The role of the Ca vacancy in the determination of the europium position in the energy gap, its valence state and spectroscopic properties in KCa(PO3)3.

A new very promising red phosphor KCa1-xEux(PO3)3 (x = 1-5%) has been grown by the solid state method. Its luminescent quantum efficiency is close to 100% and the emission is stable over a wide temperature range i.e. 90% and 60% of the room temperature emission intensity remains at 200 °C and at 600 °C, respectively. The chromaticity coordinates were calculated as being x = 0.63, y = 0.37. The IR and Raman spectra were measured, and the maximum phonon energy of KCa1-xEux(PO3)3 is 1276 cm(-1). In the measured emission and excitation spectra of all samples only Eu(3+) ion emission was observed, emission of Eu(2+) is not present. Quantum mechanical calculations showed that in a perfect crystal the 5d levels of Eu(2+) are embedded in the conduction band. Consequently, neither absorption nor emission assigned to the Eu(2+) ions could be observed. The presence of a calcium vacancy is crucial for the explanation of the observed spectrum. The existence of a Ca(2+) vacancy compensates for the charge of Eu(3+) and results in the creation of the magnetic moment which moves the 4f levels to the valence band. Thus, transitions to the Eu(3+) excited levels located in the energy band gap are observed.

Structural and optical properties of nano-sized K3Nd(PO4)2:Yb3+ orthophosphate.

Nanocrystals of tripotassium neodymium bis-phosphate(V) doped with ytterbium ions, K3Nd(PO4)2: Yb3+, were synthesized by Pechini method. The obtained grains, having an average size of about 40 nm, were characterised by X-ray, electron microscopic, electron absorption, luminescence and IR studies. Moreover, fluorescence decay studies were carried out at room temperature. The energy transfer from the Nd3+ to Yb3+ was described and discussed. The results were compared to those of the K3Nd(PO4)2 bulk crystal.