Inorganic phosphors : compositions, preparation, and optical properties

Abstract

About a decade ago, one of us (WMY), in response to a federal broad agency announcement, initiated an effort to establish a baseline for the state of knowledge concerning the methodology for synthesis and the optical properties of a variety of phosphors used for display and other technical applications. Though for various reasons this effort ultimately turned futile, several members of the phosphor/luminescence community called my attention to an existing backlog of published and unpublished literature addressed to this subject. This resulted, for example, in our becoming aware of the existence of the Phosphor Handbook published in Japanese under the auspices of the Japan Phosphor Society and led to its eventual translation and publication as the Phosphor Handbook, a volume in the CRC Lasers and Optical Sciences and Technology Series.

In connection with efforts to establish a phosphor database, Ronald Petersen (of Motorola, at the time) first presented us with a copy of Willi Lehmann’s opus (Phosphor Cookbook) on methods for synthesis and properties of over 200 phosphors. This report dates from the late 1970’s and covered the majority of phosphors then in use. Dr. Lehmann, of course, was a principal in the development of many of the phosphors included in his cookbook. He later updated and extended this work in 1988 in his Phosphor Tables in which the phosphor properties of over 300 luminescent materials were summarized in tabular form. A copy of these tables, which was prepared for a publication that never appeared, was preserved and given to us by Dr. Henry Ivey. Henry had a close working relationship with Willi at Westinghouse as the Foreword to this volume attests.

The scholarship contained in the Phosphor Cookbook and the Phosphor Tables is quite remarkable and comprises a great deal of meticulous and careful work characterizing Willi Lehmann’s career as a phosphor synthesizer. The list of materials presented in the compilations is large and the manuscripts preserve and summarize synthesis and optical data on most of the commonly used phosphors (as well as some less common ones). In the absence of any systematic database on phosphors, the two unpublished manuscripts represent a reasonably complete summary of the state of knowledge on phosphors up to the late 1980’s.

Though it might be argued that the art of phosphors synthesis and characterization has advanced considerably since Lehmann’s time, we believe that these contributions need to be preserved as part of the phosphor art. Thus, it appeared to us that the content of these two unpublished manuscripts fully deserved publication as a record, if nothing else, of past methodologies; these methodologies are often abandoned and forgotten but often need to be rediscovered and revived when circumstances warrant it. Almost all modern phosphors are synthesized by solid-state reactions at high temperatures. Updated versions of these techniques are presented in this volume along with other techniques such as sol–gel and combustion that have been developed in the past few decades.

This volume is divided into two parts. Most of the contents of Lehmann’s Phosphor Cookbook and Phosphor Tables are preserved in the first part with either no or only slight changes in style and format. The phosphor data presented in Section 4 combine the results of both manuscripts. However, no composition or preparation information was included in the Phosphor Tables; thus such information is absent for many compounds. In the second part of the volume we have attempted to supplement Lehmann’s work with additional

developments including recent synthesis methods and new phosphors. Because of the plethora of phosphor compositions reported in recent decades, the listing is not exhaustive but rather representative of some of the more significant phosphors developed in recent years. We have restricted consideration to materials that are accessible in the open literature and have not included any recipes or description of phosphors that are proprietary. Only a relatively few phosphors have achieved commercial success. Section 8 presents a list of many commercial phosphor and scintillator materials and the peak wavelength of their emission. Finally, three appendices have been added. The first presents an historical perspective on phosphors; in the second a table of phosphors is arranged in order of emission wavelength as a guide in selecting phosphors for particular applications. The third gives a brief summary of Willi Lehmann’s life.

It may be noted that the elements belonging to series such as the lanthanides (4f) have chemical behaviors that are nearly identical to each other. It follows that recipes for compounds doped with a certain ion of a series very likely will also be effective for other members of that series. Other considerations (such as ion sizes) will enter, so that the synthesis of any new compounds remains an area of experimentation; a good beginning point, however, would be with the procedures that are presented here. The preparation methods described in this volume generally entail the use of laboratory procedures which are normally encountered in solid-state chemistry and which expose the experimenter to the usual perils. As such, we emphasize that all normal safety precautions (fume hoods, eye protection, etc.) should be observed in the preparation and synthesis of the phosphors described in the volume.

The American Ceramic Society in collaboration with the National Institutes of Standards and Technology (NIST) has continued to publish and revise Phase Diagrams for Ceramists (Vols. I–VI) and the sequel Phase Equilibrium Diagrams (Vols. VII–XII); these volumes contain a great deal of material which is extremely useful in developing an understanding as to what can and cannot be synthesized. Much additional information on the synthesis and characterization of a phosphor or luminescent material information can be found in the aforementioned Phosphor Handbook.

In this effort we have benefitted from numerous comments, suggestions, and contributions from our Editorial Board. We are very appreciative of their help and that of Ron Petersen and Henry Ivey for having preserved the original manuscripts. We are also very thankful to the Lehmann family for giving their permission to use this material. We note with special appreciation the excellent work of Sergei Basun in preparing the many figures and the final manuscript, Sarah Dunning for typing the manuscript, Mike Caplinger and Jeff Deroshia for their computing assistance, and the valuable interactions with CRC Project Editor James McGovern and Development Manager Helena Redshaw.

We are aware that, as noted in the Foreword, Willi Lehmann was anxious to have the material that he had prepared with such care published in some form. We hope that the publication of Inorganic Phosphors serves to fulfill his wish. Indeed, this volume should be considered a tribute to this unusual individual and his contributions to the phosphor art.