Solid‐state light‐emitting diodes (LEDs) are driving the lighting industry towards efficient and environmentally friendly lighting and displays. Current challenges encompass efficient and low‐cost down‐shifting phosphors with tuned emission colors. Green light lies on the low‐loss optical transmission window in plastic optical fibers and plays a special role in the regulation of the human and plant circadian rhythms. Moreover, green‐emitting phosphors may suppress the “green gap” found in semiconductor‐based LEDs. In this work, a UV‐photostable green‐emitting complex, Tb(NaI)3(H2O)2, with NaI = nalidixic acid (1‐ethyl‐1,4‐dihydro‐7‐methyl‐4‐oxo‐1,8‐naftiridine‐3‐carboxylic acid), was incorporated into tripodal organic‐inorganic hybrid materials. The hybrid hosts boost the absolute emission quantum yield from ≈ 0.11 (isolated complex) to ≈ 0.82 (doped hybrid), which is the largest value reported for Tb3+‐based hybrid phosphors. A green‐emitting LED was fabricated by coating a near‐UV LED (365 nm) with a Tb3+‐activated organic‐inorganic hybrid having pure‐green‐colored light with Commission International de l'Eclairage color coordinates and an efficacy value of (0.33, 0.59) and 1.3 lm W–1, respectively. Green‐emitting LEDs were fabricated by coating commercial near‐UV‐emitting LEDs (365 nm) with high emission quantum yield (≈ 0.82) and photostable UV down‐shifting Tb3+‐activated organic‐inorganic hybrids prepared by the sol‐gel method. The fabricated devices revealed pure CIE colour coordinates in the green spectral region and luminous efficacy of ≈ 1.3 lm W–1.