## 5 Luminescence and Imaging
In addition to producing permanent magnets and microwave filters, it can finally be concluded that Y\({}_{2}\)O\({}_{3}\) NPs morphology and  
Figure 6: Confocal photoluminescence image of (1, 3, and 5) mol.% Eu\({}^{3}\)-doped Y\({}_{2}\)O\({}_{3}\) nanoparticles annealed at 900 \({}^{\circ}\)C (0 ex = 410 nm). (Reprinted with permission from Reference [125] Copyright © 2017 Elsevier.) size of particles enhanced its apparent elegant nature, and can be used in high-resolution display optical devices. NPs technology is quite a speedily developing field and is showing a bright scope for biomedical applications. Recently, advanced techniques, such as photonics, and biophotonics research, have turned to a particular emphasis on the development of surface extended and functionalized NPs for therapeutic diagnosis and targeted treatments for several diseases. Bioimaging and predicting disease markers required fabricated NPs with a nanosize of 25 nm. Y\({}_{2}\)O\({}_{3}\) NPs were found to possess two photons that enabled them to convert infrared light to visible light. Another related study has demonstrated that an organic, inorganic hybrid class with yttrium oxides NPs were synthesized using a sol-gel process with proper zirconium side, yttrium chloride, water, and chloroform to obtain H bonds between Zn-OH group. A single step of the sol-gel process was followed to precipitate NPs, possessing ketoprofen used for controlled drug delivery [36]). Such synthesized NPs derived by the sol-gel method enable a novel approach for a controlled drug delivery system. Microscopic NIR fluorescence images of histological sections of mice kidney confirmed that within 1 h, some 50 and 250 nm nanoparticles had entered the glomerulus part of the kidney, suggesting that some of the injected nanoparticles may be excreted. NIR fluorescence emission from histological sections of the liver samples confirmed the difference in the distribution patterns of PEG-b-PAAc-modified and unmodified Er\({}^{3+}\):Y\({}_{2}\)O\({}_{3}\) (Figure 7). Figure 7: Fluorescence emission from mice liver samples after 24 h injection period with (**a**) bare, and (**b**) poly(ethylene glycol-_b_ poly(acrylic acid)c (PEG-_b_-PAAc)-modified Er\({}^{3+}\):Y\({}_{2}\)O\({}_{3}\) nanoparticles (250 nm); (**c**,**d**) bright-field images of bare and PEG-b-PAAc-modified samples, respectively (scale bar: 25 \(\upmu\)m). (Reprinted with permission from Reference [142]. Copyright © 2013 American Chemical Society). The NIR fluorescence area in Figure 7a,b denotes the distribution of Er\({}^{3+}\):Y\({}_{2}\)O\({}_{3}\) in the blood vessels of mice liver. This observation shows that PEG-b-PAAc modification significantly reduced the agglomeration of Er\({}^{3+}\):Y\({}_{2}\)O\({}_{3}\) under physiological conditions. Further investigations by inductively coupled plasma mass spectrometry, including the quantification of Er\({}^{3+}\):Y\({}_{2}\)O\({}_{3}\) present in mice organs, are recently underway [142]. Near-infrared bioimaging (NIR) is a growing field in optical research. Because of the absence of strong scattering and color fading of phosphors, they could offer persistent color and perfect imaging. Trivalent-rare-earth ion-doped Y\({}_{2}\)O\({}_{3}\) nanocrystals have been synthesized, and their photoluminescence properties have been studied under 980 nm laser diode excitation. The ratio of the intensity of green luminescence to that of red luminescence has decreased with an increase of concentration of Yb\({}^{3+}\)Yb\({}^{3+}\) in Er\({}^{3+}\) doped Y\({}_{2}\)O\({}_{3}\) nanocrystals. Insufficient quantities of Yb\({}^{3+}\) to Er\({}^{3+}\) the bright red emission near 660 nm has been predominant due to the 4F\({}_{9}\)/2-4I\({}_{15}\)/24F\({}_{9}\)/2-4I\({}_{15}\)/2 transition of Er\({}^{3+}\). The primary color components are in these red, green, and blue emissions, from which a wide spectrum of colors, including white, would be produced by appropriately mixing them.