Efficient multiphoton upconversion and synthesis route dependent emission tunability in GdPO4:Ho3+, Yb3+ nanocrystals

Abstract

Double rare earth ion doped GdPO₄ nanocrystals with multiform morphologies, such as nanoparticles, nanospheres, and nanorods have been synthesized via four different routes namely a facile solid-state reaction (SSR) method, low temperature co-precipitation (CPP), pechini type sol–gel (SG) and an auto combustion process (ACP). All the methods produce crystalline nanoparticles with dimensions ranging from a few nm to tens of nm but with different morphologies. We systematically investigated the photoluminescence properties of GdPO₄:Ho³⁺, Yb³⁺ nanocrystals under IR (980 nm) excitation and observed that the emission colour is green for the sample synthesized by the SG route whereas all other samples predominantly emit in the red due to efficient energy transfer from Yb³⁺ to emitter Ho³⁺ in the GdPO₄ host. The upconversion was found to be a two photon process in GdPO₄:Ho³⁺, Yb³⁺ nanocrystals and synthesis route dependent emission tunability suggests different intra level phonon relaxation routes.