Scintillation characteristics such as the pulse height, energy resolution, and decay time of single crystals of Tl-doped NaI (Tl:NaI), Ce-doped Lu2SiO5 (Ce:LSO), Ce-doped YAlO3 (Ce:YAP), Ce-doped Gd3(Al,Ga)5O12 (Ce:GAGG), Pr-doped Lu3Al5O12 (Pr:LuAG), undoped LuAG, and Ce-doped Y3Al5O12 (Ce:YAG) transparent ceramics were compared at 25–150 °C to simulate well logging conditions. For increasing temperature, the light output of the scintillators decreased, mostly because of thermal quenching. Among these samples, Pr:LuAG demonstrated the highest scintillation performance at 150 °C.

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The paper deals with segregation of rare earth doping cations in solid-state hosts. Increased concentration of Ce3+ and Nd3+ on the grain boundaries of transparent garnet optical ceramics was recently reported. These experimental results correlate well with low segregation coefficients of Ce3+ and Nd3+ large rare earth cations and the higher segregation coefficients for small rare earth cations like Yb3+ in the garnet structure observed in the melt crystal growth and thin film liquid phase epitaxy from flux. Thus, the segregation in solid-state grain growth is qualitatively similar to that observed in the melt/flux growth of the garnet single crystals. The data on segregation in the melt/flux crystal growth are widely available and can be used for preliminary estimation of the dopant distribution in the ceramics produced from the solid state. This information could help to predict distribution of doping cations in the solid state hosts that is important in development of uniform and highly efficient optical materials.

The micro-pulling-down technique is a crystal growth method that has been mostly developed since 1992. The general scheme of the growth system is relatively simple: the melt (oxide, fluoride, metal) residing in a crucible is transported in downward through microcapillary channel(s) made in the bottom of the crucible. Two driving forces (capillary action and gravity) support the delivery of the melt to the liquid/solid growth interface formed under the crucible due to a properly established temperature gradient. Appropriate configuration of the crucible bottom allows for controlling of the crystal shape (fibers, rods, tubes, plates) and the dimensions of the crystals' cross sections that range approximately from 0.1 to 10 mm. A great number of scientifically and industrially important optical crystal fibers have been successfully produced using this method.

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Ce-doped lantanium-gadolinium pyrosilicate (La,Ce,Gd) 2 Si 2 O 7 (Ce:La-GPS), crystals with various content of rare-earth elements were produced from the melt, and their optimal La/Gd ratio was examined. It was found that Ce:La-GPS single crystals of acceptable optical quality can be produced from the melts ranging from La 0.5 Gd 1.5 Si 2 O 7 to La 1.0 Gd 1.0 Si 2 O 7 and containing about 1 atom % Ce with respect to the host rare-earths of La and Gd. The crystal growth was performed by the micro-pulling-down and Czochralski methods. The crystals were chemically uniform along the growth axis, and their composition was equal to that of the melt, thus corresponding to vicinity of congruent melting composition. Spatial distribution of Ce in La-GPS was also inspected, and no variation of Ce content was detected as a result of its similarity to one of the host cations (La) regarding the size. Basic optical and scintillation properties of the Ce:La-GPS crystals are also reported, and it is demonstrated that partial substitution of Gd with La has no negative impact on crystal growth and physical performance of the crystals.

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