Eu2+, Dy3+: Sr2B5O9Cl,a new blue-emitting phosphor with long persistence

A new Eu²⁺, Dy³⁺: Sr₂B₅O₉Cl phosphor with long persistence was synthesized in a reducing atmosphere by a solid-state reaction process. The pure-phase phosphor was obtained by calcination at 900 °C. The introduction of Eu²⁺ into the lattice of the matrix resulted in a broad blue emission centered at 423 nm, which was due to the characteristic 4f6⁵d¹ to 4f⁷ energy transfer of Eu²⁺ ions. Both Eu-doped and Dy/Eu-codoped phosphors displayed afterglow behaviors due to the electron traps generated by the incorporation of tri-valanced rare earth cations into the original Sr lattice sites. The afterglow of Eu²⁺: Sr₂B₅O₉Cl and Eu²⁺, Dy³⁺: Sr₂B₅O₉Cl phosphors showed standard double exponential decay behaviors, and the Eu²⁺/Dy³⁺ co-doped sample demonstrated better afterglow properties than Eu²⁺-doped one. A longer lifetime for the electrons was confirmed after the afterglow decay curve simulation. Based on the analysis of thermally stimulated luminescence (TSL), the difference in afterglow was attributed to the different trap concentrations induced by the Dy³⁺ (Eu³⁺) doping in the Sr₂B₅O₉Cl matrix.     

Luminescence properties of a novel greenish-blue emission long persistent phosphor Sr3TaAl3Si2O14:Pr3+

Pr³⁺exhibits prominent red emission in most oxide phosphors, which derives from the ¹D₂→³H₄ transition, and green or blue emission from ³P₀→³H_{4, 5} transitions are normally less intense in most cases. However, a greenish-blue emission was observed from Sr₃TaAl₃Si₂O₁₄:Pr³⁺prepared via solid state reaction. All as-prepared phosphors were studied systematically by X-ray diffraction (XRD), photoluminescence spectra, decay curves, long afterglow (LAG) spectra and thermoluminescence (TL) glow curves. Based on the excitation and emission spectra, the Sr₃TaAl₃Si₂O₁₄ (STAS) host is proved to be a self-activated luminescent host lattice. In the emission spectra for Pr³⁺doped STAS, the predominant greenish-blue emission locating at ~489 nm and ~507 nm coming from ³P_0,1→³H₄ transitions were observed. And the different mechanisms for concentration quenching in both cases were discussed. At last, a model was proposed on the basis of experimental results to discuss the LAG mechanism of STAS:Pr³⁺in detail.     

A new mechanoluminescence phosphor Na3Sc2(PO4)3:Eu2+: Phase transition-assisted defect formation in a polymorphic composition

A new mechanoluminescent phosphor was developed from a sodium (Na) superionic conductor (NASICON)-structured Na₃Sc₂(PO₄)₃:Eu²⁺ phosphor that is known for its self-healing properties. The compound that crystalized assuming monoclinic C2/c symmetry was found to be blue-emitting, with no noticeable persistent luminescence. Thermoluminescence analysis showed that the phosphor had two prominent distinct thermal emission bands corresponding to the high-temperature β- and γ-phases of the composition. The mechanoluminescence properties of the material that does not have any persistent luminescence at room temperature were investigated by imparting impulsive strain. The compound on charging with 365 nm radiation was found to have significant mechanoluminescent emission originating from shallow defects present in the β-phase of composition that formed by the stress-induced phase transition process. Its emission characteristics and temporal behavior were investigated by varying the impact velocity.     

Red,green and blue-violet emission coexistence in white-light-emitting Ca3SiO4Cl2:Bi3+, Li+, Eu2+, Eu3+ phosphor

A series of emission-tunable Ca₃SiO₄Cl₂:Bi³⁺, Li⁺, Euⁿ⁺(n =2, 3) (CSC:Bi³⁺, Li⁺, Euⁿ⁺) phosphors have been synthesized via sol-gel method. The X-ray diffraction results indicate that the as-synthesized phosphors crystallize in a low temperature phase with the space group of P21/c. Energy transfer from Bi³⁺ to Eu³⁺/Eu²⁺ exists in CSC:Bi³⁺, Li⁺, Euⁿ⁺ phosphors. Under the excitation of 327 or 365 nm, the Ca_2.98−ySiO₄Cl₂:0.01Bi³⁺, 0.01Li⁺, yEuⁿ⁺(y=0.0001–0.002) phosphors show an intense green emission band around 505 nm, while under the excitation of 264 nm, three emission bands centered around 396 nm (Bi³⁺), 505 nm (Eu²⁺) and 614 nm (Eu³⁺) are observed and tunable colors from blue-violet to green or white are achieved in these phosphors by varying the content of Eu. White-light emission with the color coordinate (0.312, 0.328) is obtained in Ca_2.978SiO₄Cl₂:0.01Bi³⁺, 0.01Li⁺, 0.002Euⁿ⁺(n =2, 3). Based on these results, the as-prepared CSC:Bi³⁺, Li⁺, Eu²⁺, Eu³⁺ phosphors can act as color-tunable and single-phase white emission phosphors for potential applications in UV-excited white LEDs.     

Red-shift and improved afterglow of Sr3Al2-xBxO5Cl2:Eu2+, Dy3+ phosphors via a cation substitution strategy

Sr₃Al_2-xB_xO₅Cl₂:Eu²⁺, Dy³⁺ (x = 0, 0.2, 0.4) long persistent phosphors were prepared via solid-state process. The pristine Sr₃Al₂O₅Cl₂:Eu²⁺, Dy³⁺ phosphor exhibits orange/red broad band emission around 609 nm, which can be attributed to the electric radiation transitions 4f⁶5 d¹→4f⁷ of Eu²⁺. Upon the same excitation, the B³⁺-doped Sr₃Al_2-xB_xO₅Cl₂:Eu²⁺, Dy³⁺ phosphors display red-shift from 609 nm to 625 nm with increasing B³⁺ concentrations. The XRD patterns show that Al³⁺ can be replaced by B³⁺ in the host lattice at the tetrahedral site, which causes lattice contraction and crystal field enhancement, and thereafter achieves the red-shift on the emission spectrum. The XPS investigation provides direct evidence of the dominant 2-valent europium in the phosphor, which can be ascribed for the broad band emission of the prepared phosphors. The afterglow of all phosphors show standard double exponential decay behavior, and the afterglow of Sr₃Al₂O₅Cl₂:Eu²⁺, Dy³⁺is rather weak, while the sample co-doped with B³⁺shows longer and stronger afterglow, as confirmed after the curve simulation. The analysis of thermally stimulated luminescence showed that, when B³⁺ is introduced, a much deeper trap is created, and the density of the electron trap is also significantly increased. As a result, B³⁺ ions caused redshift and enhanced afterglow for the Sr₃Al_2-xB_xO₅Cl₂:Eu²⁺, Dy³⁺ phosphor.     

Thermoluminescence study of Eu3+ doped Na2Sr2Al2PO4Cl9 phosphor via doping of singly,doubly and triply ionized ions

We report here thermoluminescence properties of Eu³⁺ doped Na₂Sr₂Al₂PO₄Cl₉ phosphor via doping of singly, doubly and triply ionized ions on the basis of PL studies done for this sample. The proposed sample was synthesized using solid state reaction method. Vibrational feature of this phosphor was confirmed by FT-IR spectra. This sample shows high degrees of crystallinity. All subseries are irradiated with ⁶⁰Co- γ (gamma) source and thermoluminescence studies were done for all subseries formed by doping of singly, doubly and triply ionized ions. The result shows that all the series give highest TL intensity at low dose rate. On doping of triply doped ionized ion (Y³⁺), TL intensity is enhanced to some extent. Deconvolution of broad TL glow data formed for some sample were done by using TLAnal computerized software. Thermoluminescence studies of these Eu³⁺ doped SrYAl₃O₇ phosphor were done by Nucleonix TL 1009I thermoluminescence (TL) reader. Trapping parameters of each phosphor such as activation energy (E), order of kinetics (b) and frequency factor (s) were calculated by Chen's peak shape method, Initial rise method and Ilich method. Thus, the singly, doubly and triply ionized ions co-doped with Na₂Sr₂Al₂PO₄Cl₉: Eu³⁺phosphor may be used in high dose thermoluminescence dosimetric application in various fields.     

Optical absorption and selective thermal emission in directionally solidified Al2O3-Er3Al5O12 and Al2O3-Er3Al5O12-ZrO2 eutectics

Al₂O₃-Er₃Al₅O₁₂ and Al₂O₃-Er₃Al₅O₁₂-ZrO₂ eutectic ceramic rods were directionally solidified using the laser floating zone technique at several growth rates. Binary eutectic microstructure consisted in a three-dimensional interpenetrated network of the eutectic phases whereas the ternary eutectic showed a geometrical microstructure at low growth rates and a nanofibrillar pattern at high rates. The microstructure size was strongly dependent on the growth rate, decreasing when the processing rate increased. The optical absorption was measured in the samples at room temperature and Judd–Ofelt analysis was used to model the optical absorption of the Er³⁺ ions. Thermal emission of the eutectic rods was studied at temperatures up to 1600 °C. An intense narrow emission band at 1.55 μm matching with the sensitive region of the GaSb photoconverter was obtained. The intensity of the selective emission band is larger for the binary eutectic than for the ternary compound and increases as the microstructural size decreases.     

Effect of singly,doubly and triply ionized ions on downconversion photoluminescence in Eu3+ doped Na2Sr2Al2PO4Cl9 phosphor: A comparative study

We report a change in the red photoluminescence of the Eu³⁺ doped Na₂Sr₂Al₂PO₄Cl₉ phosphor via doping of singly, doubly and triply ionized ions. The synthesized phosphors show good crystalline nature. The EDS analysis confirms the presence of desired elements in the phosphor samples. The vibrational feature of the phosphor was confirmed by FTIR analysis. The photoluminescence excitation spectra of the phosphor show three peaks at 317, 395 and 467 nm. The Eu³⁺ doped Na₂Sr₂Al₂PO₄Cl₉ phosphor emits intense red color on excitations with 395 and 467 nm wavelengths. However, the photoluminescence intensity of the phosphor is larger for 395 nm excitation. When the singly, doubly and triply ionized ions are co-doped in the Eu³⁺ doped Na₂Sr₂Al₂PO₄Cl₉ phosphor (i.e. F⁻, WO₄²⁻, MoO₄²⁻, VO₄³⁻, La³⁺, and Y³⁺) the photoluminescence intensity of the phosphor is decreased significantly. The decrease in photoluminescence intensity is due to change in local crystal structure created by these ions. Interestingly, the photoluminescence intensity of phosphor increases many times when the (Y³⁺) ion incorporated phosphor is excited with 317 nm wavelength. The CIE diagram shows color emitted in the red region of visible spectrum and the color purity is larger for triply ionized (Y³⁺) ion. Thus, the singly, doubly and triply ionized ions activated Na₂Sr₂Al₂PO₄Cl₉: Eu³⁺ phosphor may be used in displays devices, photonic devices, solid state lighting and white LEDs.     

Persistent photoluminescence emission from SrTa2O6:Pr3+ phosphor prepared at different temperatures

Phosphors with persistent emission are of interest for security and emergency signage, and medical diagnosis. Three SrTa₂O₆:Pr³⁺phosphor samples with persistent emission were prepared by solid state reaction at 1200, 1400 and 1500 °C. Structural crystallization was shown to improve with an increase in temperature as identified by X-ray diffraction. The scanning electron microscopy images showed that the particles of the phosphor were agglomerated and co-melting was induced by increasing the synthesis temperature. The ion distribution in the phosphors was determined using the time of flight secondary ion mass spectroscopy. The red emission was obtained from the D₂→³H₄ and the ³P₀→³H₆ transitions at 608 and 619 nm, respectively. The main absorption occurred at 225 nm (5.5 eV), and the band gap (E_g) calculations confirmed that it corresponds to band-to-band excitation. Another excitation due to charge transfer at 300 nm was also obtained which makes the phosphor suitable to be used in red light emitting diodes. The persistent emission time parameters (260–296 s) were calculated from the phosphorescence decay curves using the second order exponential decay equation. The corresponding electron trapping centers were determined using the thermoluminescence spectroscopy, and the activation energy was determined using the initial rise method.     

Blue-red dual color emitting phosphor Cs2NaLuCl6: Sb3+, Ho3+ for plant growth LEDs

The phosphor-converted light emitting diode (pc-LED) is an efficient light source to adjust growth rhythm and raise yield of plant. Blue and red light play the dominant role in the process of plant growth, thus it is meaningful to search the blue-red dual emission phosphors with high quantum field and better thermal stability for developing plant growth LED. Herein, the blue-red dual emission phosphors were synthesized by co-doping Sb³⁺ and Ho³⁺ into the Cs₂NaLuCl₆, which emitted blue (454 nm) to red (657 nm) light with increasing the content of Ho³⁺ to 25% and their relative intensity could be tuned through adjusting the concentration of Ho³⁺ due to the efficient energy transfer from Sb³⁺ to Ho³⁺. The intensity of blue emission from Sb³⁺ and red emission from Ho³⁺ could maintain 78.4 and 75.8% of the room temperature at 150 °C, respectively. Furthermore, the spectra of fabricated blue and red LEDs match well with the absorption of carotenoid, Phytochrome and Chlorophyll b, implying the samples possess great application potential in plant growth LED.     

Enhanced luminescence and energy transfer performance of double perovskite structure Gd2MgTiO6:Bi3+, Mn4+ phosphor for indoor plant growth LED lighting

Deep-red light emitting phosphors are widely used in LEDs for indoor plant growth because of the critical role played by red light in plant growth. The luminescence properties of deep-red phosphors are still not well understood at present. An energy transfer strategy is a common and effective method to improve luminescence properties. In principle, the energy transfer process may occur when the sensitizer's emission spectra overlap with the activator's excitation spectra. In this work, Bi³⁺ and Mn⁴⁺ were incorporated into the matrix of Gd₂MgTiO₆ as sensitisers and activators, respectively. Mn⁴⁺ ions tend to occupy the [TiO₆] octahedral site and the Bi³⁺ ions are expected to substituted in the site of Gd³⁺. The energy transfer process from Bi³⁺ to Mn⁴⁺ was realised and the photoluminescence (PL) intensity of Mn⁴⁺ increased with the doping content of Bi³⁺. Upon excitation at 375 nm, the PL intensity of Mn⁴⁺ increased to 116.4% when the doping concentration of Bi³⁺ reached 0.3%. Finally, the pc-LED devices were prepared by a Gd₂MgTiO₆:Bi³⁺, Mn⁴⁺ phosphor. The high red luminescence indicated that this phosphor has potential applications in indoor LED lighting.     

Low-temperature microwave synthesis and luminescence properties of far-red emission ZnGa2O4:Cr3+ phosphor for plant cultivation

In this work, microwave (MW) sintering method is employed to synthesize far-red (FR) emission ZnGa₂O₄:Cr³⁺ phosphor at a lower sintering temperature (900 °C), comparing with the conventional high temperature solid-state sintering (SS) method. Micrometer-size phosphor particles with smooth morphology are obtained due to the MW-induced small temperature gradient between the constituent particles upon the local dielectric volumetric heating. The MW sintering ZnGa₂O₄:Cr³⁺ phosphor exhibited excitable properties at the wavelengths of 260 nm, 410 nm and 550 nm, and the intensity of photoluminescence excitation (PLE) at 260 nm showed a dramatic enhancement, which is 2–3 times higher than that of SS sintering sample due to MW “non-thermal effect” in reducing the defect amount in the ZnGa₂O₄ host latices. These results together with decay time, thermal quenching and color coordinate evaluations showed that synthesis of FR emission ZnGa₂O₄:Cr³⁺ by MW-sintering method has advantages of high efficiency, energy saving and least environmental threats.     

Effect of Ga3+ ion doping on emission thermal stability and efficiency of MgAl2O4:Cr3+ phosphor

In this work, we fabricated a novel spinel-type phosphor material MgAl_2−xGa_xO₄ doped with Cr³⁺ by the high-temperature solid-state sintering method. The crystal field environment of the spinel was tuned by replacing the Al ions with Ga³⁺ ions of different concentrations. The cell volume and D_q/B gradient increase from 2.82 to 2.62 with increasing Ga³⁺ ion doping concentration. This also implies a gradual decrease in the field strength of the crystal. Based on this, the excitation spectra of MgAl_1.995−xGa_xO₄:0.5%Cr³⁺ phosphors yield a redshift. Increasing the Ga³⁺ ion doping concentration also improves the emission intensity and thermal stability of the phosphors, and the emission intensity of the Ga³⁺-doped phosphors is significantly increased. For a Ga/Al ratio of 1, the thermal stability of the phosphor emission is optimal. The emission intensity at 140°C can maintain 76% of the emission intensity at room temperature, indicating that appropriate Ga³⁺ ion doping can improve the emission efficiency and thermal stability of the phosphors.     

Sr3GdLi(PO4)3F:Eu2+, Mn2+: A tunable blue-white color emitting phosphor via energy transfer for near-UV white LEDs

A series of Eu²⁺ and Mn²⁺ co-doping Sr₃GdLi(PO₄)₃F phosphors have been synthesized through high temperature solid state reaction. Eu²⁺ single doped Sr₃GdLi(PO₄)₃F phosphors have an efficient excitation in the range of 230–430 nm, which is in good agreement with the commercial near-ultraviolet (n-UV) LED chips, and gives intense blue emission centering at 445 nm. The critical distance of the Eu²⁺ ions in Sr₃GdLi(PO₄)₃F is computed and demonstrated that the concentration quenching mechanism of Eu²⁺ is mostly caused by the dipole-dipole interaction. By co-doping Eu²⁺ and Mn²⁺ ions in the Sr₃GdLi(PO₄)₃F host, the energy transfer from Eu²⁺ to Mn²⁺ that can be discovered. With the increase of Mn²⁺ content, emission color can be adjusted from blue to white under excitation of 380 nm, corresponding to chromatic coordinates change from (0.189, 0.108) to (0.319, 0.277). The energy transfer from Eu²⁺ to Mn²⁺ ions is proven to be a dipole-dipole mechanism on the basis of the experimental results and analysis of photoluminescence spectra and decay curves. This study infers that the obtained Sr₃GdLi(PO₄)₃F:Eu²⁺, Mn²⁺ phosphors may be a potential candidate for n-UV LEDs.     

Broadband near-infrared double-perovskite phosphor Sr2ScTaO6:Cr3+, Yb3+ for NIR pc-LED applications

The broadband near-infrared (NIR) phosphor converted light emitting diode (NIR pc-LED) has garnered unprecedented attention due to its crucial role in NIR applications. However, there remains a scarcity of efficient broadband NIR luminescence materials capable of emitting NIR light with wavelengths greater than 800 nm. This study reports the synthesis, crystal structure and photoluminescence (PL) properties for double perovskite Sr₂ScTaO₆:Cr³⁺ phosphors which exhibit a broadband NIR emission in the 650–1250 nm range, peaking at∼815 nm with the full width at half maximum (FWHM) of 161 nm. The observed broadband emission arises from two distinct Cr³⁺ centers, namely Sc³⁺ and Ta⁵⁺ octahedral sites within the Sr₂ScTaO₆ structure, as demonstrated by luminescence and decay kinetic analysis. A significant enhancement of the thermal stability and a remarkable broadening of the FWHM (from 161 to 275 nm) are achieved by employing Yb³⁺ co-doping strategy. The efficient energy transfer from Cr³⁺ to Yb³⁺ was confirmed through emission and excitation spectra, as well as luminescence decay measurements. Finally, Sr₂ScTaO₆:Cr³⁺-Yb³⁺ phosphor was integrated with a 470 nm blue LED chip to fabricate a NIR pc-LED device, and its potential application in night vision was evaluated.     

A novel single-phase Na3.6Y1.8(PO4)3:Bi3+,Eu3+ phosphor for tunable and white light emission

A new type of Bi³⁺,Eu³⁺ single- and co-doped Na_3.6Y_1.8(PO₄)₃ phosphate phosphors were manufactured using conventional high-temperature solid-state reaction technique to explore their application for solid-state lighting. The crystal structure, luminescent properties, luminescent mechanism and quantum efficiency were thoroughly explored. Results show that there are two crystallization sites for Bi³⁺ and Eu³⁺ ions. Upon the excitation of 342 and 373 nm, Bi³⁺ single-doped phosphors exhibit green and blue emission, derived from the ³P₁ to ¹S₀ transition of Bi³⁺ located in different occupancy sites. Thanks to radiative energy transfer process from Bi³⁺ to Eu³⁺, adjustable emission could be acquired by altering Eu³⁺ content in co-doped phosphors. Pure white-light emission with quantum efficiency value of 22.9% can be realized in Na_3.6Y_1.8(PO₄)₃:0.01Bi³⁺,0.1Eu³⁺ sample and the integrated intensity of white light emission at 417 K remains 85% of that at room temperature. Our results indicate that Na_3.6Y_1.8(PO₄)₃:Bi³⁺,Eu³⁺ phosphors have feasible application in high-power ultraviolet driven solid-state lighting.     

Luminescent properties and LED Application of Broadband Near-Infrared Emitting NaInGe2O6: Cr3+ phosphors

A NIR-emitting Cr³⁺-activated phosphors (NaInGe₂O₆: Cr³⁺) covering whole NIR-I region (700–1200 nm) were successfully designed and prepared via solid-state reaction. XRD and Rietveld refinement verified that the octahedral In³⁺ site is the preferred site of Cr³⁺ substitution in NaInGe₂O₆ structure. The synthesized NaInGe₂O₆: Cr³⁺ phosphors exhibit two strong absorption bands at 480 and 700 nm, and show a mountain-like single-band emission at 900 nm with FWHM = 175 nm. The crystal field parameters are calculated using steady-state spectral data, in which a low Dq/B value of 1.89 is obtained and results in this broadband NIR emission. NaInGe₂O₆: Cr³⁺ exhibits good emission thermal stability, i.e. 55 % of room temperature intensity at 373 K. Besides, an efficient NIR pc-LED is fabricated and shows NIR output of 25.2 mW@120 mA. This broadband NaInGe₂O₆: Cr³⁺ NIR phosphor could be merged into pc-LED package for hand-held spectrometers, security cameras and vivo biomarkers.     

Enhance the luminescence properties of Ca14Al10Zn6O35:Ti4+ phosphor via cation vacancies engineering of Ca2+ and Zn2+

Ti⁴⁺-activated zinc calcium aluminate phosphors, owing to their excellent luminescence properties, nontoxicity, environment friendliness and low price, have a certain prospect in the field of plant cultivation. In this study, we have successfully synthesized a series of Ca_14-yAl_10-xZn_6-zO₃₅:xTi⁴⁺ (CAZO:Ti⁴⁺) phosphors through a high-temperature solid-state method. Furthermore, the emission spectrum of CAZO:Ti⁴⁺ located in bluish violet-emitting band, and has an emission peak at 378?nm upon the excitation of 268?nm due to the charge transfer of Ti⁴⁺-O^2-. Moreover, the luminescence intensity of as-synthetized phosphors can be improved by cation vacancies engineering to compensate for charge unbalance. Especially, the luminescence intensity could be further improved when the Ca²⁺ vacancy is 0.35?mol or the Zn²⁺ vacancy is 0.275?mol. Furthermore, the X-ray powder diffraction (XRD) analysis and crystal structure are checked and confirmed that the synthesized material is pure phase. The concentration quenching mechanism, FT-IR spectra, UV–vis absorption properties, lifetimes and electron transition process of Ca_14-yAl_10-xZn_6-zO₃₅: xTi⁴⁺ were discussed in detail. From the above, the phosphor has a potential application for plant growth field due to its broad bluish violet emission.     

Dopant and compositional modulation triggered long-wavelength ultra-broadband and tunable NIR emission in MgO: Cr3+ phosphor for NIR spectroscopy applications

Efficient ultra-broadband near-infrared (NIR) phosphors with long-wavelength (λ_max > 850 nm) and wide full width at half-maximum (FWHM, >200 nm) have sparked tremendous interest, demonstrating their immense potential in NIR spectroscopy technology. Nevertheless, the development of NIR spectroscopy technology suffers from the restricted capability to efficiently emit the ultra-broadband NIR light. Herein, the synergetic enhancement strategy of heterogeneous substitution and compositional modulation was applied to create a novel Cr³⁺ doped long-wavelength ultra-broadband MgO: Cr³⁺, Ga³⁺ phosphor, which exhibited a long-wavelength ultra-broadband NIR emission (λ_max = 850 nm) covering the range of 650–1300 nm on the electromagnetic spectrum with the FWHM of more than 200 nm under the excitation of 468 nm light. Furthermore, the tunable NIR emission from 818 nm to 862 nm with an optimized quantum efficiency of 30% was accomplished by the Ga³⁺ ions substitution and Cr³⁺ ions modulation. The phosphor exhibited remarkable thermal stability up to 100 °C, remaining 83% of the integrated emission intensity at room temperature. A prototype of the NIR phosphor-converted LED (pc-LED) demonstrated that the novel MgO: Cr³⁺, Ga³⁺ phosphor possessed a relatively strong NIR output power (15.05 mW at 100 mA driven current) with a photoelectric conversion efficiency of 5.53%, which is impressive compared with other Cr³⁺-doped long-wavelength ultra-broadband phosphors. This work not only proposes a novel long-wavelength ultra-broadband NIR phosphors with industrialization and great application prospect in night vision but highlights a synergetic enhancement strategy to effectively boost the performance of long-wavelength ultra-broadband NIR pc-LED light sources.     

Luminescence properties and energy transfer investigations of Sr2B2O5:Ce3+,Tb3+ phosphors

Ce³⁺ and Tb³⁺ co-doped Sr₂B₂O₅ phosphors were synthesized by the solid-state method. X-ray diffraction (XRD) was used to characterize the phase structure. The luminescent properties of Ce³⁺ and Tb³⁺ co-doped Sr₂B₂O₅ phosphors were investigated by using the photoluminescence emission, excitation spectra and reflectance spectra, respectively. The excitation spectra indicate that this phosphor can be effectively excited by near ultraviolet (n-UV) light of 317 nm. Under the excitation of 317 nm, Sr₂B₂O₅:Ce³⁺,Tb³⁺ phosphors exhibited blue emission corresponding to the f–d transition of Ce³⁺ ions and green emission bands corresponding to the f–f transition of Tb³⁺ ions, respectively. The Reflectance spectra of the Sr₂B₂O₅:Ce³⁺,Tb³⁺ phosphors are noted that combine with Ce³⁺ and Tb³⁺ ion absorptions. Effective energy transfer occurred from Ce³⁺ to Tb³⁺ in Sr₂B₂O₅ host due to the observed spectra overlap between the emission spectrum of Ce³⁺ ion and the excitation spectrum of Tb³⁺ ion. The energy transfer efficiency from Ce³⁺ ion to Tb³⁺ ion was also calculated to be 90%. The phosphor Sr₂B₂O₅:Ce³⁺,Tb³⁺ could be considered as one of double emission phosphor for n-UV excited white light emitting diodes.