Tuning luminescence from NIR-I to NIR-II in Cr3+-doped olivine phosphors for nondestructive analysis

Journal of Materials Chemistry C .Issue 16, 2021

Graphical abstract: Tuning luminescence from NIR-I to NIR-II in Cr3+-doped olivine phosphors for nondestructive analysis

The practical application of near-infrared (NIR) phosphors is hindered due to their limited light emitting region and narrow bandwidth. Here, we report a series of Cr3+-doped olivine phosphors, (Mg1−xLix)(Mg1−xScx)GeO4:Cr3+, with tunable luminescence from NIR-I to NIR II based on crystallographic site engineering. By using a [Li+–Sc3+] unit substituting for a [Mg2+–Mg2+] unit, the NIR luminescence can be largely tuned from 940 nm to 1110 nm, and the corresponding FWHM can be modified from 236 to ∼300 nm. The internal quantum efficiency (IQE) and external quantum efficiency (EQE) of Mg2GeO4:1% Cr3+ were measured to be 48.19% and 16.38%, respectively. The photoluminescence of the phosphors matches well with the absorption of several functional groups. By measuring the NIR absorption of different liquids illuminated by NIR light from our phosphors, qualitative and quantitative analysis can be realized. These results suggest that the super-broad NIR luminescence of (Mg1−xLix)(Mg1−xScx)GeO4:Cr3+ has potential applications as light sources for nondestructive food analysis.

 

Orange super-long persistent luminescent materials: (Sr1-xBax)3SiO5:Eu2+,Nb5+

 Mater. Chem. Front., 2021, 5, 333-340

image file: d0qm00488j-f1.tif

Persistent luminescent materials are widely used as night-vision and marking materials in various important fields. Although significant achievements have been made in blue and green persistent luminescent (PersL) materials, the research and development of PersL materials in the warm-color region (550–660 nm) are relatively lacking. Only the orange PersL phosphor Y2O2S:Eu3+,Mg2+,Ti4+ (∼610 nm) and deep red PersL phosphor (Ca1−xSrx)S:Eu2+,Tm3+ (∼650 nm) fulfill the demands of commercial applications. However, sulfide phosphors have poor chemical stability and a relatively short persistent duration time. Herein, we report a series of orange PersL materials, (Sr1−xBax)3SiO5:Eu2+,Nb5+, which exhibit a strong PersL emission band at 550–670 nm and a super-long persistent time of more than 20 h at the 0.32 mcd m−2 threshold value after UV radiation. These new orange PersL materials are compared to the commercial warm-color sulfide PersL phosphor, Y2O2S:Eu,Mg,Ti, with regards to PersL time and brightness, and it is determined that they would have great potential applications.

Broadband deep‐red‐to‐near‐infrared emission from Mn2+ in strong crystal‐field of nitride MgAlSiN3

 J Am Ceram Soc., 2020; 103: 6793– 6800. https://doi.org/10.1111/jace.17304

Broadband near‐infrared (NIR) phosphors have received increasing attention for fabricating phosphor‐converted light‐emitting diodes (pc‐LEDs) as NIR light source. Most of the reported broadband NIR phosphors originate from Cr3+ in weak crystal field environments. Herein, we report a luminescent material, MgAlSiN3:Mn2+ with CaAlSiN3‐type structure, demonstrating that broadband deep‐red‐to‐NIR emission can be achieved via doping Mn2+ into crystallographic sites with strong crystal field in inorganic solids. This phosphor is synthesized via easy‐handle solid‐state reaction, and the optimized sample, (Mg0.93Mn0.07) AlSiN3 shows an emission band with peak at ~754 nm, FWHM of 150 nm, and internal quantum efficiency of 70.1%. The photoluminescence intensity can further be enhanced by co‐doping Eu2+ as sensitizer. This work provides a new strategy for discovering new broadband NIR phosphors using Mn2+ in strong crystal field as luminescence center.

Crystal structure and photoluminescence properties of (Y1−xCex)4Si2O7N2

Opt. Mater., 2010, 33, 1, 91. https://doi.org/10.1016/j.optmat.2010.08.011

Oxonitridosilicate compounds with compositions of (Y1−xCex)4Si2O7N2 (x = 0–0.1) compounds have been synthesized. The relations of structure, photoluminescence properties and Ce content have been studied. These compounds have a broad band excitation covering from 350 to 450 nm and a broad band emission covering from 450 to 575 nm. There exist four different types of photoluminescence centers, which correspond to four different crystallographic sites accommodating the Ce3+ dopants in the lattice. The energy transfer among Ce3+ ions in different sites enhance with the increasing Ce content, leading to red-shift of the emission peaks and concentration quenching. The relationship between crystallographic sites of Ce3+ ions and luminescence properties is established. (Y1−xCex)4Si2O7N2 is a promising phosphor for use in white light-emitting diodes.

Stability of divalent/trivalent oxidation state of europium in some Sr-based inorganic compounds

J. Lumin., 2012, 132, 7, 1768. https://doi.org/10.1016/j.jlumin.2012.02.013

This work investigates the stability of Eu2+ and Eu3+ in some Sr-based inorganic compounds. Generally reducing condition is adopted in order to obtain Eu2+, however, the Eu doped SrAl2O4/SrLaAlO4 case indicates that for some compounds Eu3+ is stabilized even in reducing atmosphere. Bond valence method is applied to explain this phenomenon and it reveals that crystal structure also determines the valence state of europium cations along with reducing/oxidizing condition. An analysis of other Eu doped Sr-based materials is performed which shows the relationship between Eu2+/Eu3+ stability and the Global Instability Index (GII). This research provides a guideline for synthesizing specific novel Eu2+/Eu3+ phosphors.

Photoluminescence properties of Y5Si3O12N:Ce3+ blue-emitting phosphors for white LED

J. Alloys Compd., 2012, 521, 77. https://doi.org/10.1016/j.jallcom.2012.01.044

Blue oxonitridosilicate phosphors with compositions of (Y1−xCex)5Si3O12N (x = 0–0.1) have been synthesized. The structures, photoluminescence properties and the relations between the structure and luminescence have been investigated and discussed. The atomic positions and the lattice parameters of Y5Si3O12N were acquired. Y atoms occupy two crystallographic sites (Y(1) and Y(2)) in the structure. Ce3+ ions were substituted for Y3+ ions and two types of photoluminescence centers (Ce(1)3+ and Ce(2)3+) have been formed. The excitation and emission processes of Ce(1)3+ and Ce(2)3+ photoluminescence centers were identified and studied. The concentration- and temperature-dependent properties of these Y5Si3O12N:Ce3+ phosphors were investigated. This study shows these blue Y5Si3O12N:Ce3+ phosphors the potential applications in the three-RGB phosphor-converted white LEDs.

An investigation of crystal chemistry and luminescence properties of Eu-doped pure-nitride α–sialon fabricated by the alloy-nitridation method

J. Lumin., 2012, 132, 9, 2390. https://doi.org/10.1016/j.jlumin.2012.04.006

A novel synthesis route of Eu2+-doped pure-nitride α-sialons has been reported. It is through an alloy-nitridation method at ∼2173 K in nitrogen atmosphere, with stable alloys (CaAl, SiEu), AlN, and α-Si3N4 powders as starting materials. A linear relationship between the lattice parameters and m values of (Ca0.995Eu0.005)m/2Si12−mAlmN16 compositions is obtained, indicating that our samples contain very little oxygen, i.e. herein so-called Eu-doped pure-nitride α-sialons. The (Ca0.995Eu0.005)m/2Si12−mAlmN16 compounds with 2.4≤m≤4.0 give the strongest emission. The emission shifts to longer wavelength with m values increasing as well as Eu contents increasing. (Ca0.995Eu0.005)m/2Si12−mAlmN16 compositions with smaller m values exhibit better thermal quenching properties.

Thermochromic material Sr2SiO4:Eu2+ based on displacive transformation

J. Lumin., 2014, 152, 199. https://doi.org/10.1016/j.jlumin.2013.11.023.

Strontium silicate Sr2SiO4 undergoes a displacive phase transformation around 85 °C. However, the steady state spectra involved in the process lacks investigation. In this paper, two kinds of Sr2SiO4:Eu2+ with and without Ba ions are synthesized. They are tested for XRD patterns and luminescent spectra at varying temperatures. The results show that Ba ions could effectively suppress the phase transition. For sample without Ba, temperature-dependent XRD patterns confirm the occurrence of phase transition and the emission peak positions at varying temperatures demonstrate a hysteresis behavior. The color of sample heated to 100 °C under UV illumination is distinguishable from that unheated. This structure-sensitive behavior make Sr2SiO4:Eu2+ as potential thermochromic material.

Peak wavelength selection guides of chip and phosphors for phosphor-converted white light-emitting diodes

Rare Met., 2014, 33, 1, 80. https://link.springer.com/article/10.1007/s12598-013-0210-2.

The dependences of light efficiency of radiation (LER) and color-rendering index (CRI) of trichromatic white light-emitting diode (wLED), composed of blue LED die, green/yellow, and red phosphors, on the peak wavelength of each primary were investigated by theoretical calculations, at correlative color temperature (CCT) from 2,700 to 6,500 K. The peak wavelength of InGaN based blue LED chip ranges from 450 to 471 nm, while those of Ca3Sc2Si3O12:Ce3+, b-SiAlON:Eu2+, and Y3Al5O12:Ce3+ based green/yellow phosphors range from 511 to 572 nm, and those of Sr2Si5N8:Eu2+ and CaAlSiN3:Eu2+ red phosphors range from 620 to 650 nm, which cover almost all the practically used, commercially available wave bands until now. Then, based on the results, selection guides of peak wavelengths for blue LED chip and phosphors to obtain tradeoff LER >280 lm·W−1 as well as CRI >80 in all CCTs are proposed. The favorable wave bands of each primary are suggested.

Optimization of light efficacy and angular color uniformity by hybrid phosphor particle size for white light-emitting diode

Rare Met., 2014, 33, 3, 348. https://link.springer.com/article/10.1007/s12598-013-0216-9.

In this study, small- and large-particle-diameter phosphor powders were mixed together (hybrid phosphors) to balance light efficacy and angular color uniformity and pursue optimal results. Phosphor with small-particle-diameter of 4 μm was employed and it was mixed into each large-particle-diameter phosphor of 10, 16, 22, and 26 μm, at mass percentage from 0 % to 50 % with an interval of 10 %, respectively. Remote phosphor package was adopted and overall phosphor concentration was kept constant for better comparison. Moreover, absorption coefficient μ abs, scattering coefficient μ sca and extinction coefficient μ ext of each hybrid phosphors were calculated based on Mie theory to further discuss the experiment results. Results show that, the introduction of small-particle-diameter phosphor to large one can highly improve angular color uniformity while only slightly reduce light efficacy. The optimal performance with angular color uniformity of 91.6 % as well as normalized light efficacy of 95.7 % is achieved in the white light emitting diode with hybrid phosphors consisting of 60 wt% powder of 22 μm and 40 wt% powder of 4 μm.