Strong structural phase sensitive rare-earth photoluminescence color flips in KLaF4:RE3+ (RE3+= Eu3+, Er3+/Yb3+) nanocrystals

摘要

Systematic and strong rare-earth photoluminescence (PL) color flips that are highly sensitive to structural phase transformation in KLaF4:RE3+(RE3+= Eu3+, Er3+/Yb3+) nanocrystals are demonstrated. Room-temperature wet chemical synthesis at various reaction times involves a systematic conversion from cubic (alpha, space groupFm (3) over barm) to hexagonal (beta, space groupP (6) over bar 2m) polymorph nanocrystals of 4 to 8 nm sizes. The unusual down-conversion photoluminescence (DC-PL) asymmetric ratio of the hypersensitive transition (D-5(0)-> F-7(2), Red) to that of nearly invariant transition (D-5(0)-> F-7(1), Orange) (R/O from 1.2 to 3.0) of KLaF4:Eu3+ is substantially affected by the site-selective occupancy and local symmetry around the Eu(3+)ions, according to crystal packing transformation. The NIR excited up-conversion photoluminescence (UC-PL) of Er3+ ions produces a strong color flip from green (H-2(11/2) and S-4(3/2)) to red (F-4(9/2)) dominated emissions based on their cubic or hexagonal crystal packing. The site occupancy and phonon energies strongly influence various nonlinear energy transfer mechanisms within RE(3+)ion energies and the results are explained accordingly. The present study substantially reveals the local host effects and these two distinct polymorph nanoparticles can be potentially utilized for color-specific studies related to applications such as color-specific biologicalin vitroandin vivoimaging and other optoelectronic device applications.