TOF-SIMS and laser-SNMS investigations of dopant distribution in nanophosphors

Characterization of industrially important nanophosphors such as ZnS:Mn2+, SrAl2O4:Eu2+, Dy3+ and Gd2O2S:Pr3+ was undertaken with a view to optimize their synthesis methods. To investigate the crystallinity, particle size, efficiency and homogeneity in doping of Mn in ZnS; Eu and Dy in SrAl2O4 and Pr in Gd2O2S, analytical techniques such as XRD, TEM, PL, TOF-SIMS and laser-SNMS were employed. The XRD and TEM studies revealed the average particle sizes to be between 2 and 15 nm. Photoluminescence (PL) studies carried out for the nanophosphors confirm the effectiveness of doping in the host lattices. TOF-SIMS spectral analysis showed the formation of the crystal (host lattice) with the presence of different dopants. The chemical imaging mode of TOF-SIMS suggested homogeneous doping in ZnS:Mn2+ nanophosphor while in the case of SrAl2O4:Eu2+, Dy3+ the degree of homogeneity of doping was found to be considerably less. The broad band of PL in SrAl2O4:Eu2+, Dy3+ nanophosphor may be attributed to such an inhomogeneity to some extent. In the case of Gd2O2S:Pr3+, the PL was found to be brightest at the higher energy region. But because of very low level doping of Pr3+ in the Gd2O2S lattice, additional laser-SNMS studies were carried out for analysing the doping distribution using chemical imaging data, which indicated a high degree of homogeneity.