Optical and structural characterisation of pure and Pr3+ doped LaPO4 and CePO4 nanocrystals

The rod- and stick-shaped nanocrystalline cerium and lanthanum orthophosphates, pure and Pr3+ doped, have been synthesised by the hydrothermal method in acidic (pH 1) or alkaline (pH 11) environment. Subsequent calcination of as-obtained powders at different temperatures, 500 and 900 °C, led to the formation of hexagonal and monoclinic phases, respectively. The hexagonal phase at room temperature has been identified as hydrated orthophosphate with zeolite water inside the channels of the structure. The monoclinic phase is free of water.The average grain size is about 12–30 nm depending on the calcination temperature and preparation conditions. The structural, morphological and optical (vibrational and luminescent) properties have been characterised and their changes due to the temperature and different acidity in the starting materials have been studied.

► The nanoparticles (12–30 nm) of hydrated (hexagonal) and water-free (monoclinic) phases of lanthanum and cerium orthophosphates La(Ce)PO4 were obtained by the hydrothermal method.
► Differences between hexagonal and monoclinic nanocrystals are very well reflected in the vibrational spectra and a slight influence of the environment conditions (pH) of the crystallisation is found.
► The structure differences and environment conditions of the crystallisation (pH) play role in the luminescent properties.