Two Types of Europium-Based Photoconversion Covers for Greenhouse Farming with Different Effects on Plants

In the present work, we investigated the effect of light conversion using europium (Eu(III))-based photoconversion covers on the cultivation of agricultural plants and their resistance to stress conditions. Two types of europium nanoparticles were used. The first one was obtained from europium oxide (Eu2O3) by laser fragmentation. The second one was Eu3+:LaF3 nanocrystals obtained by hydrothermal-microwave treatment, the content of europium ions in which was 50% of the total amount of cations. Tomatoes (Solanum lycopersicum) and cucumbers (Cucumis sativus) were used as model plants. It was shown that plants grown under cover with Eu2O3 (PCC-Eu2O3) were 30–40% larger, gave a higher yield, and the activation of gas exchange processes and the light phase of photosynthesis in the leaves in response to the lighting was faster. On the contrary, plants grown under cover with Eu3+:LaF3 (PCC-Eu3+:LaF3) tended to slow down the rate of biomass accumulation and decrease the rate of gas exchange activation. It was shown that photoconversion covers change the resistance of plants to stress conditions: if plants grown under PCC-Eu2O3 became more sensitive to heat (+40 °C) and cold (+4 °C) treatment, then plants grown under PCC-Eu3+:LaF3 became more resistant to high and low temperatures. It was found that PCC-Eu2O3 inhibited the development of the phytopathogen Phytophthora infestans on tomato plants. It was assumed that changes in the illumination spectrum by the photoconversion covers cause both the activation of plant growth in the case of Eu2O3 and an increase in plant resistance in the case of Eu3+:LaF3 applications.