Purcell enhancement of fluorescence from silicon-vacancy color centers in Mie-resonant luminescent diamond particles

Over the past two decades, nanosized diamond particles with various luminescent defects have found numerous applications in many areas from quantum technologies to medical science. The size and shape of diamond particles can affect drastically the luminescence of embedded color centers. Here we study diamond particles of 250–450 nm in size containing silicon-vacancy (SiV) centers. Using dark-field scattering spectroscopy, we found that fundamental Mie resonances are excited in the spectral range of interest. We then measured the fluorescence saturation curves under continuous excitation to estimate the effects of the excitation and Purcell factor enhancement on the luminescent properties of the studied particles. The results show that the saturation excitation intensity differs by several times for particles of different sizes which is well explained by the numerical model that takes into account both the Parcell factor enhancement and resonant excitation.

Influence of Pumping Regime on Temperature Resolution in Nanothermometry

In recent years, optical nanothermometers have seen huge improvements in terms of precision as well as versatility, and several research efforts have been directed at adapting novel active materials or further optimizing the temperature sensitivity. The signal-to-noise ratio of the emission lines is commonly seen as the only limitation regarding high precision measurements. The role of re-absorption caused by a population of lower energy levels, however, has so far been neglected as a potential bottleneck for both high resolution and material selection. In this work, we conduct a study of the time dependent evolution of population densities in different luminescence nanothermometer classes under the commonly used pulsed excitation scheme. It is shown that the population of lower energy levels varies when the pump source fluctuates in terms of power and pulse duration. This leads to a significant degradation in temperature resolution, with limiting values of 0.5 K for common systems. Our study on the error margin indicates that either short pulsed or continuous excitation should be preferred for high precision measurements. Additionally, we derive conversion factors, enabling the re-calibration of currently available intensity ratio measurements to the steady state regime, thus facilitating the transition from pulse regimes to continuous excitation.

Influence of Cyclic Loading on the Internal Friction Measured on Magnesium Alloys AZ31, AZ61 and AZ91

The article is aimed on the analysis of the influence of cyclic loading on the internal friction measured on magnesium alloys, especially AZ31, AZ61 and AZ91, after homogenization annealing. Microplastic processe and dissipation of energy within the alloys are evaluated and investigated by internal friction measurements. In experimental measurements resonance method was used, which is based on continuous excitation of oscillations of specimens. Measurements were performed at final excitation voltages of 5 V, 6 V and 7 V.

Effect of Structure and Cyclic Loading on the Internal Damping Capacity

The damping capacity, which was characterized by dissipating of mechanical energy, was examined in magnesium alloys (AZ31, AZ61 and AZ91). Internal damping is usually divided into three regions, namely the regions in which the internal damping is strain independent, weakly dependent and strongly dependent. The article is focused on the critical amplitudes of deformation which separate the strain independent, weakly dependent and strongly dependent regions. In experimental measurements resonance method was used, which is based on continuous excitation of oscillations of the specimen and the entire apparatus vibrates at a frequency which is near to the resonance.