###### Abstract  
Oscillations of gas bubbles in liquids irradiated with acoustic pressure waves may result in an intriguing physical phenomenon called sonoluminescence, where a collapsing bubble emits the in a broad optical spectral range. However, the intensity of the so-generated light is typically weak for practical purposes. Recently, it has been demonstrated that nanoparticles can be used to increase the efficiency of sonoluminescence, thereby enabling one to generate light that is intense enough for a number of applications in photonics, biomedicine, and materials science. In this article, we review the latest achievements in the field of nanoparticle-enhanced sonoluminescence and showcase the perspectives of their practical applications. gas bubble; oscillations; cavitation; sonoluminescence; photonics; biophotonics; fluorescence; plasmonics; Purcell effect; metamaterials +
Footnote †: journal: Applied  
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suitable for opening the BBB and delivering drugs through it, where the bubble collapses non-spherically, forming a powerful jet [17; 18; 19]. The physics of non-spherically collapsing bubbles is more complex, but, in general, similar to that of spherically collapsing bubbles that we discuss in continuation. Apart from their applications in biomedicine, bubbles have also been used for texture tailoring in the food industry [20], natural gas recovery in the petroleum industry [21], material synthesis in materials sciences [22], lab-on-a-chip devices [23], wastewater treatment systems [24], sonochemistry (enhancement and alternation of chemical reactions by means of ultrasound) [25; 26], sonoprocessing [25; 27], and underwater acoustic communication [28; 29]. Moreover, it has been hypothesised that the acoustic and fluid mechanical properties of bubbles in the primordial ocean might have contributed to the origin of life on Earth [30] and that the presence of bubbles in the brain and their collapse might be associated with blast-induced neurotraumas [31; 32]. The physics of gas bubbles is also relevant to processes taking place during underwater explosions [33]. However, the aforementioned list of properties and practical applications of bubbles is notcomplete. In this article, we focus on the well-established capability of an oscillating bubble to emit light in a broad optical spectral range via the process called sonoluminescence [34; 35; 36; 37; 38]. As schematically shown in Figure 1a, while a bubble in the bulk of liquid periodically expands and collapses under the pressure of an ultrasound wave, at certain experimental conditions, the shrinkage of the bubble can result in the emission of pulses of light [34; 35]. The intensity of the emitted light is typically higher in experiments involving individual bubbles [35] compared with the case of multibubble  
Figure 1: **(a)** Schematic radius vs. time diagram for a gas bubble oscillating in the bulk of water. Bubble shapes at different times are shown above the curve during a single oscillation cycle. The pressure inside a bubble is high at the beginning and at the end of the oscillation cycle and is low in the middle. **(b)** Illustration of the principle of drug delivery through the blood–brain barrier (BBB) using gas bubbles inside a small blood vessel of the brain. Bubble oscillations are driven by an ultrasound wave transducer located outside the head, and the drug (small spheres in the picture) passes through the wall of the blood vessel when the bubble either reaches its maximum radius or collapses and forms a water jet. Reproduced from [11] under the terms of a Creative Commons license.