Deep-red emitting SrNaZrO3:Mn4+ phosphor for greenhouse cultivation LEDs application

Abstract

A sequence of deep red-emitting phosphors, Sr_0.9Na_0.2Zr_1-xO₃:Mn⁴⁺, was synthesized using a modified sol-gel method. The Rietveld analysis indicates that the optical properties are influenced by the coordination environment of the host material. The Zr atom's $4a$ site symmetry is occupied by Mn²⁺ and Mn⁴⁺ ions in an octahedral coordination, leading to a reduction in $V_o^{°°}\text{.}$ When excited at 325 nm, photoluminescence (PL) at room temperature (303.15 K) and higher temperatures exhibited strong blue emission at 423 nm and a zero-phonon deep-red emission band at 698 nm. These emissions stem from the ⁴T₁→⁶A₁ and ²E_g → ⁴A_2g transition in the 3d orbit of manganese ions. At higher concentrations, PL intensity was quenched due to energy transfer and exchange interactions between adjacent ions. Temperature-dependent PL measurements showed a quenching in emission intensity with increasing temperature, attributed to the dominance of nonradiative transitions. The Sr_0.9Na_0.2Zr_1-xO₃:_0.01Mn⁴⁺ nanophosphors demonstrated high stability, retaining 50 % of their emission intensity at 422 K, with a thermal relative sensitivity of 2.49 %K⁻¹. The red phosphor achieved CIE color coordinates of (0.707, 0.293), comparable to commercial NTSC-standard red-emitting phosphors, with 93 % color purity. These properties make it suitable for applications in thermal optical sensors and high-power LEDs.