Probing the optical properties and luminescence mechanism of a UV-emitting SrBPO5 :Ce3+ phosphor

Optical and thermal properties of rare earth-doped K4 Ca(PO4 )2 phosphor

The luminescent properties and energy transfer (ET) mechanism in the Ln³⁺ pair of the RE³⁺ (RE = Eu³⁺ , Ce³⁺ , Dy³⁺ and Sm³⁺ ) doped K₄ Ca(PO₄ )₂ phosphor were successfully investigated using a conventional high-temperature solid-state reaction. In the near infrared (NIR) range, Ce³⁺ -doped K₄ Ca(PO₄ )₂ phosphor exhibited a UV-Vis. emission band, whereas K₄ Ca(PO₄ )₂ :Dy³⁺ exhibited characteristic emission bands centred at 481 and 576 nm in the near-ultraviolet excitation range. The possibility of ET from Ce³⁺ to Dy³⁺ in K₄ Ca(PO₄ )₂ phosphor was confirmed by a significant increase in the photoluminescence intensity of the Dy³⁺ ion based on the spectral overlap of acceptor and donor ions. X-ray diffraction, Fourier-transform infrared and thermogravimetric analysis/differential thermal analysis TGA/DTA were carried out to study phase purity, presence of functional groups and amount of weight loss under different temperature regimes. Therefore, the RE³⁺ -doped K₄ Ca(PO₄ )₂ phosphor may be a stable phosphor host for light-emitting diode applications.

UV excited blue to green emitting Tb3+ activated sodium calcium metasilicate color tunable phosphor for luminescent devices

Tb³⁺ doped Na₄ Ca₄ Si₆ O₁₈ (NCMS: Tb³⁺ ) phosphors have been synthesized via solid state reaction route with increasing dopant concentration. The phase identification studies for NCMS: Tb³⁺ phosphors have been done through X-ray diffraction (XRD) technique. The XRD patterns for as-synthesized phosphors showed satisfactory agreement with the standard pattern (JCPDS card no. 75-1687) of pure phase of Na₄ Ca₄ Si₆ O₁₈ compound. The morphology and size of particles have been illustrated with scanning electron microscope (SEM) micrographs. The photoluminescence excitation (PLE) spectrum of Tb³⁺ doped Na₄ Ca₄ Si₆ O₁₈ phosphor depicts the strong excitation peak obtained in UV spectral region. The trivalent terbium activated NCMS phosphors excited under UV region (232 nm wavelength) exhibit intense emission in blue (350-470) and green (470-650) spectral regions. With increasing the concentration of Tb³⁺ ions in host matrix, the emission color shifts from blue to green region due to cross relaxation energy transfer (CRET) mechanism and shows the tunable behaviour of Tb³⁺ activated as-synthesized NCMS phosphor. The aforementioned results manifest that Tb³⁺ activated sodium calcium metasilicate phosphor has an immense potential to contribute as a green and blue-green emitting component in lighting and display device applications.

Influence of interstitial UO22+ doping on the valence control of Eu and energy transfer to substitutional Eu3+ and Sm3+ in SrBPO5

Controlling the valence mixing of Eu³⁺/Eu²⁺ and energy transfer between activator ions in solid solution is an important process to improve the efficiency and specificity of phosphors. In this work, the structural and optical properties of stillwellite type SrBPO₅ doped with uranium/europium/samarium, as prepared by conventional solid-state reaction synthesis, were investigated. PXRD studies and Rietveld analysis were carried out to determine the structure, phase purity, and coordination environment of the dopants in the host matrix. Samarium existed only as a trivalent cation in SrBPO₅ synthesised in an air atmosphere, whereas europium exhibited abnormal reduction and Eu²⁺ co-existed with Eu³⁺. Unlike Eu and Sm, which replaced Sr at its sites, uranium gets stabilised as UO₂²⁺ in the interstitial vacant space in the SrBPO₅ lattice. Uranium co-doping strongly influenced the Eu valence distribution by favouring the re-oxidation of Eu²⁺ to Eu³⁺. Possible mechanisms of Eu abnormal reduction in SrBPO₅ and Eu valence control based on the electron transfer from substitutional Eu²⁺ to interstitial UO₂²⁺ are discussed. The photoluminescence and time-resolved photoluminescence properties of Eu/Sm/U doped SrBPO₅ were investigated systematically. Uranium co-doping significantly enhanced the emission intensities of trivalent Eu and Sm through the exchange-type energy transfer. Besides, the Eu³⁺ luminescence intensity was further amplified in the presence of uranium due to the partial oxidation of Eu²⁺ to Eu³⁺. By controlling the uranium to Eu concentration ratio, the Eu-SrBPO₅ phosphor could be tuned to different CIE coordinates.

SrBPO5: Ce3+, Dy3+ - A cold white-light emitting phosphor

A single-component white-light emitting phosphor SrBPO₅: Ce³⁺, Dy³⁺ with high color purity, good quantum efficiency and high thermal stability was prepared through the conventional high temperature solid state reaction. PXRD studies confirmed its phase purity. The suitability of Strontium borophosphate as a host for phosphor was confirmed through DFT calculations. The presence of Ce³⁺ along with Dy³⁺ in this host resulted in efficient energy transfer from Ce³⁺ to Dy³⁺ through a non-radiative multipole-multipole mechanism leading to the enhancement of Dy³⁺ luminescence towards white light emission. Lifetime decay and time-resolved emission studies confirmed the energy transfer along with multisite occupancy of Ce³⁺. In addition to energy transfer, the thermal stability of the phosphor was confirmed through temperature-dependent photoluminescence studies and the particle shape, size, uniformity of dopants of the phosphor was studied using the SEM and EDX spectroscopy.