Sharp-Line Near-Infrared Emission from Tetrahedron-Occupied Ni²⁺ in Ca₂GeO₄

As far as we are concerned, the phenomenon of Ni2+ luminescencein tetrahedral coordination has not been reported. For the first time,a new NIR phosphor Ca2GeO4:Ni2+ isdeveloped in this work. It is found that the NIR emission from thisphosphor is a sharp peak attributed to the unusual Ni2+-occupied GeO4 site in the lattice, instead of the conventionalbroadband luminescence of Ni2+ in the octahedrally coordinatedsite. Crystal-field analysis has been applied, and the parameters Dq, B, and & UDelta; are calculated to revealthe relationship between the emission profile and the crystal fieldstrength. The optimal Ni2+ doping concentration is foundto be 1%. Ca2GeO4:Ni2+ provides anefficient sharp-line (fwhm = 16 nm) emission centered at 1164 nm whichoriginates from the (1) T (2) & RARR; (3) T (1) transition with an internalquantum efficiency of 23.1% and a decay lifetime of about 300 & mu;s.This work could provide some new insights to explore novel NIR luminescentmaterials based on transition-metal elements. A new NIR phosphor Ca2GeO4:Ni2+ was developed which provided an efficientsharp-line (fwhm= 16 nm) emission centered at 1164 nm from the (1) T (2) & RARR; (3) T (1) transition, attributed to the unusual Ni2+-occupiedGeO(4) site in the lattice.