Structure, Morphology and Luminescence of BiPO4:Pr Compounds

The results of synthesis procedure for praseodymium-doped bismuth orthophosphate polycrystalline samples as well as their characterization by X-ray diffraction, scanning electron microscopy and luminescent spectroscopy are presented. It is found that doping leads to phase transformation from high temperature monoclinic to low temperature monoclinic phase of BiPO4. Scanning electron microscopy studies show that particles with 100-200 nm sizes are dominant, but some micro-sizes particles are also present in the samples. It was assumed that prism-shaped particles related with high temperature phase of BiPO
₄
and the rod-shaped - with low temperature phase. At room temperature and under excitation into absorption band of praseodymium ions the studied samples revealed intensive orange/red luminescence. There was no intrinsic luminescence of phosphate host observed at such conditions. Simultaneous analysis of structural and spectroscopic data shows that depopulation of
³
P
_l
multiplet of Pr
³
+ ions take place resulting in increasing of population of
³
p
₀
and
¹
D
₂
levels. The most luminescence bands in spectra correspond to radiative transitions from abovementioned levels. It was assumed that crystal phase transformation, multiphonon and cross-relaxation processes have influence on luminescence characteristics of Pr
³⁺
- doped BiPO
₄
.