High-brightness Bi3+ activated Gd2GeO5 blue phosphor for white light-emitting diodes: Synthesis, characterization, and thermal stability

Abstract

Phosphor-converted white light-emitting diodes (pc-WLEDs) are excellent energy-efficient artificial light sources for solid-state lighting applications. An important approach to produce high-color-rendering pc-WLEDs is the utilization of an ultraviolet (UV) LED chip to stimulate the red/green/blue multi-color phosphors, so the development of high-efficiency and thermal-stable broadband blue-emitting phosphor is highly significant. Herein, we report a high-brightness blue-emitting Bi3+-activated Gd2GeO5 phosphor for UV-pumped pc-WLEDs, and its crystal structure, morphology, luminescence properties, CIE color coordinates, and thermal stability have been systematically studied. These blue phosphors doped with different Bi3+ concentrations have been prepared by the conventional high-temperature solid-state reaction method with calcination at 1300 °C for 12 h in air atmosphere. Under 324 nm excitation, these Gd2GeO5:Bi3+ phosphors generate an intense broadband blue emission in the 350–650 nm wavelength range peaking around 449 nm, and the sample doped with 0.5 mol% Bi3+ shows the highest emission intensity, along with emission bandwidth of 87 nm and CIE color coordinates of (0.1478, 0.1161). The emission intensity of Gd2GeO5:Bi3+ sample is about 77% of that of commercial BaMgAl10O17:Eu2+ blue phosphor (emission peak: 446 nm; bandwidth: 56 nm). Spectroscopic studies on temperature-dependent emission spectra reveal that the Gd2GeO5:0.5%Bi3+ blue phosphor exhibits excellent thermal stability, only 13% emission intensity is lost at 423 K.