Eu3+ heavily doped tellurite glass ceramic as an efficient red phosphor for white LED

Abstract

To design a phosphor for near ultraviolet (n-UV) based white light emitting diodes (wLED) with low correlated color temperature (CCT) and high CRI, a series of highly Eu3+ activated tellurite samples was prepared. Glass ceramic (GC) containing Eu2Te6O15 microcrystals were obtained as a function of crystallization time from 0 to 4 h at 435 °C. X-ray diffraction (XRD) and cathodoluminescence measurement confirm the existence Eu2Te6O15 microcrystals in translucent glass ceramic, improving the luminescence properties of the samples. Upon 393 nm excitation two intense emission bands centered at 594 nm and 614 nm were observed with an increase of 200% for the crystallized samples at 435 °C for 4 h with respect to as-fabricated glasses. Radiometric properties of heavily (10 mol %) Eu3+ doped samples as a function of crystallization time were investigated and the maximum luminous efficacy (LE) obtained is 12.01 lm/W for a crystallization time of 4 h. A green phosphor (SrBaSiO4:Eu2+) on top of samples was used the construct a white light-emitting diode and the results show that the color coordinate temperature (CCT) can be tuned from 4729 K to 3405 K as crystallization time increase from 0 to 4 h with a diminishing of LE from 34.3 to 19 lm/W. The results show that tellurite glass and GC present enormous potential as phosphor converters in solid state lighting application.