We demonstrate novel organic light‐emitting diode (LED) materials that contain a green phosphorescent dye (dmbpy)Re(CO)3Cl (dmbpy = 4,4′‐dimethyl‐2,2′‐bipyridine), and a red fluorescent dye 4‐dicyanomethylene‐6‐(p‐dimethylaminostyryl)‐2‐methyl‐4H‐pyran (DCM) as dopants and polyvinylcarbazole (PVK) as the host. The photoluminescence (PL) and electroluminescence (EL) properties of these complex materials were studied. The energy transfer efficiency from PVK host to DCM is increased by the (dmbpy)Re(CO)3Cl co‐dopant, which has an emission energy between that of PVK and DCM. The (dmbpy)Re(CO)3Cl, which emits a long‐lived phosphorescence, is used as an energy coupler, providing the possibility to harvest both singlet and triplet energy in the devices. The pure red emission from DCM was observed from PL and EL spectra of (dmbpy)Re(CO)3‐Cl(> 2.0 wt.‐%):DCM(> 0.5 wt. %) doped PVK films, demonstrating an efficient energy transfer from PVK and (dmbpy)Re(CO)3‐Cl to DCM. By optimizing the concentration of DCM and (dmbpy)Re(CO)3Cl in PVK, a maximum EL quantum efficiency of 0.42 cd A–1 at a current density of 9.5 mA cm–2 was obtained. The EL quantum efficiency of the doubly doped device is significantly enhanced in comparison with both a DCM‐only doped PVK device and a DCM‐doped PVK device with the green fluorescent dye Alq3 as co‐dopant. The improvement in the operating characteristics of the phosphorescent and fluorescent dye doubly doped device is attributed to efficient energy transfer in the system, in which both triplet and singlet excitons are used for resultant emission in the polymer device.

A superconducting Transition-Edge Sensor (TES) with low-T c is essential in a high resolution calorimetric detection. With a motivation of developing sensitive calorimeters for applications in cryogenic neutrinoless double beta decay searches, we have been investigating methods to reduce the T c of an Ir film down to 20 mK. Utilizing the proximity effect between a superconductor and a normal metal, we found two room temperature fabrication recipes of making Ir-based low-T c films. In the first approach, an Ir film sandwiched between two Au films, a Au/Ir/Au trilayer, has a tunable T c in the range of 20-100 mK depending on the relative thicknesses. In the second approach, a paramagnetic Pt thin film is used to create Ir/Pt bilayer with a tunable T c in the same range. We present detailed study of fabrication and characterization of Ir-based low-T c films, and compare the experimental results to theoretical models. We show that Ir-based films with predictable and reproducible critical temperature can be consistently fabricated for use in large scale detector applications.

We are developing a low-T c -TES based large area and low threshold detector targeting a variety of potential applications. The detector consists of a 50.8 mm diameter Si wafer as the substrate and radiation absorber, a single Ir/Pt bilayer TES sensor in the center, and normal metal Au pads added to the TES to strengthen the TES-absorber thermal coupling. Tight TES-absorber thermal coupling improves detector sensitivity and response uniformity. Here we report on the electron-phonon (e-ph) coupling strengths for the Ir/Pt bilayer and Au that are measured with our prototype detectors and TES devices. We found that a second weak thermal link besides the one due to e-ph coupling in Ir/Pt or Au was required to explain our data. With the effects of the second weak link accounted for, the extracted e-ph coupling constant Σ for Ir/Pt bilayer in the T c range between 32 mK and 70 mK is 1.9 × 10 8 WK -5 m -3 , and Σ 's for Au at 40 mK and 55 mK are 2.2 × 10 9 WK -5 m -3 and 3.2 × 10 9 WK -5 m -3 , respectively.

One way of making a transition-edge sensor (TES) is by utilizing the proximity effect, in which the T C of a superconducting film is reduced with a normal metal film in metallic contact. The T C of a bilayer TES can be estimated by solving the Usadel equations with given boundary conditions. The classical boundary conditions of a bilayer include a specific interface resistance being temperature-independent. In this paper, we will introduce a temperature-dependent specific interface resistance. By fitting the measured T C data of Ir/Au bilayers from the literature to a T C calculation model, we will compare the fit parameters and fit errors with the temperaturedependent specific interface resistance described in this work and with the classical temperature-independent specific interface resistance.

Fig. 1 (a) SEM image of multilayered CoNi/Cu nanowires with t(CoNi) = 155 ± 9 nm and t(Cu) = 18 ± 3 nm, (b) Schematic representation showing the wire axis and applied magnetic field direction, and (c) Coercivity as a function of the angle q between the external field and wire axis for CoNi/Cu nanowires with t(CoNi) of 7.5 ± 1.0 mm, and (d) 6.8 ± 0.8 nm.