Combustion synthesis of germanium phosphates Gd11–x–yYbxEryGeP3O26 and their luminescence properties

Resumo

The formation of germanium phosphates Gd_11–x–yYb_xEr_yGeP₃O₂₆ containing 1 at % Er and 5 to 20 at % Yb upon gel combustion and annealing of intermediates was studied. Structure formation in germanium phosphates was shown to start with the crystallization of phosphate Gd₃PO₇ followed by its reaction with Gd₂GeO₅ to yield Gd₁₁GeP₃O₂₆. The compounds prepared are crystallized in triclinic crystal system (space group P1). The unit cell parameters and unit cell volumes of Gd_11–x–yYb_xEr_yGeP₃O₂₆ decrease with increasing dopant concentration in the phosphor: from V = 555 ų in Gd_10.34Yb_0.55Er_0.11GeP₃O₂₆, where Yb: Er = 5: 1, to V = 549 ų in Gd_9.24Yb_1.65Er_0.11GeP₃O₂₆, where Yb: Er = 15: 1. Upconversion luminescence spectra of germanium phosphates Gd_11–x–yYb_xEr_yGeP₃O₂₆ were recorded. The luminescence spectra featured two bands: a strong band in the red, corresponding to the transition ⁴F_9/2→ ⁴I_15/2 (660 nm), and a weaker band in the green, corresponding to two transitions: ²H_11/2 → ⁴I_15/2 (λ = 525 nm) and ⁴S_3/2 → ⁴I_15/2 (λ = 550 nm) of Er³⁺ ions. The energy yields (B_en, %) were determined for the prepared phosphors. The highest value B_en = 0.54% was observed in phosphor Gd_10.765Yb_0.125Er_0.11GeP₃O₂₆ where Yb: Er = 15: 1.