Single crystal growth, optical absorption and luminescence properties under VUV-UV synchrotron excitation of type III Pr3+:KGd(PO3)4.

Scintillator materials are widely used for a variety of applications such as high energy physics, astrophysics and medical imaging. Since the ideal scintillator does not exist, the search for scintillators with suitable properties for each application is of great interest. Here, Pr3+-doped KGd(PO3)4 bulk single crystals with monoclinic structure (space group: P21) are grown from high temperature solutions and their structural, thermal and optical properties are studied as possible candidates for scintillation material. The change in the unit cell parameters as a function of the Pr3+ level of doping and temperature is studied. Differential thermal analysis reveals that KGd0.942Pr0.058(PO3)4 is stable until 1140 K. The 5d3, 5d2 and 5d1 levels of Pr3+ with respect to the 3H4 ground state are centred at 166, 196 and 218 nm, respectively, in this host. The luminescence of KGd0.990Pr0.010(PO3)4, by exciting these 5d levels, shows intense emissions centred at 256 and 265 nm from the 5d1 to 3F3,4 and 1G4 levels of Pr3+ with a short decay time of 6 ns. The 6P3/2,5/2,7/2 → 8S7/2 transitions of Gd3+ appear after exciting the 5d levels of Pr3+ and the 4 f levels of Gd3+, showing an energy transfer between Pr3+ and Gd3+.

Single crystal growth, optical absorption and luminescence properties under VUV-UV synchrotron excitation of type III Ce3+:KGd(PO3)4, a promising scintillator material.

Scintillator materials have gained great interest for many applications, among which the medical applications stand out. Nowadays, the research is focused on finding new scintillator materials with properties that suit the needs of each application. In particular, for medical diagnosis a fast and intense response under high-energy radiation excitation is of great importance. Here, type III Ce3+-doped KGd(PO3)4 single crystals with high crystalline quality are grown and optically characterized as a new promising scintillator material. The 4f → 5d electronic transitions of Ce3+ are identified by optical absorption. The optical absorption cross section of Ce3+ for the electronic transition from the 2F5/2 to the 5d1 level is 370 × 10-20 cm2. The luminescence of KGd0.996Ce0.004(PO3)4 crystal by exciting the 5d levels of Ce3+ with VUV-UV synchrotron radiation shows down-shifting properties with strong emissions at 322 and 342 nm from the 5d1 to 2F5/2 and 2F7/2 levels of Ce3+ with a short decay time of ~16 ns, which is very suitable for scintillator applications. Moreover, these intense emissions are also observed when Gd3+ is excited since an energy transfer from Gd3+ to Ce3+ exists.

Optimization of the Synthesis and Physical Characterization of Praseodymium-Doped Type III KGd(PO3)4 Nanocrystals.

Scintillator materials are used as detectors in the ray imaging techniques for medical diagnosis. Because the ideal medical scintillator material does not exist, many efforts are being made to find new materials that satisfy a greater number of properties. Here, the synthesis conditions of Pr:KGd(PO3)4 nanocrystals by the modified Pechini method are optimized to obtain a single crystalline phase of those that form the polymorphism of KGd(PO3)4. The interest lies in the type III phase because less quenching by Pr3+ concentration is expected. By performing transmittance measurements and because of the wide transparency window of the type III KGd(PO3)4 host, the 3H4 → 5d1 absorption transition of Pr3+ has been observed in the vacuum ultraviolet spectral range. After creating electron-hole pairs in the host due to the excitation of the material by X-ray radiation, the bands corresponding to the 5d1 → 3H4, 3H5, 3H6 and 5d1 → 3F3, 3F4, 1G4 transitions of Pr3+ have been observed in the near-visible spectral range, being these 5d → 4f transitions interesting for scintillation applications. Therefore, the type III Pr:KGd(PO3)4 nanocrystals allow the conversion from high-energy radiation to visible or near-visible light.