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To find suitable matrix materials for rare earth (Ln3+) ions has always been key to developing Ln3+-doped phosphor materials. High-entropy oxides (HEOs), benefiting from the multiple ionic occupations and lattice distortions with lowered local symmetry, might be rather promising to generate photoluminescence (PL) emissions, which however unfortunately are not yet explored. Here, we report a Sm3+-doped Ca(Zr0.2Ti0.2Sn0.2Hf0.2Nb0.2)O3 (Ca(M5)O3) orange-red-emitting phosphor. The structure, photoluminescence (PL) properties, chromatic properties and temperature-dependent PL are systematically studied. The high entropy structure brings about superlattice satellites with the reflection vector. The doping of Sm3+ ions is helpful in grain growth of the HEO ceramics. The charge transfer state (CTS) presenting the energy transfer from the matrix to dopants (O2−-Sm3+) in excitation spectra was observed with the center at around 290 nm. The temperature-dependent PL study reveals excellent thermal stability. In addition, the relation between the high entropy structure and PL enhancement is comprehensively studied. These findings can provide some new ideas for the development of Ln3+-doped phosphors and the application of high entropy oxide materials. [ABSTRACT FROM AUTHOR]

It is widely accepted that localized electron hopping induces colossal permittivity in the bulk of transition-metal-based materials. However, the mechanism and the control of the electron hopping process remain to be explored. In this work, the effect of the B-site environment and multiple Cu valence-states on electron hopping were experimentally revealed in the LiCuNb2.95M0.05O9 (M = Mg, Ti) systems. The results demonstrated that Mg/Ti substitution for Nb5+ at the B-site effectively causes multivalent states of A-site Cu cations, i.e. Cu+/Cu2+/Cu3+, and distorted NbO6 octahedra. Upon Mg/Ti substitution, the dielectric permittivity was enhanced by approximately two orders of magnitude (at 1 kHz and 300 K) and an additional dielectric relaxation was induced. More importantly, it was revealed that the B-site substitution effectively adjusted the activation energy and average distances for the electron hopping. [ABSTRACT FROM AUTHOR]

Host-sensitized rare-earth-ion lighting has emerged as a promising route to realize single-phase white-light emission due to effectively overcoming the self-absorption problems within multiple phosphors. However, the involved energy transfer mechanism that refers to the kinetic processes of host-sensitized excitation and the complex interactions between excitons and activators are far beyond understood. Here, a single-phase white-light-emitting phosphor, Dy3+ doped LaInO3 (Dy-LIO), is explored through tuning the exciton behaviors and host-sensitized emission. As phosphors are excited through the interband transiton, the LIO host presents a broadband blue emission due to the recombination of self-trapped excitons (STEs), and Dy3+ ions acquire the excitation energy by grabbing STEs for lighting. Dy3+ doping reduces the InO6 octahedron distortion and meanwhile releases excitons, which in turn are captured by Dy3+ activators for energy transfer. Thus, dopant Dy3+ emits effective blue and yellow luminescence. In addition, the combined action of the undermined STE emission and the promoted Dy3+ luminescence generates a warm-white-light, which exihibits excellent thermal stability. The results reveal the exciton-mediated energy transfer processes from host (LIO) to activators (Dy3+) in Dy-LIO, with the energy transfer efficiency obtained as high as 77.2%. These findings build up a clear energy transfer mechanism between excitons and activators and further suggests a promising way to explore single-phase white-light-emitting phosphors. [ABSTRACT FROM AUTHOR]

Localized polaron hopping is one of the common mechanisms of colossal permittivity in oxides; however, its formation still remains to be explored. In this study, the effect of the cation arrangement on polaron formation and dielectric responses was experimentally revealed in two polymorphs of NiNb2O6, i.e., the ordered columbite (c-NiNb2O6) and the disordered rutile (r-NiNb2O6) phases. Nb4+-type polarons and typical long-range conduction induced dielectric dispersion were observed in c-NiNb2O6, while Ni+-type polarons and colossal permittivity were found in r-NiNb2O6. A broad and temperature-independent (in linewidth) EPR band at g ∼ 1.982 was observed in c-NiNb2O6. In contrast, r-NiNb2O6 exhibited the coexistence of a broad band (g ∼ 2.816), which showed the dipolar broadening effect, and a sharp band (g ∼ 2.076), which was significantly enhanced at T ∼ 580 K. The correlation between EPR band broadening and an increased conductivity was also evidenced. The results suggest the existence of delocalized Nb4+ polarons in ordered c-NiNb2O6, and that the Ni/Nb disordering facilitated the formation of localized Ni+ polaron, which induced colossal permittivity in r-NiNb2O6. [ABSTRACT FROM AUTHOR]