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 CsSr3La(PO4)3F:xEu3+ 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 CsSr3La(PO4)3F belongs to the hexagonal system with space group P63/m (176), displaying two polyhedral structures [AⅠO9] and [AⅡO6F]. The band gap (Eg) of the material CsSr3La(PO4)3F is 5.823 eV. At the excitation of 393 nm, CsSr3La(PO4)3F:30 mol%Eu3+ phosphor exhibits a primarily significant emission peak at 703 nm, referring to the 5D0→7F4 transition due to a highly polarizable chemical environment and a distorted coordination polyhedron around Eu3+ ions. The concentration quenching process is attributed to the quadrupole-quadrupole interaction between Eu3+ ions, with the maximum luminescence intensity achieved at a doping content of 30 mol%. At 420 K, the emission intensity of the CsSr3La(PO4)3F:30 mol%Eu3+ 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 (Sa and Sr) 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 (Ra) 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.