A New Co-Substitution Strategy as a Model to Study a Rare-Earth-Free Spinel-Type Phosphor with Red Emissions and Its Application in Light-Emitting Diodes

Qijian Zhu; Jiansheng Huo; Yanlan Lin; Mengqing Li; Wanqiang Liu; Jinwei Gao; Qianming Wang

doi:10.1021/acs.inorgchem.9b02731

A New Co-Substitution Strategy as a Model to Study a Rare-Earth-Free Spinel-Type Phosphor with Red Emissions and Its Application in Light-Emitting Diodes

Inorg Chem. 2020 Jan 6;59(1):433-442. doi: 10.1021/acs.inorgchem.9b02731. Epub 2019 Dec 12.

Authors

Qijian Zhu¹, Jiansheng Huo¹, Yanlan Lin¹, Mengqing Li¹, Wanqiang Liu², Jinwei Gao³, Qianming Wang¹

Affiliations

¹ Key Laboratory of Theoretical Chemistry of Environment, Ministry of Education, School of Chemistry , South China Normal University , Guangzhou 510006 , PR China.
² School of Chemistry and Chemical Engineering , Hunan University of Science and Technology , Xiangtan 411201 , PR China.
³ Guangdong Provincial Engineering Technology Research Center for Transparent Conductive Materials , South China Normal University , Guangzhou 510006 , PR China.

PMID: 31829630
DOI: 10.1021/acs.inorgchem.9b02731

Abstract

The substitution of metal sites in Mg₂TiO₄ substrate leads to charge imbalance that will be closely related to a variety of changes including lattice structure, cell distortion, and photophysical properties. Herein, the co-substitution strategy of [Ga³⁺-Ga³⁺] for [Mg²⁺-Ti⁴⁺] and Sn⁴⁺ for Ti⁴⁺ achieves for the first time the novel Mg₃Ga₂SnO₈ (MGS):xMn⁴⁺ (x = 0-3%) phosphors with efficient red emissions. In terms of X-ray powder diffraction (XRD) and Rietveld refinement analysis, MGS:Mn⁴⁺ possesses a structure isotypic of Mg₂TiO₄ in the cubic space group Fd3̅m (227). There are two types of octahedra for Mn⁴⁺ ions in this structure, where Ga³⁺ ions completely occupy a group of octahedral sites and Mg²⁺/Sn⁴⁺ has been randomly distributed over another group of octahedral sites. A strong excitation band in the broad spectral range (220-550 nm) has been identified, thus facilitating the commercial uses for blue LED chips excitation. An intense red emission band at 680 nm has been observed due to the characteristic ²E_g-⁴A_2g transition of Mn⁴⁺ ions. A concentration quenching effect occurs when the Mn⁴⁺ content exceeds 1.5%, and the quenching mechanism is demonstrated to be dipole-quadrupole interactions. Temperature-dependent luminescence measurements support its good thermal stability, and the corresponding activation energy E_a is determined to be 0.2552 eV. The possible luminous mechanism of the Mn⁴⁺ ion is explained by the Tanabe-Sugano energy level diagram. The crystal field strength and the Racah parameters together with the nephelauxetic ratio are also determined for Mn⁴⁺ in the MGS lattice. High color rendition warm white-light-emitting diodes (WLEDs) based on the optimal phosphor MGS:1.5%Mn⁴⁺,1.5%Li⁺ possess a color rendering index and color temperature of 85.6 and 3658 K, respectively. Its feasibility for application in solid-state white lighting has been verified.