Research On The Synthesis And Spectral Characterization Of The Rare Earth Doped Aluminate Phosphors

White-light emitting diodes(WLEDs) is considered as the fourth generation solid-state lighting with advantages over conventional lighting sources(e.g., incandescent, fluorescent and highintensity discharge lamps), because they are energy-saving, compact and rigid, long-lived and environmentally benign. The commercial WLEDs using only YAG:Ce is undesirable for indoor use due to the lack of sufficient red spectral component. Therefore, investigations have been mainly focused on the development of novel red emitting phosphors. Recently, La Sr2 Al O5(LSA) host lattice doped with rare earth ions have attracted much attentionis because of their excellent properties, such as high luminous efficiency, no environmental pollution, tunable emission color and low cost.In this paper, we synthesized a series of La1-xSr2 Al O5:x Eu(0<x?1.0) red emitting phosphors by high-temperature solid state reactions under oxidative and reductive atmospheres, respectively. The photoluminescence properties, fluorescence quenching mechanism and valence-change behavior of europium ions in La Sr2 Al O5 were systematically investigated. Through substituting the cations in the host lattice, the crystal structure and chemical composition of the aluminate hosts were controlled, therefore, the emission of the Eu2+ in La Sr2 Al O5 was succefully tuned. The main work and achievements can be summarized as the following:(1)The luminescent properties of Eu3+ in La Sr2 Al O5 were systematically investigated. For La Sr2 Al O5:Eu3+ phosphor prepared in air atmosphere, Eu3+ ions occupy the La3+ sites and exhibit characteristic sharp lines originating from the 5D1 and 5D0 levels to 7FJ transitions. With the increase of Eu3+ concentration, the chromaticity coordinates of La1-xSr2 Al O5:x Eu3+ phosphors can be turned from(0.479, 0.453) to(0.621, 0.358). The quenching process of 5D1â†'7F1 emission is attributed to cross-relaxation. The dominant line emission 5D0â†'7F2 is quenched due to the exchange interaction of Eu3+.(2)The photoluminescence properties and valence-change behavior of europium ions in La Sr2 Al O5 were systematically investigated. For La Sr2 Al O5:Eu3+/Eu2+ phosphor prepared in reductive atmosphere, it shows the presence of both Eu3+ and Eu2+. Eu3+ ions occupy the La3+ sites while Eu2+ ions occupy the two different Sr2+ sites. The Eu3+ in La Sr2 Al O5 can be excited by a UV light with characteristic sharp lines originating from the 5D1 and 5D0 levels to 7FJ transitions. The Eu2+ in La Sr2 Al O5 can be excited by a blue light with an intense broad red emission band centered at 610nm(a full width at half maximum of 110nm) with color coordinates of(0.611, 0.368). The internal quantum efficiency was measured to be ～42%, indicating that this phosphor has a great potential in blue-chip pumped white light emitting diodes.(3)The crystal field environment in the La Sr2 Al O5 was effectively tuned through substituting the cations in the host lattice, therefore the emission spectra of the Eu2+ were tuned by changing the crystal field strength and the covalence of the coordination environment. For example, through substituting Sr2+ by Ca2+, the emission peak of Eu2+ can be turned from 610 nm to 620 nm with an increasing of intensity of 89%. A warm white light(Ra=91, CCT=3960K) was achieved when combining the La0.5Sr1.4Ca0.6Al O5:0.5Eu3+/Eu2+ red phosphor and La Sr2 Al O5:Ce3+ yellow phosphor with a blue light-emitting diode.