Neutron detection scintillators based on rare-earth activated transparent glass and glass-ceramics are reported. Ce3+ doped gadolinium halides in 6LiF modified aluminosilicate glass matrices were synthesized by a melt-quench method followed by annealing. Their optical properties and alpha, neutron scintillation performance were investigated and compared to conventional 6Li-based scintillating glass.

Trivalent rare earth ions in crystalline or fiber hosts are among the most successful of laser materials, but new dopant-host combinations and more detailed understanding of existing materials continue to be needed. This paper presents a few examples from the work of our team at the Army Research Laboratory, highlighting the interrelation between spectroscopic properties and laser behavior. It focuses on bulk solids, though rare-earth-doped fiber lasers are also extremely important. One system discussed is Nd:YAG, particularly concentration quenching in heavily doped ceramic YAG. Spectroscopic properties of Yb:Y2O3 and Yb:Sc2O3 help to elucidate their laser performance. Spectra indicate that Er:YAG is more promising than Er:Sc2O3 for room temperature laser operation, but that the reverse is true for operation at and somewhat above liquid nitrogen temperature.

The radiation-induced displacement damage in yttrium borate (YBO3) is studied under X-ray, proton, and alpha irradiation. The photoluminescence (PL) was tested before and after irradiation to determine whether damage occurred and whether it could be queried by examining the PL spectrum. Two different dopants (cerium and europium) were used to activate the phosphor because each provides not only a different spectral signature but also a different mechanism for altering the spectrum between the pre- and post-PL measurements. X-rays, being primarily ionizing radiation, did not show any significant change between the pre and post measurements. We expected protons and alphas to damage the crystal structure, evidence of which could be seen in the change in the spectra before and after irradiation. However, we found no change under alpha exposure (3.6 × 1010 particles/cm2) and a significant change after proton exposure (5 × 1015 particles/cm2). While the material appears to be sensitive to protons, we cannot rule out its sensitivity to alphas because the alpha fluence may be too low to show an effect. This result provides strong indication that our materials are being damaged by particle radiation and that the radiation effects can be quantified.

Chitosan (CHIT), a natural biopolymer, has established its applicability in numerous studies including, tissue scaffolds, topical antimicrobial agents, glucose biosensors and drug delivery platforms. Among these applications, biosensors utilizing CHIT has been championed due its excellent film-forming ability, biocompatibility, good adhesion, non-toxicity, and susceptibility to chemical modification due to the presence of plentiful amino groups and hydroxyl groups. The challenge in development of many biosensing materials is that they should offer robust and tunable characteristics (fluorescence, magnetic, thermal, etc.) while remaining biocompatible. In this work, a facile method was developed to synthesize biocompatible hetero-nanoparticles which inherently display multifunctionality based on a few interchangeable components. As an example, we present a system composed of rare earth metal oxide (REMO) nanoparticles, Er doped Y2O3, with the attachment of gold nanostructures using CHIT. The resulting REMO@CHIT@Au0 hybrid nanoparticles are capable of displaying tunable optical properties due to the surface plasmon resonance of the gold nanoparticles useful to photoacoustic applications. An overview of the nanostructure components are given followed by morphological and spectroscopic analyses. The results of the characterizations are the focus of our future work towards the applicability of these systems to biological sensing, detection and contrast agents.

Blue-green emitted barium silicate phosphors, Ba4Si6O16:Eu2+ and Ba5Si8O21:Eu2+, were prepared by a conventional solid-state reaction. In these hosts, the corner-sharing [SiO4] tetrahedral formed a chain framework structure. These silicate phosphors can be efficiently excited by n-UV light, yielding an intense blue-green emission. Under excitation by near UV light, the emission bands are broader than that of the Ba2SiO4:Eu2+ phosphor.

Tb and Yb co-doped oxyfluoride glasses were fabricated in a lithium-lanthanum-aluminosilicate matrix by a melt-quench technique. Glass-ceramics were obtained by appropriate heat treatment of the as-prepared glasses. Visible to near-infrared down-conversion quantum cutting was studied for samples with different thermal annealing temperatures and time. Laser light at 488 nm was used to excite Tb3+ ions while Yb3+ ions were excited by energy transfer from the excited Tb3+ ions. Near-infrared emission at 940 – 1020 nm was observed. It has been found that the emission at 940 – 1020 nm increased significantly from the glass-ceramic compared to that of the as-prepared glass. This result suggests that the energy-transfer efficiency increases in glass-ceramics compared to that in glass. A significant portion of rare-earth ions may be incorporated inside LaF3 nanoparticles (NPs) in the glass-ceramic. Because the Yb3+ emission at 940 – 1020 nm is matched well with the band gap of crystalline Si, the quantum cutting effect may have its potential application in silicon-based solar cells.

Colloidal particles (CPs) have been the subject of intensive studies and have attracted increasing attention from the scientific community. In this contribution, we present the design and synthesis of luminescent colloidal crystal films. Rare earth complexes as the photoluminescent source is introduced into the polymeric nanospheres system, the diameter can be controlled by changing the polymeric reaction condition, which can act as building blocks to prepare diverse functional materials. Further, three-dimensional (3-D) colloidal crystal films with excellent fluorescent properties are fabricated by self-organization of the monodispersed polymeric nanospheres. The colloidal crystal film indicates a photonic band gap, which depends on the diameter and size-dispersing of the nanospheres building blocks. It shows potential applications in fabricating optical devices, data storage, chemical and biological sensors, and color displays.

In this work, lanthanide-doped, sodium yttrium fluoride nanocrystals were prepared and dispersed in a solvent consisting of 90 vol% toluene and 10 vol% methyl benzoate. Poly (methyl methacrylate) polymer was dissolved in the solvent, in addition to the nanocrystals. Inks were printed using direct-write techniques. Substrates used included Kapton®, bond paper, metal and glass. Stencil patterns and QR codes were printed with these inks. An overview of direct write printing for security applications is given. On many substrates, these printed traces are difficult to detect in ambient lighting, but can be easily read using near-infrared (NIR) illumination, making them very useful for covert and semi-covert security printing applications.

A pulsed laser deposition system was employed to fabricate thin films of Li7La3Zr2O12 solid electrolyte. The deposition process was carried out at room-temperature, resulting in amorphous films. These as-deposited films had a large optical band gap of 5.13 eV, and exhibited a lithium-ion conductivity of 3.35×10-7 S/cm. The films were then annealed, and the effect of annealing on the optical and electrical properties of the films was examined. After annealing at 1000 °C, the films were found to be cubic with a narrower band gap of 3.64 eV. In addition, these annealed films showed an inferior ionic conductivity than the as-deposited ones.

Erbium-Ytterbium codoped nanophosphor systems are explored for high efficiency upconversion. The NIR to visible upconversion from 1550 nm and 980 nm excitation are of particular interest to us for biomedical applications such as imaging, sensing, and photodynamic therapy. Variations in synthesis method and rare earth concentration are carried out in sodium, potassium, and transition metal based phosphor materials. The spectroscopic properties of the material dry and in biologically appropriate solution are taken. After bioconjugation, these particles will be used in a mouse model to demonstrate that cancer imaging with a near-infrared excitation source is possible.

Monte Carlo simulations are used to perform an atomic scale modelling of the magnetic properties of epitaxial exchange-coupled DyFe2/YFe2 superlattices. These samples, extremely well-researched experimentally, are constituted by a hard ferrimagnet DyFe2 and a soft ferrimagnet YFe2 antiferromagnetically coupled. Depending on the layers and on the temperature, the field dependence of the magnetization depth profile is complex. In this work, we reproduce by Monte Carlo simulations hysteresis loops for the net and compound-specific magnetizations at different temperatures, and assess the quality of the results by a direct comparison to experimental hysteresis loops.

Inorganic erbium-doped glasses are widely used in telecommunications due to the sharp intra-atomic 4I13/2 → 4I15/2 transition in the 4f orbital of erbium resulting in an emission at ∼ 1.5 μm, which is the low loss window of silica optical fibres. The limited erbium concentration of about 1020 ions/cm3 in inorganic erbium-doped glasses and the low absorption coefficient of the Er3+ ions, imply that relatively long lengths of fibre are required. Organic erbium complexes present higher absorption cross sections due to the photosensitization of erbium by the organic conjugated ligands and broader emission bands than those of the free Er3+ ions. Such properties open the possibility to develop compact, low power and broadband infrared emitting devices. We present the study of an organic fluorinated erbium complex exhibiting 1.5 μm luminescence lifetime of several hundreds of microseconds measured on thin film. The organic complex has been deposited by vacuum sublimation technique. This deposition method allows the realization of an erbium-doped thin film without the help of an organic polymer matrix, which is a potential source of vibrationnal luminescence quenching. We report the synthesis, the sublimation process, and the characterization of the thin films. The chemical structure of the complex is assessed by FTIR, NMR and MALDI-TOF. Chemical integrity of the thin film after vacuum deposition is determined by FTIR. The morphology of the thin film is characterized by X-ray diffraction experiments. The optical properties of the thin film are determined by spectroscopic ellipsometry, UV-Vis-NIR absorption spectroscopy and time resolved NIR photoluminescence spectroscopy.

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.

A new hybrid material system that consists of ceria attached silica nanoparticles has been developed. Because of the versatile properties of silica and antioxidant properties of ceria nanoparticles, this material system is ideally suited for biomedical applications. The silica particles of size ∼50nm were synthesized by the Stöber synthesis method and ceria nanoparticles of size ∼2-3nm was attached to the silica surface using a hetrocoagulation method. The presence of silanol groups on the surface of silica particles mediated homogenous nucleation of ceria which were attached to silica surface by Si-O-Ce bonding. The formations of silica-ceria hybrid nanostructures were characterized by X-photoelectron spectroscopy (XPS) and high resolution transmission electron microscopy (HRTEM). The HRTEM image confirms the formation of individual crystallites of ceria nanoparticles attached to the silica surface. The XPS analysis indicates that ceria nanoparticles are chemically bonded to surface of silica and possess mixture of +3 and +4 chemical states.

Er doped ZnO (Er:ZnO) thin films with Er concentration from 0.1 to 3.6 at. % were prepared by dual beam ion beam sputter deposition at room temperature. Experimental results show that as Er concentration increases from 0.1 to 1.1 at. %, the resistivity of the as-deposited Er:ZnO film decreases from 560 Ω·cm to a minimum of 0.23 Ω·cm, while further increasing Er concentration to 3.6 at. % results in increase of the resistivity to 4.2 kΩ·cm. The as-deposited Er:ZnO with Er concentration of 1.1 at.% also exhibits the highest carrier concentration of 2.3×1019 cm-3. None of the as-deposited Er:ZnO films show 1.5 μm emission without post-growth annealing. Er:ZnO film with Er concentration at 0.5~1.1 at.% shows the strongest 1.5 μm emission after annealing at 700 ~ 900°C, while all the Er:ZnO film becomes semi-insulating after annealing. The discrepancy between the processing conditions for optimized carrier concentration and optimized optically activated Er ions may due to the formation of the pseudo-octahedral structure after annealing that favors the 1.5 μm emission.

The Pr2Co7 alloys are known to crystallize in two polymorphic forms: a hexagonal of the Ce2Ni7 type structure and a rhombohedral of the Gd2Co7 one. They were synthesized by mechanical milling and subsequent annealing in high vacuum. In this work, we focus on the structural study of these phases using X-ray diffraction and transmission electron microscopy. Also, we present the evolution of magnetic properties of these compounds vs the annealing temperature. The coercivity increases with annealing temperature reaching a maximum for TA = 800 °C. The highest is equal to 18 kOe at 293 K and 23 kOe at 10 K. The high magnetic properties observed in these nanostructured Pr2Co7 intermetallic alloys have their origin in its relatively high uniaxial magnetocrystalline anisotropy field, and in the homogeneous nanostructure developed by mechanical milling process and subsequent annealing. This high coercivity is attributed to the high anisotropy field of the Pr2Co7 phase and its nanoscale grain size. This leads to the formation of a magnetically hard Pr2Co7 phase.