Thermoanalysis and Emission Properties of Eu3+/Eu2+ in Eu3+-Doped Xerogels

Investigation on structure and photoluminescence properties of Ho3+ doped Ca3(VO4)2 phosphors for luminescent devices

This study focuses on the synthesis and characterization of Ho3+ doped Ca3(VO4)2 phosphor for potential application in solid-state lighting technology. A citrate-based sol-gel process is optimized to achieve sheet-like morphologies in the phosphor material. The investigation reveals UV absorption at 371 nm, indicating a band gap of 3.28 eV. Emission transitions at (506, 541, and 651) nm are observed when excited at 451 nm, with an optimal Ho3+ concentration of 0.05 mol resulting in robust green emission at 541 nm. The concentration quenching in Ca3(VO4)2:xHo3+ phosphors is discussed in detail with Blesse's and Dexter's models. The concentration quenching effect found in the studied samples is due to the dipole-dipole interactions. Judd-Ofelt intensity parameters were calculated from the excitation bands, and for Ω 2, Ω 4, and Ω 6 are (0.16, 0.17, and 0.36) × 10-20 cm2, respectively. The emission properties for the (5S2 + 5F4) → 5I8 and 5F5 → 5I8 transitions are also estimated with J-O parameters. The higher magnitude of branching ratios (83%) and emission cross-sections (1.6 × 10-21 cm2) suggest that the Ca3(VO4)2:0.05Ho3+ phosphor materials may be suitable for efficient green-emitting device applications. The CIE coordinates confirm the potential of Ho3+-doped phosphors for green emissions, making them suitable for solid-state lighting and display technology.

Laser excited long lasting luminescence in CaAl₂O₄: Eu³⁺/Eu²⁺+Nd³⁺ phosphor

The europium and neodymium oxides doped nano-structured calcium aluminate phosphor samples have prepared through combustion technique and their luminescence properties are studied using laser excitations. Samples prepared in open atmosphere showed the presence of both Eu(3+) and Eu(2+) states and their ratio changes with calcination temperature. Single Eu(3+)/Eu(2+) ions doped sample has found to give broad emission at 450 nm without the persistence glow while the Eu(3+)+Nd(3+) ions codoped sample has shown persistence glow at 450 nm (Eu(2+)) on 355 nm laser excitation. Wavelength selective excitations show that 266 nm excitation gives the intense emissions from both Eu(3+) and Eu(2+) states with no afterglow but 355 nm excitation gives negligible emission from Eu(3+) ions and a strong afterglow at 450 nm wavelength. The mechanism of wavelength dependent phosphorescence has been discussed. Studies on Stark splittings and their relative intensities in emission spectra of Eu(3+) ions have shown that Eu(3+) ion can be used as excellent probe of crystal structure.

Lanthanide-containing light-emitting organic-inorganic hybrids: a bet on the future

Interest in lanthanide-containing organic-inorganic hybrids has grown considerably during the last decade, with the concomitant fabrication of materials with tunable attributes offering modulated properties. The potential of these materials relies on exploiting the synergy between the intrinsic characteristics of sol-gel derived hosts (highly controlled purity, versatile shaping and patterning, excellent optical quality, easy control of the refractive index, photosensitivity, encapsulation of large amounts of isolated emitting centers protected by the host) and the luminescence features of trivalent lanthanide ions (high luminescence quantum yield, narrow bandwidth, long-lived emission, large Stokes shifts, ligand-dependent luminescence sensitization). Promising applications may be envisaged, such as light-emitting devices, active waveguides in the visible and near-IR spectral regions, active coatings, and bio-medical actuators and sensors, opening up exciting directions in materials science and related technologies with significant implications in the integration, miniaturization, and multifunctionalization of devices. This review provides an overview of the latest advances in Ln(3+)-containing siloxane-based hybrids, with emphasis on the different possible synthetic strategies, photoluminescence features, empirical determination.