Structural and optical study on antimony-silicate glasses doped with thulium ions

Structural and spectroscopic features of high color purity red-emitting phosphors Sr19Mg2(PO4)14: Re3+ (Re3+= Eu3+, Sm3+, Pr3+)

The discovery of high color purity red-emitting phosphors is a major challenge for solid-state lighting materials. Benefitting from highly condensed and flexible framework structure of β-Ca₃(PO₄)₂-type compounds, we have successfully prepared three different kinds of novel high color purity red-emitting phosphors Sr₁₉Mg₂(PO₄)₁₄: Re³⁺ (Re³⁺= Eu³⁺, Sm³⁺, Pr³⁺) by using traditional sintering method. Rietveld refinement, SEM measurement, absorption spectra, emission/excitation spectra, fluorescence decay analysis and emission spectra in terms of different temperature were investigated and discussed clearly. The matrix optical band gap was calculated to be 4.5 eV by reflection data, which indicated the suitable host for rare earth doping. The single doped Eu³⁺, Sm³⁺ and Pr³⁺ phosphors could respectively exhibit characteristic and strong red emission peaks at 614 nm, 598 nm and 642 nm when excited by (near) ultraviolet radiation. Excitingly, all samples could obtain high color purity with the value of 91.6%, 90.6% and 84.8% for Eu³⁺, Sm³⁺, Pr³⁺ ions, respectively. Moreover, the thermal stability can stay strong which still keep over 75% at 150℃ when comparing with that at atmospheric temperature. The quantum efficiency (QE) is another important parameter for phosphors which were measured to be 46.6% for Eu³⁺, 53.1% for Sm³⁺ and 10.3% for Pr³⁺. The present work indicates that the Sr₁₉Mg₂(PO₄)₁₄: Re³⁺ phosphors are efficient red components with extraordinary color purity and high quantum efficiency for industrial applications as solid-state lighting materials.

Controllable luminescence and efficient energy transfer investigation of a novel white light emission phosphor Ca19Na2Mg(PO4)14: Dy3+, Tm3+ with high thermal stability

White light emission phosphors are widely researched for application in lighting and display fields. However, the poor thermal stability is a real problem for the known single-phased white phosphors, which limits their further application. In this paper, Ca₁₉Na₂Mg(PO₄)₁₄: xDy³⁺, yTm³⁺ (CNMP, 0 ≤ x ≤ 0.06, y = 0, 0.01) phosphors with adjustable emission and good thermal stability are synthesized. The X-ray diffraction and X-ray energy dispersive spectrometer measurement distinctly confirm the successful synthesis of CNMP: xDy³⁺, yTm³⁺ (CNMP, 0 ≤ x ≤ 0.06, y = 0, 0.01). The photoluminescence results reveal that CNMP: Dy³⁺ shows characteristic excitation peaks in the range of 350-450 nm, and mainly exhibits strong yellow emission around 575 nm ascribed to the ⁴F_9/2-⁶H_13/2 transitions of Dy³⁺. To compensate the deficiency of blue light emission of CNMP: Dy³⁺, the trivalent Tm³⁺ ion is co-doped owing to its characteristic blue emission at 450 nm due to its ¹D₂-³F₄ transitions. Therefore, the emission of CNMP: Dy³⁺, Tm³⁺ can be tuned from blue light region with CIE coordinates of (0.1649, 0.0387) to white light region with CIE coordinates of (0.3001, 0.3003) and finally move to yellow light region with CIE coordinates of (0.3732, 0.4493) through adjusting the doping ratio of Dy³⁺/Tm³⁺. The energy transfer efficiency and the energy transfer mechanism from Tm³⁺ to Dy³⁺ are further investigated. Moreover, CNMP: Dy³⁺, Tm³⁺ exhibites a high thermal stability and the emission intensity still keeps 84% of the initial intensity of Dy³⁺ at 230 °C. These outstanding properties show that Ca₁₉Na₂Mg(PO₄)₁₄: Dy³⁺, Tm³⁺ have great advantages and potentiality for applying in solid state lighting.

Spectroscopy and energy transfer in lead borate glasses doubly doped with Tm3+ and Dy3+ ions

Lead borate glasses singly and doubly doped with Tm³⁺ and Dy³⁺ were prepared by traditional melt-quenching technique. The emission spectra of rare earths in studied glass systems were registered under different excitation wavelengths. The observed emission bands are located in the visible spectral region. They correspond to ¹D₂→³F₄ (blue) and ¹G₄→³H₆ (blue) transitions of Tm³⁺ as well as ⁴F_9/2→⁶H_15/2 (blue), ⁴F_9/2→⁶H_13/2 (yellow) and ⁴F_9/2→⁶H_11/2 (red) transitions of Dy³⁺. Moreover, the energy transfer process from Tm³⁺ to Dy³⁺ was observed. The luminescence bands originating to characteristic transitions of thulium and dysprosium ions are present on emission spectra under direct excitation of Tm³⁺. Luminescence lifetimes for the excited states of Tm³⁺ and Dy³⁺ ions in lead borate glass were also determined based on decay measurements. The luminescence intensities and lifetimes depend significantly on the relative concentrations of the optically active dopants.