Rare-earth phosphors for the control of LED's color output: state of the art

Inorganic light-emitting diodes (LEDs) nowadays provide an economic and energy efficient way of lighting both at home and in the industry. Red, green, and yellow LEDs have been available since the 1970s; the advent of blue LEDs in 1990s, and in particular the availability of high-brightness blue sources, has made high-efficiency white lighting sources possible. Indeed, one of the main ways of producing white light-emitting solid-state sources is to use a phosphor material to convert monochromatic light from a blue or UV LED to broad-spectrum white light. More generally, the most important characteristics of a LED-phosphor source are the quality and stability of its colour or peak emission wavelength. In the recent years there have been very many papers analysing the characteristics of different phosphors based on rare earth ions embedded in different hosts. A better knowledge of the photoluminescence properties of rareearth- doped materials is important for energy saving, not only in the case of solid state lighting but also for frequency conversion applied to solar cells. Here we present some of our results, together with a brief review of the recent advances in this area.