A novel red-emitting phosphor Mg2Y2Al2Si2O12:Ce3+/Mn2+ for blue chip-based white LEDs

Traditional white light-emitting diodes (LEDs) (blue chip + YAG:Ce³⁺ yellow phosphor) have the limitation of red deficiency, which limits their application in the illumination field. The single cation/anion substitution or co-doping of activators can increase the red component; however, the large energy loss is attributed to the ultra-long Stokes shift and energy transfer. This work attempts to utilize the short-distance Stokes shift and a small amount of energy transfer to increase the red component in two steps. First, based on a large number of previous research results, the Mg₂Y₂Al₂Si₂O₁₂:Ce³⁺ phosphor is selected. Second, additional enhancement of the red component in the emission spectrum was achieved by ion co-doping Mn²⁺ into Mg₂Y₂Al₂Si₂O₁₂:Ce³⁺. The emission peaks for samples Mg₂Y₂Al₂Si₂O₁₂:Ce³⁺,Mn²⁺ shift from 600 to 635 nm with increase in the concentration of Mn²⁺, and the emission spectra intensity of Mg_1.97Y_1.93Al₂Si₂O₁₂:0.07 Ce³⁺,0.03 Mn²⁺ anomalously increased by ∼37%, which was attributed to the increase in the distance between Ce³⁺ ions because of the doping of Mn²⁺ ions, and reduction in the concentration of defects in the crystal, resulting in the energy loss decreases of Ce³⁺. The emission peak of Mg_1.97Y_1.93Al₂Si₂O₁₂:0.07 Ce³⁺,0.03 Mn²⁺ shifts to 618 nm and the quantum efficiency was as high as 83.07%. Furthermore, this sample has high thermal stability and the emission intensity was still 80.14% at 120 °C. As such, it has great potential in the application of white LEDs.

The change of the emission spectra of Mg_1.93Y_2-xAl₂Si₂O₁₂:0.07Ce³⁺, xMn²⁺ originates from the change of the structure and the energy transfer between ions.     

Luminescence properties and energy transfer of the near-infrared phosphor Ca3In2Ge3O12:Cr3+,Nd3+

The double doping strategy based on energy transfer is an effective way to regulate the NIR spectral distribution. In this work, Ca₃In₂Ge₃O₁₂:xNd³⁺ (CIG:xNd³⁺) and Ca_3−xIn_1.93Ge₃O₁₂:0.07Cr³⁺,yNd³⁺ (CIG:0.07Cr³⁺,yNd³⁺) phosphors are successfully prepared via a high-temperature solid-state method. CIG:0.07Cr³⁺ shows broadband emission centered at 804 nm, which covers most of the excitation peaks of Nd³⁺ ions. Under excitation at 480 nm, Cr³⁺ can provide effective energy transfer to Nd³⁺. In addition, CIG:0.07Cr³⁺,0.15Nd³⁺ has good temperature stability, and maintains 68.98% of the room-temperature intensity at 150 °C. The phosphors can convert short-wave photons to long-wave photons and enhance solar cell utilization, demonstrating the potential application of this material in solar spectral conversion technology.

Improvement of the luminescence properties of Ca₃In₂Ge₃O₁₂:Cr³⁺,Nd³⁺via energy transfer and its potential application in silicon solar cells.     

Novel red-emitting phosphor Li2MgZrO4:Mn4+,Ga3+ for warm white LEDs based on blue-emitting chip

Li₂MgZrO₄:Mn⁴⁺,Ga³⁺ phosphors are synthesized via a conventional high-temperature solid-state reaction. The red emission of Mn⁴⁺ is enhanced 6.68 times and 13.0 times under 352 nm and 468 nm excitation when Ga³⁺ ions with a concentration of 40% are introduced into the phosphor. The thermal stability of the phosphor is also slightly improved by Ga³⁺ doping. It is believed that the Ga_Zr dopants in the Li₂MgZrO₄ host not only stabilize Mn ions in the 4+ state, but also lower the symmetry of Mn⁴⁺ sites, resulting in the significant improvement of the luminescence performance, especially under blue excitation. The results might provide meaningful reference to seek high-performance Mn⁴⁺ doped oxide phosphors for W-LED applications based on a blue-emitting InGaN chip.

PLE spectra of the phosphors. Inset (a) excitation intensity at 352 nm and 468 nm as function of doping Ga³⁺ concentration. Inset (b) ratio of excitation intensity at 468 nm to that at 352 nm as function of Ga³⁺ concentration.     

Enhanced photoluminescence and energy transfer performance of Y3Al4GaO12:Mn4+,Dy3+ phosphors for plant growth LED lights

Plant growth LEDs have attracted broad attention in modern society, desperate for specific phosphors with a characteristic emission band. A novel Mn⁴⁺ and Dy³⁺ co-doped Y₃Al₄GaO₁₂ phosphor were successfully prepared through a conventional high-temperature solid-state reaction. A three band emission including red (625–700 nm), orange (550–607 nm) and blue (462–490 nm) is observed in these phosphors when excited under a near-UV lamp, which is ascribed to ²E → ⁴A₂ of Mn⁴⁺, ⁴F_9/2 → ⁶H_15/2 and ⁴F_9/2 → ⁶H_13/2 of Dy³⁺, respectively. The three emissions match the absorption spectra of chlorophyll A and chlorophyll B well. Meanwhile, the energy transfer from Dy³⁺ to Mn⁴⁺ was confirmed by the luminescence spectra and lifetime analysis. Finally, an LED device was fabricated that consisted of a 365 nm ultraviolet chip and the Y₃Al₄GaO₁₂:Mn⁴⁺,Dy³⁺ phosphor. The excellent properties indicate that the synthesized phosphor has a promising application in the optical agricultural industry.

Enhanced photoluminescence properties and confirmed energy transfer in a YAGO:Mn⁴⁺,Dy³⁺ phosphor.     

Luminescence properties,energy transfer and thermal stability of white emitting phosphor Sr3(PO4)2:Ce3+/Tb3+/Mn2+ for white LEDs

A series of Sr₃(PO₄)₂:Ce³⁺/Mn²⁺/Tb³⁺ phosphors were synthesized by a high temperature solid phase method. After introducing Ce³⁺ as sensitizer in Sr₃(PO₄)₂:Ce³⁺/Mn²⁺, the efficient energy transfer from Ce³⁺ to Mn²⁺ was observed and analyzed in detail, and Sr₃(PO₄)₂:Ce³⁺/Mn²⁺ was demonstrated to be color tunable, changing from blue to orange red. In addition, Tb³⁺ ion, which mainly emits green light, was further added into the Sr₃(PO₄)₂:Ce³⁺/Mn²⁺. Due to the addition of this green emission, the white emitting phosphors with good quality were obtained. At the same time, the energy transfer mechanisms among Ce³⁺, Tb³⁺ and Mn²⁺ ions were also analyzed in detail. The results show that Sr₃(PO₄)₂:Ce³⁺/Mn²⁺/Tb³⁺ is a promising candidate for white light emitting diodes.

The tunable emission phosphor was realized by the energy transfer.     

Preparing and testing the reliability of long-afterglow SrAl2O4:Eu2+, Dy3+ phosphor flexible films for temperature sensing

Owing to its stability and environment-friendly properties, the SrAl₂O₄:Eu²⁺, Dy³⁺ (SAOED) phosphor has attracted major scientific interest. With various applications, such as in emergency signage, luminous paints, and traffic signs, it can have a considerable impact on everyday activities. However, SrAl₂O₄ easily undergoes hydrolysis in the presence of atmospheric moisture. To remedy this, we prepared a phosphor film by spin coating to improve its water resistance. The SAOED was coated with epoxy resin glue without destroying the SrAl₂O₄ crystals. A series of reliability tests were conducted on the phosphor films and bare phosphors: high-temperature and high-humidity (HT) tests, thermal-cycling (TC) tests, and xenon lamp aging (XLG) tests. Then, the crystal phase, surface morphology, photoluminescence (PL), afterglow decay, and temperature-dependent PL were analyzed. The X-ray diffraction patterns show that the hydrolysis reaction of SAOED occurred easily, with the SrAl₂O₄ phase becoming the Sr₃Al₂ (OH)₁₂ phase and SrAl₃O₅(OH) generated under HT tests. The PL intensity of the thin film of SAOED decreased 57.2%, 79.3%, and 98.8% after HT tests, XLG tests for 168 h, and TC tests with 10 repetitions from 233 K to 423 K, respectively. Moreover, the afterglow decay time of the SAOED phosphor film was longer than that of bare phosphors. The developed flexible films are excellent candidates for temperature sensing because they exhibit temperature-dependent PL intensity and are highly sensitive to surrounding temperature variation 300–420 K. Thus, SAOED films with stable luminescent signals can be used in energy-efficient, long-lasting temperature-sensing devices, which, apart from being environment-friendly, play a role in improving public safety infrastructure.

Owing to its stability and environment-friendly properties, the SrAl₂O₄:Eu²⁺, Dy³⁺ (SAOED) phosphor has attracted major scientific interest.     

Luminescence and energy transfer of Tm3+ and Dy3+ co-doped Na3ScSi2O7 phosphors

A series of Tm³⁺ and Dy³⁺ ions single- or co-doped Na₃ScSi₂O₇ (NSSO) phosphors were prepared by a conventional solid state reaction method. The X-ray diffraction (XRD) patterns, photoluminescence (PL) properties, fluorescence decay curve and energy transfer behavior of the samples were studied. The XRD patterns show that all the diffraction peaks of the samples are consistent with the JCPDS standard data. Under UV excitation, the singly doped NSSO phosphors with Tm³⁺ and Dy³⁺ ions show blue and yellow characteristic emission. The emission color of NSSO:Tm³⁺,Dy³⁺ can be adjusted by the corresponding Tm³⁺–Dy³⁺ energy transfer. In addition, the chromaticity coordinate of NSSO:0.04Tm³⁺,0.13Dy³⁺ is (0.3195, 0.3214), which is close to the ideal white light (0.333, 0.33). These results show that NSSO:Tm³⁺,Dy³⁺ has potential application value in white light emitting diodes (WLEDs).

A series of Tm³⁺ and Dy³⁺ ions single- or co-doped Na₃ScSi₂O₇ (NSSO) phosphors were prepared by a conventional solid state reaction method.     

Design,synthesis and characterization of a novel bluish-green long-lasting phosphorescence phosphor BaLu2Si3O10:Eu2+, Nd3+

Through drawing upon a solid-state reaction, a newly proposed long-lasting phosphor BaLu₂Si₃O₁₀:Eu²⁺, Nd³⁺ is presented and prepared in this work. The thermoluminescence properties of the phosphor are substantially extended, and the long-lasting phosphorescence behavior is markedly intensified by virtue of the consolidation of Nd³⁺ ions which serve as trap centers. In line with density functional theory calculations, the conduction band is mostly composed of Lu 5d states while the Ba 5d states only have a tiny contribution. We analyzed the relationship between the phosphor’s electronic structure and its optical properties. The photoluminescence emission spectrum shows a blue emitting band with a wide asymmetric property and an extremum of 426 nm, arising from the 5d–4f transitions of the Eu²⁺ ions which occupy the Ba and Lu sites. It is asserted that the long-lasting phosphorescence of the Eu²⁺ ions which take up both Ba and Lu sites stems from the special form of conduction band and the occupying environment of the emission center. Yet, they have different contributions and induce an interesting phenomenon in which the blue emitting phosphor shows a bluish-green phosphorescence. The long-lasting phosphorescence can last in excess of 6 h at the recognized intensity level (0.32 mcd m⁻²) after excitation for 10 min. This work provides a new way of thinking for the development of multicolored LLP materials. This work analyzes and sheds light on the specific courses and provides a likely mechanism for the process.

A newly proposed bluish-green emitting long-lasting phosphor, BaLu₂Si₃O₁₀:Eu²⁺, Nd³⁺, with prominent LLP properties is successfully achieved via a high temperature solid state method.     

Synthesis and photoluminescence properties of Eu3+-activated LiCa3ZnV3O12 white-emitting phosphors

Single-component white-emitting phosphors are highly promising for applications in phosphor-converted white light-emitting diodes. In this paper, novel single-phase LiCa_3(1−x)ZnV₃O₁₂:Eu³⁺ (x = 0–0.05) phosphors with tunable white emissions were prepared by a conventional solid-state reaction. The LiCa₃ZnV₃O₁₂ (x = 0) phosphor showed an efficient self-activated bluish-green emission due to the V⁵⁺–O²⁻ charge transfer transition of the [VO₄]³⁻ groups, and possessed an intense broad excitation spectrum in the 250–400 nm wavelength range. Together with the [VO₄]³⁻ emission, the red emission of Eu³⁺ ions was also observed in LiCa_3(1−x)ZnV₃O₁₂:Eu³⁺ phosphors. The energy transfer from the [VO₄]³⁻ groups to the Eu³⁺ ions was studied. Importantly, the emission colors of LiCa_3(1−x)ZnV₃O₁₂:Eu³⁺ phosphors varied from greenish-blue to whitish and then to red with increasing Eu³⁺ content and the white-light emission was realized in the single-phase phosphor of LiCa₃ZnV₃O₁₂:0.003Eu³⁺ by combining the [VO₄]³⁻-emission and the Eu³⁺-emission. The energy-transfer efficiency from [VO₄]³⁻ groups to Eu³⁺ ions in the LiCa₃ZnV₃O₁₂:0.003Eu³⁺ sample was determined to be about 52% and the internal quantum efficiency of the LiCa₃ZnV₃O₁₂:0.003Eu³⁺ phosphor was found to be about 41.5%. In addition, the CIE chromaticity coordinates of LiCa₃ZnV₃O₁₂:0.003Eu³⁺ were (x = 0.3374, y = 0.3596), and the correlated color temperature was estimated to be about 5311 K.

A novel high-efficiency white-emitting LiCa₃ZnV₃O₁₂:Eu³⁺ phosphor was developed.     

Luminescence,energy transfer,colour modulation and up-conversion mechanisms of Yb3+, Tm3+ and Ho3+ co-doped Y6MoO12

A series of novel up-conversion luminescent Yb³⁺/Ln³⁺ (Tm³⁺, Ho³⁺, Tm³⁺/Ho³⁺)-doped Y₆MoO₁₂ (YMO) nanocrystals were synthesized using the sol–gel method. The consistent spherical morphology of the nanocrystals with different doping ratios was found to be profiting from the homogenisation and rapid agglomeration of the composition in the gel state and calcining process. The X-ray diffraction (XRD) and field-emission scanning electron microscope images were employed to confirm perfect crystallinity and uniform morphology. Photoluminescence spectra and decay curves were used to characterize the optical properties of the synthesized samples. The YMO:Yb³⁺/Ln³⁺ (Tm³⁺, Ho³⁺, Tm³⁺/Ho³⁺) nanocrystals were excited by near-infrared photons and emitted photons distributed in blue, green, and red bands with a wide colour gamut, and even white colour, by optimising the relative doping concentrations of the activator ions. The energy conversion mechanism in the up-conversion process was studied using power-dependent luminescence and is depicted in the energy level diagram. In addition, 70% of the luminescence intensity of YMO can be preserved after annealing at 700 °C, and the temperature sensing was tested in the range 298–498 K. These merits of multicolour emissions in the visible region and good stability endow the as-prepared nanocrystals with potential applications in the fields of optical data storage, encryption, sensing, and other multifunctional photonic technologies.

Up-conversion materials based on YMO were successfully synthesized by the sol–gel method, and the luminescence colour tuning was achieved by changing the type and concentration of dopant ions (Tm³⁺, Ho³⁺).     

Significantly enhanced photoluminescence and thermal stability of La3Si8N11O4:Ce3+,Tb3+via the Ce3+ → Tb3+ energy transfer: a blue-green phosphor for ultraviolet LEDs

A series of Ce³⁺-, Tb³⁺- and Ce³⁺/Tb³⁺-doped La₃Si₈N₁₁O₄ phosphors were synthesized by gas-pressure sintering (GPS). The energy transfer between Ce³⁺ and Tb³⁺ occurred in the co-doped samples, leading to a tunable emission color from blue to green under the 360 nm excitation. The energy transfer mechanism was controlled by the dipole–dipole interaction. The Ce³⁺/Tb³⁺ co-doped sample had an external quantum efficiency of 46.7%, about 5.6 times higher than the Tb-doped La₃Si₈N₁₁O₄ phosphor (8.3%). The thermal quenching of the Tb³⁺ emission in La₃Si₈N₁₁O₄:Tb,Ce was greatly reduced from 74 to 30% at 250 °C, owing to the energy transfer from Ce³⁺ to Tb³⁺. The blue-green La₃Si₈N₁₁O₄:0.01Ce,0.05Tb phosphor was testified to fabricate a warm white LED that showed a high color rendering index of 90.2 and a correlated color temperature of 3570 K. The results suggested that the co-doped La₃Si₈N₁₁O₄:Ce,Tb phosphor could be a potential blue-green down-conversion luminescent material for use in UV-LED pumped wLEDs.

The peak emission intensity and thermal stability of Tb³⁺ in codoped La₃Si₈N₁₁O₄:Ce,Tb sample are strongly enhanced via Ce³⁺ to Tb³⁺ energy transfer.     

Tunable emission from green to red in the GdSr2AlO5:Tb3+,Eu3+ phosphor via efficient energy transfer

Herein, a series of GdSr₂AlO₅:Tb³⁺,Eu³⁺ phosphors were successfully synthesized through a high temperature solid-state reaction, and their crystal structures as well as photoluminescence properties were investigated in detail. Compared to the intense emission of ⁵D₀ → ⁷F₁ or ⁵D₀ → ⁷F₂ transition of Eu³⁺, another strong emission corresponding to ⁵D₀ → ⁷F₄ was observed. Concentration quenching is not obvious in Tb³⁺ or Eu³⁺-doped GdSr₂AlO₅ because structure isolation and energy transfer (ET) of Gd³⁺ → Eu³⁺ and Gd³⁺ → Tb³⁺ were found. Moreover, the energy transfer process from Tb³⁺ to Eu³⁺ was verified by the overlap of luminescence spectra and the variation of lifetime. Energy transfer mechanism was determined to be a dipole–dipole interaction, and ET efficiency as well as quantum efficiency were also obtained. Moreover, the emission color of GdSr₂AlO₅:Tb³⁺,Eu³⁺ can be tuned from green to red by altering the ratio of Tb³⁺/Eu³⁺. These results indicate that the GdSr₂AlO₅:Tb³⁺,Eu³⁺ phosphor is a promising single-component white light-emitting phosphor.

The emission spectra of GdSr₂AlO₅:2%Tb³⁺,x%Eu³⁺ (x = 0, 0.5, 1, 2, 3, and 5) under 275 nm excitation. (b) Variation tendency of the green emission of Tb³⁺ and the red emission of Eu³⁺.     

Luminescence properties and energy transfer of K3LuF6:Tb3+,Eu3+ multicolor phosphors with a cryolite structure

In recent years, compounds with a cryolite structure have become excellent hosts for luminescent materials. In this paper, Tb³⁺ doped and Tb³⁺/Eu³⁺ co-doped K₃LuF₆ phosphors were prepared via a high temperature solid phase sintering method. The XRD, SEM, as well as photoluminescence excitation (PLE) and emission (PL) spectra were measured to investigate the structure and luminescence properties of the as-prepared samples. In the Tb³⁺/Eu³⁺ co-doped K₃LuF₆ samples, both characteristic emission spectra of Tb³⁺ and Eu³⁺ could be observed and the emission color of the K₃LuF₆:0.12Tb³⁺,xEu³⁺ phosphors could be adjusted from green to yellowish pink and the corresponding CIE values could be regulated from (0.2781, 0.5407) in the green area to (0.4331, 0.3556) in the yellowish pink area by controlling the concentration ratio of Eu³⁺/Tb³⁺. In addition, the energy transfer mechanism in Tb³⁺/Eu³⁺ co-doped K₃LuF₆ was calculated to be a quadrupole–quadrupole interaction from Tb³⁺ to Eu³⁺ based on the Dexter''s equation.

Single-phase multicolor phosphors with a cryolite structure were obtained via energy transfer from Tb³⁺ to Eu³⁺.     

Size dependent optical temperature sensing properties of Y2O3: Tb3+, Eu3+ nanophosphors

Using urea as a precipitation agent, Tb³⁺, Eu³⁺ co-doped Y₂O₃ nanophosphors were synthesized by a homogeneous precipitation method. The sizes of the sample particles were controlled by changing the molar ratio of the urea and rare earth ions. The microstructure and crystallographic structure of the sample were determined through powder X-ray diffraction (PXRD) and field emission scanning electron microscopy (FE-SEM). The test results show that the sample is body centered cubic. As the molar ratio of urea to rare earth ions increases, the size of the sample particles decreases. The temperature-dependent emission spectra of Tb³⁺, Eu³⁺ co-doped Y₂O₃ phosphors with different particle sizes were measured. The results showed that because the fluorescence intensity ratio (FIR) of Tb³⁺ and Eu³⁺ varies with temperature, it can be used to visually reflect changes in temperature. In addition, the temperature sensing sensitivity of Tb³⁺ and Eu³⁺ co-doped Y₂O₃ phosphors increased upon a decrease in the particle size, but the relative sensitivity decreased with a decrease in the particle size. The physical mechanism of the sensitivity and relative sensitivity changes with the size of the sample particles was also explained.

Using urea as a precipitation agent, Tb³⁺, Eu³⁺ co-doped Y₂O₃ nanophosphors were synthesized by a homogeneous precipitation method. The size dependence-optical temperature sensing properties of nanophosphors have been studied.     

Study of a color-tunable long afterglow phosphor Gd1.5Y1.5Ga3Al2O12:Tb3+: luminescence properties and mechanism

Long afterglow phosphors play a significant role in practical applications. However, due to their complex electronic structures, it is difficult to obtain tunable long afterglow phosphors. Herein, a novel long afterglow phosphor, Gd_1.5Y_1.5Ga₃Al₂O₁₂:Tb³⁺, was successfully synthesized. Its detailed structural information was extracted via the Rietveld method, and its corresponding optical properties were further systematically explored via photoluminescence (PL), phosphorescence and thermoluminescence (TL) spectroscopy. Both the photoluminescence and long afterglow properties showed tunable behavior with a variation in the concentration of Tb³⁺. The investigation of the tunability of its photoluminescence and long afterglow properties revealed that the cross-relaxation energy transfer mechanism contributes to its tunable character. Meanwhile, long-lasting phosphorescence could be observed for a few hours by the naked eye in a dark environment after discontinuing the UV irradiation. Due to the potential existence of the photo-excited (Tb³⁺)⁺, the defect clusters were proposed, with oxygen vacancies acting as electron trapping centers and (Tb³⁺)⁺ attracting holes. Finally, an appropriate mechanism for the tunable long afterglow emission was proposed.

Long afterglow phosphors play a significant role in practical applications.     

Mn4+-activated Li3Mg2SbO6 as an ultrabright fluoride-free red-emitting phosphor for warm white light-emitting diodes

In this paper, we report on highly efficient Mn⁴⁺-activated double perovskite Li₃Mg₂SbO₆ (LMS) red-emitting phosphors. These LMS:Mn⁴⁺ phosphors can be efficiently excited over a broad wavelength band from 235 nm to 600 nm peaking at 344 nm and 469 nm, and exhibited an intense red emission band with a range from 600 nm to 800 nm centered around 651 nm. The optimal Mn⁴⁺ doping concentration of LMS:Mn⁴⁺ was 0.6 mol% and its internal quantum efficiency can reach as high as 83%. Besides, the thermal quenching effect on the optical property was also analyzed. Finally, a warm white light-emitting diode (WLED) lamp was fabricated by using a 454 nm InGaN blue LED chip combined with a blend of YAG:Ce³⁺ yellow phosphors and the as-prepared LMS:0.6% Mn⁴⁺ red phosphors, which showed bright white light with CIE chromaticity coordinates (0.4093, 0.3725), correlated color temperature (CCT = 3254 K), color rendering index (CRI = 81) and luminous efficacy (LE = 87 lm/W).

Mn⁴⁺-activated Li₃Mg₂SbO₆ red-emitting phosphor with internal quantum efficiency as high as 83% was developed for blue-pumped warm-white light-emitting diodes.     

Novel Eu3+-activated Ba2Y5B5O17 red-emitting phosphors for white LEDs: high color purity,high quantum efficiency and excellent thermal stability

Eu³⁺-activated Ba₂Y₅B₅O₁₇ (Ba₂Y_5−xEu_xB₅O₁₇; x = 0.1–1) red-emitting phosphors were synthesized by the conventional high temperature solid-state reaction method in an air atmosphere. Powder X-ray diffraction (XRD) analysis confirmed the pure phase formation of the as-synthesized phosphors. Morphological studies were performed using field emission-scanning electron microscopy (FE-SEM). The photoluminescence spectra, lifetimes, color coordinates and internal quantum efficiency (IQE) as well as the temperature-dependent emission spectra were investigated systematically. Upon 396 nm excitation, Ba₂Y_5−xEu_xB₅O₁₇ showed red emission peaking at 616 nm which was attributed to the ⁵D₀ → ⁷F₂ electric dipole transition of Eu³⁺ ions. Meanwhile, the influences of different concentrations of Eu³⁺ ions on the PL intensity were also discussed. The optimum concentration of Eu³⁺ ions in the Ba₂Y_5−xEu_xB₅O₁₇ phosphors was found to be x = 0.8. The concentration quenching mechanism was attributed to the dipole–dipole interaction and the critical distance (R_c) for energy transfer among Eu³⁺ ions was determined to be 5.64 Å. The asymmetry ratio [(⁵D₀ → ⁷F₂)/(⁵D₀ → ⁷F₁)] of Ba₂Y_4.2Eu_0.8B₅O₁₇ phosphors was calculated to be 3.82. The fluorescence decay lifetimes were also determined for Ba₂Y_5−xEu_xB₅O₁₇ phosphors. In addition, the CIE color coordinates of the Ba₂Y_4.2Eu_0.8B₅O₁₇ phosphors (x = 0.653, y = 0.345) were found to be very close to the National Television System Committee (NTSC) standard values (x = 0.670, y = 0.330) of red emission and also showed high color purity (∼94.3%). The corresponding internal quantum efficiency of the Ba₂Y_4.2Eu_0.8B₅O₁₇ sample was measured to be 47.2%. Furthermore, the as-synthesized phosphors exhibited good thermal stability with an activation energy of 0.282 eV. The above results revealed that the red emitting Ba₂Y_4.2Eu_0.8B₅O₁₇ phosphors could be potential candidates for application in near-UV excited white light emitting diodes.

A novel Ba₂Y₅B₅O₁₇:Eu³⁺ red-emitting phosphor with high color purity, high quantum efficiency and excellent thermal stability was developed.     

Luminescence properties of ZnGa2O4:Cr3+,Bi3+ nanophosphors for thermometry applications

Chromium(iii) and bismuth(iii) co-doped ZnGa₂O₄ nanoparticles are synthesized by a hydrothermal method assisted by microwave heating. The obtained nanoparticles, with a diameter smaller than 10 nm, present good luminescence emission in the deep red range centered at 695 nm after coating with a silica layer and calcination at 1000 °C during 2 h. Persistent luminescence and photoluminescence properties are investigated at several temperatures. Bandwidth and luminescence intensity ratio of persistent emission do not present enough change with temperature to obtain a competitive nanothermometer with high sensitivity. Nevertheless, persistent luminescence decay curves present a significant shape change since the trap levels involved in the deexcitation mechanism are unfilled with increase of temperature. Even if the sensitivity reaches 1.7% °C⁻¹ at 190 °C, the repeatability is not optimal. Furthermore, photoluminescent lifetime in the millisecond range extracted from the photoluminescence decay profiles drastically decreases with temperature increase. This variation is attributed to the thermal equilibrium between two thermally coupled chromium(iii) levels (²E and ⁴T₂) that have very different deexcitation lifetimes. For ZnGa₂O₄:Cr³⁺_0.5%,Bi³⁺_0.5%, the temperature sensitivity reaches 1.93% °C⁻¹ at 200 °C. Therefore, this kind of nanoparticle is a very promising thermal sensor for temperature determination at the nanoscale.

Luminescence properties of chromium(iii) and bismuth(iii) co-doped ZnGa₂O₄ nanoparticles are investigated for thermometry applications.     

Optical and structural properties of the Fe3+-doped Lu3Al5O12:Ce3+ garnet phosphor

A novel series of Lu₃Al_5−xFe_xO₁₂:Ce³⁺ (0.00 ≤ x ≤ 0.45) garnets were obtained by the solid-state reaction method at 1200 °C. The obtained materials were characterized by X-ray diffraction, Rietveld refinement, UV-Vis diffuse reflectance spectroscopy, absorption spectroscopy, and photoluminescence spectroscopy. Fe³⁺ doping allowed obtaining pure-phase materials at temperatures and times below those reported up to now. On the other hand, the materials reached an improved blue absorption and a tunable emission from green to orange. These optical properties are attributable to a red-shift phenomenon due to an increase of the crystal field splitting in the Ce³⁺ energy-levels. Moreover, the obtained phosphors exhibited a high quantum yield (55–67%), excellent thermal photoluminescence stability (up to 200 °C), and high color conversion, making the obtained phosphors promising candidates for w-LEDs.

A novel series of Lu₃Al_5−xFe_xO₁₂:Ce³⁺ (0.00 ≤ x ≤ 0.45) garnets were obtained by the solid-state reaction method at 1200 °C.     

Crystal structure,optical spectroscopy and energy transfer properties in NaZnPO4:Ce3+, Tb3+ phosphors for UV-based LEDs

A new series of Ce³⁺, Tb³⁺ singly doped and Ce³⁺/Tb³⁺ co-doped NaZnPO₄ (NZPO) phosphors have been synthesized via a high-temperature solid-state reaction method at 800 °C. The crystal cell structure, luminescence proprieties, energy transfer, and chromaticity coordinates of the as-prepared phosphors were investigated in detail. The photoluminescence spectra of NZPO:Ce³⁺ phosphors exhibited broad emission in the 300–380 nm range, while under UV excitation, the singly doped NZPO:Tb³⁺ phosphor showed emission peaks at ∼485–690 nm among which the green emission peak appears at ∼543 nm. The Tb³⁺ green emission was significantly enhanced almost 20 times via energy transfer from Ce³⁺ to Tb³⁺. The energy transfer (ET) mechanism from Ce³⁺ to Tb³⁺ in NZPO is identified to be a resonant type via the dipole–dipole interaction mechanism with an ET efficiency of 91%. Intense green emission is obtained at very low Tb³⁺ concentrations under 285 nm excitation, making NZPO:Ce³⁺/Tb³⁺ an efficient UV-excited green phosphor. The NaZnPO₄:Ce³⁺/Tb³⁺ phosphors are promising UV convertible materials of green light for UV -LEDs applications.

A series of Ce³⁺, Tb³⁺ and, Ce³⁺/Tb³⁺ doped NaZnPO₄(NZPO) phosphors synthesized via the high-temperature solid-state reaction method were investigated.