Scintillation phenomenon in solids : History, principles, characteristics and

practical applications

Martin NiklInstitute of Physics, AS CR, Prague, Czech Republic

Internet search for the word “scintillator” provides

52,600 sitesusing Yahoo search engine …

…..but what is it good for ???

• Principle

• Something from their history

• Technology of preparation

• Underlying physics

• Parameters, characteristics and methods

• Applications

• An example of concerted research at aluminum garnets

• Suggested literature

Principle of a scintillator

10-12 10-10 10-8 10-6 10-4 0,01 1

wavelength [m]

infrared radio, TVmobile phones, etc.

visiblelight

VUV-UV

X-raysgamma

rays

1 photon n photons (keV - GeV) (2 - 4 eV)

scintillator Counting of HE photons!

Fast response needed !

Why we need it….above few keV there are no efficient direct-conversion detection elements (photon-to-electrical pulse)

Scintillation detector =scintillator+photodetector

⇒ registration of X-rays or γ-radiation, energetic particles or ions.

Scintillator TRANSFORMS high-energy photons into photons in UV/VIS spectral region, which one can easy and with high sensitivity register by the conventional detectors.

PD, APD, CMOS, CCD …Si, GaAs, GaN, InGaN, SiC, diamond

NaI:Tl

CsI:Tl

CdWO4

CsI

LiI:EuCaF

2 :Eu

1940 1960 1980 2000

CsI:Na

Bi4 Ge3 O

12

YAlO3 :Ce

BaF2 (fast)

Gd2 SiO

5 :CeCeF

3

PbWO4

Lu2 SiO

5 :Ce

LuAlO3 :Ce

Y3 Al5 O

12 :Ce

Lu3 Al5 O

12 :Ce

LaX3 :Ce(X=Cl,Br)

LuI3 :Ce

Lu3 Al5 O

12 :Pr

Year of introduction of a scintillation material

History of scintillatorsstarts short after the discovery of X-rays at the end of 19th century …

CaWO4

powder in 1896

Bulk single crystals

W.C. Roentgen, Science 3, 227 (1896)

chamber

carbon heater

carbon

Pt crucible

computercontrol

rotary pumpdiffusion pump 8inch-size BaF 2

Yoshikawa Lab, IMRAM, Tohoku university, Sendai, Japan

Czochralski technology

Czochralski grown YAlO 3:Ce, Lu3Al 5O12:Ce,

CRYTUR LtD. Turnov, CR

Czochralski grown PbWO4IP Prague, CR

Micro-pulling-down technology

After heater

Ir crucible

Seed crystal

Grown crystal

melt

<RF heating µµµµ-PD furnace>

Quartz tube

Ar

Alumina stage

Work coil

BaF2 crystal

φ1mm

φ3mm

Grown crystals

Yoshikawa Lab, IMRAM, Tohoku university, Sendai, Japan

Undoped YAP

Pr 0.1 mol%

Pr 0.5 mol%

Other solid state systems&technologies

LPE-grown single crystalline films,Y(Lu)AG:Ce,

Vapour deposited column-shaped CsI:Tl Diameter ~ 3

µm, length > 0.5 mm.

SrHfO3:Pb micro-crystalline phosphor

YAG-based optical ceramics

Ce-doped silica glass sol-gel technology(to make scint.fibers

Veronese Fr-1)

Physics of scintillators

CONVERSION TRANSPORT LUMINESCENCE

! Ecore<Eg

Conduction band

Eg

e

e

e e

h

h

h

h

traps

Valence band

Core band

HE

pho

ton

abso

rptio

n

CONVERSION -interaction of a high-energy photon with a material through photoeffect, Compton effect, pair production, appearance of electron-hole pairs and their thermalization

TRANSPORT - diffusion of electron-hole pairs (excitons) through the material, possible (repeated) trapping at defects, nonradiative recombination

LUMINESCENCE -trapping of charge carriers at the luminescence centre and their radiative recombination

Parameters, characteristics and methods

• Integral scintillation efficiency

• Photoelectron (Light) yield and Energy resolution

• Emission wavelength

• Speed of scintillation response

• Density (Zeff)

• Radiation resistance

• Chemical composition

• Price

Material with all the top parameters doesn’t exist so that there is always a search for tailored materials for particular applicationswhere only one or more parameters are recognized as the critical ones

Integral scintillation efficiency

0

5 104

1 105

1.5 105

2 105

2.5 105

3 105

300 400 500 600 700

Radioluminescence spectra (X-ray 35 kV, RT)

Bi4Ge

3O

12-standard

Gd2SiO

5:Ce

(Lu1.96

Y0.04

)SiO5:Ce

Inte

nsity

[arb

. uni

ts]

Wavelength [nm]

Absolute comparison of radioluminescence spectraof a material with the standard samplein the same experimental conditions

0

1 104

2 104

3 104

4 104

5 104

6 104

350 450 550 650 750

Radioluminescence spectra (X-ray 35 kV, RT)

BGO standard

PbWO4 no.178b

PbWO4 no.178f

Inte

nsity

[arb

. uni

ts]

Wavelength [nm]

Integral efficiency η=β.S.Q equals to multiplied sub-efficiencies of the conversion, transport and luminescence stages

Photoelectron (Light) yield

1

10

100

1000

0 500 1000 1500

Photoelectron yield of YAP:Ce

Excitation - 662keV photons (137Cs)

num

ber

of p

ulse

s/ch

anne

l

no. of channel

∆∆∆∆A

A0

energetic resolution = ∆∆∆∆A/A0

photopeak

Compton edge

Light yield measurement consists in the measurement of the charge collected at the photomultiplier anode within certain time gate(typ. 1 µs), i.e. U.I.∆∆∆∆t, after the absorption of high energy photon. Result of measurement is scaled within multichannel analyzer memory (pulse height analysismode) and repeated many times to get reasonable statistics and well-resolved photopeak (obtained only if complete absorption of HE photon can be obtained in the sample, i.e. sufficiently big sample is needed).

Energy resolution is defined from the FWHM of the photopeak. (typical values are 5-15% at 662 keV)

Photoelectron yield divided by quantum efficiency of photocathode providesLight yield - given in [photons/MeV]the best classical materials as NaI:Tl,CsI:Tlgive 40 000-50 000 phot/MeV , BGO gives 8 000 phot/MeV.

Photoelectron (light) yield nonproportionality

The non-proportionality of the Nphels(E) photoelectron yield of LuAG:Pr Cz-grown crystal normalized to Nphelsyield of 137Cs 662 keV energy line

See also Vasil’ev Mo-3, Moszynski Tu-13

Photoelectron yield value (per MeV) depends on the energy of the incoming HE photons !!

Conversion of high energy photon into many electron-hole pairs at the end of Conversion stage is many-step process with non-unique pathway. Elementary steps are differing in “production yield” of final e-h pairs, closely spaced excitations may interact, material defects make it even more complex, etc.

Emission wavelength versus photodetector spectral response

0

0.4

0.8

200 400 600

Radioluminescence spectra :CeF

3 (a), YAlO

3:Ce (b) Lu

3Al

5O

12 (c)

Inte

nsity

[arb

.uni

ts]

Wavelength [nm]

a b

ground statesplitting

of Ce3+

c

Position of the emission spectrum is important for the choice of the photodetector. In the case (a) PMT with quartz window (more expensive) is needed, (b) is an optimum position for a standard S20-photocathode PMT, (c) is better suited for a photodiode (or CCD) detector.

Today, however, there is tremendous development of UV-sensitive semiconductor photodetectorsbased on SiC, GaAlN and diamond!

Optical coupling between scintillator and photodetector

By far not all the UV/visible light generated in scintillator can be delivered to the photodetector due to self-absorption, internal reflection, scattering losses, etc.

1 µµmm

Si mold

Patternedpolymer

GaNdiode struct.

Photonic bandgap on the surface for better light extraction !!

Speed of scintillation response

1 photon n photons (keV - GeV) (1 - 6 eV) I(t) = ΣA iexp[-t/τi]

t

I(t)

t0 t0 t

I(t)

scintillator

Duration of the output light pulse is determined by the luminescence decay time of the emission centers, but also by the timing characteristics of the transportstage

Examples of scintillation decay

0.001

0.01

0.1

1

0 100 200 300 400 500 600 700

PL decay, exc = 335 nmScint.decay, exc = 511 keV

inte

nsity

[arb

.uni

ts]

time [ns]

decay times:60-70 ns

54 ns

LuAG:Ce0.12%

IS

Itot

alpha = IS/I

tot x 100%

600-900 ns

time

excitation

emission

50µs

“Background increase” due to slow decay components in scint. decay

10

100

1000

0 200 400 600 800

LYSO:Ce Photonics

Inte

nsity

[arb

. uni

ts]

time [ns]

decay time:45 ns

In Ce-doped scintillators the shallow electron trapsare responsible for s lower scint i l lat ion components

Trapping-detrapping Processes

Ionizing radiation

(X, γ…)

Valence band

Conduction band

Lground

hνRadioluminescence

A – direct process

T

B – delayed process

ET

e

h

Lexc

Studied by TSL and TSC experiments (lectures in next days)

Radiation damage (resistance)

0,2

0,6

1

1,4

0

0,4

0,8

1,2

300 400 500 600 700

Absorption spectra of YAP:Ce

abso

rban

ce

lumin. intensity

wavelength (nm)

absorption spectrabefore (A

0) and

after (Airr

) X-ray irradiation

(dose 500 Gy)

luminescence spectrum

Induced absorption is caused by the relocation of charge carriers into the deep traps(can be monitored by TSL measurement above RT). Occupied deep traps introduce the additional=induced absorption bands (color centers).

In the case of YAP:Ce such traps can be partly suppressed by tetravalent Zr4+ ion doping.

0

0,4

0,8

1,5 2 2,5 3 3,5 4

Induced absorption spectrum µ(λ)YAP:Ce, D=500 Gy, RT

ia (cm-1)

G1 ia (cm-1)

G2 ia (cm-1)

G3 ia (cm-1)

G1+G2+G3

ia (

cm-1

)

E (eV)

µ(λ) = 2.3×(1/l )×(A irr (λ) - A0 (λ))

Lu2SiO5:

Ce

Bi4Ge3O12Lu3Al5O12:Ce

YAlO3:

Ce

PbWO4LaBr3:CeCsI:TlChem.Compos.

7.417.136.67 5.368.235.084.51Density

g/cm3

40/--/30055-65/

500-103

20-38/

100-104

2+10/

100-104

16/

--

--/1000Decay tm

[ns]

Fast/slow

2.7-3.2x104

8x1031.5-1.9x104

~2x1041-3x1026.3x1044-5x104LY

Pho/MeV

Fast/slow

420490530-580360-380410/500380400/565Emission

Max.[nm]

Fast/slow

Parameters of selected scintillation materials

High energy physics

Particle physics, Particle physics, ……

X&Neutron-based

Remote detectionRemote detection

Medical application

PET, SPECT, CTPET, SPECT, CT

Security check

XX--ray scanningray scanning

Other applications

Radon detection, geologyRadon detection, geologyComputed tomographyComputed tomography

Nondestructive analysis

Applications of Applications of scintillatorsscintillators

Checking point

Detector ring (inner diam. ~ 0.8 m)

PositronEmissionTomography

Collinearly emitted annihilation quanta detected in coincidence

DetectorsBGO + PM

Radiation in Medicine Diagnostics Radioisotope imaging

Radiopharmaceutical

Coming Lu(Gd)2SiO5:Ce TOF, DOI modifications under development

http://www.epub.org.br/cm/n01/pet/pet_hist.htm

PET systemsSiemens-CTI

Simultaneous PET and MR imaging

1D positionsensitivedetector(rotating)

X-rayComputedTomography

3rd generation

X-ray fan beam (rotating)

X-ray source(rotating)

Centre of rotation

Radiation in Medicine Diagnostics

+

Typical X-irradiation dose in a CT scan is 20x higher than that of simple lung check ….should be used with caution!

CT – „whole body“ spiral scan

my knees

Security check … by far not only luggages!

�About 200 millions of containers travel every year, and only about 1 to 2 % of them are directly controlled !!!

�Check for drugs, explosives, radioactive material at seaports and airports HOMELAND SECURITY!!!

� multiple irradiation sources(X-ray, neutrons)

� sensitive not only to material density, but also to its elemental composition (explosives)

� on-line evaluation of moving goods

� mobile stations with short installation times

� easy to handle and use

Remote detectionRemote detection

Checking point

irradiation source detector

•high light yield and mechanically/chemically stable scintillator for X-ray detection

•tuned-composition (Li-B-Gd containing) material for neutron detection

Compact Muon Solenoid detector in Large Hadron Collider in CERN, Geneva

PbWO4-based calorimetric detector

search for Higg’sboson ……

about 80,000 single crystal blocksof about 3x3x22 cm (12 m3 ) produced in Russia and China, LHC launch expected 10/2009!

High resolution 2D-imaging experiment under X-ray (accelerated electrons)

X - Ray (Lu)YAG:Ce CCDX - Ray (Lu)YAG:Ce CCD

thin YAG:Ceplate

thin optical glue

glass support

Sub-µm resolution needed!

Better 2D-resolution requires thinner scintillator layer !

optics

Made by CRYTUR Ltd, CR

Scintillator screens, experimental set-up

LPE-grown LuAG:Ce-on-YAG films and single crystal plate on substrate

Experimental set-up for 2D imaging

Whole LPE film on one side and 5 µm on the other side were polished away

X-ray source

X-ray cameraobject

7067616210092

0.50.50.50.533

172915272020

LuAG:CeLuAG:CeLu0.8Y0.2AG:CeLu0.6Y0.4AG:CeLuAG:CeLuAG:Ce

LPE SCFLPE SCFLPE SCFLPE SCFBulk CzBulk Cz

Lu-6Lu-9Lu-11Lu-16Cz-2Cz-3

Scintil. eff[%]

Substrate [mm]

Film/plate[µµµµm]

Film/plate material

Sample type

Sample name

Overview of the scintillator screens used

2D imaging capability of LPE films and SC plates

SEM image of 8 µµµµm thick wire grid

The grid image obtained by Lu-6 sample screen (upper left) with the detail of wire crossing (lower left) and the same picture obtained by Cz-3 sample screen (right)

Some more images by SC LuAG:Ce plate sensor

A circuit fromcalculator

A tick

Aluminum structure

Coaxial cablewith BNC connector

Strategy for scintillator materials researchCorrelation of several techniques at specifically prepared sample set under well-defined technological conditions:

�Time-resolved emission spectroscopy– to interconnect the luminescence (scintillation) kinetics with the occurrence or non of the defects visualized by the above techniques

�Specific experiments for determination of scintillation characteristics (Phel. yield, scintillation decay, radiation damage)

�Thermoluminescence– to visualize trapping states, which take part in the radiative processes, spectra can advise on recombination sites

�Thermally stimulated currents– to visualize complementary nonradiative processes

�Electron paramagnetic (spin) resonance– to understand location of unpaired-spin-containing trapping centers

Integral eff. & LY in Ce3+-doped Y3Al5O12 and Lu3Al5O12

0

5 104

1 105

1.5 105

2 105

2.5 105

3 105

3.5 105

4 105

200 400 600

YAG:Ce0.32%LuAG:Ce0.12%BGO x5

Inte

nsity

(ar

bitr

ary

units

)

Wavelength (nm)

x5

X-ray excitedluminescence Light yield (1 µs time gate)

Best YAG:Ce∼ 3x BGO

Best LuAG:Ce∼ 60% of YAG:Ce

A lot of “slow light”in these materials

Retrapping of electrons at shallow traps before their radiative recombination at Ce3+ ionsNikl et al, pss (a) 201, R41 (2004)

10

100

1000

600 1000 1400 1800

inte

nsi

ty [

arb

.un

its]

time [ns]

LuAG:CeScintillation decay pulsed x-ray, em = 500 nm

58 ns (30%)

150 ns + 600 ns (70%)

Ce-doped YAG and LuAG

0

1 106

2 106

3 106

4 106

5 106

6 106

7 106

8 106

50 100 150 200 250 300

TS

L in

tens

ity (

arb.

uni

ts)

temperature (K)

LuAG:Ce0.12%TSL after X-rayirr. at 10 K

YAG:Ce0.32%

0.001

0.01

0.1

1

100 200 300 400 500 600 700

PL decay, exc = 335 nmScint.decay, exc = 511 keV

inte

nsity

[arb

.uni

ts]

time [ns]

decay times:60-70 ns

54 ns

LuAG:Ce0.12%

levels of YAG:Ce0.32%

A number of the electron traps indicated by TSL glow curve below RT delays electron delivery to Ce4+ and slows down the scintillation response

time

excitation

emission

50µs

“Background increase” due to slow decay components in scint. decay

Antisite defects in YAG and LuAG single crystals

Exchange of Y(Lu) and Al ions is an inevitable consequence of the growth from high temperature melt

CB

VB

Electrontrap

0

0.6

1.2

1.5 2 2.5 3 3.5 4TS

L no

rm. i

nten

sity

Energy (eV)

T=92 K

Comparison of YAG:Cesingle crystal and optical ceramics

0.0 100

1.0 107

2.0 107

50 100 150 200 250 300

single crystal

ceramics

TS

L in

ten

sity

(a

rb.

un

its)

Temperature (K)

TSL peak at 92 K is the dominant feature in all YAG:Ce single crystals studied

Sintering temperature of ceramics is about 1700 0C applied for several hours, while SC growths from the melt close to 1970 0C

Concentration of YAl antisitedefects strongly decreases with preparation temperature(absent in LPE-grown layers – Zorenko et al, Funct. Mater. 9, (2002) 291 )

TSL glow curve X-ray irr. at 10 K

TSL spectra

∆E = 0.18 eV

Mihokova et al, J.Lumin.2006

TSL peak at 92 K is due to liberation of electron from the antisite YAl

defect trap and recombination with Ce4+ hole center.

Ce3+ 1µµµµm

Electron traps related to the antisite LuAl

defects in LuAG:Ce

102

104

106

50 150 250

SC-1820SC-1700LPE-9300LPE-18000

TS

L in

tens

ity (

arb.

uni

ts)

Temperature (K)

TSL glow curves Triple peak structure at 142 K, 167 K and 190 K is always dominant in single crystals,

while it is completely absent in Liquid Phase Epitaxy-grown layers.

TSL spectra within these peaks contain only Ce3+ emission

Liberation of electrons from the antisite-defect-related trap and their recombination with Ce4+ is proposed to explain TSL characteristics in this temperature region

Nikl et al, phys.stat.sol. (b) 242, R119 (2005)

∆E =0.29 eV0.40 eV0.47 eV

As the energy depth of AD-related trap is higher with respect to YAG:Ce, it explains more detrimental influence on scintillation decay and LY characteristics!!

Antisite defects in Al garnetsHigh-resolution spectroscopy of the Nd3+

satellite emission lines in YAG:NdLupei et al., Phys. Rev. B 51, 8 (1995)

XRD from an increase of lattice constant in YGG:Yb single crystal and ceramicsShirinyan et al, NIM A 537 (2005)

Newly by EPR evidenced Ce3+Al and

Ce3+ perturbed by LuAl centers!

Laguta et al, LUMDETR 2006, Lviv

200 300 400 500 600 700 800

B (mT)

Ce3+ in bulk LuAGB II [110], T=20 K

Ce3+⇒ Lu3+

Ce1Ce2 Ce3

Ce3+ at Lu site perturbed by the LuAl antisite defect ⇒ Ce and LuAl

defect might be spatially correlated!!

Ce2, Ce3 belong to the Ce3+ at Al sites

TSL dependence on the Ce concentration in LuAG:Ce – region 1 and 2

0

1

50 150 250

0.12w%Ce0.07w%Ce0.03w%Ceundoped

TS

L in

tens

ity (

arb.

uni

ts)

Temperature (K)

undopedx 20

TSL glow curves

Diminishing of “undoped-related”TSL features within 50-80 K with increasing Ce concentration

Competition between TSL signals within 50-120 K and 120-200 K !

After X-ray irradiation at any T ∈ (10-100) K phosphorescence decay doesn’t depend on temperature and follows t-1 law

Tunneling processbetween the trapped electron and hole counterparts (spatially correlated)

104

106

108

1010

1012

1014

1016

10 100 1000 10000Pho

spho

resc

ence

inte

nsity

(ar

b. u

nits

)

Time (s)

100 K

90 K

80 K

70 K60 K

50 K40 K30 K

20 K10 K

I(t) ∼∼∼∼ t -p

1.00

0.99

1.021.031.091.13

1.071.09

1.17

1.11p =

Scintillation decay of LuAG:Ce at RT

100

1000

0.12w%Ce power-exp fit I(t)

Inte

nsity

[arb

.uni

ts]

I(t) = 0.175exp[-t/56.4ns]+

+ 1.7/(60+0.24ns*t)-0.998+43

-3

-2

-1

0

1

2

10 100 1000

power+exp. fit2-exp. fit

wei

ghte

d re

sidu

als

R(t

)

time [ns]

0

2

4

6

0 0.04 0.08 0.12

coef

ficie

nt a

lph

a

concentration Ce [w%]

The exponential and power function components account for the first and second stage of the scintillation decay, respectively.

Consideration of tunneling-driven recombination provides a physical ground for the slower scintillation decay component in LuAG:Ce, which can’t be explained by thermal detrapping and recombination via conduction band as calculated detrapping times are too long.

Instead, coefficient alpha and amplitude of the 140 K TSL peak seem to be correlatedand related to the time development of recombination processes at similar time scales

Radiative recombination process in LuAG:Ce (Pr)

CB

VB

Ce3+

(Pr3+)

At RT τ > 30 µs

~ t-1

AD-related electron

trap

Above 50 K there is possibly already

thermally assisted tunnelling process

(slight T dependence of p)

hν

Admixture of Ga to suppress AD-related trapping phenomena in LuAG:Pr (Ce)

0

1 105

2 105

3 105

4 105

5 105

6 105

7 105

200 300 400 500 600

Radioluminescence spectra LuAG:Pr (0.25%)

85 K

295 K

Inte

nsity

[arb

. uni

ts]

Wavelength [nm]

host

Pr3+

0

2 104

4 104

6 104

8 104

1 105

200 300 400 500 600 700

RT-193C

Inte

nsity

[pho

t/s]

Wavelength [nm]

Lu3(Ga

0.05Al

0.95)5O

12:Pr

0 100

2 106

4 106

6 106

50 150 250

TSL glow curves, x-irradiation at 10 K

x = 0

x = 0.1

x = 0.2

x = 0.4

TS

L in

tens

ity

Temperature [K]

Lu3(Ga

xAl

1-x)5O

12:Pr3+

0.01

0.1

1

0 200 400 600

Lu3Al

5O

12:Pr 1%

Lu3(Ga

0.4Al

0.6)5O

12:Pr1%

2-exp. fit I(t)

inte

nsity

[arb

.uni

ts]

time [ns]

I(t) = 0.58exp[-t/10.4ns ]+0.96exp[-t/21.3ns ]+0.013

Scintillation decay at RT, 22Na

Nikl et al, Appl.Phys. Letters 88, 141916 (2006)

Energy transfer and storage in LuAG:Ce(Pr) SC

�Electron traps associated with LuAl antisite defectswere evidenced in LuAG host. TSL triple peak at 142 K, 167 K and 190 K (region 2) is due to electron libration from LuAl trap and its recombination with the Ce4+ (Pr4+) hole center. In YAG host an analogous situation holds for 92 K TSL peak.

�EPR evidences a possibility of spatial correlation of Ce3+ and LuAl defect, which is reflected in the existence of tunneling process observed in TSLglow curves (region 1) supported by the t-1 course of low temperature phosphorescence decay.

�TSL process thus indicates the existence of both thermally activated “above-the-gap” (region 2) and “sub-gap tunneling” (region 1) recombination processesbetween an AD-trapped electron and Ce4+ (Pr4+) hole center, where the latter process is responsible for the observed slower component in the scintillation decay.

� Ga-admixture considerably diminished the AD-trap related phenomena: host luminescence suppressed, TSL peaks washed out, scintillation decay accelerated. However, it seems that LuAl defects could be “burried” in the lowered bottom of CB rather than simply suppressed due to the Ga occupation of the Al octahedral site. Somewhat lowered LY and form of the Pr3+ excitation spectra within 170-200 nm might indicate an additional nonradiative loss channel induced by the Ga doping.

Perspectives�Sources of energetic radiation and particles are more and more used in different fields of human activity ⇒ increasing need fortailoredscintillation materials

�Difficult to “invent” competitive completely new materials as in some parameters we are close to intrinsic limits, but new technologies (ceramics) can bring unexpected solutions

�Lack of the detailed understanding the physical mechanisms in existing materials ⇒ room for their optimization(recent example of PbWO4)

�Driving forces for scintillator development will come from medical and high-tech industrial applications, homeland security, space technology

Suggested literature• G. F. Knoll: Radiation Detection and Measurement (Wiley, New York 2000)• G. Blasse, B. C. Grabmaier: Luminescent Materials (Springer, Berlin 1994)• P. A. Rodnyi: Physical Processes in Inorganic Scintillators (CRC Press, Boca

Raton 1997)• L. H. Brixner: New X-ray phosphors, Mater. Chem. Phys. 16, 253-281 (1987)• M. Ishii, M. Kobayashi: Single crystals for radiation detectors, Prog. Cryst.

Growth Charact. Mater. 23, 245-311 (1992)• C. W. E. van Eijk: Inorganic-scintillator development, Nucl. Instrum. Methods

Phys. Res. A 460, 1-14 (2001)• M. J. Weber: Inorganic scintillators: today and tomorrow, J. Lumin. 100, 35-45

(2002)• M. Nikl: Scintillation detectors for x-rays, Meas. Sci. Technol. 17, R37-R54

(2006)• D. J. Robbins: On predicting the maximum efficiency of phosphor systems

excited by ionizing-radiation, J. Electrochem. Soc. 127, 2694-2702 (1980)• A. Lempicki, A. J. Wojtowicz, E. Berman: Fundamental limits of scintillator

performance, Nucl. Instrum. Methods Phys. Res. A 333, 304-311 (1993)• P. A. Rodnyi, P. Dorenbos, C. W. E. van Eijk: Energy loss in inorganic

scintillators, Phys. Stat. Sol. B 187, 15-29 (1995)• M. Nikl, V.V. Laguta and A. Vedda, Complex oxide scintillators: Material

defects and scintillation performance. Phys. Stat. sol. (b) 245, 1701-1722 (2008). • G. Bizarri et al, An analytical model of nonproportional scintillator light yield in

terms of recombination rates. J.Appl. Phys. 105, 044507 (2009)