Solid solution material of rare earth element fluoride (polycrystal and single crystal), and method for preparation thereof, and radiation detector and test device

A rare earth fluoride solid solution single crystal wherein said rare earth fluoride solid solution single crystal is a rare earth fluoride solid solution material comprising a plurality of mutually combined rare earth fluorides having different ion radii, respectively;

• wherein said rare earth fluoride solid solution material includes cations having an averaged ion radius which is in a size equal to or less than an ion radius of La3+ and larger than an ion radius of Sm3+, or in a size smaller than an ion radius of Gd3+ and larger than an ion radius of Er3+;
• wherein said rare earth fluoride solid solution material includes Ce, and is free of primary phase transitions over a temperature range from room temperature to a melting point of said rare earth fluoride solid solution;
• and
• wherein said rare earth fluoride solid solution single crystal includes an alkaline earth metal (AE) which is one or more of Mg, Ca, Sr, and Ba.

A rare earth fluoride solid solution single crystal wherein said rare earth fluoride solid solution single crystal is a rare earth fluoride solid solution material comprising a plurality of mutually combined rare earth fluorides having different ion radii, respectively;

• wherein said rare earth fluoride solid solution material includes cations having an averaged ion radius which is in a size equal to or less than an ion radius of La3+ and larger than an ion radius of Sm3+, or in a size smaller than an ion radius of Gd3+ and larger than an ion radius of Er3+;
• wherein said rare earth fluoride solid solution material includes Ce, and is free of primary phase transitions over a temperature range from room temperature to a melting point of said rare earth fluoride solid solution;
• and
• wherein said rare earth fluoride solid solution material has fluorescence components at least one of which has a decay time of 50 nsec or shorter at a room temperature.

A rare earth fluoride solid solution single crystal wherein said rare earth fluoride solid solution single crystal is represented by (REyRE′1−y)F3 (0.2<y<0.9), wherein RE represents one or two or more selected from the group consisting of Sm, Eu, and Gd, and RE′ represents one or two or more selected from the group consisting of Er, Tm, Yb, Lu, and Y, except for GdyY1−yF3, GdyEr1−yF3, and Gdy(YEr)1−yF3);

• and
• wherein the solid solution material of rare earth element fluoride is free of primary phase transitions over a temperature range from room temperature to a melting point of said rare earth fluoride solid solution;
• and
• wherein said rare earth fluoride solid solution material has fluorescence components at least one of which has a decay time of 50 nsec or shorter at a room temperature.