Exploitation of Eu³⁺ red luminescence through order–disorder structural transitions in lanthanide stannate pyrochlores for warm white LED applications

Abstract

Eu ions epitomize excellent structural probes for the detection of disorder induced by structural variations in stannate pyrochlores due to their relatively simple energy level structure. In this context, we have synthesized a series of Eu doped LnYSnNbO:0.15Eu (Ln = La, Gd, Y, and Lu) red phosphors via a high temperature solid state reaction method to explore the influence of phase evolution on the luminescence properties. The substitution of Ln ions in the A sites of the pyrochlore induces a structural transition from an ordered pyrochlore to a disordered fluorite structure with decreasing ionic radius. The diminishing trend of the characteristic superstructure peaks in the XRD pattern and the broadening of Raman modes with lanthanide substitution clearly substantiate the disorder induced in the cationic sublattice. These phosphors exhibit strong absorption in the near UV region and emit red luminescence under 392 nm excitation, which also correlates to their crystal structures. Their luminescence properties were enhanced with the increased ordering of cations from Lu to La. The more ordered structure of the La system favors a more uniform distribution of Eu ions, preventing cluster formation, and thus improving the luminescence properties. The splitting of the D-F transition of the Eu ions further provides a clue for the structural transition in support of the XRD and Raman analysis. The long range ordering, ligand polarizability, and covalent nature of the Eu bonding influence the emission probability and improve the quantum efficiency of the La host. Eu emissions resulting from D-F transitions are significantly improved with increases in the concentration of Eu ions in the La host. The distortion of the A site symmetry and the red shift of the charge transfer band with Eu doping in the LaYSnNbO system leads to an enhanced electric dipole transition. The extent of the distortion in the EuO polyhedra is reflected in the quantum efficiency values and J-O intensity parameters, Ω and Ω, which are a measure of the degree of polarizability of the Eu-O bonds in the lattice. Our results suggest that we can manipulate the Eu red luminescence in lanthanide stannate pyrochlores through order-disorder structural transitions.

Synthesis and Characterization of Pyrochlore-Type Praseodymium Stannate Nanoparticles: An Effective Electrocatalyst for Detection of Nitrofurazone Drug in Biological Samples

“…To explore the structure of the as-prepared sample, the Raman spectra of Pr 2 Sn 2 O 7 NPs are recorded in the range of 100−800 cm −1 as represented in Figure 1B. Moreover, it is well discussed in the previous literature that the ideal pyrochlore structured oxide shows six active Raman modes corresponding to (A−O) as well as (B−O) vibrational bonds, which is described by factor group analysis, 36 and is given below 38 Further, the peak at 409 cm −1 is attributed to the A 1g mode corresponding to the SnO 6 (torsional mode), 38 and the well-resolved peak at 519 cm −1 is coupled to the Sn−O stretching. 39 The Raman bands at 668 cm −1 were assigned to the F 2g modes and it occurs with the overlap of Sn−O bending and vibrational stretching caused by the Pr−O bonds.…”

“…To explore the structure of the as-prepared sample, the Raman spectra of Pr 2 Sn 2 O 7 NPs are recorded in the range of 100–800 cm –1 as represented in Figure B. Moreover, it is well discussed in the previous literature that the ideal pyrochlore structured oxide shows six active Raman modes corresponding to (A–O) as well as (B–O) vibrational bonds, which is described by factor group analysis, and is given below Here, the F 2g mode is ascribed to the A–O and B–O bond stretching vibrations with bending vibrations, the A 1g mode corresponds to the O–B–O bending vibrations, and the E g mode represents the B–O 6 bending vibrations. The Raman signal at 190 cm –1 belongs to the lattice soft modes, which is related to Sn–O bending vibration modes .…”

Cationic pair substitution in LaAlO3:Mn4+ for octahedral-tilting-dependent zero-phonon line

“…Generally, a long decay time is obtained for luminescence centers in a symmetrical surrounding, while a short decay time is observed when the luminescence centers are located in the distorted site. 33 Fig. S3 and S4 † show the fluorescence decay curves corresponding to Mn 4+ in the LBAT:0.001Mn 4+ (x = 0-0.2) and LYAG:0.001Mn 4+ (y = 0-0.2) phosphors under excitation at 340 nm, as monitored at 726 nm at room temperature and at 77 K. All decay curves are found to be well fitted by a single exponential function, suggesting the single site occu- pancy of the Mn 4+ in the host lattice.…”

Ultra-bright and thermally stable deep red emitting doped yttrium zirconate nanoparticles for tunable white LEDs and indoor plant growth

“…28 As an activator for the phosphor material, Eu 3+ is a promising candidate for red emission due to its unique properties such as narrow red emission, a sensitive transition which depends on the chemical surrounding, and the long lifetime of the chemical species. 26,29 The red emission is in the region from 603 to 630 nm which corresponds to the 5 D 0 -7 F 2 transition.…”