This paper reports the initial results of an original and simple method to elaborate flexible, self-standing, and thick luminescent films suitable for optical devices. PVP/Y3Ga5O12:Tb3+ nanocomposite films have been successfully achieved from a sol-gel derived Y3Ga5O12:Tb3+ powder and an alcoholic solution of poly-N-vinylpyrrolidone (PVP). The structural, morphological, and optical properties of these nanocomposite films have been studied and compared to those of a pristine PVP film and Y3Ga5O12:Tb3+ powder. The nanocomposite films were characterized by infrared and Raman spectroscopies as well as scanning and transmission electron microscopies (SEM and TEM) and demonstrated good dispersion of the phosphor particles within the polymer matrix via an alveolar mesostructure. The optical properties of these nanocomposites were fully characterized, and both their excitation and emission spectra and decay curves were recorded. Furthermore, photostability of the nanocomposite films and of the luminescent raw powder has been studied after exposure to an accelerated artificial photoageing at wavelengths higher than 300 nm. The elaboration process used is both tunable and applicable to a large variety of powders and polymers because it does not require any additive to form homogeneous and easily shapeable phosphor/polymer nanocomposites applicable in a large variety of optical devices such as solid-state-lighting.