A novel fluorapatite-type deep-red CsSr3La(PO4)3F:Eu3+ phosphor with intense 5D0-7F4 transition for temperature sensors, plant growth lighting, and w-LEDs

The synthesis of CsSr 3 La(PO 4 ) 3 F: x Eu 3+ phosphors ( x  = 1, 2, 5, 10, 20, 30, 40, and 50 mol%) with fluorapatite-type structure was successfully accomplished through a direct solid-state reaction in this work. A systematic characterization was carried out, encompassing the crystal structure, phase composition , morphology, optical properties , and diverse applications of the samples. The crystalline structure of CsSr 3 La(PO 4 ) 3 F belongs to the hexagonal system with space group P 6 3 / m (176), displaying two polyhedral structures [A Ⅰ O 9 ] and [A Ⅱ O 6 F]. The band gap ( E g ) of the material CsSr 3 La(PO 4 ) 3 F is 5.823 eV. At the excitation of 393 nm, CsSr 3 La(PO 4 ) 3 F:30 mol%Eu 3+ phosphor exhibits a primarily significant emission peak at 703 nm, referring to the 5 D 0 → 7 F 4 transition due to a highly polarizable chemical environment and a distorted coordination polyhedron around Eu 3+ ions. The concentration quenching process is attributed to the quadrupole-quadrupole interaction between Eu 3+ ions, with the maximum luminescence intensity achieved at a doping content of 30 mol%. At 420 K, the emission intensity of the CsSr 3 La(PO 4 ) 3 F:30 mol%Eu 3+ phosphor can still maintain 75.04 % of the emission intensity observed at 300 K. The value of activation energy is 0.18 eV. The maximum absolute and relative thermal sensitivities ( S a and S r ) for the temperature sensor can reach 5.25 × 10 −4  K −1 and 7.71 % K −1 , respectively. The made-up red LED is well-suited to meet the light requirements for the growth and development of plants. The fabricated white light-emitting diode (w-LED) has a relatively high color rendering index ( R a ) of 89 and a suitable correlated color temperature (CCT) of 4392 K. The phosphors have applications in temperature sensors, plant growth lighting, and w-LEDs.