Phase characterization and tunable photoluminescence of Eu-doped strontium-substituted nanohalophosphate

Abstract

Nanocrystalline Eu-doped powders, Ca 5− x Sr x (PO 4) 3(OH):Eu 3+, were prepared from chemical solutions at room temperature. The crystalline phase and photoluminescence (PL) properties of the halophosphate powders were studied in terms of solution pH value and annealing atmosphere. At pH=2, both Ca 8.3Sr 1.7(PO 4) 6Cl 2 and Ca 8.3Sr 1.7(PO 4) 6(OH) 2 phases were detected, but an increase in solution pH value over 7 led to the formation of only Ca 8.3Sr 1.7(PO 4) 6(OH) 2 phase. After annealed at 850 °C, the sample prepared in pH=2 solution shows stronger blue emission than that prepared in pH=10 in the reducing atmosphere. However, for the samples annealed in air atmosphere, the blue emission still can be observed that can be attributed to the reduction of Eu 3+→Eu 2+. The relative intensity of blue to red emissions is dominated not only by annealing atmosphere but also by crystalline phase formed in the sample. These results indicate that the PL properties can be tunable by controlling the solution pH value (crystalline phase) and changing annealing atmosphere.