Development of Yttrium Doped PWO Crystals for Physics Applications

1. Development of Yttrium Doped PWO Crystals for Physics Applications Qun Deng on Behalf of PWO Group Shanghai Institute of Ceramics Chinese Academy of Sciences

2. Outline • Segregation coefficient of the yttrium in PbWO4 crystal. • Performance of the yttrium doped PbWO4 crystals.a • The transmittance and the birefringence.b • Progress on stability. amost results published in NIM A480 (2002), 468 b http://www.hep.caltech/edu/~zhu/cms_020305.ppt

3. Crystal Growth Bridgman Technology

4. Typical Bridgman Furnace with 28 Crucibles.

5. Yttrium Distribution in Crystal • The segregation coefficient ke, defined as the ratio of the dopant concentration in the bulk crystal (Ccrystal) to that in the melt (Cmelt), describes the ability of the dopant to be incorporated into the solid phase, (1) • Assuming a slow, steady state growth process, the distribution of a dopant concentration in a crystal can be expressed as (2) g is defined as the ratio of the volume of solidification part of the ingot to the whole volume of the melt. • The solution of Equation 2 is (3) • Taking logarithm, Equation 3 can be written as a linear equation: (4)

6. Yttrium Distribution in Crystal(cont.) • The Glow Discharge Mass Spectroscopy (GDMS) was used to determine yttrium concentration in crystals. • A fit to the GDMS data extracts the yttrium segregation coefficient ke in PbWO4. Ke = 0.91  0.04

7. Performance of the yttrium doped PWO crystals • Longitudinal transmittance • Emission • Light output uniformity • Decay kinetics • Radiation damage • Color centers

8. Longitudinal Transmittance Grown along c axis Progress observed during crystal development

9. Longitudinal Transmittance at 360 nm

10. Emission 9 krad/h Excitation & Emission not affected by  ray radiation.

11. Light Output Uniformity Light response Uniformity is not affected by radiation

12. Decay Kinetics 90 and 95% of light output in 50 and 100 ns respectively

13. Radiation Damage Damage is dose rate dependent, reaching equilibrium under constant dose rate; 5 to 15% loss of light output at 15 rad/h

14. Radiation damage test at Protvino* Dose rate dependence also observed under hadron irradiation *BteV-int-2001/20

15. Summary of Light Output Measurements Sample LO (1/MeV) Fraction (%) LO (%) at R (rad/h) ID p.e.  50ns/1s 100ns/1s 15 100 500 1000 SIC-S301 9.4 63.5 92.0 96.6 96.6 87.3 79.5 74.3 SIC-S347 9.9 66.9 91.3 97.8 95.1 88.6 82.1 78.0 SIC-S392 8.4 56.8 92.0 97.3 98.2 91.3 83.6 80.2 SIC-S412 8.3 56.1 94.6 98.6 98.2 91.2 85.9 85.3 SIC-S643 8.9 60.1 88.8 98.9 88.3 79.8 --- --- SIC-S762 10.6 71.6 85.6 94.2 91.5 84.2 81.4 --- SIC-606 10.4 70.3 88.3 98.4 91.7 79.3 --- --- SIC-678 10.4 70.3 85.2 93.5 94.2 76.0 59.6 --- SIC-679 10.8 73.0 85.0 94.7 93.5 73.5 57.3 --- SIC-U685 11.4 81.4 91.3 97.9 90.4 --- --- --- SIC-U686 10.8 92.1 97.5 98.5 --- --- --- 77.1 SIC-U688 11.1 79.3 90.5 95.5 91.9 --- --- --- SIC-U689 10.4 74.3 92.6 96.3 95.5 --- --- --- SIC-U690 12.3 87.9 90.1 96.5 92.7 --- --- --- SIC-U691 10.8 77.1 91.8 97.7 94.7 --- --- --- SIC-U692 10.5 75.0 98.5 93.2 --- --- --- 92.0

16. Color Centers C1: 3.07 eV (400 nm) / 0.76 eV, C2: 2.30 eV (540 nm) / 0.19 eV

17. PWO crystal is anisotropic, its crystallographic axis a and b is equivalent, while axis c is different with a and b; PWO crystals grown along the c axis have lower theoretical limit in longitudinal transmittance; PWO crystals grown along the c axis are isotropic transversely. Transmittance and Birefringence Bridgman: grown along the c axis

18. PWO Crystals Grown along c Axis PWO crystals grown along the c axis are isotropic transversely

19. PWO Crystals Grown along c Axis(cont.) Good longitudinal uniformity in the transverse transmittance

20. Stability 35 rad/h 35 rad/h Crystals Produced in 1999

21. Impurities in Crystal

22. Results of K,Na doping Na: 20 ppm; K: 20 ppm

23. Stability (cont.) • Light yield increases under irradiation(instability) was observed, it can be explained by preexisting color centers in the crystal which were bleached by scintillation light; • Color centers result from shallow trap defects concentrated in later part of crystal; • SOLUTION: stoichiometric tuning and raw material purification.

24. Longitudinal Transmittance at 420 nm

25. Radiation Damage results of 2001

26. Summary • The concentration of yttrium ions in PbWO4 crystals is rather uniform, the segregation coefficient is 0.910.04. • The scintillation light of yttrium doped PbWO4 crystals has a broad distribution with a peak at 420 nm, the luminescence spectra and longitudinal light response uniformity are not affected by the  – ray irradiations. • Yttrium doping is effective in reducing slow scintillation component, the ratio between light outputs integrated in 100 and 1000 ns is about 95%. • The yttrium doped PbWO4 crystals have good radiation hardness.

27. Summary (cont.) • The radiation induced absorption in all yttrium doped samples can be decomposed to two common color centers peaked at 400 nm (3.07 eV) and 540 nm (2.30 eV) with widths of 0.76 eV and 0.19 eV respectively. • Because of the birefringence PWO crystals grown along the c axis are isotropic transversely. Also because of the birefringence PWO crystals grown along the c axis have lower theoretical limit in longitudinal transmittance, which is slightly more profound in the short wavelength region. • Crystal instability is essentially eliminatedby stoichiometric tuning and raw material purification.