Luminescent converters based on nanocellulose + K3Tb(PO4)2:Eu composite films

Abstract

The advantages of cellulose and its derivatives as the latest materials for devices that generate, store, and convert electricity are their low cost, environmental friendliness, ease of recycling and the ability to be manufactured in various ways and from various raw materials, including agricultural waste. This predetermines the relevance of their study as materials for modern technology and electronics. The research aims to determine the luminescent characteristics of composite films made based on nanocellulose and polycrystalline oxide K3Tb0.9Eu0.1(PO4)2. Optical microscopy and the spectral-luminescence method were used to characterise the films and their initial components. It was found that crystallites with an average size of about 50mm are distributed quite evenly in the film “nanocellulose+K3Tb0.9Eu0.1(PO4)2”. A Raman scattering band with a maximum of 564 nm under laser excitation at 473 nm was observed for the investigated samples in the form of suspensions. The intensity of photoluminescence of nanocellulose in suspension and films is low compared to the luminescence of oxide as a filler. The luminescence of Eu3+ ions is intense in the red region of the spectrum. The calculated values of the degree of asymmetry indicate low symmetry of the positions occupied by europium ions in the oxide and the contribution of Tb3+ ion emission to the overall spectrum of the composite film. The study results show that the luminescence of Eu3+ ions is sensitised by Tb3+ ions, which absorb the excitation light and then transfer energy to europium ions. The position of the absorption bands of Eu3+ and Tb3+ ions in the ultraviolet region of the spectrum and the intense emission of Eu3+ in the red region indicates the prospects of using nanocellulose+ K3Tb0.9Eu0.1(PO4)2 films to improve the efficiency of solar panels. Testing of the films under the excitation of luminescence by ultraviolet radiation of an LED (λex=375 nm) showed the possibility of developing white LEDs on their basis. In particular, the chromaticity coordinates of the uncoated LED were (x=0.214; y=0.079), and the use of a film composite as a coating causes a shift in the coordinates to the red region: x=0.304, y=0.196. The obtained results on the morphology and luminescent properties can be used to optimise the composition and manufacturing conditions of composite films of the following types “nanocellulose+K3Tb0.9Eu0.1(PO4)2” for use as fluorescent converters in LEDs or solar panels