The efficiency of RGB phosphors
The µUV LED display which obtains full color by exciting RGB (red, green, blue) phosphors with UV LEDs has the same principle with plasma displays, so conventional color conversion process technology can be applied. We verified that we could get sufficient luminous efficiency for the display. It is necessary to consider various factors such as cell shape, reflective material, sealing resin and phosphor coating method when making a display. We have already developed a technology not to deteriorate the efficiency when UV LED chips are micronized, and we have stepped forward to realize the µUV LED display.
Method of verification
Our group dared to use conventional UV LED (P/N : NS385L-3SVR) with a wavelength of 385nm and RGB phosphor sheets (Mitsubishi Chemical Corp.) and the total radiant flux and the radiant flux of each color were measured by an integrating sphere . And the photoluminescence efficiency was delivered.
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·UV LED (P/N : NS385L-3SVR) Optical output power: 970mW(IF:500mA) EQE:60.0% |
NS385L-3SVR (mounted on Al substrate) |
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·Red phosphor【(SrCa)AlSiN3:Eu】 ·Green phosphor【SiAlON:Eu】 ·Blue phosphor 【(Sr,Ba)10(PO4)6Cl2:Eu】 |
The RGB phosphor sheets were directly fixed above NS385L-3SVR and the radiant flux were measured.
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Photoluminescence and power conversion efficiency (WPE)
of RGB phosphors
Table 1 and Fig. 1 show the measurement data.
Photoluminescence efficiency is 40% or more and power conversion efficiency is 20% or more for all RGB phosphors when using NS385L-3SVR with total radiant flux value: 93.9mW (power conversion efficiency: 59.3%) at 50mA. In particular, it can be seen that the "power conversion efficiency: 22.4%" of the red phosphor is much higher than the "external quantum efficiency (EQE): 4.6%" of the current InGaN based red LED that officially presented.
Table 1: Measurement data
| Red phosphor | Green phosphor | Blue phosphor | |
| Total radiant flux [mW] | 47.9 | 42.2 | 48.0 |
| Each color radiant flux [mW] | 35.5 | 33.9 | 41.8 |
| Photoluminescence efficiency (Conversion efficiency to each color [%]) | 43.4 | 39.5 | 47.6 |
| Power conversion efficiency (WPE[%]) | 22.4 | 21.4 | 26.4 |
Figure 1: Spectrum of each phosphor excited by UV LED
