Review: Down Conversion Materials for Solid‐State Lighting

Abstract

The wavelength down conversion approach to solid‐state lighting (SSL) uses down conversion materials to produce visible light when excited by near‐UV or blue emission from InGaN LEDs. This review discusses two classes of down conversion materials: phosphors and semiconductor quantum dots (QDs). Strong absorption of the excitation wavelength; high luminous efficacy of radiation, which enables white light with a high color rendering index and a low correlated color temperature; high quantum efficiency; and thermal and chemical stability are some of the criteria for down converters used in SSL. This review addresses the challenges in the development of down converters that satisfy all these criteria. We will discuss the advantages and disadvantages of several phosphor compositions for blue and near‐UV LEDs. The use of core/shell architectures to improve the photoluminescence and moisture resistance of phosphors is presented. QDs are another class of down conversion materials for near‐UV and blue LEDs. Strategies to improve the photostability and reduce the thermal quenching of QDs include strain‐graded core/shell interfaces and alloying. We discuss Cd‐containing II–VI QDs, and Cd‐free III–V and I–III–VI QDs and their potential for SSL applications. Finally, a description of different methods to integrate the phosphors and QDs with the LED is given.

Surface-specific visible light luminescence from composite metal oxide nanocrystals

“…The quest for luminescent materials of sufficient availability, low price, and biocompatibility is at the heart of nanomaterials research and development with applications in areas such as sensing, lighting, medicine, nanoparticle transport, and the detection of electromagnetic fields [1][2][3][4][5][6]. Perhaps the most commercially important application of luminescent materials is in solid-state lighting (SSL) devices based on blue and near-UV light-emitting diodes (LEDs) [1,6].…”

“…Perhaps the most commercially important application of luminescent materials is in solid-state lighting (SSL) devices based on blue and near-UV light-emitting diodes (LEDs) [1,6]. While white light can be generated using a combination of separate blue, green, and red light-emitting diodes, in practice much higher efficiencies and better light distribution characteristics are achieved using luminescent materials as downconverters which absorb blue/UV light and emit in the visible spectrum [6].…”

“…Improving the efficiency, lifetime, and light-quality of SSL devices while reducing their cost is dependent on developing improved luminescent downconverting materials [1]. Current commercial SSL downconverters use rareearth phosphors such as Ce 3? or Eu 2?…”

“…For these reasons, there is a great deal of interest in exploring alternative luminescent materials for SSL applications, such as quantum dots (QDs) and inorganic-organic nanocomposites. Such materials should be non-toxic, widely available, safe, and inexpensive to extract and process, thermally and photostable, have high quantum yields, and desirable downconversion characteristics [1]. While luminescent materials satisfying some of these requirements have been demonstrated, there is as yet no material which meets all of them.…”

“…The luminescence energies can be easily tuned by varying the particle size and shape, and they exhibit a very high quantum yield. On the other hand, QDs are complex nanomaterials to synthesize, often contain toxic elements like Cd, and there are also issues associated with photostability and thermal quenching [1]. Another class of materials system is characterized by dopants (e.g., rare-earth ions) embedded in an inorganic particle which act as luminescence centers (Fig.…”