<p>Novel rare-earth-free far-red-emitting phosphors, Zn₂SnO₄:3% Cr³⁺ (ZTO:Cr³⁺) and Zn₂SnO₄:3% Cr³⁺, 0.6% Al³⁺ (ZTO:Cr³⁺, Al³⁺), were synthesized using a modified high-energy planetary ball milling technique, followed by post-annealing at 1200°C in air. The phosphors presented emission spectra that matched well with plants’ far-red absorption peak of phytochrome pigment. The ZTO:Cr³⁺, Al³⁺ phosphor displayed a blueshift in the photoluminescence excitation (PLE) spectra and in the broadband photoluminescence (PL) emission peak compared to ZTO:Cr³⁺. Under blue light excitation, the ZTO:Cr³⁺, Al³⁺ phosphor demonstrated internal quantum efficiency, absorption efficiency, and external quantum efficiency of 83.5%, 40.2%, and 40%, respectively. The PL intensity decreased by only 18% when heated to 473&#xa0;K, indicating strong thermal stability. A light-emitting diode (LED) device created by coating ZTO:Cr³⁺, Al³⁺ onto a blue LED chip exhibited a photoelectric spectrum with two peaks at 450&#xa0;nm and 730&#xa0;nm, achieving photoelectric conversion efficiency of 16.3%, with output power of 27.52&#xa0;mW under current and voltage of 0.1504&#xa0;A and 3.029&#xa0;V, respectively. LED bulbs comprising six LEDs, each containing ZTO:Cr³⁺, Al³⁺ phosphor mixed with a commercial 660&#xa0;nm red phosphor with varying mass percentages and a blue LED chip, were successfully produced. The devices showed luminous flux of 55&#xa0;lm and were used for in situ testing to control the flowering of chrysanthemum plants. Chrysanthemum plants illuminated by LED bulbs demonstrated a better flower bud blossoming rate than the reference plant, highlighting ZTO:Cr³⁺, Al³⁺ as a promising phosphor for agricultural LED fabrication.</p>