Application of luminescent converters for the correction of the spectra of white LEDs

Introduction.The growing use of highly efficient blue light-emitting diodes (LEDs) in lighting the premises requires the correction of the primary emission spectra, most prominently, for light-hygienic reasons. Indeed, spectra... [ view full abstract ]

Introduction.

The growing use of highly efficient blue light-emitting diodes (LEDs) in lighting the premises requires the correction of the primary emission spectra, most prominently, for light-hygienic reasons. Indeed, spectra of the LED sources, particularly, of the ones with a color temperature of 6500 K, are overloaded with a dark-blue component, which affects circadian rhythms and have adverse consequences for the eyes. 

Materials: Luminophores (luminescent converters, LC) were used in the work: coumarin 334 (C334), coumarin 343 (C343) and surfactants: Brij 35 (B35), Triton X 100 (T100), Tween 40 (T40) «Sigma-Aldrich». 

Methods: Fluorescence spectra (FS), fluorescence excitation spectra (FES), fluorescence quantum yields φ_F were measured on a retrofitted SDL-2 (LOMO, Soviet Union) spectroscopic unit, which consisted of an MDR-12 excitation monochromator and an MDR-23 registration monochromator. 

Results:

The peak of the white light LED is in the center of the phosphor excitation (absorption) band, and the spectral dip in the emission spectrum of this LED coincides with the maximum of the fluorescence spectrum of the phosphor (Fig. 1). It can be seen from Fig. 2 that the blue band ~ 450 nm is significantly weakened in the total spectrum obtained after superimposing the polymer film on the LED, owing to the phosphor absorption, and instead of the spectral "dip" of ~ 480 nm, a steep slope of the rising radiation band (460–485 nm). 

• Fig 1. Comparison: of FES (1, 2) and FS (3, 4) coumarin 334 (1, 3) and coumarin 343 (2, 4) in the matrix of PC with T40 as a detergent (l_mon = 505 nm; λ_exc = 420 nm); spectra of a LED lamp with a color temperature of 6500 K (5).
• Fig. 2. Normalized spectra of a LED lamp with a color temperature of 6500 K without LC (1) and with LC based on C334 (2) and C343 (3) in PC with T40 as a detergent.

Conclusion: The principal possibility of target correction of the emission spectra of LED lamps by means of luminescent converters based on luminophors in a polymer matrix is demonstrated.