Structure Refinement and Two-Center Luminescence of Ca3La3(BO3)5:Ce3+ under VUV–UV Excitation

Stable color-tunable Ca3Y(GaO)3(BO3)4:Bi3+/Tb3+/Eu3+ phosphors for application in n-UV-pumped wLEDs

For further development of light sources, white light-emitting diodes (wLEDs) have attracted widespread attention as promising next-generation light sources fabricated via the combination of phosphors and LED chips. However, latent defects, such as chemical/thermal instability, low color rendering index (CRI) and high correlated color temperature (CCT), of current mainstream wLEDs seriously hinder their further large-scale implementation. Herein, in order to overcome these limitations, single-phase color-tunable gaudefroyite (Ca3Y(GaO)3(BO3)4 (CYGB)) tridoped with Bi3+/Tb3+/Eu3+ ions was synthesized for the first time and detailed characterisation was performed via high-temperature solid-state reaction and structural/spectral analyses, respectively. Radius difference percentage calculations and Rietveld refinements indicate that dopants occupy both Y3+ and Ca2+ sites but preferably the Y3+ site over the Ca2+ site due to the same valence state. Through subtly regulating the (co)doping contents and skillfully utilizing the energy transfer (ET) strategy from the allowed transition of blue light-emitting Bi to the forbidden transition of green/red light-emitting Tb/Eu, the color hue (including white light) of highly efficient PL can be easily tuned according to the need. Meanwhile, composition/content-optimized white light-emitting CYGB:2%Bi/10%Tb/12%Eu also shows splendid chemical/thermal stability. Finally, as a proof-of-concept experiment, the CYGB:2%Bi/10%Tb/12%Eu phosphor-converted wLED (pc-wLED) was fabricated and encapsulated via the up-to-date remote 'capping' method, which imparted attractive performances. Altogether, the stable CYGB:Bi/Tb/Eu phosphor is a promising candidate for application in lighting/display fields.

Ce3+-Doped Li2Ca5Gd(BO3)5 Phosphors with Multiple Luminescent Centers and High Pressure Sensitivity under Near UV Excitation

The performance of Ce3+-based phosphors under mechanical high pressures becomes attractive due to the potential application as a visual pressure sensor. Li2Ca5Gd(BO3)5 was selected as the host for the Ce3+ doping. Rietveld refinements reveal that rare earth cations occupy M1, M2, and M3 sites, and indeed, the photoluminescent spectra of Li2Ca5Gd1-xCex(BO3)5 (0.005 ≤ x ≤ 0.15) exhibit the characteristic of multiple activators, defined as CeI, CeII, and CeIII, with the maximal emission wavelength at ∼444, 419, and 378 nm, respectively. The optimal internal and external quantum efficiencies are 86.29% for x = 0.005 and 20.26% for x = 0.10, respectively, under the NUV excitation at 363 nm. In-situ high pressure emission spectra under 375 nm excitation exhibit an overall red-shift, and the linear pressure susceptibilities up to 6.7 GPa for CeI and CeII centers are -390 and -279 cm-1/GPa, respectively, which is probably the largest among Ce3+-doped oxides and oxysalts. Due to the above superiorities, Ce3+-doped LCGB possesses a high potential as a visual pressure sensor, and this is a successful study on the structure-property relationship of inorganic materials.

Multisite-Occupancy-Driven Efficient Multiple Energy Transfer: A Straightforward Strategy to Achieve Single-Composition White-Light Emission in Ce3+-, Tb3+-, and Mn2+-Doped Silicate Phosphors

It is unquestionably true that site occupation and energy transfer play important roles in the luminescent properties of optical materials from both practical applications and theoretical research. In this paper, multisite-occupancy-driven multiple energy transfers were used as a straightforward strategy to achieve single-composition white-light emission in Ce³⁺-, Tb³⁺-, and Mn²⁺-doped Ba_1.2Ca_0.8SiO₄ (BCS) phosphors. The Ce³⁺-, Tb³⁺-, and Mn²⁺-doped T-phase orthosilicate BCS samples were synthesized by traditional solid-state reactions. The phase composition was checked via X-ray diffraction (XRD), and the luminescent properties were systematically studied by photoluminescence spectroscopy and fluorescence decay curves. A detailed study on the efficient and multiple energy transfers of Ce I → Mn²⁺, Ce II → Tb³⁺, and Ce II → Tb³⁺ → Mn²⁺ was carried out. Satisfactorily, the selected phosphor exhibits a high internal quantum efficiency (QE) of 81% and good thermal stability. In addition, an evident negative thermal quenching phenomenon, i.e., the emission intensity increases with increasing temperature, is provided. Moreover, the mechanism of negative thermal quenching was proposed. On the basis of these excellent luminescence properties, a white LED with color-rendering index (R_a = 89) was fabricated by integrating the phosphor on an n-UV 365 nm chip. These results show that the materials present potential application in the field of phosphor-converted white LEDs.

Impacts of 5d electron binding energy and electron–phonon coupling on luminescence of Ce3+ in Li6Y(BO3)3

In this work, the crystal structure and electronic structure as well as the synchrotron radiation vacuum ultraviolet-ultraviolet-visible (VUV-UV-vis) luminescence properties of Li₆Y(BO₃)₃ (LYBO):Ce³⁺ phosphors were investigated in detail. The Rietveld refinement and DFT calculation reveal the P2₁/c monoclinic crystal phase and the direct band gap of the LYBO compound, respectively. Only one kind of Ce³⁺ 4f–5d transition is resolved in terms of the low temperature VUV-UV excitation, UV-vis emission spectra and luminescence decay curves. Furthermore, by constructing the vacuum referred binding energy (VRBE) scheme and applying the frequency-degenerate vibrational model, the impacts of 5d electron binding energy and electron–phonon coupling on luminescence of Ce³⁺ in LYBO are analysed. The results show that the Ce³⁺ emission in LYBO possesses a moderate intrinsic thermal stability. With the increase in concentration, the thermal stability of the emission gets worse due to the possible thermally-activated concentration quenching. In addition, the simulation of Ce³⁺ emission profile at low temperature reveals that the 4f–5d electronic transitions of Ce³⁺ ions can be treated to couple with one frequency-degenerate vibrational mode having the effective phonon energy of ∼257 cm⁻¹ with the corresponding Huang–Rhys parameter of ∼6, which indicates a strong electron–phonon interaction of Ce³⁺ luminescence in the Li₆Y(BO₃)₃ host. Finally, the X-ray excited luminescence spectrum of the LYBO:5%Ce³⁺ phosphor is measured to check the potential scintillator applications.

The critical issues of Ce³⁺ luminescence including thermal stability and spectral profile are discussed in this work.

Analysis of the structure and abnormal photoluminescence of a red-emitting LiMgBO3:Mn2+ phosphor

In LiMgBO₃:Mn²⁺ phosphor, the origin of the abnormal luminescence (deep red emission) of Mn²⁺ in five-coordinated configuration has been disclosed.

Novel yellowish-green light-emitting Ca10(PO4)6O:Ce3+ phosphor: structural refinement, preferential site occupancy and color tuning

Novel yellowish-green emitting Ca₁₀(PO₄)₆O:Ce³⁺ phosphor are obtained through controlling the preferential site occupancy of Ce³⁺ ions.

Structural evolution induced preferential occupancy of designated cation sites by Eu2+ in M5(Si3O9)2 (M = Sr, Ba, Y, Mn) phosphors

A schematic presentation for the unexpected blue-shifted luminescence of Eu²⁺ in M₅(Si₃O₉)₂ (M = Sr, Ba, Y, Eu, Mn) based on the preferential occupancy at the designated cation sites.

Combination cation substitution tuning of yellow-orange emitting phosphor Mg2Y2Al2Si2O12:Ce3+

A yellow-orange emitting garnet phosphor Mg₂Y₂Al₂Si₂O₁₂:Ce³⁺ was prepared through combination substitution, and a high colour rendering index white LED lamp was achieved.

Recent progress in luminescence tuning of Ce3+and Eu2+-activated phosphors for pc-WLEDs

This review is devoted to several approaches to realize spectral tuning for improving the luminescence performance of Ce³⁺and Eu²⁺-activated pc-WLED phosphors.

Structure and photoluminescence characteristics of europium(iii) doped in CaAl2Si2O8phosphors

A series of Eu³⁺activated CaAl₂Si₂O₈phosphors have been synthesized at 1350 °C in air, and their photoluminescence properties have been investigated as a function of activator concentrations.

A novel tunable Na2Ba6(Si2O7)(SiO4)2:Ce3+,Mn2+ phosphor with excellent thermal stability for white light emitting diodes

In this paper, Ce³⁺ doped and Ce³⁺,Mn²⁺ co-doped Na₂Ba₆(Si₂O₇)(SiO₄)₂ phosphors were synthesized via a high temperature solid-state reaction.