Far-red emission of CaYAlO4:Mn4+ synthesized by co-precipitation method

Abstract

Light absorption of the most plants is in range of blue (440 nm), deep-red (660 nm) and far-red around 700-740 nm. The deep-red and far-red light plays important roles in reactions of photomorphogenesis of plants. Although red emission phosphors have been researched extensively for white light-emitting diodes, deep-red and far-red emission phosphors for plant growth have been reported inadequately. Thus, in this work, far-red emitting CaYAlO₄:Mn⁴⁺ phosphor was synthesized by co-precipitation method coupled with various annealing temperature from 800^oC to 1300^oC for 5 h. The crystal structure, morphology, and photoluminescence properties of CaYAlO₄:Mn⁴⁺ phosphors were investigated in detail. The crystallinity of the phosphor belongs to tetragonal system with space group I4/mmm. Y³⁺ and Ca²⁺ ions are coordinated by nine oxygen atoms to form [YO₉] and [CaO₉] polyhedrons, and the Al³⁺ ions are coordinated by six oxygen atoms forming [AlO₆] octahedrons that provided suitable sites for Mn⁴⁺ ions. The obtained sample showed an irregular surface morphology with micro size particles. Under the excitation of 320 nm, CaYAlO₄:Mn⁴⁺ phosphors gave bright far-red emission around 710 nm due to the ²E_g→⁴A_2g transition of Mn⁴⁺ ions. The critical concentration of Mn⁴⁺ doped in CaYAlO₄ host lattice is 0.5 mol.%. The results show that the CaYAlO₄:Mn⁴⁺ phosphors may be applied to indoor plant growth illumination.