Method for purifying an inorganic material using a tube having a bend between a first end and a second end of the tube

1. A method for purifying an inorganic material, the method comprising:

loading a starting inorganic material comprising one or more impurity elements into a tube having a first end, a second end, and a body connecting the first end and the second end, wherein the body of the tube forms a bend between the first end of the tube and the second end of the tube;

evacuating the tube to reduce a pressure in the tube;

sealing the evacuated tube to form a sealed, evacuated tube that is sealed at the first end and the second end;

mounting the sealed, evacuated tube in a furnace having a first temperature zone and a second temperature zone, wherein the sealed, evacuated tube is mounted with its first end in the first temperature zone, its second end in the second temperature zone, and its bend directed upward, such that the bend is elevated above the first end of the tube, the second end of the tube and the first and second ends of the tube are directed downward, and a top of the bend is at a highest part of the tube;

increasing the temperature in the first temperature zone to a temperature that is sufficiently high to melt and volatilize the starting inorganic material in the first end of the tube, while maintaining the temperature in the second temperature zone at a temperature lower than the temperature in the first temperature zone, wherein the volatilized inorganic material condenses on a wall of the body of the tube in the second temperature zone and flows down to the second end of the tube under the force of gravity; and

solidifying the condensed inorganic material that collects in the second end of the tube to provide a purified inorganic material having a lower impurity concentration than the inorganic starting material.

2. The method of claim 1 , wherein the concentration of one or more of the impurity elements in the purified inorganic material is at least a factor of 10 less than the concentration of those impurity elements in the starting inorganic material.

3. The method of claim 1 , wherein the impurity concentration in the purified inorganic material is no greater than 1 ppm, atomic basis.

4. The method of claim 1 , wherein the starting inorganic material is a thallium compound.

5. The method of claim 4 , wherein the thallium compound is TlI, Tl 2 Se, Tl 2 S, or a combination of two or more thereof.

6. The method of claim 1 , wherein the starting inorganic material is elemental S, Se, or Cd.

7. The method of claim 1 , wherein the inorganic material is a thallium chalcohalide.

8. The method of claim 7 , wherein the one or more impurity elements include Al, Pb, Bi, Si, or a combination of two or more thereof.

9. The method of claim 1 , wherein the mounted, sealed, evacuated tube forms an inverted v-shape extending from the first end to the second end, and the bend is the apex of the inverted v-shape.

10. The method of claim 1 , wherein sealing the opening of the evacuated tube comprises flame sealing the opening of the evacuated tube.

11. The method of claim 9 , wherein sealing the opening of the evacuated tube comprises flame sealing the opening of the evacuated tube.

12. The method of claim 11 , wherein the ampoule is a silica ampoule.

13. The method of claim 1 , wherein the tube consists of the first end, the second end, and the body connecting the first end and the second end.

14. A method of forming a purified thallium chalcohalide, the method comprising:

loading a thallium chalcohalide precursor material comprising one or more impurity elements into a tube having a first end, a second end, and a body connecting the first end and the second end, wherein the body of the tube forms a bend between the first end of the tube and the second end of the tube;

evacuating the tube to reduce a pressure in the tube;

sealing the evacuated tube to form a sealed, evacuated tube that is sealed at the first end and the second end;

mounting the sealed, evacuated tube in a furnace having a first temperature zone and a second temperature zone, wherein the sealed, evacuated tube is mounted with its first end in the first temperature zone, its second end in the second temperature zone, and its bend directed upward, such that the bend is elevated above the first end of the tube, the second end of the tube and the first and second ends of the tube are directed downward, and a top of the bend is at a highest part of the tube;

increasing the temperature in the first temperature zone to a temperature that is sufficiently high to melt and volatilize the thallium chalcohalide precursor material in the first end of the tube, while maintaining the temperature in the second temperature zone at a temperature lower than the temperature in the first temperature zone, wherein the volatilized thallium chalcohalide precursor material condenses on a wall of the body of the tube in the second temperature zone and flows down to the second end of the tube under the force of gravity;

solidifying the condensed thallium chalcohalide precursor material that collects in the second end of the tube to provide a purified thallium chalcohalide precursor material having a lower impurity concentration than the thallium chalcohalide precursor starting material; and

reacting the purified thallium chalcohalide precursor material with one or more additional thallium chalcohalide precursor materials to form the purified thallium chalcohalide.

15. The method of claim 14 , wherein one of more impurities whose concentration is lower in the purified thallium chalcohalide precursor material than in the thallium chalcohalide precursor starting material are impurities that introduce deep electronic levels in the bandgap of the purified thallium chalcohalide.

16. The method of claim 15 , wherein the purified thallium chalcohalide is Tl 6 SI 4 or Tl 6 SeI 4 .

17. The method of claim 16 , wherein the one or more impurities comprise Al, Pb, Bi, Si, or a combination of two or more thereof.