Czochralski Growth, Optical, Scintillation, and Defect Properties of Cu²⁺ Codoped Lu₂SiO₅:Ce³⁺ Single Crystals

Abstract

Divalent cation codoping, such as with Ca 2+ and Mg 2+ , is beneficial for the scintillation performance enhancement of Czochralski-grown Lu 2 SiO 5 :Ce (LSO:Ce) single crystals for nuclear medical imaging applications, but with that benefit comes a tendency toward acentric growth due to the reduced surface tension of the melt. Here, we present a divalent Cu codoping strategy to achieve a simultaneous improvement of light yield, energy resolution, scintillation decay, and afterglow in LSO:Ce single crystals without destabilizing the solid−liquid interface or promoting acentric growth. High-quality 32-mm-diameter and 110mm-long LSO:Ce single crystals codoped with 0.1 and 0.3 atom % Cu 2+ ions in the melt were successfully grown using the Czochralski method. While the surface tension of the LSO melt does decrease with Cu 2+ codoping, analogous to the effect of Ca 2+ codoping, it is not reduced enough to affect the crystal growth stability or diameter control. With 0.1 atom % Cu 2+ codoping, the scintillation light yield of LSO:Ce can be significantly enhanced from 32 000 to 39 000 photons/MeV with an improved enegy resolution of 9% at 662 keV, and a reduced afterglow at room temperature. A continuous shortening of scintillation decay time with Cu 2+ codoping is ascribed to the combined effect of enhanced thermal ionization from the Ce 3+ 5d 1 state and a reduction of the emission contribution from Ce2 centers, i.e., in the site neighboring six oxygens. Thermoluminescence and afterglow measurements are utilized to study the defect structure and explain the variation in scintillation yield.

The Effect of Be Co‐Doping on Luminescence Properties of Gd3Al3Ga2O12:Ce Glass Ceramics

“…The Ce 3+ PL decay time is shortening upon Li + or Cu 2+ co‐doping in the Y 3 Al 5 O 12 (YAG) or Lu 2 SiO 5 (LSO) hosts. [ 44–46 ] However, there, the shortening of the Ce 3+ decay time was accompanied by the increase in light yield (LY) and afterglow. The observed effects were explained by the dissociation of spatially correlated oxygen vacancies ( V O ) and Ce centers or the suppression of V O creation due to Li + co‐doping in LSO:Ce,Li.…”

Laser Floating Zone: General Overview Focusing on the Oxyorthosilicates Growth

“…However, it is important to highlight that these high refractory silicates were grown by the CZ method [1-5, 35-37, 39-41]. For example, Ryba-Romanovski et al [1] developed solid state yellow lasers based on (Lu x Gd 1-x ) 2 SiO 5 :Sm crystals by CZ, while Wu et al [41] have recently grown Cu co-doped Ce:Lu 2 SiO 5 crystals at 1.5 mm h −1 using a iridium crucible under nitrogen atmosphere for application as scintillators. Furthermore, other approaches for oxyorthosilicates production have been employed during the last years using different methods, like pulsed laser deposition [42], sol-gel [43] or solid-state diffusional process [44].…”

“…Lutetium oxyorthosilicate (Lu 2 SiO 5 , LSO) has attracted the attention of researchers due to their favorable thermal and optical properties, which make it suitable as host materials to be used in photonics as laser media [3][4][5][6] or scintillators [7,41,59]. The main technique for producing LSO crystals is usually the CZ method.…”

Enhancement of Scintillation Properties of LYSO:Ce Crystals by Al Codoping

“…As for LYSO:Ce, the typical approach is a partial substitution of the rare earth ions by divalent cations, such as Ca 2+ , Mg 2+ , , which can enhance the LY and shorten the decay time due to the decrease of deep-level traps associated with oxygen vacancies (V O ·· ) and the introduction of Ce 4+ ions . The presence of Ce 4+ bypasses the initial hole capture process of Ce 3+ emission and thus improves the excitation transfer efficiency. ,, It has been found that the codopants (Cu 2+ and Li + ) can reduce the decay time of Lu 2 SiO 5 :Ce crystals, which is due to the enhancement of the thermal ionization of the Ce 3+ 5d 1 state and the suppression of the slow emission of Ce2, which is sixfold coordinated by an oxygen atom. , It thus appears that codoping by the low-valent ion is a promising strategy to improve the scintillation performance of LYSO:Ce crystals.…”