High CRI in phosphor-in-doped glass under near-ultraviolet excitation for warm white light-emitting diode

Abstract

A series of phosphor-in-doped glass (PiDG) were fabricated through a CO2 laser heating, blending commercial green phosphor SrAl2O4:Eu2+ and Eu3+-doped boro-tellurite glass powders. Translucent PiDGs with low loss of the emissive properties of the SrAl2O4:Eu2+ phosphor can be only achieved through CO2 laser heating; whereas, sintering of PiDGs by means of the conventional method (electric furnace) lead to opaque samples with loss of entire of green emission. Long exposure time of the CO2 laser modifies the PiDGs melt volume due to temperature rise, increasing their diameter and thickness. The fast cooling of CO2 laser approach allows the sintering of transparent PiDGs, avoiding opaque samples and low radiometric properties. A warm white light-emitting diode (w-LED) prototype was fabricated by placing PiDGs on top of a near-ultraviolet (n-UV) chip at 385 nm, showing a high color rendering index (CRI) and a low correlated color temperature (CCT) of 88 and 2369 K respectively. However, a lower CCT with a detriment of CRI can be achieved by using a low SrAl2O4:Eu2+ phosphor concentration. The PiDGs obtained show enormous potential to be applied as a phosphor converter in warm w-LEDs for residential applications.