Far‐red‐emitting YAl3(BO3)4:Cr3+ phosphors with excellent thermal stability and high luminescent yield for plant growth LEDs

Phosphors‐converted LEDs (pc‐LEDs) are excellent artificial light sources for indoor plant cultivation, in which the far‐red‐emitting component (700−780 nm) plays an important role in regulating the photomorphogenesis of plants. Accordingly, highly efficient and thermally stable far‐red‐emitting phosphors are indispensable for developing high‐performance plant cultivation pc‐LEDs. Herein, far‐red‐emitting YAl3(BO3)4:Cr3+ (YAB:Cr3+) phosphors were synthesized by solid‐state reaction, and their photoluminescence characteristics, thermal quenching, quantum yield (QY), and application in pc‐LEDs were systematically investigated. The YAB:Cr3+ phosphor has an intense broadband absorption to the blue light, simultaneously exhibiting the sharp‐line 2E emission and the broadband 4 T2 emission of Cr3+ with a QY of ~86.7%. The far‐red broadband emissions of YAB:Cr3+ centered at ~735 nm show a high resemblance to the active‐state (PFR) absorption of plant phytochrome. Moreover, the YAB:Cr3+ phosphor shows the thermally enhanced luminescence at temperatures of 303−393 K and the near‐zero thermal quenching up to 423 K. The anomalous thermal enhancement is attributed to the temperature‐dependent repopulation between 2E and 4 T2 states. Finally, a pc‐LED device was fabricated with the YAB:Cr3+ phosphor and blue chip, exhibiting the light out power of ~50.6 mW and energy conversion efficiency of ~17.4% at 100 mA drive current, respectively. The exceptional PL features including suitable excitation/emission wavelengths, suppressed thermal quenching and high QY make YAB:Cr3+ phosphors very promising for applications in plant growth pc‐LEDs.