Using rare earth doped thiosilicate phosphors in white light emitting LEDs: Towards low colour temperature and high colour rendering

Rare earth doped thiosilicates are promising materials for use in phosphor converted light emitting diodes (pcLEDs). These phosphors (including the hosts Ca2SiS4, BaSi2S5 and Ba2SiS4 in combination with Ce3+ and/or Eu2+ doping) cover the entire visible part of the spectrum, as the emission colour can be changed from deep blue to red. The photoluminescence emission spectrum and the overlap of the excitation spectrum with the emission of pumping LEDs is evaluated. The trade-off between high colour rendering and high electrical-to-optical power efficiency is discussed by simulation with both blue and UV emitting LEDs. Finally, a phosphor combination with low colour temperature (3000 K) and high colour rendering (CRI = 93) is proposed.