that cavity growth in Ni₃Al occurs in a quasi-equilibrium manner. The observations further suggest that the formation of crack-like cavities is primarily due to coalescence and, therefore, not representative of the growth mechanism of individual cavities.     

Sub-10 nm lanthanide-doped SrFCl nanoprobes:Controlled synthesis,optical properties and bioimaging

Alkaline-earth dihalide nanocrystals(NCs) such as SrFCl, owing to their high chemical stability and low phonon energy, are excellent host materials for lanthanide(Ln~(3+)) doping to achieve desirable optical properties for various bioapplications, Herein, we report a novel strategy for the synthesis of sub-10 nm Ln~(3+)-doped SrFCl NCs with efficient upconverting and downshifting luminescence through a facile onestep hot-injection method. Utilizing the temperature-dependent upconverting luminescence(UCL) from the thermally coupled ~2H_(11/2) and ~4S_(3/2) levels of Er~(3+), we showed the potential of SrFCl:Yb,Er NCs as sensitive UCL nanoprobes for non-contact thermal sensing with a maximum detection sensitivity of 0.0066 K~(-1), which is among the highest values for thermal sensing based on Er~(3+)-activated UCL nanoprobes. Furthermore, by employing the intense downshifting luminescence from Tb~(3+) and Eu~(3+), we demonstrated the successful use of biotinylated SrFCl:Ce,Tb and SrFCl:Eu~(3+) nanoprobes for biotin receptor-targeted cancer cell imaging, thus revealing the great promise of SrFCl:Ln~(3+) nanoprobes for versatile bioapplications.     

Polymerisation shrinkage around composite resin restorations--an in vitro study

The aim of this study was to determine the degree of penetration of a fluorescent adhesive at the margins of 3 brands of posterior composite resin restorative materials. Seventy-eight extracted human premolar teeth were used. Class II cavities were prepared on both approximal surfaces of each tooth in such a manner that the gingival wall was situated apical to the amelo-cemental junction. The enamel of the cavity walls was bevelled, etched and treated with the enamel bonding agent recommended by the manufacturer. The 3 brands of composite resin used were: Fulfil, Estilux Posterior and P 50. The teeth were divided at random into 3 groups of 26 premolars each. The mesial and distal cavities of each tooth in the group were filled with the same brand. The resin was inserted in two increments in both the mesial and distal cavities and polymerised. The margins of one restoration in each tooth was coated with fluorescent adhesive and cured. All the restored teeth were embedded in clear epoxy resin and then sectioned. The mounted sections were examined at 100X magnification with fluorescent light. The polymerisation contraction gap at different areas of the tooth/restoration interface and the degree of penetration of the fluorescent adhesive into the gap was determined. The fluorescent adhesive penetrated the contraction gaps in all 3 posterior restorative materials to varying degrees. The defects observed were similar in all 3 brands and the differences in degree of penetration were not statistically significant (p > 0.05).