Pesticide-induced photoluminescence quenching of ultra-small Eu3+-activated phosphate and vanadate nanoparticles

The aim of this research was to investigate the luminescent behavior of ultra-small Eu3+-activated phosphate and vanadate nanoparticles in the presence of pesticides.Nanoparticles have an average diameter of approximately 2 nm with a narrow size distribution.The monazite crystal structure of phosphate-based particles(space group P121/n1)and single tetragonal zircon-type structure of vanadate-based particles(space group of I41/amd)have been confirmed using X-ray diffraction measurements.All synthesized Eu3+-activated colloidal nanoparticles show sharp emission peaks in the red spectral region.Photoluminescence measurements revealed emission quenching upon addition of millimolar concentrations of following pesticides:4-Chloro-2-methyl-phenoxyacetic acid(MCPA),2,4-Dichlorophenoxyacetic acid(2,4-D)and N-(phosphonomethyl)glycine(Glyphosate).In both phosphate and vanadate-based colloidal nanoparticles luminescence quenching is more evident in the presence of 2,4-D pesticide with the lowest limit of detection(0.7μM)obtained for phosphate-based nanoparticles.

Mn^(5+)-activated Ca_(6)Ba(PO_(4))_(4)O near-infrared phosphor and its application in luminescence thermometry

The near-infrared luminescence of Ca_(6)Ba(PO_(4))_(4)O∶Mn^(5+)is demonstrated and explained.When excited into the broad and strong absorption band that spans the 500-1000 nm spectral range,this phosphor provides an ultranarrow(FWHM=5 nm)emission centered at 1140 nm that originates from a spin-forbidden ^(1)E → ^(3)A_(2) transition with a 37.5%internal quantum efficiency and an excited-state lifetime of about 350 μs.We derived the crystal field and Racah parameters and calculated the appropriate Tanabe-Sugano diagram for this phosphor.We found that 1E emission quenches due to the thermally-assisted cross-over with the ^(3)T_(2) state and that the relatively high Debye temperature of 783 K of Ca_(6)Ba(PO_(4))_(4)O facilitates efficient emission.Since Ca_(6)Ba(PO_(4))_(4)O also provides efficient yellow emission of the Eu^(2+)dopant,we calculated and explained its electronic band structure,the partial and total density of states,effective Mulliken charges of all ions,elastic constants,Debye temperature,and vibrational spectra.Finally,we demonstrated the application of phosphor in a luminescence intensity ratio thermometry and obtained a relative sensitivity of 1.92%K^(-1) and a temperature resolution of 0.2 K in the range of physiological temperatures.