ABSTRACT
Upconverting nanoparticles (UCNPs) are well-known for their capacity to convert near-infrared light into UV/visible light, benefitting various applications where light triggering is required. At the nanoscale, loss of luminescence intensity is observed and thus, a decrease in photoluminescence quantum yield (PLQY), usually ascribed to surface quenching. We evaluate this by measuring the PLQY of NaGdF4:Er3+,Yb3+ UCNPs as a function of size (ca. 15 to 100 nm) and shape (spheres, cubes, hexagons). Our results show that the PLQY of α-phase NaGdF4 Er3+,Yb3+ surpasses that of ß-NaGdF4 for sizes below 20 nm, an observation related to distortion of the crystal lattice when the UCNPs become smaller. The present study also underlines that particle shape must not be neglected as a relevant parameter for PLQY. In fact, based on a mathematical nucleus/hull volumetric model, shape was found to be particularly relevant in the 20 to 60 nm size range of the investigated UCNPs.
ABSTRACT
A seismocardiography based methodology is introduced for predicting the start and the end of diastole to be used in diastolic timed vibrations. An accelerometer was placed on the sternum of 142 participants (120 healthy and 22 ischemic heart patients) to record Seismocardiogram (SCG). It is claimed that SCG, in combination with electrocardiogram (ECG), provides a mechanism for predicting diastole. It is demonstrated that prediction of the aortic valve closure point in the SCG signal helps start the vibrator in time to cover most of the isovolumic relaxation period. Also, through prediction of the mitral valve closure point, safety of the technique can be assessed by estimation of the amount of unwanted vibrations applied during the isovolumic contraction period.
