The metal-ligand complex tris(2,2'-bipyridine)ruthenium(II) chloride (Ru probe) displays a broad emission spectrum ranging from 540 to 730 nm. The emission spectra of Ru probe were measured when placed on top of a one-dimensional photonic crystal (1DPC), which supports both Bloch surface wave (BSW) and internal modes for wavelengths below 640 nm and only internal modes above 640 nm. The S-polarized emission spectra, with the electric vector parallel to the 1DPC surface, were found to be strongly dependent on the observation angle through the coupling prism. Also, the usual single broad-emission spectrum of Ru probe on glass was converted into two or more narrow-band-spectrum on the 1DPC, with emission band maxima dependent on the observation angle. The two S-polarized emission band peaks for Ru probe were found to be consistent with coupling to the BSW and first internal mode (IM1) of the 1DPC. The same spectral shifts and changes in emission maxima were observed by using Kretschmann and reverse Kretschmann illuminations. As the coupling requires the emitter to be in proximity with the photonic structure, we calculated near- and far-field distributions of a dipole directly located on the 1DPC surface. Finite-Difference Time-Domain (FDTD) simulations were performed to confirm fluorophore coupling to the BSW and internal modes (IMs). Both the measured and simulated results showed that IM coupled emission is significant. Coupling to the IM mode occurred at longer wavelengths where the 1DPC did not support a BSW. These results demonstrate that a simple Bragg grating, without a BSW mode, can be used for detection of surface-bound fluorophores.

Disinfection with far UV-C radiation (<230 nm) is an effective method to inactivate harmful microorganisms like the SARS-CoV2 virus. Due to the stronger absorption than regular UV-C radiation (254 nm) and hence limited penetration into human tissues, it has the promise of enabling disinfection in occupied spaces. The best far-UV sources so far are discharge lamps based on the KrCl* excimer discharge peaking at 222 nm, however they produce longer wavelength radiation as a by-product. In current KrCl* excimer lamps usually a dichroic filter is used to suppress these undesired longer wavelengths. A phosphor-based filter is an alternative which is cheaper and easier to apply. This paper describes the results of our exploration of this opportunity. Various compounds were synthesized and characterized to find a replacement for the dichroic filter. It was found that Bi-doped ortho-borates with the pseudo-vaterite crystal structure exhibit the best absorption spectrum i.e. high transmission around 222 nm and strong absorption in the 235-280 nm range. YLuBiBO showed the best absorption spectrum in the UV-C. To suppress the unwanted Bi emission (UV-B), the excitation energy can be transferred to a co-dopant. Ho turned out to be the best co-dopant, and HoLuBiBO appeared to be the best overall candidate for the phosphor filter material. A suitable formulation for a coating suspension containing this material was found, and quite homogeneous coatings were achieved. The efficiency of these filter layers was investigated and the results in terms of exposure limit increase i.e. gain factor vs. no filter were compared with the dichroic filter. We achieved a gain factor for the Ho containing sample of up to 2.33, i.e. not as good as that of the dichroic filter (∼4.6), but a very relevant improvement, making HoLuBiBO an interesting material for a cost-effective filter for KrCl* far UV-C lamps.

Mn-doped I(II)-III-VI NCs (e.g., Mn-doped AgZnInS/ZnS NCs) possessing low-energy excitation, high brightness and long fluorescence lifetimes have been desired for time-gated fluorescence biosensing/imaging. In this type of NCs, their optical properties are significantly affected by the microscopic interactions between Mn and Mn and between Mn and host NC, the compositions of NCs, and the defects in NCs. On the other hand, it is known that Zn etching to core I(II)-III-VI NCs in NC synthesis can significantly enhance the NC brightness because Zn can exchange surface atoms (e.g., Ag and In) in NCs to minimize NC surface-defects. But for Mn-doped I(II)-III-VI NCs, Zn etching could etch out not only surface-atoms of host NCs (e.g., Ag and In) but also Mn in NCs. As a result, it could significantly affect the NC compositions and the microscopic interactions between Mn and Mn as well as between Mn and host NC, and thus the optical properties of NCs (like lifetime and absorption/emission spectra). Therefore, it is needed to investigate how Zn etching would affect the optical properties of such Mn-doped NCs. In this study, a series of Mn-doped AgZnInS NCs with different Mn doping levels were prepared through nucleation doping, and then Zn etching was applied to etch these core NCs. To identify the effects of Zn etching on NC optical properties, ZnS coating (a different ZnS shelling approach by injecting Zn precursor and S precursor alternately in synthesis) was performed on the same Mn:AgZnInS NCs, and the optical properties of NCs with these two different ZnS shelling approaches were compared. Experimental results showed that under appropriate Mn doping levels in synthesis, Zn etching instead of ZnS coating can produce low-energy excitable NCs with higher QYs and longer lifetimes, which would further facilitate the use of such NCs in time-gated fluorescence measurement. To understand the reasons for the different optical properties under different ZnS shelling approaches, the material characteristics of the prepared NCs were further measured/analyzed and the possible fluorescence mechanisms were discussed.

Chemical sensing in living systems demands optical sensors that are bright, stable, and sensitive to the rapid dynamics of chemical signaling. Lanthanide-doped upconverting nanoparticles (UCNPs) efficiently convert near infrared (NIR) light to higher energy emission and allow biological systems to be imaged with no measurable background or photobleaching, and with reduced scatter for subsurface experiments. Despite their advantages as imaging probes, UCNPs have little innate chemical sensing ability and require pairing with organic fluorophores to act as biosensors, although the design of stable UCNP-fluorophore hybrids with efficient upconverted energy transfer (UET) has remained a challenge. Here, we report Yb- and Er-doped UCNP-fluorophore conjugates with UET efficiencies up to 88%, and photostabilities 100-fold greater by UET excitation than those of the free fluorophores under direct excitation. Despite adding distance between Er donors and organic acceptors, thin inert shells significantly enhance overall emission without compromising UET efficiency. This can be explained by the large increase in quantum yield of Er donors at the core/shell interface and the large number of fluorophore acceptors at the surface. Sensors excited by UET show increases in photostability well beyond those reported for other methods for increasing the longevity of organic fluorophores, and those covalently attached to UCNP surface polymers show greater chemical stability than those directly coordinated to the nanocrystal surface. By conjugating other fluorescent chemosensors to UCNPs, these hybrids may be extended to a series of NIR-responsive biosensors for quantifying the dynamic chemical populations critical for cell signaling.

Radiation therapy is one of the primary therapeutic techniques for treating cancer, administered to nearly two-thirds of all cancer patients. Although largely effective in killing cancer cells, radiation therapy, like other forms of cancer treatment, has difficulty dealing with hypoxic regions within solid tumors. The incomplete killing of cancer cells can lead to recurrence and relapse. The research presented here is investigating the enhancement of the efficacy of radiation therapy by using scintillating nanoparticles that emit UV photons. UV photons, with wavelengths between 230 nm and 280 nm, are able to inactivate cells due to their direct interaction with DNA, causing a variety of forms of damage. UV-emitting nanoparticles will enhance the treatment in two ways: first by generating UV photons in the immediate vicinity of cancer cells, leading to direct and oxygen-independent DNA damage, and second by down-converting the applied higher energy X-rays into softer X-rays and particles that are more efficiently absorbed in the targeted tumor region. The end result will be nanoparticles with a higher efficacy in the treatment of hypoxic cells in the tumor, filling an important, unmet clinical need. Our preliminary experiments show an increase in cell death using scintillating LuPO:Pr nanoparticles over that achieved by the primary radiation alone. This work describes the fabrication of the nanoparticles, their physical characterization, and the spectroscopic characterization of the UV emission. The work also presents results that demonstrate an enhanced efficacy of cell killing with x-rays and a low unspecific toxicity of the nanoparticles.

Polycrystalline cerium activated lutetium oxyorthosilicate (LSO:Ce) is highly desirable technique to make cost effective and highly reproducible radiation detectors for medical imaging. In this article methods to improve transparency in polycrystalline LSO:Ce were explored. Two commercially available powders of different particulate sizes (average particle size 30 and 1500 nm) were evaluated for producing dense LSO:Ce by pressure assisted densification routes, such as hot pressing and hot isostatic pressing. Consolidation of the powders at optimum conditions produced three polycrystalline ceramics with average grain sizes of 500 nm, 700 and 2000 nm. Microstructural evolution studies showed that for grain sizes larger than 1 µm, anisotropy in thermal expansion coefficient and elastic constants of LSO, resulted in residual stress at grain boundaries and triple points that led to intragranular microcracking. However, reducing the grain size below 1 µm effectively avoids microcracking, leading to more favorable optical properties. The optical scattering profiles generated by a Stover scatterometer, measured by a He-Ne laser of wavelength 633 nm, showed that by reducing the grain size from 2 µm to 500 nm, the in-line transmission increased by a factor of 10. Although these values were encouraging and showed that small changes in grain size could increase transmission by almost 3 orders of magnitude, even smaller grain sizes need to be achieved in order to get truly transparent material with high in-line transmission.

The influence of converse piezoelectric effect on the electro-optic coefficient of single domain relaxor-based 0.93Pb(Zn(1/3)Nb(2/3))O(3)-0.07PbTiO(3) (PZN-0.07PT) has been quantified under ambient conditions. It was found that the large piezoelectric constants d(31) and d(33) have significant influence to the half-wave voltage of electro-optic modulators. For single domain PZN-0.07PT crystal, Vπ13T is reduced by a factor of 8 and Vπ13L can be decreased by more than an order of magnitude due to the large piezoelectric effect. Compared to commonly used electro-optic crystal LiNbO(3) and BaTiO(3), PZN-xPT single crystal is much superior for optic phase modulation applications because they have much higher linear electro-optic coefficients and much lower half-wave voltage when piezoelectric strain influence is considered.

In this paper we report on the fabrication and characterization of SrHfO(3):Ce ceramics. Powders were prepared by solid-state synthesis using metal oxides and carbonates. X-ray diffraction measurements showed that phase-pure SrHfO(3) is formed at 1200°C. Inductively coupled plasma spectroscopy confirmed the purity and composition of each batch. SrHfO(3) exhibits several phase changes in the solid, but this does not appear to be detrimental to the ceramics. Microprobe experiments showed uniform elemental grain composition, whereas aluminum added as charge compensation for trivalent cerium congregated at grain boundaries and triple points. Radioluminescence spectra revealed that the light yield decreases when the concentration of excess Sr increases. The decrease in the light yield may be related to the change of Ce(3+) into Ce(4+) ions. For stoichiometric SrHfO(3):Ce, the light yield is about four times that of bismuth germanate (BGO), the conventional benchmark, indicating great potential for many scintillator applications.