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

Abstract

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.

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

“…The sizes obtained were a* × b × c* = 7.6-13.6 mm × 17.1-24.1 mm × 10.7-13.6 mm and the weights ranged from 2.7 to 6.9 g. As can be seen in Table 1, the crystal dimension in b direction was always higher than in a* and c* directions. This faster growth in the b crystallographic direction has already been reported by us for different doping KGd(PO 3 ) 4 crystals [16][17][18] and is in agreement with the non-presence of the (010) crystalline face. The growth rate of the {hkl} form is inversely proportional to interplanar spacing d hkl and the sequence in this crystal is d 001 > d 100 > d 020 .…”

“…The saturation temperature of all solutions was around 993 K and no significant changes were observed with Pr 3+ doping at the levels studied in this work. The saturation temperature is slightly higher than that previously reported for the crystal growth of Ce:KGd(PO 3 ) 4 crystals 18 grown in similar experimental conditions. The crystals obtained were generally transparent, free of inclusions and cracks, and slightly greenish due to Pr 3+ doping.…”

“…In this work, the value of the 3 H 4 → 5d 1 transition of Pr 3+ in phosphate hosts varies from 212 nm for LaP 3 O 9 30 , through 222 nm for YPO 4 30,31 , to 224 nm for YP 3 O 9 30 . In addition, since the average energy difference of the first spin-allowed 4 f → 5d transition of Pr 3+ ( 3 H 4 → 5d 1 ) with respect to the transition of Ce 3+ ( 2 F 5/2 → 5d 1 ) in the same host 29 is 12240 ± 750 cm −1 and because the 2 F 5/2 → 5d 1 transition of Ce 3+ in KGd(PO 3 ) 4 is centred at 302.5 nm (33058 cm −1 , 4.10 eV) 18 , the expected position of the 3 H 4 → 5d 1 transition of Pr 3+ in KGd(PO 3 ) 4 is in the range 217.2-224.5 nm (46048-44548 cm −1 , 5.71-5.52 eV). Therefore the experimental position of the 3 H 4 → 5d 1 transition of Pr 3+ in KGd(PO 3 ) 4 (218 nm) is consistent with the values found in other phosphates and within the calculated range.…”

“…Given the calculations explained in our previous work on type III Ce:KGd(PO 3 ) 4 single crystals 18 , the energy of the exciton creation (E ex ) and the approximate energy difference from the bottom of the conduction band to the top of the valence band (E VC ) of the type III KGd(PO 3 ) 4 host were predicted at 7.57 eV (164 nm) and at 8.17 eV (152 nm), respectively. Therefore, as already mentioned in the previous work, the E ex band could appear in the excitation spectra ( Fig.…”

“…Considering the literature mentioned above, the 5d → 4 f transitions of Pr 3+ in KGd(PO 3 ) 4 host is expected to have decay times faster than Ce 3+ in the same host. Ce 3+ -doped KGd(PO 3 ) 4 single crystals have already been studied and show interesting luminescence characteristics for scintillator applications 18 . The aim of this paper is therefore to grow Pr:KGd(PO 3 ) 4 single crystals from high temperature solutions with different Pr 3+ concentrations in order to characterize their thermal stability, study their optical absorption and luminescence properties under UV-VUV synchrotron excitation, and discuss their usefulness as a new scintillator material.…”