Defect-Driven Radioluminescence Sensitization in Scintillators: The Case of Lu₂Si₂O₇:Pr

Abstract

A prompt transport of radiation induced free carriers toward luminescence centers is a key factor for an efficient conversion of high energy radiation into light in scintillator materials. However, the transport stage of the scintillation process can be hampered by the presence of lattice imperfections. In this study, we investigated the increase of radioluminescence (RL) efficiency after prolonged material irradiation. The general character of the phenomenon was revealed by its occurrence in several scintillator crystals like Lu2Si2O7:Pr, Bi3Ge4O12, Lu3Al5O12:Ce, and Lu0.3Y0.7AlO3:Ce. A detailed investigation was carried out for Lu2Si2O7:Pr. We demonstrated that the RL efficiency increase is due to the progressive filling of traps responsible for the thermoluminescence glow peaks at 460 and 515 K, which compete with Pr3+ centers in free carrier trapping during irradiation. Correspondingly, their emptying results in the recovery of the initial lowest RL efficiency. Spatial correlation between traps and Pr3+ ions was evidenced by the detection of an a-thermal tunneling afterglow between trap levels and 4f excited states of Pr3+. Such hysteresis phenomenon represents a memory of previous irradiations that remains stored in the crystal. It is a further effect caused by traps, which deserves attention like other manifestations of defects in scintillators like the reduction of light yield and the occurrence of slow tails in the scintillation time decay.

Infrared luminescence for real time ionizing radiation detection

“…Indeed, as for many other scintillation materials, [21][22][23][24] the RL sensitivity of the Yb-doped silica fiber was observed to increase as a consequence of a prolonged exposition to ionizing radiation.…”

“…[21][22][23][24] This competing process, being dependent on the concentration of empty traps with respect to that of the luminescent centers, becomes less relevant as traps are progressively populated during the irradiation, and it runs out once the competing traps are totally filled.…”

Optical properties and radiation hardness of Pr-doped sol-gel silica: Influence of fiber drawing process

“…In the field of scintillators, the increase of the light yield or RL signal in relation to irradiation history is known as hysteresis or "bright burn". At first, the phenomenon of carrier trapping by localized defects competes with the radiative recombination, but, as the fraction of occupied traps progressively increases, the recombination process becomes more probable [27]. The phenomenon can have both a temporary and a permanent character, depending on the temporal stability of the involved traps.…”

Структура и динамика решетки Lu-=SUB=-2-=/SUB=-Si-=SUB=-2-=/SUB=-O-=SUB=-7-=/SUB=-: ab initio расчет

“…Активированный ионами Ce 3+ лютециевый пиросиликат является мо-нокристаллическим сцинтиллятором с превосходными характеристиками [5]. В работе [6] [11]. В данной работе проведено ab initio исследование в рамках подхода молекулярных орбиталей, построенных как линейная комбинация атом-ных орбиталей (МО ЛКАО) и получены колебательные спектры комбинационного рассеяния света монокри-сталла пиросиликата лютеция для двух поляризаций xy и yy.…”