Method of enhancing performance of cerium doped lutetium orthosilicate crystals and crystals produced thereby

• US 20050253072A1
• Filed: 01/09/2004
• Published: 11/17/2005
• Est. Priority Date: 01/09/2004
• Status: Active Grant

• Current Assignee: Crystal Photonics Incorporated
• Original Assignee: Crystal Photonics Incorporated
• Inventors: Chai, Bruce
• Granted Patent: US 7,151,261 B2
• Time in Patent Office: Days
• US Class Current: 250/361.R
• CPC Class Codes: C04B 2235/3224 Rare earth oxide or oxide forming salts thereof, e.g. scandium oxide
• CPC Class Codes: C04B 2235/3427 Silicates other than clay, e.g. water glass
• CPC Class Codes: C04B 2235/76 Crystal structural characteristics, e.g. symmetry
• CPC Class Codes: C04B 2235/9646 Optical properties
• CPC Class Codes: C04B 35/16 based on silicates other than clay zircon C04B35/48
• CPC Class Codes: C09K 11/77742 Silicates
• CPC Class Codes: C30B 29/34 Silicates
• CPC Class Codes: C30B 31/06 by contacting with diffusion material in the gaseous state
• CPC Class Codes: C30B 33/02 Heat treatment C30B33/04, C30B33/06 take precedence

Abstract

A method for enhancing the light yield of a single crystal of cerium doped lutetium orthosilicate (LSO) in response to irradiation with high energy radiation includes diffusing oxygen into the crystal by heating the crystal for a period of time in an ambient containing oxygen. This process of thermal oxygenation of the crystal effectively supplies oxygen to fill at least some of the oxygen vacancies in the body of monocrystalline LSO. A scintillation detector comprises a monocrystalline body of LSO enhanced by oxygen diffusion into the crystal.

Claims

1. A method of enhancing performance of a body of monocrystalline cerium doped lutetium orthosilicate (LSO) in response to irradiation with high energy radiation, the method comprising:

diffusing oxygen into the body of monocrystalline LSO by heating the body for a period of time in an ambient containing oxygen.

2. The method of claim 1, wherein diffusing is carried out so that the body of monocrystalline LSO is fully oxygenated.

3. The method of claim 1, wherein diffusing is carried out so that the cerium is not further oxidized to a 4+ state.

4. The method of claim 1, wherein diffusing is carried out so that the body of monocrystalline LSO is not visually yellow in color.

5. The method of claim 1, further comprising forming the body of monocrystalline LSO to have at least one dimension no greater than about 20 mm.

6. The method of claim 5, wherein forming the body comprises forming the body to have a rod shape.

7. The method of claim 5, wherein forming the body comprises forming the body to have a rectangular shape.

8. The method of claim 1, wherein the oxygen containing ambient comprises air at atmospheric pressure.

9. The method of claim 1, wherein the oxygen containing ambient is at a pressure above atmospheric.

10. The method of claim 1, wherein the oxygen containing ambient has an oxygen concentration higher than in air.

11. The method of claim 1, wherein heating the body of monocrystalline LSO comprises heating the body to a temperature in a range of between about 1100°

to 1400°

C.

12. The method of claim 1, wherein heating the body of monocrystalline LSO comprises heating the body to a temperature of approximately 1400°

C.

13. The method of claim 1, wherein the period of time is in a range of about 30 to 120 hours.

14. The method of claim 1, wherein the period of time is approximately 30 hours.

15. The method of claim 1, wherein prior to being enhanced the LSO single crystal consists of Ce:

Lu₂SiO_5-Z where z ranges from approximately greater than 0 to less than 5.

16. The method of claim 1, wherein the diffusing results in increased performance based upon a light yield of the body of monocrystalline LSO.

17. The method of claim 1, wherein the diffusing results in increased performance based upon an improved energy resolution of the body of monocrystalline LSO.

18. The method of claim 1, wherein the diffusing results in increased performance based upon at least a 10% improvement in the energy resolution of the monocrystalline body.

19. A method of enhancing performance of a body of monocrystalline cerium doped lutetium orthosilicate (LSO) in response to irradiation with high energy radiation, the body of monocrystalline LSO having oxygen vacancies therein, the method comprising:

supplying oxygen to fill at least some of the oxygen vacancies in the body of monocrystalline LSO.

20. The method of claim 19, wherein supplying is carried out so that the body of monocrystalline LSO is fully oxygenated.

21. The method of claim 19, wherein supplying is carried out so that the cerium is not further oxidized to a 4+ state.

22. The method of claim 19, wherein supplying is carried out so that the body of monocrystalline LSO is not visually yellow in color.

23. The method of claim 19, further comprising forming the body of monocrystalline LSO to have at least one dimension no greater than about 20 mm.

24. The method of claim 19, wherein supplying comprises exposing the body of monocrystalline LSO to air at atmospheric pressure, and at an elevated temperature.

25. The method of claim 24, wherein supplying the elevated temperature is in a range of between about 1100°

to 1400°

C.

26. The method of claim 24, wherein the exposing is for period of time in a range of about 30 to 120 hours.

27. The method of claim 19, wherein prior to being enhanced the LSO single crystal consists of Ce:

Lu₂SiO_5-Z z ranges from greater than 0 to less than 5.0.

28. The method of claim 19, wherein the diffusing results in increased performance based upon at least one of a light yield of the body of monocrystalline LSO;

and an energy resolution of the body of monocrystalline LSO.

29. A scintillation detector comprising:

a monocrystalline body having the general formula of Ce;

Lu₂SiO_5-Z wherein z is approximately zero; and

said monocrystalline body also having a light yield of greater than approximately six times that of bismuth germanate (BGO).

30. The scintillation detector of claim 29, wherein said monocrystalline body also has an energy resolution which is at least approximately 10% improved over that of a monocrystalline body having the general formula Ce_2x(Lu_1-yY_y)_2(1-x)SiO_5-Z where x ranges from approximately 0.00001 to approximately 0.05, y ranges from approximately greater than zero to approximately less than 1.00, and wherein z is greater than zero.

31. The scintillation detector of claim 29, wherein said monocrystalline body has at least one dimension not greater than about 20 mm.

32. The scintillation detector of claim 29, wherein said monocrystalline body has a rod shape.

33. The scintillation detector of claim 29, wherein said monocrystalline body has a rectangular shape.

34. The scintillation detector of claim 29, further comprising a photon detector coupled to said monocrystalline body.

35. A scintillation detector comprising:

a monocrystalline body having the general formula of Ce;

Lu₂SiO_5-Z wherein z is approximately zero; and

wherein said monocrystalline body also has an energy resolution which is at least 10% improved over that of a monocrystalline body having the general formula Ce;

Lu₂SiO_5-Z where z is greater than zero.

36. The scintillation detector of claim 35, wherein said monocrystalline body has at least one dimension not greater than about 20 mm.

37. The scintillation detector of claim 35, wherein said monocrystalline body has a rod shape.

38. The scintillation detector of claim 35, wherein said monocrystalline body has a rectangular shape.

39. The scintillation detector of claim 35, further comprising a photon detector coupled to said monocrystalline body.