Concentration and temperature dependence of Pr3+ f-f emissions in La(PO3)3

La(PO3)3 activated with different concentrations of Pr3+ was synthesized by a solid-state process. The obtained powder was composed of chunks of several microns in size, typical for this type of synthesis. X-ray diffraction confirmed an orthorhombic crystal structure with the C2221 space group. The electronic band structures and density of states of La(PO3)3 and La(PO3)3:Pr3+ are calculated and presented. The visible and near-infrared emissions from Pr3+ [Xe]4f2 → [Xe]4f2 electronic transitions were detected under 442 nm excitation. The red emission from the 1D2 state dominates visible spectra while emissions from the 3P0,1,2 states have smaller intensities. The 1D2 emission centered around 1020 nm is detected in the near-infrared spectral range. Intensities of 3P0 emissions increased with an increase in Pr concentration, while 1D2 emissions decreased in intensity. We found that the main process responsible for the 1D2 state decay is the Pr(1D2) + Pr(3H4) → Pr(1G4) + Pr(3F3,4) cross-relaxation between two Pr ions of electric dipole-dipole character. This finding is supported by 1D2 emission decay measurements, which revealed a reduction of average decay constants from 242 μs for a 0.5 mol% doped sample to 11 μs for a 10 mol% doped sample and an increasingly stronger non-exponential behavior of emission decay patterns with an increase in Pr3+ concentration.