Microcavity LEDs

Among other specific applications of PTs as light-emitting materials, it is necessary to mention microcavity LEDs prepared with PTs 422 and 416 [525,526] and nano-LEDs demonstrated for a device with patterned contact structure, and PT 422 blended in a PMMA matrix that emits from phase-separated nanodomains (50-200 nm) [527,528]. 

FIGURE 4.3. (a) Schematic structure of a microcavity LED with an Alq emitting layer. The top mirror is the electron-injecting contact and the bottom mirror is a three-period dielectric quarter-wave stack (QWS) with Si02(n = 1.5) and SixNy(n = 2.2). (b) Electroluminescence spectrum from a cavity LED compared with that from a noncavity LED. The noncavity LED possesses the same layer structure as shown in (a), but has no QWS. 

Single Mode and Multimode Planar Microcavity LEDs... 

FIGURE 4.8. Electroluminescence spectrum from a three-mode microcavity LED, in which the three peaks are at 488, 543, and 610 nm. The EL spectrum from a noncavity device is shown for comparison. 

The effects produced by a planar microcavity on the electroluminescence characteristics of organic materials have been described. A number of organic and polymeric semiconductors have been employed by various groups in studies on microcavity LEDs. However, for detailed descriptions, three categories of emissive materials have been considered undoped Alq, Alq doped with 0.5% pyrromethene, and Alq+NAPOXA. Alq has a broad free-space emission spectrum spanning the... 

Fig. 29.18 Structure of a microcavity LED as investigated in Ref. 138. The substrate consisted of DBR on glass [Balz-ers BD 100 143 03] (see Fig. 29.2), with an ITO film of thickness about 96 nm deposited by rf sputtering. The ITO acts as the bottom electrode and is treated as a transparent spacer with an index of refraction of n = 1.8 in the cavity device. The PPV layer was of thicknesses 160 10 nm.

Figure 18. Emission spectra of the microcavity LEDs with different BCB thicknesses, compared with the emission spectrum of a non-cavity LED (top).

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