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 KGd_0.942Pr_0.058(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 KGd_0.990Pr_0.010(PO₃)₄, by exciting these 5d levels, shows intense emissions centred at 256 and 265 nm from the 5d₁ to ³F_3,4 and ¹G₄ levels of Pr³⁺ with a short decay time of 6 ns. The ⁶P_3/2,5/2,7/2 → ⁸S_7/2 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⁺.