Site substitution and tunable luminescence of Eu2+ activated Ba1-xSrxLiZn3(PO4)3 phosphor for plant growth

The regulation of emission wavelength, luminescence intensity, and thermal stability in phosphors is essential for plant growth applications. This study explores the site substitution and tunable luminescence of Eu²⁺ in Ba_1-xSr_xLiZn₃(PO₄)₃, where Ba is partially replaced by Sr. Initially, Eu²⁺ occupies only the Ba²⁺ site within a highly symmetrical crystal structure. As Sr²⁺ substitutes Ba²⁺, a new emission band emerges at 420 nm, attributed to crystal field splitting and centroid displacement changes. The local environment of the Eu²⁺ has changed due to Sr²⁺ substitution for Ba²⁺. When x changing from 0 to 0.4, the emission peak red-shifts from 387 nm to 420 nm, with luminescence intensity reaching 485 % of the initial value. The incorporation of Sr²⁺ induces cation disorder, broadening the band gap. This disorder enhances thermal stability, as evidenced by the luminescence intensity at 150 °C increasing from 60.5 % (x = 0) to 64.2 % (x = 0.4) relative to the initial intensity at 25 °C. The optimized B_0.59S_0.4LZP:0.01Eu²⁺ phosphor aligns well with plant pigment absorption spectra. Artificial plant growth experiments under natural and LED supplementary light showed a 13.40 % increase in hydrocotyle vulgaris weight after 15 days, indicating the potential of B_0.99-xS_xLZP:0.01Eu²⁺ as a blue phosphor for plant growth LEDs.