Laser excitation of red, green, blue and trichromatic white rare-earth phosphors for solid-state lighting applications

Phosphors for solid-state lighting, based on a number of different compositional schemes and driven by light from blue light-emitting diodes (LEDs) are widely used for lighting applications. The low efficiency of pump LEDs at high drive currents (droop effect) limits the amount of light produced by conventional LED and phosphor combination. Pumping with laser diodes (LDs) can circumvent this limitation. In this paper we report on the characterisation of individual and a mixture of KEu(WO 4 ) 2 (red), BaMg 2 Al 16 O 27 :Eu, Mn (green) and (Sr,Mg) 2 SiO 4 :Eu (blue) phosphors, excited by a CW-driven LD operating at 404 nm. The activator ion in each of these phosphors is, respectively, Eu 3+ , Mn 2+ and Eu 2+ . Characteristics of light produced with each phosphor, variations with incident light power and phosphor temperature as well as effects from phosphor ageing are described. Results of comparison between pumping with coherent and incoherent light at the same wavelength are also described.