LuAG:Ce Single Crystal Films For High
2D-resolution Scintillation Detectors
J. Touš, K. Blažek, Crytur Ltd. Turnov, Czech Republic
M. Nikl, N. Solovieva, J.A. Mares, Institute of Physics ASCR, Prague, Czech Republic
Yu. Zorenko, V. Gorbenko, I.F. University, Lviv, Ukraine

Abstract
Apart from the bulk scintillator segments used in different geometries in applications in high energy physics, medical or otherapplications, there is also a need for thin (several or tens of micrometers) and large area (up to 50 mm) single crystal plates orfilms to be used with position sensitive photodetectors (CCD), which can enable imaging of tiny objects in the X-ray (electron)
beam down to micrometer scale.
Lu-based compounds are under intense research as they often reach high density together with an excellent scintillation figureof-merit. LuAG:Ce (Lu3Al5O12:Ce) has recently been reported to be a highly efficient scintillator material, the scintillation efficiencyof which can reach up to 700% of BGO under X-ray excitation, while its light yield is lowered down to less then 200% of BGO due todelayed recombination phenomena.
In this contribution, the imaging ability of LuAG:Ce (Lu3Al5O12:Ce) films grown by Liquid Phase Epitaxy (LPE) is demonstrated andcompared with a thin plate of the same thickness made from bulk LuAG:Ce crystal. The integral scintillation efficiency, quality ofimage and 2D-resolution achievable in such scintillation detectors will be discussed .

Experiment
LPE-grown LuAG:Ce films grown from a PbO-B2O3 melt-solution are compared to a thin plate made from bulk LuAG:Ce crystal
grown by the Czochralski method using a molybdenum crucible under a reductive atmosphere. The LPE samples were lightly
polished down to 20 micrometers thickness. The bulk crystal thin plate was about the same thickness and was glued onto aglass substrate.

Experimental setup

Optical Quality Inspection
Bulk plate! The optical quality was inspected by an optical microscope.
LPE grown film samples! The integral scintillation efficiency was measured by a high-sensitive digital
CCD camera using an X-ray beam (Cu-anticathode, 40kV/2mA).
! The 2D resolution was inspected using the same X-ray beam and an imaging technique. A very small object with defined
dimensions was placed between the X-ray source and imaging screen (LPE film or bulk plate) and the absorption image
was taken by the CCD camera. The X-ray source had an anode spot of several micrometers to avoid the smear effect.

Results and Discussion

LPE films

Integral Scintillation
Efficiency

The imaging plate made from bulk single crystal was optically clean.
The LPE film samples had optical defects. The shining spots in some parts of the film are structural irregularities(incrustations, bubbles of melt/solution, etc.), which cause light scattering.

Images of samples exposed to X-ray
bulk plate (left), LPE sample (right)

Experimental setup

The samples were exposed to X-rays from a Bede micro-source (40kV/2mA). The
images were taken by the Crytur High-res X-ray CCD camera. The exposure time
was 500 ms and the image was averaged 25 times.

2D Resolution Capability
A golden grid with wires eight micrometers thick (see the SEM image below) was imaged using an X-ray sourcewith a Cu anticathode. The grid was place close to the imaging screen. The absorption image was detected by a
Crytur X-ray Hi-res CCD camera. The exposure time was five seconds.

The image of the grid taken byusing the bulk LuAG screen

SEM image of the gridThin LuAG:Ce plate

The intensity in a particular part of the scintillation
light-emitting area of every sample was averaged.
Relative values of the intensity are in the table. TheLPE films reach up to 76% of the best bulk sample.

The image of the grid taken byusing the LPE screen

SampletypeBulk 1
Bulk 2
Bulk 3
LPE 1
LPE 2
LPE 3
LPE 4
LPE 5LPE 6
LPE 7

RelativeIntensity
100%
93%90%
76%62%
70%
52%
50%
42%
42%

The line profiles of a grid wire
(LPE and bulk screens)

Both types of screens provide similar resolution. The image taken by the bulk screen has better contrast due to the higher
intensity of the light emitted (better s/n ratio). The line profile of a grid wire shows the resolution of the imaging system used.

Details of the grids(left-bulk, right LPE)

Conclusions
Optical Quality
The LuAG:Ce LPE films were compared toLuAG:Ce bulk plates. The optical quality of LPE
films needs improvement for applications inhigh resolution imaging.

Crytur Ltd., Palackého 175,511 01, Turnov
Czech Republic

Phone: +420 481 319 511
FAX: +420 481 322 323
E-mail: crytur@crytur.cz
http://www.crytur.com

Integral Scintillation Efficiency
The intensity of the LPE films(detected by the CCD camera) is up to
76% of the intensity of the bulk plate.

High Resolution in Imaging
The resolution of the LPE films is comparable to
the resolution achieved by bulk plates. Theresolution achieved by the 20 micrometers thick
LuAG:Ce imaging plate is about 1 micrometer.

Acknowledgement
This research has been supported by Czech Ministryof Industry and Trade Project No.: FT-TA/100