Far-red emitting NaAl5O8: Cr3+ phosphors with high thermal stability for plant cultivation applications

Developing far-red phosphors with high thermal stability and spectral matching is of great significance for plant growth light-emitting diodes (LEDs). In this paper, NaAl 5 O 8 : Cr 3+ far-red emitting phosphors were synthesized by the high-temperature solid-phase reaction method. The crystal field parameters, luminescence properties, and thermal quenching behavior were investigated in detail. The NaAl 5 O 8 : Cr 3+ phosphor showed a far-red emission band centered at 707 nm, which is attributed to the 2 E→ 4 A 2 transition of Cr 3+ ions. Notably, NaAl 5 O 8 : Cr 3+ phosphor exhibited outstanding thermal stability, with an integrated emission intensity reaching 109 % at 423 K compared to that at room temperature (298 K), corresponding to a 9 % increase in emission intensity at high temperature. The full width at half maximum in the temperature-dependent emission spectra increased with increasing temperature. Eventually, a prototype LED device was fabricated by integrating the NaAl 5 O 8 : Cr 3+ phosphors and a commercial 410 nm LED chip. The obtained electroluminescence spectrum of the LED was well matched with the absorption band of the photosensitive pigment P FR , and the fabricated LED performed well in plant cultivation applications. In the sunflower plant growth experiment, the average growth rate under pc-LED irradiation was 1.8 times that under sunlight. These results indicate that NaAl 5 O 8 : Cr 3+ phosphor has great potential for application in plant growth LEDs.