Eu3+-Doped Sr2LaF7 Nanopowders as Efficient Red and Deep-Red Emitters for Advanced Horticultural Lighting

Abstract Our study presents Eu3+-activated Sr2LaF7 nanophosphors with efficient red and deep-red emission, 555% enhanced intensity, and outstanding thermal stability—ideal for next-generation plant growth light-emitting diodes (LEDs). Phosphors applied in agricultural LEDs for plant growth are designed to convert electrical energy into light within the photosynthetically active radiation range, covering wavelengths from 400 to 700 nm. For that purpose, a series of Sr2La1-xEuxF7 (x = 0, 0.05, 0.1, 0.15, 0.2, 0.4, 0.5, 0.6, 0.8) luminescent nanopowders were prepared. Transmission electron microscopy shows nanoparticles of ∼33 nm size. The Sr2LaF7 sample bandgap of 8.8 eV was determined using the reflected electron energy loss spectroscopy method. Photoluminescence measurements show highly efficient red and deep-red emission, with an optimal concentration of 50 mol% of Eu3+, which exhibits a remarkable 555% emission enhancement compared to 5 mol% of Eu3+. The most prominent emission peaks are around 600 nm (orange/red) and 700 nm (deep red). The observed lifetimes are long; they gradually decrease as the Eu concentration increases, from 14.9 ms for x = 0.05 to 8.3 ms for x = 0.8. Temperature-dependent luminescence spectra to 200 °C indicate that the optimal sample exhibits outstanding thermal stability, with emission intensity retaining 97% of its room-temperature value. The quantum efficiency of the optimized sample is 52.73%. The high emission efficiency, wide bandgap, good thermal stability, and unusual dominant 700 nm deep-red emission make these samples promising nanophosphors for LED-based indoor plant growth.