## 5 Luminescence and Imaging
The emission observed in the (514-700) nm range is ascribed to the well-known Eu\({}^{3+}\) 5D0\(\rightarrow\)7 FJ (J\(\frac{1}{4}\) 0, 1, 2, 3 and 4) transitions. This prompts the formation of rare earth oxide by igniting first during heating, which leads to a combustion decomposition reaction. Y\({}_{2}\)O\({}_{3}\): Eu\({}^{3+}\) microcrystalline structures were obtained using thiourea as organic fuel [127]. [PERSON] et al. [65] synthesized Y\({}_{2}\)O\({}_{3}\) powder phosphors without metal activators by the sol-gel method, and they show an intense bluish-white emission (ranging 350 to 600 nm, centered at 416 nm) under a wide range of UV light excitation of 235-400 nm. Since Y\({}^{3+}\) itself is non-luminous, the observed luminescence from the Y\({}_{2}\)O\({}_{3}\) samples must be related to chemical-bond breakage with resultant carbon formation, and/or the non-stoichiometry created by the oxygen deficiency in the system [129; 130; 131]. Here, the luminescent mechanisms have been ascribed to the carbon impurities in the Y\({}_{2}\)O\({}_{3}\) host. This phosphor can be potentially used as a new efficient blue-emitting material for white LEDs [65]. Y\({}_{2}\)O\({}_{3}\) is used in the multicolor imaging technique to understand the biological activity of cells using cathode luminescence (CL). In CL imaging, Y\({}_{2}\)O\({}_{3}\):Tm; Y\({}_{2}\)O\({}_{3}\):Tb, and Y\({}_{2}\)O\({}_{3}\):Eu were involved as phosphors [132]. Y\({}_{2}\)O\({}_{3}\) doped with europium was reported for the emission of red-orange color using agitation by cathode luminescence [133]. Recent literature emphasized that using the CL characteristics of Y\({}_{2}\)O\({}_{3}\) with dope Eu, a thin film can be generated by applying the magnetron sputtering method [134]. This is an advanced key technology for biomedical research to image biological materials and is used for photodynamic therapy, the high sensitivity and superior resolution being attributed to its drug delivery system [135; 136]. The mechanism involved is traditionally boilable for imaging, covering organic dyes (fluorescent protein and quantum dots). Such a boilable process has been used for fluorescence bioimaging (FBI) ultraviolet excitation or UV light. The fluorescent protein used themselves and biological organelles are damaged in responding to phototoxicity, due to the heavy quantum energy of the exciting light. A recent study demonstrated the surface modifications of Y\({}_{2}\)O\({}_{3}\)-Er with a couple of layers of PAAc used as interfacing materials, and acetal PeG-b-DAMA contributes to the successful NIR imaging of NPs [137]. NPs size of (10-200) nm was found to be suitable for infrared excitation. Another study explained Plasmon-enhanced up-conversion was reported in Au/Sio Y\({}_{2}\)O\({}_{3}\), in which Yb\({}^{3+}\) and Er\({}_{2}\) showed a strong NIR emission under NIR excitation. [PERSON] et al. also noticed NIR emission across the swine colon wall [122]. Moreover, yttrium oxide was used as functional GAN-based MOS devices. High-power lasers are applied in materials processing, remote sensing, communications, and inertial confinement fusion (ICF) [138]. Y\({}_{2}\)O\({}_{3}\) doped NPs exhibit ceramic laser materials, and act as an added advantage. Another investigation demonstrated Tm-doped Y\({}_{2}\)O\({}_{3}\) could be used as an eye safety laser [139]. Moreover, Y\({}_{2}\)O\({}_{3}\) acts as active microwave filters [140; 141]. Therefore, Y\({}_{2}\)O\({}_{3}\) can be a candidate in luminescent display devices for a non-toxic, good host for light-emitting materials in laser and sensor devices, and used as a phosphor in LED. Current literature favored that Y\({}_{2}\)O\({}_{3}\) can be used in advanced technology photodynamic therapy and the drug delivery system.