Effect of Electron Traps on Scintillation of Praseodymium Activated Lu$_3$Al$_5$O$_{12}$

Abstract

Abstract-In this paper we present the studies performed on a set of Lu 3 Al 5 O 12 :Pr (LuAG:Pr) crystals with praseodymium concentration between 1.5 and 10%, grown by the micro-pulling-down ( PD) technique. The research comprises the measurements of X-ray excited emission spectra and 137 Cs gamma-ray pulse height spectra in a range from 78 to 600 K, and thermoluminescence glow curves. Based on experimental data we discuss the dependence of scintillation properties of Lu 3 Al 5 O 12 :Pr on praseodymium content and temperature. The main attention is focused on a distinct increase of scintillation yield with temperature, which we attribute to existence of shallow electron traps and their temperature-dependent contribution to scintillation of LuAG:Pr. An active role of traps is demonstrated by a novel experiment combining X-ray and laser excitation.

33000 photons per MeV from mixed (Lu_075Y_025)_3Al_5O_12:Pr scintillator crystals

“…This feature, reflected by a characteristic Y = Y (T) curve presented in Fig. 2 (Y -yield, T -temperature), was soon attributed to the existence of shallow electron traps and their contribution to the energy transfer from the LuAG host to the Pr 3+ ions, resulting in the temperature-dependent yield deterioration [14]. It became clear that if only the aforesaid curve could be shifted to the left by about 100-150 K, the RT scintillation yield of LuAG:Pr would be increased to the maximum value available for this material.…”

Non-resonant X-ray/laser interaction spectroscopy as a method for assessing charge competition, trapping and luminescence efficiency in wide band-gap materials

“…Lu 3 Al 5 O 12 has a bandgap energy of $ 7 eV [12] and was first investigated as a potential scintillator material with excellent characteristics when doped with Pr, by Nikl et al [13]. The Pr defects are introduced in their 3+ charge state, emitting fast luminescence in the range 300-400 nm via the characteristic Pr 3 + 4f5d-4f 2 transition [14]. The NaAlSi 3 O 8 used was a natural specimen, with a measured bandgap energy of 7.7 eV [15].…”

Scintillation properties of μPD-grown Y4Al2O9:Pr (YAM:Pr) crystals

“…A prominent scintillation yield of as much as 33,000 ph/MeV has been observed for (Lu 0.75 Y 0.25 ) 3 Al 5 O 12 :Pr [6], whereas a further increase of the content of yttrium against lutetium results in a decreasing yield, returning for Y 3 Al 5 O 12 :Pr (YAG:Pr) to the level known for LuAG:Pr [6,7]. Note the light output of RE 3 Al 5 O 12 :Pr crystals is very sensitive to the content of praseodymium: for LuAG:Pr the maximum yield is reached at a real concentration of Pr 3+ ions between 0.2% and 0.3% [1,8], whilst for YAG:Pr an optimal concentration appears to be even an order of magnitude lower [9].…”