Ce3+-activated Ca2LuAl3Si2O12: A blue-light-excited broadband cyan-emitting garnet phosphor with an ultra-small Stokes shift for high performance white light-emitting diodes
Recently, low-cost, blue-light-excited, and cyan-emitting phosphors have become increasingly important for commercial white light-emitting diode (LED). In this study, a new garnet-type phosphor, Ca 2 LuAl 3 Si 2 O 12 : Ce 3+ (CLASO: Ce 3+ ) with a small Stokes shift and a broad cyan-emitting band, was successfully developed through an ion-replacement technique. Rietveld refinement results confirmed its garnet structure with small crystallographic parameters of a = 11.8850(4) Å and V = 1678.81(18) Å 3 . The CLASO: Ce 3+ phosphor featured two wide absorption bands in the 280–500 nm range, with a maximal peak at 445 nm, matching well with the emission wavelengths of commercial blue LED chips. Upon 445 nm excitation, the optimal CLASO: 0.04Ce 3+ phosphor exhibited a broad cyan-emitting band peaking at 504 nm, with a full width at half maximum of 103 nm. This made it an ideal candidate for filling the cyan gap of blue-pumped white LEDs, thereby enhancing the color rendering index. The excitation and emission spectra of CLASO: Ce 3+ phosphor revealed an ultra-small Stokes shift of 2631 cm −1 , which was attributed to its exceptionally strong structural rigidity – an important factor for energy conversion and luminescent stability. Moreover, the internal quantum efficiency of CLASO: 0.06Ce 3+ was found to be 88 %. Finally, a phosphor converted LED device was assembled using a 445 nm blue LED chip and CLASO: 0.06Ce 3+ cyan phosphors. The device exhibited a high luminous efficacy of 119 lm/W and an excellent stability. The exploration of the relationship between the Stokes shift and photoluminescence properties provides a novel approach to improving phosphors for high performance white LED.
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