Enhancement of luminescence properties and thermal stability of near-UV-excitable KSr1-x-yCayPO4:xEu3+ red phosphors by substituting Sr with Ca for white LEDs

Narrow-band red phosphors excited by near-ultraviolet light (n-UV) are significant for enhancing the R9 index and can produce high color rendering white LEDs. A range of KSr 1-x-y Ca y PO 4 :xEu 3+ red phosphors were synthesized by high-temperature solid-state reaction method. We investigated the effects of partially substituting Sr 2+ ions with Ca 2+ ions on the phosphors' crystal structure, photoluminescence and thermal stability. Significantly, incorporating Ca 2+ ions enhances the luminescent properties and thermal stability. Under n-UV light excitation, all samples exhibit red emission around 614 nm, corresponding to the 5 D 0 → 7 F 2 transition of Eu 3+ ions. At the doping concentration of Eu 3+ ions (x = 0.08), an optimal KSr 0.52 Ca 0.4 PO 4 :0.08Eu 3+ (y = 0.4) sample was obtained. The excitation wavelength exhibited a slight violet shift from 398 nm to 396 nm. At 150 °C, the luminescence intensity of KSr 0.92 PO 4 :0.08Eu 3+ remains 80.1 % of its value at room temperature, while that of KSr 0.52 Ca 0.4 PO 4 :0.08Eu 3+ reaches 89.7 %. White LED device can be fabricated by combining the as-prepared KSr 0.52 Ca 0.4 PO 4 :0.08Eu 3+ red phosphor with commercial BaMgAl 10 O 17 :Eu 2+ blue and (Ba, Sr) 2 SiO 4 :Eu 2+ green phosphors, along with encapsulation using n-UV LED chip (395–400 nm). The device emits bright white light and exhibits a high color rendering index (Ra = 87.6, R9 = 89.8) and suitable correlated color temperature (CCT = 5523 K) at 300 mA drive current. The results demonstrate that this work provides new application prospects for the fabrication of high color rendering white LEDs using n-UV light.