Well-Performed Green Phosphor BaY4Si5O17:Ce3+,Tb3+ with High Quantum Efficiency and Thermal Stability.

For Tb3+-doped green phosphors, the energy transfer from Ce3+ to Tb3+ can largely enhance the absorption of excitation; however, obtaining phosphors that exhibit both high quantum efficiency and thermal stability continues to pose a significant challenge. Herein, we established a paradigm to achieve novel silicate BaY4Si5O17 (BYSO):Ce3+,Tb3+. The near-ultraviolet light efficiently excites the BYSO:Ce3+ material, causing it to emit light at a wavelength of 408 nm. The photoluminescence of BYSO:0.12Ce3+ exhibits a relatively small Stokes shift and a thermal stability of 89.8% of the 303 K emission intensity at 423 K (89.8%@423 K). The energy transfer (ET) from Ce3+ to Tb3+ ions can be readily constructed in BYSO:Ce3+,Tb3+ utilizing the overlap between the Ce3+ emission and the Tb3+ excitation. The ET efficiency from the Ce3+ to Tb3+ ions reached 83.8% at y = 1.2 and a maximum of 94.6%. Finally, the optimized phosphor BYSO:0.12Ce3+,1.2Tb3+ had an internal quantum efficiency of 94.4% and had excellent thermal stability (96.1%@423 K). Our work pointed out the avenue to novel green phosphors with high efficiency and thermal stability by choosing appropriate host and construct efficient ET.

Detection of laser-associated heating in the brain during simultaneous fMRI and optogenetic stimulation.

PURPOSE: To calculate temperatures from T2 *-weighted images collected during optogenetic fMRI based on proton resonance frequency (PRF) shift thermometry, to monitor confounding heating effects and determine appropriate light parameters for optogenetic stimulation. METHODS: fMRI is mainly based on long-TE gradient-recalled echo acquisitions that are also suitable for measuring small temperature changes via the PRF shift. A motion- and respiration-robust processing pipeline was developed to calculate temperature changes based on the PRF shift directly from the T2 *-weighted images collected for fMRI with a two-shot 2D gradient-recalled echo-EPI sequence at 9.4T. Optogenetic fMRI protocols which differed in stimulation durations (3, 6 and 9 s) within a total block duration of 30 s were applied in a squirrel monkey to validate the methods with blue and green light (20 Hz, 30 mW) delivery interleaved between periods. General linear modeling was performed on the resulting time series temperature maps to verify if light delivery with each protocol resulted in significant heating in the brain around the optical fiber. RESULTS: The temperature SD was 0.05°C with the proposed imaging protocol and processing. Statistical analysis showed that the optogenetic stimulation protocol with a 3 s stimulation duration did not result in significant temperature rises. Significant temperature rises up to 0.13°C (p < 0. 05) were observed with 6 and 9 s stimulation durations for blue and green light. CONCLUSION: The proposed processing pipeline can be useful for the design of optogenetic stimulation protocols and for monitoring confounding heating effects.

Direct localisation of the human pedunculopontine nucleus using MRI: a coordinate and fibre-tracking study.

OBJECTIVES: To image the pedunculopontine tegmental nucleus (PPN), a deep brain stimulation (DBS) target for Parkinson disease, using MRI with validated results. METHODS: This study used the MP2RAGE sequence with high resolution and enhanced grey-white matter contrast on a 7-T ultra-high-field MRI system to image the PPN as well as a diffusion spectrum imaging method on a 3-T MRI system to reconstruct the main fibre systems surrounding the PPN. The coordinates of the rostral and caudal PPN poles of both sides were measured in relation to the third and fourth ventricular landmarks on the 7-T image. RESULTS: The boundary of the PPN was delineated, and showed morphology consistent with previous histological works. The main fibres around the PPN were reconstructed. The pole coordinate results combined with the fibre spatial relationships validate the imaging results. CONCLUSIONS: A practical protocol is provided to directly localise the PPN using MRI; the position and morphology of the PPN can be obtained and validated by locating its poles relative to two ventricular landmarks and by inspecting its spatial relationship with the surrounding fibre systems. This technique can be potentially used in clinics to define the boundary of the PPN before DBS surgery for treatment of Parkinson disease in a more precise and reliable manner. KEY POINTS: • Combined information helps localise the PPN as a DBS target for PD patients • Scan the PPN at 7 T and measure its coordinates against different ventricular landmarks • Reconstruct the main fibres around the PPN using diffusion spectrum imaging.

Bright white light emission from lanthanide oxide LaGdO3 for LED lighting by Bi3+ to Eu3+ energy transfer.

Phosphors with intrinsic white light emission are of great potential in constructing high-quality white LEDs (WLEDs). In this work, we propose the use of energy transfer from Bi3+ to Eu3+ ions for white light emission. A unique Bi3+-activated phosphor LaGdO3 (LGO):Bi3+ was generated using the conventional high-temperature solid-state process. An energy transfer was established by introducing Eu3+ into the phosphor composition. The emission colour of LGO:Bi3+,Eu3+ phosphors changes from cyan to white to orange-red depending on the Bi3+/Eu3+ doping proportion. The energy transfer between the Bi3+ and Eu3+ ions results from the dipole-dipole interaction. The LGO:Bi3+,Eu3+ phosphors were combined with a near-ultraviolet chip to successfully create a single-component WLED device with a colour-rendering index of 92.4. Our work demonstrates the energy transfer as a route for single-component white light emission and makes LGO:Bi3+,Eu3+ phosphors one of the candidate materials for near-ultraviolet lighting.

RF shielding designs for birdcage coils for preclinical MRI at 9.4 T.

Birdcage coils are widely used in preclinical MRI as they perform well, allow for quadrature drive, and can provide a homogeneous transmit field. Unlike in larger bore scanners, an RF shield is essential to avoid strong cross-talk with gradient coils that are in close proximity. However, gradient switching induces eddy currents that heat the shield and coil and impair the temporal signal-to-noise ratio (tSNR). The motivation of this study is to investigate the performance of different designs of RF shields on a birdcage coil used for high resolution functional MRI of small primates at 9.4 T. We found the choice of materials for RF shields significantly affected ghosting and tSNR in fMRI scans. Both ultrathin foils and a slotted pattern reduce eddy currents and improve imaging quality. Our results also demonstrate that a 9-um-thick copper foil is sufficiently thin to reduce the eddy current effects for high-resolution fMRI scans and there is no need for high-cost 4-um-thick foil. For slotted shields, our results demonstrate that the number of slots should be carefully considered, and an excessive number of slots can lead to a lower SNR and tSNR. We believe the results from this study can be used as a reference to design future RF coil shields selection for preclinical scanners.

Optimization of a quadrature birdcage coil for functional imaging of squirrel monkey brain at 9.4T.

A quadrature transmit/receive birdcage coil was optimized for squirrel monkey functional imaging at the high field of 9.4 T. The coil length was chosen to gain maximum coil efficiency/signal-to-noise ratio (SNR) and meanwhile provide enough homogenous RF field in the whole brain area. Based on the numerical simulation results, a 16-rung high-pass birdcage coil with the optimal length of 9 cm was constructed and evaluated on phantom and in vivo experiments. Compared to a general-purpose non-optimized coil, it exhibits approximately 25% in vivo SNR improvement. In addition to the volume coil, details about how to design and construct the associated animal preparation system were provided.