Structures and Polymorph-Sensitive Luminescence Properties of BiPO₄/Eu Grown in Hydrothermal Conditions

Abstract

In this work, BiPO4/Eu of different polymorphs was prepared using a simple hydrothermal method. It is found that a hexagonal phase (HP) was formed at 100 °C, which transformed to a low-temperature monoclinic phase (LTMP) when hydrothermal temperature was increased to 160 °C. This LTMP transformed reversely to HP when the temperature increased beyond 180 °C. This phase evolution is quite distinct from those when using high-temperature calcinations (CrystEngComm201113). Accompanying this phase evolution, sample morphology varied from homogeneous rodlike shape to prismlike shape, while the lattice strain features changed from tensile to compressive, and then to tensile, as followed by a decrease in symmetry of tetragonal PO4 groups from pseudo-T d to C 1. These variations were closely related to the reaction mechanism in solution chemistry, in which two interfacial processes were indicated, differing from the ionic diffusion process during calcination. As a consequence, luminescence properties become sensitive to polymorphs. All Judd–Ofelt parameters (Ωλ, λ = 2, 4, 6) were calculated to evaluate the asymmetric nature for the polymorph-sensitive luminescence. It is found that the Ω2 value for HP was 1.66 × 10–20 cm2, which increased to 2.10 × 10–20 cm2 for LTMP; meanwhile, the quantum efficiency increased from 9.33% for HP to 36.09% for LTMP. These results demonstrated that BiPO4 of different polymorphs can be obtained through the hydrothermal method, which may enrich the significance of solution chemistry in preparing advanced materials of tailored functionalities.

Enhanced luminescence properties of BiPO4:Eu3+ phosphors prepared by hydrothermal method

“…It can be seen that all of the emission spectra have the same profile in addition to the luminescence intensity. The weak emission intensity of S1 sample can be attributed to the OH oscillators from the hydrated hexagonal phase, which is in good agreement with the results of XRD analysis [18]. At cation/anion molar ratio equal to 1:2.5 (S3), the luminescence intensity is enhanced than that of the other two samples, which may be attributed to the high crystallinity.…”

Full Color Emission in ZnGa2O4: Simultaneous Control of the Spherical Morphology, Luminescent, and Electric Properties via Hydrothermal Approach

“…Taking χ (O) = 3.2 and χ (Eu) = 1.75, the band position for Eu 3+ ‐O 2− CTB is calculated to be at 238 nm (about 42 000 cm −1 ) which is lower than that of 290 nm obtained in the present ZnGa 2 O 4 : Eu 3+ system, but the result is consistent with BiPO 4 : Eu 3+ , LaOF: Eu 3+ , nanosized Y 2 O 3 : Eu 3+ , YVO4: Eu 3+ and sol‐gel derived ZnGa 2 O 4 : Eu 3+ systems. [12c],[33a], The red shift of the CTB may result from the difference between bulk materials and nanoscale materials for the equation valued for bulk phosphors and the nephelauxetic effect. [33a],[34c] In addition, the enhancement of the absorption intensity about the band from 350 to 400 nm comparing with the host material further confirms the absorption originating from Eu 3+ ions, as shown in Figure S6 (Supporting Information).…”

BiPO4@glucose-based C core–shell nanorod heterojunction photocatalyst with enhanced photocatalytic activity

“…The bands at 554 and 596 cm À1 can be assigned to the y 4 bending vibration of PO 4 groups. The band at 406 cm À1 corresponded to the y 2 bending vibration of the PO 4 unit [27]. With the increase of glucose content, the peaks of BiPO 4 @C samples weakened gradually and eventually disappeared, and no any other peak appeared.…”