Synthesis and photoluminescence enhancement of Ca3Sr3(VO4)4:Eu3+ red phosphors by co-doping with La3+

In this study, a series of red-emitting Ca₃Sr₃(VO₄)₄:Eu³⁺ phosphors co-doped with La³⁺ was prepared using the combustion method. The microstructures, morphologies, and photoluminescence properties of the phosphors were investigated. All Ca₃Sr₃(VO₄)₄:Eu³⁺, La³⁺ samples synthesized at temperatures greater than 700 ℃ exhibited the same standard rhombohedral structure of Ca₃Sr₃(VO₄)₄. Furthermore, the Ca₃Sr₃(VO₄)₄:Eu³⁺, La³⁺ phosphor was effectively excited by near-ultraviolet light of 393 nm and blue light of 464 nm. The strong excitation peak at 464 nm corresponded to the ⁷F₀→⁵D₂ electron transition of Eu³⁺. The strong emission peak observed at 619 nm corresponded to the ⁵D₀→⁷F₂ electron transition of Eu³⁺. Co-doping with La³⁺ significantly improved the emission intensity of Ca₃Sr₃(VO₄)₄:Eu³⁺ red phosphors. The optimum luminescence of the phosphor was observed at Eu³⁺ and La³⁺ concentrations of 5% and 6%, respectively. Moreover, co-doping with La³⁺ also improved the fluorescence lifetime and thermal stability of the Ca₃Sr₃(VO₄)₄:Eu³⁺ phosphor. The CIE chromaticity coordinate of Ca₃Sr₃(VO₄)₄:0.05Eu³⁺, 0.06La³⁺ was closer to the NTSC standard for red phosphors than those of other commercial phosphors; moreover, it had greater color purity than that of all the samples tested. The red emission intensity of Ca₃Sr₃(VO₄)₄:0.05Eu³⁺, 0.06La³⁺ at 619 nm was ~1.53 times that of Ca₃Sr₃(VO₄)₄:0.05Eu³⁺ and 2.63 times that of SrS:Eu²⁺. The introduction of charge compensators could further increase the emission intensity of Ca₃Sr₃(VO₄)₄:Eu³⁺, La³⁺ red phosphors. The phosphors synthesized herein are promising red-emitting phosphors for applications in white light-emitting diodes under irradiation by blue chips.     

Enhanced luminescence properties of Eu3+ in La2MoO6 by nonsensitization of Bi3+

It was unusual for Bi³⁺ ions to enhance the emission intensity of phosphors via nonsensitization. Here, La₂MoO₆:Eu³⁺, Bi³⁺ phosphors were successfully synthesized by a high temperature solid-state reaction method in air atmosphere. As the increase of doping concentration of Bi³⁺, the emission spectra of La₂MoO₆:Eu³⁺, Bi³⁺ phosphors had obvious shifts, splits and the enhancement of intensities, which indicated that the characteristics of the phosphors were modified. To analyze these phenomena, the crystal structure refinements, spectral characteristic analyze and Judd-Ofelt theoretical calculation were mainly performed. Bi³⁺ ions played the role of the nonsensitizer and affected the distortion of the crystal, the sites of Eu³⁺ ions, the field splitting energy and the internal quantum yield. Moreover the nephelauxetic effects of Bi³⁺ ions and the ET process caused synergistically the life times of La₂MoO₆:Eu³⁺, Bi³⁺ phosphors to increase and then gradually decrease. The CIE coordinates of phosphors changed within a small range. This study might be instrumental in promoting the further application of Bi³⁺ ions in rare earth luminescent materials.     

Preparation and Luminescence Properties of Eu2+ and Mn2+ Coactivated Tricalcium Phosphate Phosphors

Eu²⁺ and Mn²⁺ coactivated β–Ca₃(PO₄)₂ (TCP) phosphors have been prepared by high‐temperature solid‐state reaction. The site occupation and photoluminescence properties of Eu²⁺ and Mn²⁺ have been identified and discussed in detail. The energy transfer from Eu²⁺ to Mn²⁺ in TCP: Eu²⁺, Mn²⁺ phosphors has been validated and demonstrated to be a resonant type via a dipole‐quadrupole mechanism, and the critical distance (R_C) calculated by concentration quenching method is 21.76 Å. A color‐tunable emission from violet‐blue to red in TCP: Eu²⁺, Mn²⁺ phosphors can be realized via the energy transfer from Eu²⁺ to Mn²⁺ ions.     

Versatile Ca2LnSbO6:Eu3+/Mn4+ (Ln = La,Y, Gd,and Lu) phosphors for temperature sensing and plant growth LED

A multifunctional double-perovskite-type Ca₂LnSbO₆ (Ln = La, Y, Gd, and Lu) phosphors with Eu³⁺ and Mn⁴⁺ co-doped were successfully synthesized and designed to simultaneously apply to temperature sensing and plant growth LED. With temperature varying from 303 to 523 K, the integrated intensity of Mn⁴⁺ ions (²E_g → ⁴A_2g) markedly decline swifter comparing to Eu³⁺ ions (⁵D₀ → ⁷F₂) due to the thermal quenching effect. It implies that Mn⁴⁺ is susceptive to the temperature in this work. Eu³⁺ exhibits high heat resistance, which can be selected as a calibration parameter for the fluorescence intensity ratio temperature sensor. The maximum relative sensitivity (S_r) values of Ca₂LnSbO₆:1%Eu³⁺, 0.5%Mn⁴⁺ (Ln = La, Y, and Gd) phosphor are estimated as 2.19% K⁻¹ at 443 K, 1.68% K⁻¹ at 503 K, and 1.80% K⁻¹ at 483 K, respectively. They are superior to many recent emerging phosphors. Moreover, upon 365 nm excitation, Ca₂LnSbO₆:1%Eu, 0.5%Mn (Ln = La, Y, Gd, and Lu) phosphors display a wide red emission peaking at 696, 680, 677, and 684 nm, respectively. They come from the overlapped of ²E_g–⁴A_2g of Mn⁴⁺ and ⁵D₀–⁷F₄ transition of Eu³⁺. Their full widths at half maximum are 34, 35, 35, and 29 nm, respectively. They are all perfectly overlapping the absorption curves of chlorophyll a and chlorophyll b, and their fabricated red phosphor-converted light-emitting diode device ulteriorly corroborated the promising applications for plant growth. Markedly, the systematic analysis of their crystal chemistry and site preferentially occupancy is first reported and discussed by the bond valence theory.     

Zero-thermal-quenching of LiAl5O8: Eu2+, Mn2+ phosphors by energy transfer and defects engineering

The photoluminescence behavior of inorganic phosphors is generally influenced by thermal stability, which determines the luminescence efficiency of the corresponding devices. Here, a series of Eu²⁺, Mn²⁺ co-doped LiAl₅O₈ blue-green-emitting phosphors with thermal robust are successfully fabricated. The concentration-dependent emission spectra and the decay curves of the as-obtained LiAl₅O₈: Eu²⁺, Mn²⁺ samples manifest the occurrence of the energy transfer from Eu²⁺ to Mn²⁺ ions via dipole-dipole interaction, and the corresponding emitted colors are gradually modulated from blue to green under the excitation of 310 nm. Moreover, the zero-thermal-quenching luminescence is observed when the operation temperature is up to 423 K, which is attributed to the energy release from the trapping centers to emitting centers (Eu²⁺ and Mn²⁺) at high temperature. Furthermore, a warm white light-emitting diodes (WLEDs) device with correlated color temperature of 5061 K, a color rendering index of 80.6 and long-term stability is fabricated by combining UV LED chip (λ_ex = 310 nm), as-obtained LiAl₅O₈: Eu²⁺, Mn²⁺ phosphor, commercially available red phosphor and green phosphor. These results prove the potential application of the as-obtained LiAl₅O₈: Eu²⁺, Mn²⁺ phosphor for UV-pumped WLEDs devices.     

Cyan-emitting Ba0.45Ca2.5La6(SiO4)6: 0.05 Eu2+ and Ba1.45Ca1.5La6(SiO4)6:0.05 Eu2+ solid-solution phosphors for white light-emitting diodes

Two cyan-emitting phosphors with different bandwidths were successfully synthesized through the high-temperature solid-state method in a reducing atmosphere. The crystal structures, morphologies, and luminescence properties of the as-prepared phosphors were investigated. The Rietveld refinements of the powder X-ray diffraction (XRD) data demonstrated the single phase of the samples, and two crystallographic sites of La³⁺ were observed in the crystal structure. Under the excitation of UV light, both Ba_0.45Ca_2.5La₆(SiO₄)₆: 0.05 Eu²⁺ and Ba_1.45Ca_1.5La₆(SiO₄)₆: 0.05 Eu²⁺ phosphors emitted cyan light due to the 4f⁶5 d¹→4f⁷ transitions of the Eu²⁺ ion. The emission spectra could be well fitted by two component Gaussian peaks corresponding to two different coordination environments of the Eu²⁺ ions. The temperature-dependent photoluminescence spectra show a large difference on the thermal stability between the two phosphors. The two phosphors exhibit effective absorption of near-UV light and their internal quantum efficiencies (IQEs) were calculated as 31.5% and 42.4% under 295 nm UV-light excitation. The experimental results indicate that the novel cyan phosphors might have potential applications in white light-emitting diodes (LEDs) based on the near-UV LED chip.     

Luminescence enhancement of Mn4+-activated double-perovskite phosphors for LEDs through a co-replacement strategy

Phosphors doped with Mn⁴⁺ ions have strong emission in the red and far-red light regions and are therefore used as red phosphors for indoor plant cultivation light-emitting diodes (LEDs) and white LEDs (w-LEDs). This paper introduces La₂Mg(Mg_1/3Ta_2/3)O₆: Mn⁴⁺ (Mg₂La₃TaO₉: Mn⁴⁺) red phosphors prepared by conventional high-temperature solid-phase method. The broad excitation band of Mg₂La₃TaO₉: Mn⁴⁺ phosphor is effectively excited by ultraviolet and blue light in the range of 250–600 nm, with the emission of 707 nm centered on far-red light. The phosphor has a high color purity of 99.07% and an internal quantum efficiency of 59.87%. To further enhance the performance of the phosphor, a cation substitution method was adopted in this paper to synthesize La₂Mg(Al_1/2Ta_1/2)O₆: Mn⁴⁺ phosphor by replacing [1/3Mg²⁺–2/3Ta⁵⁺] in La₂Mg(Mg_1/3Ta_2/3)O₆: Mn⁴⁺ with [1/2Al³⁺–1/2Ta⁵⁺]. The luminescence intensity and thermal stability of the samples were enhanced. The emission spectrum of the Mg₂La₃TaO₉: Mn⁴⁺ samples matched well with the phytochrome P_FR (phytochrome that absorbs far-red light) and is suitable for the preparation of LEDs for indoor plant cultivation. The concentration quenching effect of the samples was investigated, the main mechanism of which is the electric dipole–dipole interaction. Red LEDs and w-LEDs devices were prepared with the synthesized phosphors that produce light stably at different currents. The w-LEDs have a correlated color temperature of 5310 K and a color rendering index of 80.1. Therefore, these samples are expected to be used as red components for w-LEDs.     

Decay Behavior in Ce3+‐doped La3Si6N11 and Lu3Al5O12 Phosphors

Ce³⁺‐activated light emitting diode (LED) phosphors have been extensively examined for photoluminescence, and have been the focus of many detailed structural studies. However, reports of the decay curves of Ce³⁺‐activated LED phosphors are rare. Although we have reported the decay behaviors of several Eu²⁺‐activated LED phosphors such as Sr₂SiO₄, Sr₂Si₅N₈, and CaAlSiN₃, we have never conducted an in‐depth study into the decay behavior for Ce³⁺‐activated LED phosphors. For this study, we investigated the decay curves of well‐known Ce³⁺‐activated LED phosphors such as La₃Si₆N₁₁ and Lu₃Al₅O₁₂. Similar to Eu²⁺‐activated LED phosphors, the decay behavior of Ce³⁺‐activated LED phosphors was sensitive to the Ce³⁺ concentration and to the detection wavelength. There was active nonradiative energy transfer between the Ce³⁺ activators located at different sites.     

Synthesis,Structure, and Tunable Luminescence Properties of Novel Ba3NaLa(PO4)3F:Eu2+,Mn2+ Phosphors

A series of luminescent emission‐tunable phosphors Ba₃NaLa(PO₄)₃F:Eu²⁺,Mn²⁺ have been prepared by a high‐temperature solid‐state reaction. The Rietveld refinement analysis confirms that the obtained phosphors possess pure apatite crystalline phase and the sites' occupancy of dopant has been also discussed. Upon the excitation of 355 nm, the emission spectra of Ba₃NaLa(PO₄)₃F:Eu²⁺,Mn²⁺ consist of two broad bands assigned to 5d–4f transition of Eu²⁺ and ⁴T₁ (⁴G)–⁶A¹ (⁶S) transitions of Mn²⁺, respectively. Energy transfer (ET) occurs in Eu²⁺, Mn²⁺ codoped Ba₃NaLa(PO₄)₃F host. On the basis of the thorough analysis and comparison upon their excitation, emission properties, and the decay behaviors, it is demonstrated that the ET mechanism between Eu²⁺ and Mn²⁺ is ascribed to the exchange interaction, and the tunable emission color in the novel apatite host can be realized.     

Luminescence properties of Eu2+ and Mn2+ doped Sr1.7Mg0.3SiO4 phosphors

Eu²⁺, Mn²⁺ doped Sr_1.7Mg_0.3SiO₄ phosphors were prepared by high temperature solid-state reaction method. Their luminescence properties were studied. The emission spectra of Eu²⁺ singly doped Sr_1.7Mg_0.3SiO₄ consist of a blue band (455 nm) and a green band (550 nm). The relative intensities of two emissions varied with Eu²⁺ concentration. Eu²⁺ and Mn²⁺ co-doped Sr_1.7Mg_0.3SiO₄ phosphors emit three color lights and present whitish color. The blue (455 nm) and green (550 nm) emissions are attributed to the transitions of Eu²⁺, while the red (670 nm) emission is originated from the transition of Mn²⁺ ion. The results indicate the energy transfer from Eu²⁺ to Mn²⁺. The mechanism of the energy transfer is resonance-type energy transfer due to the spectral overlap between the emission of Eu²⁺and the absorption of Mn²⁺.     

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

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, (Mg_0.93Mn_0.07) 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.     

Energy transfer and multicolor tunable emission in single-phase Tb3+, Eu3+ co-doped Sr3La(PO4)3 phosphors

A series of green-to-red color-tunable Sr₃La(PO₄)₃:Tb³⁺, Eu³⁺ phosphors were prepared by high temperature solid-state method. The crystal structures, photoluminescence properties, fluorescence lifetimes, and energy transfer of Sr₃La(PO₄)₃:Tb³⁺, Eu³⁺ were systematically investigated in detail. The obtained phosphors show both a green emission from Tb³⁺ and a red emission from Eu³⁺ with considerable intensity under ultraviolet (UV) excitation (~377 nm). The emission colors of the phosphors can be tuned from green (0.304, 0.589) through yellow (0.401, 0.505) and eventually to red (0.557, 0.392) due to efficient Tb³⁺-Eu³⁺ energy transfer (ET). The Tb³⁺→Eu³⁺ energy transfer process was demonstrated to be quadrupole-quadrupole mechanism by Inokuti-Hirayama model, with maximum ET efficiency of 86.3%. The results indicate that the Sr₃La(PO₄)₃:Tb³⁺, Eu³⁺ phosphors might find potential applications in the field of lighting and displays.     

Multicolour tunable luminescence of thermal-stable Ce3+/Tb3+/Eu3+-triactivated Ca3Gd(GaO)3(BO3)4 phosphors via Ce3+ → Tb3+ → Eu3+ energy transfer for near-UV WLEDs applications

A series of single-component blue, green and red phosphors have been fabricated based on the Ca₃Gd(GaO)₃(BO₃)₄ host through doping of the Ce³⁺/Tb³⁺/Eu³⁺ ions, and their crystal structure and photoluminescence properties have been discussed in detail. A terbium bridge model via Ce³⁺ → Tb³⁺ → Eu³⁺ energy transfer has been studied. The emission colours of the phosphors can be tuned from blue (0.1661, 0.0686) to green (0.3263, 0.4791) and eventually to red (0.5284, 0.4040) under a single 344 nm UV excitation as the result of the Ce³⁺ → Tb³⁺ → Eu³⁺ energy transfer. The energy transfer mechanisms of Ce³⁺ → Tb³⁺ and Tb³⁺ → Eu³⁺ were found to be dipole-dipole interactions. Importantly, Ca₃Gd(GaO)₃(BO₃)_4:Ce³⁺,Tb³⁺,Eu³⁺ phosphors had high internal quantum efficiency. Moreover, the study on the temperature-dependent emission spectra revealed that the Ca₃Gd(GaO)₃(BO₃)_4:Ce³⁺,Tb³⁺,Eu³⁺ phosphors possessed good thermal stability. The above results indicate that the phosphors can be applied into white light-emitting diodes as single-component multi-colour 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.     

Dual-mode optical thermometry based on Bi3+/Eu3+ co-activated BaGd2O4 phosphor with high sensitivity and signal discriminability

A series of BaGd₂O₄:Bi³⁺,Eu³⁺ phosphors with dual-emitting centers were prepared by high-temperature solid-state method. X-ray diffraction (XRD), scanning electron microscope (SEM), energy dispersive spectroscopy (EDS), fluorescence spectroscopy, lifetime decay curve and variable temperature emission spectroscopy were used to systematically study the structure, luminescence performance and temperature characteristics. Under ultraviolet (UV) excitation, the BaGd₂O₄:Bi³⁺,Eu³⁺ phosphor showed a broad-band emission in the blue region corresponding to transitions of Bi³⁺ ions and the sharp red light emission corresponding to Eu³⁺ ions. The Bi³⁺ and Eu³⁺ ion emission peaks were well-separated, which meets a prerequisite for efficient temperature signal resolution measurement. The fluorescence intensity ratio (FIR) technique was used to measure the different temperature response characteristics between Bi³⁺ blue emission and Eu³⁺ red emission. When the temperature varies from 293 K to 473 K, the relative temperature sensitivity (S_r) of BaGd₂O₄:Bi³⁺,Eu³⁺ phosphors is obtained, was determined as 1.0182%K⁻¹. In addition to calculating the relative sensitivity by FIR technology, we can also obtain the value of S_r through experiments and formulas related to the decay life, and found to be 1.0651%K⁻¹. Therefore, BaGd₂O₄: Bi³⁺,Eu³⁺ phosphor is an excellent non-contact optical temperature measurement material.     

Preparation,luminescence properties,and application of temperature sensing and anti-counterfeiting of La2MgTiO6:Yb3+/Ln3+/Mn4+

The doping of transition metal ions in the up-conversion (UC) luminescent material doped with Yb³⁺/Ln³⁺ is a facile way to increase their UC luminescence intensities and alter their colors. In this study, La₂MgTiO₆:Yb³⁺/Mn⁴⁺/Ln³⁺ (Ln³⁺ = Er³⁺, Ho³⁺, and Tm³⁺) phosphors showing excellent luminescence properties were prepared by a solid-state method. The sensitivity of the La₂MgTiO₆:Yb³⁺/Ln³⁺/Mn⁴⁺ phosphor was double that without Mn⁴⁺, because Mn⁴⁺ affects the UC emissions of Ln³⁺ via energy transfer between these ions. Moreover, Mn⁴⁺ also acts as a down-conversion activator, which can combine with UC ions to achieve multi-mode luminescence at different wavelengths. Under 980 nm excitation, these samples emit green light (from Er³⁺ and Ho³⁺) and blue light (from Tm³⁺). In contrast, under 365 nm excitation, they emit red light (from Mn⁴⁺). Further testing revealed that the La₂MgTiO₆:Yb³⁺/Mn⁴⁺/Ln³⁺ phosphors have potential applications in temperature sensing and anti-counterfeiting.     

Tunable color emission in LaScO3:Bi3+,Tb3+,Eu3+ phosphor

LaScO₃:xBi³⁺,yTb³⁺,zEu³⁺ (x = 0 − 0.04, y = 0 − 0.05, z = 0 − 0.05) phosphors were prepared via high-temperature solid-state reaction. Phase identification and crystal structures of the LaScO₃:xBi³⁺,yTb³⁺,zEu³⁺ phosphors were investigated by X-ray diffraction (XRD). Crystal structure of phosphors was analyzed by Rietveld refinement and transmission electron microscopy (TEM). The luminescent performance of these trichromatic phosphors is investigated by diffuse reflection spectra and photoluminescence. The phenomenon of energy transfer from Bi³⁺ and Tb³⁺ to Eu³⁺ in LaScO₃:xBi³⁺,yTb³⁺,zEu³⁺ phosphors was investigated. By changing the ratio of x, y, and z, trichromatic can be obtained in the LaScO₃ host, including red, green, and blue emission with peak centered at 613, 544, and 428 nm, respectively. Therefore, two kinds of white light-emitting phosphors were obtained, LaScO₃:0.02Bi³⁺,0.05Tb³⁺,zEu³⁺ and LaScO₃:0.02Bi³⁺,0.03Eu³⁺,yTb³⁺. The energy transfer was characterized by decay times of the LaScO₃:xBi³⁺, yTb³⁺, zEu³⁺ phosphors. Moreover absolute internal QY and CIE chromatic coordinates are shown. The potential optical thermometry application of LaScO₃:Bi³⁺,Eu³⁺ was based on the temperature sensitivity of the fluorescence intensity ratio (FIR). The maximum S_a and S_r are 0.118 K⁻¹ (at 473.15 K) and 0.795% K⁻¹ (at 448.15 K), respectively. Hence, the LaScO₃:Bi³⁺,Eu³⁺ phosphor is a good material for optical temperature sensing.     

Deep blue,cyan, orange-red,and white multicolor emissions generated by Bi3+/Eu3+ activated KBaYSi2O7 luminescent materials for white light-emitting diodes

A variety of Bi³⁺ and/or Eu³⁺ doped KBaYSi₂O₇ phosphors with deep blue, cyan, orange-red, and white light multicolor emissions have been fabricated by a Pechini sol-gel (PSG) method. The KBaYSi₂O₇:Bi³⁺ phosphors exhibit an intense cyan emission or a unique narrow deep blue emission when excited by different wavelengths, which may bridge the cyan gap or act as a promising deep blue phosphor for white light-emitting diodes (WLEDs). The tunable multicolor emissions can be achieved by changing the Bi³⁺ doping concentrations. The Bi³⁺/Eu³⁺ co-doped KBaYSi₂O₇ phosphors display intrinsic emissions of Bi³⁺ and Eu³⁺ and an energy transfer process between Bi³⁺ and Eu³⁺ can be detected. The luminescence colors of KBaYSi₂O₇:Bi³⁺,Eu³⁺ regularly shift from blue, through cold and warm white, finally toward orange-red by adjusting the relative doping concentrations of Bi³⁺ and Eu³⁺. The single-phase white light-emitting material can be generated in both cold and warm white regions by simply varying the Eu³⁺ doping concentrations. Furthermore, three kinds of WLEDs devices are fabricated by KBaYSi₂O₇:Bi³⁺ or KBaYSi₂O₇:Bi³⁺,Eu³⁺ phosphors, which can exhibit dazzling white light emissions with eminent CIE coordinates, correlated color temperature, and color rendering index. The result offers direct evidence that the as-synthesized phosphors may be potentially applied in WLEDs and solid-state lighting.     

Synthesis and photoluminescence characterizations of Zn2+ and Tb3+ codoped CeO2 phosphors for temperature sensing applications

Cyan light-emitting Ce_0.985-xZn_xO₂:0.015 Tb³⁺ (x = 0 to 0.2) phosphors were synthesized using the ethylenediaminetetraacetic acid-assisted hydrothermal method. The X-ray diffraction and refinement analyses of the prepared phosphors indicated that the formed face-centered cubic structure remained intact even after the doping of large quantities of Zn²⁺ ions. However, the incorporation of Zn²⁺ ions increased the Ce³⁺/Ce⁴⁺ ratio, resulting in the enhancement of oxygen vacancies in the prepared phosphors. The generation of oxygen vacancies caused the evolution of a broad photoluminescence emission band ranging from 400 to 525 nm with a characteristic Tb³⁺ emission of approximately 543 nm. Two-emission regions in Ce_0.885Zn_0.1O₂:0.015 Tb³⁺ phosphors were utilized for measuring the fluorescence intensity ratio (FIR) as a function of temperature ranging from 303 to 523 K. At 523 K, the FIR values dropped to approximately 40% of the starting temperature value. The variation of FIR values followed the Boltzmann behavior. The Boltzmann fitting demonstrated the feasibility of the present phosphors for temperature sensor applications. The optimum absolute sensor sensitivity of Ce_0.885Zn_0.1O₂:0.015 Tb³⁺ phosphors was measured to be 0.0043 K⁻¹ at 398 K with a resolution of approximately 1 K⁻¹. Moderate temperature sensitivity, negligible hysteresis loop, and excellent reversibility revealed the suitability of Ce_0.885Zn_0.1O₂:0.015 Tb³⁺ phosphors for sensing the temperature in various electronic devices.     

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.