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Holeburning Storage Materials Capable of Room Temperature Cycling

IP.com Disclosure Number: IPCOM000060319D
Original Publication Date: 1986-Mar-01
Included in the Prior Art Database: 2005-Mar-08
Document File: 2 page(s) / 14K

Publishing Venue

IBM

Related People

Macfarlane, RM: AUTHOR [+4]

Abstract

Photochemical holeburning storage is a low temperature technology because only near liquid helium temperatures are hole widths narrow enough (i.e., N300 MHz) to be practically useful. All materials for this application that are known so far lose their information if they are warmed to room temperature and then returned to low temperature for reading. This volatility is undesirable in the event of refrigeration failure. Thus, a class of materials which would be capable of room temperature cycling without information loss is needed. A method has now been found for efficiently identifying materials which have this capability. An example of such a material is BaClF: Sm2+.

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Holeburning Storage Materials Capable of Room Temperature Cycling

Photochemical holeburning storage is a low temperature technology because only near liquid helium temperatures are hole widths narrow enough (i.e., N300 MHz) to be practically useful. All materials for this application that are known so far lose their information if they are warmed to room temperature and then returned to low temperature for reading. This volatility is undesirable in the event of refrigeration failure. Thus, a class of materials which would be capable of room temperature cycling without information loss is needed. A method has now been found for efficiently identifying materials which have this capability. An example of such a material is BaClF: Sm2+. Two conditions must be met for hole stability under room temperature cycling: A) The phototransformation leading to holeburning must not reverse at room temperature, and B) The microenvironments around individual optically active centers must not exhibit hysteresis or redistribution on temperature cycling; i.e. the original microenvironments must be more or less recovered such that the spectral broadening produced by any changes in these microenvironments is less than N300 MHz. By microenvironment we mean that set of parameters which, for a given optical center, define the optical frequency of the transition used for hole burning. The process for selecting holeburning materials capable of room temperature cycling is as follows: A) Materials should exhibit spectral holeburning by the mechanism of photoionization. The traps which accept the electrons produced by photoionization should be deep enough not to be emptied at room temperature, or other electron scavenging traps should exist which will retain the electrons at room temperature. Optical centers consisting of divalent rare earth ions or transition metal ions are suitable photoionizable centers, and insulating crystals with band gaps greater than about 2 eV are suitable hosts. The spectrum of trap depths and corresponding thermal de-trapping rates can be determined using the technique of thermoluminescence. In many cases, inorganic host materials will have intrinsic defects which will act as suitable deep traps (e.g., positive ion vacancies which accept electrons to form color centers).

A method of providing deep traps consists of intentional doping of the host with trivalent rare earth ions which have stable divalent states, e.g., Eu3+ . Such ions can accept the photo ionized electron, e.g., to form Eu2+, which would be a stable ion at room temperature. B) The host material should be capable of cycling from liquid helium tem...