Color Temperature Research Articles

Energy Transfer Studies on Red Emitting CaGdSbWO8: Sm3+/Eu3+ Phosphor for w-LEDs and Indoor Plant Growth Lighting System.

In the present research work, a solid-state reaction method was employed to synthesize a series of CaGd(0.95-x)SbWO8:Sm0.05Eux (x = 1, 1.5, 2, 3 and 4mol%) phosphors. The phase purity, crystallinity, morphological and compositional studies were analysed via X-ray diffraction (XRD), scanning electron microscopy (SEM) imaging, and energy dispersive spectroscopy (EDS) analysis. The Fourier transform infrared (FT-IR) spectroscopy was utilized to measure OH content in the prepared phosphor material. The diffused reflectance spectroscopy (DRS) analysis was applied to measure the optical energy band gap. The photoluminescence (PL) spectroscopy at excitation wavelengths 275 and 405nm was carried out to analyze the luminescence properties of the prepared phosphors. The intensity of emission peaks of Sm3+ ions decreased as the concentration of Eu3+ ions increased showing the energy transfer mechanism from Sm3+ to Eu3+ ions. The dipole-dipole interaction mechanism is responsible for the energy transfer between Sm3+ to Eu3+ ions as assessed using the Reisfeld approximation. The CIE coordinates of the prepared samples lie in the warm red region represented by the relatively low (3200K) value of correlated color temperature. These results show the suitability of the prepared phosphor for white light emitting diode (w-LEDs) and also in indoor plant growth lighting systems.

The effect of correlated color temperature (CCT) variation on spectral mismatch factor (SMF) for incandescent luminous flux lamps

In this research, a setup including NIS Spectroradiometer Ocean Optics HR 2000 with an uncertainty of 4.7%, a photometric bench, and a group of NIS total luminous flux standard lamps calibrated at the National Physical Laboratory (NPL) in England with an uncertainty of 0.8%, was used to measure the correlated color temperature (CCT) and spectral power distribution (SPD) of six incandescent lamps. The correlated color temperature (CCT) curves and their equations are crucial for determining the uncertainty and variations in the spectral mismatch correction factor (SMF) for each lamp. Uncertainty calculations and analyses were conducted, revealing that the correlated color temperature (CCT) of the standard lamps ranged from 2400 K and 2750 K, and the correlated color temperature (CCT) of the tested lamps ranged from 2043 K to 2095 K influencing the uncertainty. Additionally, data analysis was performed, and an uncertainty model was developed in conjunction with the measurements. The uncertainty estimation for spectral mismatch correction factors varied from 0.0011 to 0.0084 depending on the correlated color temperature.

Glare at Night-Time Driving: Effect of Correlated Color Temperature of Led Lamps.

This study aims to analyze the effect of correlated color temperature from LED glare sources on driving performance. The evaluation includes assessing the effect of disability glare on visual reaction time and rating discomfort glare using a standardized scale. LED technology is widely incorporated into various lighting systems; however, the impact of glare from oncoming car headlamps on driving performance at night-time is crucial for road safety. Twenty-three healthy young subjects participated in a laboratory-based experiment simulating night driving using a two-channel Maxwellian view optical system. Two LED lamps with correlated color temperature of 2800K and 6500K were used to generate a glare of 52 lx. Disability glare was quantified in terms of foveal reaction time and discomfort glare was rated using the de Boer scale. The results show that glare-induced effect is mitigated by an increase in background luminance. The correlated color temperature of the LED lamp does not affect either reaction time or discomfort glare rating. The greater short-wavelength emission of 6500K lamp does not intensify the effect of disability or discomfort glare, probably due to the macular pigment absorption on foveal vision and the transparency of ocular media, coupled with the involvement of other contributing factors. The correlated color temperature of the lamp is not the best descriptive parameter to identify its effect on glare. It is important to consider the impact of LED technology on visual performance to enhance road safety in critical glare situations during night driving.

Spectrophotometric and calculative determination methods of textile color-difference threshold considering the observing condition

Purpose This study aims to investigate the varying color-difference thresholds for textiles under various illuminants. Design/methodology/approach To determine color-difference thresholds, 108 fabric samples with widely ranging colors were spectrophotometrically measured and visually assessed under four illumination conditions (correlated color temperatures of 2,856 K and 6,504 K; illuminances of 100 lx and 2,000 lx). Findings The mean spectrophotometric color-difference threshold (solely based on the textile’s physical color attributes in machine vision) was 4.22 ΔE*ab; thus, a mechanically measured color difference between two textiles (regardless of illuminant) of less than 4.22 ΔE*ab indicated individuals’ inability to differentiate between two textiles. The calculated color-difference thresholds, which reflected the color differences perceived by people considering textiles’ physical color attributes and the environmental factors in which they were observed, were higher than the spectrophotometric thresholds. This meant that under various illuminants, people had greater difficulty perceiving color differences than mechanically measured spectrophotometric thresholds. Particularly, larger discrepancies between the two threshold types occurred under reddish illuminants of 2,856 K than under bluish-white illuminants of 6,504 K. Furthermore, the extent to which people perceived color differences as distinct from actual differences under illumination was larger for greenish-blue textiles than for textiles of other hues. Originality/value The determined spectrophotometric and calculative color-difference thresholds for textiles can help fashion companies predict consumers’ perceptions of the colors of their textile products under various illuminants and, accordingly, appropriately plan colors of products and create standards for color quality control.

Shock cooling emission from explosions of massive stars – III. Blue supergiants

ABSTRACT Light emission in the first hours and days following core-collapse supernovae is dominated by the escape of photons from the expanding shock-heated envelope. In preceding papers, we provided a simple analytic description of the time-dependent luminosity, L, and colour temperature, $T_{\rm col}$, as well as of the small (${\simeq} 10 {{\, \rm per\, cent}}$) deviations of the spectrum from a blackbody at low frequencies, $h\nu \lt 3T_{\rm col}$, and of ‘line dampening’ at $h\nu \gt 3T_{\rm col}$, for explosions of red supergiants (RSGs) with convective polytropic envelopes (without significant circumstellar medium). Here, we extend our work to provide similar analytic formulae for explosions of blue supergiants with radiative polytropic envelopes. The analytic formulae are calibrated against a large set of spherically symmetric multigroup (frequency-dependent) calculations for a wide range of progenitor parameters (mass, radius, and core/envelope mass ratios) and explosion energies. In these calculations, we use the opacity tables we constructed (and made publicly available), which include the contributions of bound–bound and bound–free transitions. The analytic formulae reproduce the numeric L and $T_{\rm col}$ to within 10 and 5 per cent accuracy, and the spectral energy distribution to within ${\sim} 20\!-\!40 {{\, \rm per\, cent}}$. The accuracy is similar to that achieved for RSG explosions.

Warm white light phosphors Sc2W3O12: Dy3+, Eu3+ with ultrahigh thermal stability and tunable luminescence

Phosphors for lighting applications often face challenges such as limited thermal stability, restricted tunability of emission colors, and moderate quantum efficiency. In this study, a series of Sc2W3O12: xDy3+, yEu3+ phosphors were synthesized via a high-temperature solid-state method to address these issues. Under 350 nm excitation, Sc2W3O12: xDy3+ phosphor exhibits blue (485 nm) and yellow emission peaks (577 nm), and the optimal doping concentration of Dy3+ is 3 mol%. In Sc2W3O12: 0.03Dy3+, yEu3+ phosphor, energy transfer is revealed through spectral overlap and fluorescence decay curve analysis of Dy3+ and Eu3+. The energy transfer efficiency is as high as 75 %, and the reason is explained through a combination of energy transfer mechanism and J-O theoretical calculation. By adjusting the range of y in Sc2W3O12: 0.03Dy3+, yEu3+, the correlated color temperature can be adjusted within the range of 4450 K to 3945 K, thereby achieving tunable luminescence from neutral white light to warm white light. The thermal stability of the synthesized warm white phosphor Sc2W3O12: 0.03Dy3+, 0.05Eu3+ is 90.38 % (423 K). The fluorescence intensity ratio of Eu3+ and Dy3+ at 303 K − 483 K was calculated, and its temperature sensing performance was analyzed. At 303 K, the thermal sensing factors are Samax = 0.97 % K−1 and Srmax = 0.0962 % K−1, and the actual quantum efficiency is IQE = 50.67 %. Finally, a WLED device was prepared using Sc2W3O12: 0.03Dy3+, 0.05Eu3+ phosphors. The device emits warm white light with a correlated color temperature of 3686 K. In summary, the prepared Sc2W3O12: Dy3+, Eu3+ phosphor successfully solved the challenges of limited thermal stability, tunable luminescence color and moderate quantum efficiency, and it has potential value in white light-emitting diodes (WLEDs) and optical thermometers.

High cyan-emissive CsPbCl1.5Br1.5 quantum dots borosilicate glass modified by SrO

Currently, it has been found that white light emitting diode (WLED) lack cyan light, which not only hinders high-color-quality lighting applications but also results in an excess of blue light in WLED. In this work, cyan-emissive CsPbCl1.5Br1.5 quantum dots (QDs) were synthesized in a borosilicate glass matrix using a high-temperature melting method. The findings suggest that the increasing SrO leads to a looser glass network, which in turn intensifies phase separation, promotes the crystallization of QDs and enhances the intensity of cyan PL. Significantly, after a heating-cooling cycle, the cyan-emissive glass sample still retained 97% of its initial PL, suggesting that the synthesized sample exhibited good thermal stability. Finally, the prepared cyan-emissive QDs glass was incorporated into a WLED, effectively fills the lack of cyan light in 470-500 nm, showed a color rendering index (CRI) of 78 at a correlated color temperature (CCT) of 8300 K. This study provides an effective and convenient approach to enhancing the cyan luminescence performance of QDs, highlighting the significant application potential of cyan-emissive QDs glass in optoelectronic devices.

Red-emitting phosphors NaLiXF6:Mn4+ (X = Ti, Si) for white LEDs with high color rendering index and low correlated color temperature

White light-emitting diodes (WLEDs) are widely used in various lighting applications due to their high brightness and energy efficiency. However, commercial WLEDs, which typically combine YAG:Ce3+ phosphors with blue light-emitting diode chips, often lack red components, resulting in a high correlated color temperature (CCT) and a low color rendering index (CRI). To address this issue, two novel Mn4+-doped red-emitting phosphors, NaLiTiF6 and NaLiSiF6, were synthesized using an ion exchange method. Both phosphors exhibit strong red light with a pronounced zero-phonon line (ZPL) emission under blue light excitation. Optimal photoluminescence emission intensities were observed at Mn4+ concentrations of 6% for NaLiTiF6 and 9% for NaLiSiF6. When the temperature increased from 303 K to 413 K, both phosphors demonstrated outstanding brightness and chromatic stability. Integrated into phosphor-converted light-emitting diodes (pc-LEDs), the device incorporating NaLiTiF6:6%Mn4+ achieved a CRI of 95.1 and a CCT of 3172 K, while the device with NaLiSiF6:9%Mn4+ showed a CRI of 87.9 and a CCT of 3784 K. In addition, the luminous efficacy, CRI, and CCT of both prototype pc-LEDs maintained minimal variation with increasing driving current. These results indicate the stability and suitability of the synthesized phosphors for enhancing the performance of warm WLEDs applications.

Optical and Band Gap Study of Violet-Blue Broadband Emitting Dy3+ Codoped Y2SiO5:Ce3+ Phosphor for nUV White Light-Emitting Diodes.

Y2SiO5:Ce3+, Y2SiO5:Dy3+, and Y2SiO5:Ce3+ and Dy3+ phosphors were successfully synthesized using the oxalate wet chemical method. Phase purity, emission and excitation spectra, FTIR, and the chromaticity coordinate were adopted to represent the performance of the samples. The photoluminescence (PL) spectrum Y2SiO5:Ce3+ and Dy3+ phosphor shows a broadband in violet-blue region with a bandwidth of nearly 75 nm due to combine effect of Ce3+-Dy3+ ions with another emission peaks of Dy3+ ions peaking at 574 nm. It has been discussed how the Ce3+-Dy3+ ion pair enhances the PL intensity of violet-blue light through efficient energy transfer (ET). The chromaticity coordinate of Y2SiO5:Ce3+ (1 mol%), Dy3+ (0.3 mol%) phosphors is 𝑥 = 0.167 and 𝑦 = 0.034. The CCT value is used to find color temperatures. The energy band gap and refractive index of Y2SiO5:Dy3+ are determined using the bonding parameter and Tauc's plot. Prepared phosphors might be an excellent choice for lighting applications based on all of the findings.

Development of highly thermal-stable blue emitting Y4Al2O9:Bi3+ phosphors for w-LEDs, fingerprint and data security applications

A new blue-emitting Y4Al2O9:Bi3+ (YAO:Bi3+) phosphor is synthesized using the solution combustion method with mushroom extract as a binder. Its structural properties, concentration effects, temperature-dependent luminescence, and performance in LED devices are thoroughly investigated. Upon excitation at 367 nm, a strong blue light emission at 423 nm is observed, attributed to the 3P1→1S0 transition of Bi3+. The quantum efficiency reached approximately 63.5 %. The CIE diagram shows that the emission colour falls within the intense blue region, achieving a colour purity (CP) of 94 %. YAO:Bi3+ exhibits strong absorption in the near-ultraviolet range (330–400 nm), making it suitable for LEDs powered by near-ultraviolet chips. A thermal quenching experiment revealed an activation energy (Ea) of 0.323 eV, indicating that this YAO:Bi3+ phosphor possesses good thermal stability. This study showcases the use of YAO:Bi3+ phosphor in encapsulated LED devices. The device’s Commission Internationale de l’Éclairage (CIE) coordinates are (0.325, 0.310), with a high colour rendering index (CRI) of 94.70 and a low correlated colour temperature (CCT) of 5915 K at a current of 120 mA. These properties indicate that this phosphor is suitable for developing white LED devices powered by near-ultraviolet chips. The optimized YAO:Bi3+ phosphor is employed to enhance the detection of Level I-III fingerprint (FP) details with high resolution and contrast, showing effective visualization of latent fingerprints (LFPs) on various substrates. Furthermore, it is used as a model for developing fluorescent ink, which is applied to different media. The results suggest that YAO:Bi3+ phosphor has significant potential for applications in w-LEDs, advanced forensics, and anti-counterfeiting ink technologies.

Influence of GeO2/TeO2 ratio on thermal, structure and spectroscopic properties of Dy3+-doped tellurite-germanate glass

Dy2O3-doped tellurite-germanate glasses with an increase of GeO2/TeO2 ratio (TGZ) were synthesized and characterized through X-ray diffraction (XRD), differential scanning calorimetry (DSC), Raman, absorption, and emission spectra measurements. XRD spectra of Dy3+-doped TGZ glass confirmed the amorphous structure. The TGZ glass possess the higher anti-crystallization abilities than that of the pure tellurite glass. Raman spectroscopy showed that the amount of [TeO3] and [TeO3+1] units in the glass network were gradually decreased by increasing the ratio of GeO2 to TeO2. The result was further supported by the optical band gap energy of the TGZ glass. The luminescence intensity of the sample increased with an increase in GeO2 content and reached a maximum value at 10 mol%. The chromaticity coordinates of CIE 1931 were in the warm white light range, and the corresponding color temperature range was 3400 K–3600 K. The results showed that the addition of GeO2 to Dy3+-doped tellurite glass can improve the thermal stability and luminescence performance of the white light-emitting band.

Bright tunable multicolor carbon dots for white light-emitting diodes and fingerprint detection

In this study, in order to achieve high quantum yield (QY) and tunable multicolor carbon dots, the influence of quantum size effects and surface state changes were considered comprehensively. Blue-emitting seed carbon dots (S-CDs) were synthesized using 1,2,4-benzenetricarboxylic acid and urea as precursors. Green-emitting carbon dots (G-CDs) were then prepared by oxidizing S-CDs with 3 % H2O2, followed by treatment with 0.1 M NaOH to produce strong blue-emitting carbon dots (B-CDs). Compared with S-CDs, the QY of G-CDs and B-CDs increased by 35 times and 75 times, respectively. The improvement in quantum yield (QY) and the adjustment in emission wavelength were attributed to the disruption of hydrogen bonds and modifications in surface groups caused by treatments with hydrogen peroxide and sodium hydroxide. By combining B-CDs and G-CDs with commercial red phosphors, warm W-LEDs with a color rendering index as high as 91.4 and a correlated color temperature of 5437 K was successfully prepared, which was suitable for indoor lighting. In addition, B-CDs and G-CDs were used as fluorescent markers for latent fingerprints identification on different substrates, the results showed that B-CDs and G-CDs significantly enhanced the resolution of fingerprint imaging. The synthesized G-CDs and B-CDs offer several advantages, including high quantum yield, excellent photostability, low cost and a straightforward synthesis method. These properties provide a solid material foundation for enhancing the performance of white LEDs and detecting latent fingerprints.

Synthesis of thermally stable orange light-emitting phosphors: characterization and investigations of Sm3+-doped CsCaF3 phosphors for solid-state-lighting applications

In this study, we synthesized and characterized pure CsCaF3 and CsCaF3 doped with samarium (Sm3+) ions using a solid-state method. X-ray diffraction analysis was employed to examine the crystal structure, while field emission scanning electron microscopy analyzed the surface morphology of the doped sample. A color coordinate graph was used to calculate the color, with the Commission Internationale de l'Eclairage (CIE) fitting the color of both pure and doped samples. Upon excitation at 405 nm (6H5/2→6F7/2 transition), the doped CsCaF3 emitted an orange light. The CsCaF3:Sm3+ sample (0.8 mol%) displayed 86% color purity and a color temperature of 2191 K, making it suitable for lighting applications. The thermoluminescence (TL) curve of the beta-irradiated CsCaF3:Sm3+ (0.8 mol%) sample showed peaks at 174 °C and 297 °C. Preheating techniques eliminated the low-temperature peak, and the peak temperature of maximal TL intensity (Tm) was 297 °C. The activation energy (Ea) and frequency factor (s) were determined using the peak shape method and varying heating rates. The dosage response of CsCaF3:Sm3+ (0.8 mol%) was examined for potential dosimetry applications.

Achieving pure-fluorescent color-tunable WOLED through long-range coupling of spatially separated electron–hole pairs

Abstract Color-tunable white organic light-emitting diode (CT-WOLED) with a wide correlated color temperature (CCT) offers numerous advantages in meeting human daily needs related to circadian rhythm. The study of CCT variation trends and the rules governing the expansion of the CCT range will help further improve the performance of such devices. This research proposes an effective strategy for achieving high-efficiency fluorescent CT-WOLEDs through long-range radiative coupling of spatially separated electron–hole pairs. After inserting a 5 nm thick DMAC-DPS layer between the donor (TAPC) and the acceptor (PO-T2T), the charge transfer excitons between TAPC and PO-T2T still exist. As the voltage increases, holes selectively undergo different photophysical processes, resulting in a wide CCT range. This demonstrates the extraordinary potential of spatially separated electron–hole pairs in regulating luminescent properties. By further introducing a bulk exciplex and the conventional red fluorescent dye DCJTB, the device’s efficiency, brightness, and CCT range have been further optimized. Additionally, significant highest occupied molecular orbital energy level difference between the hole transport layer TAPC and the spacer layer facilitates hole accumulation at the TAPC/spacer interface, thereby enhancing the long-range coupling effect. In device E, we achieved a wide CCT range of 2774 K along with a high external quantum efficiency of 9.2%. The results indicate that our proposed long-range coupling strategy not only enables a wide CCT range but also ensures broad spectral emission and high electroluminescence efficiency, providing new possibilities for the field of intelligent lighting.

Sodium doped CsPbI3-PMMA composite electrospun fibrous membranes for aqueous photocatalyst and LED

All-inorganic CsPbI3 halide perovskite nanocrystals exhibit excellent photoluminescent properties, but their ambient instability presents a challenge. Adding dopants has been an effective way to improve stability. However, very few work was done for CsPbI3, which is relevant for optoelectronic and photovoltaic applications. Here sodium doped CsPbI3 nanocrystals were precipitated in situ in PMMA polymer matrix at room temperature using an electrospinning technique. It was found that the sodium doping improved the photoluminescence intensity and stability of Na-doped CsPbI3@PMMA electrospun fibrous membranes (EFMs) both in air and in water with an optimal concentration of Na/Pb = 0.75. It is speculated that sodium doping creates a core–shell structure with the sodium passivates the shell while the emission wavelength of the core blue-shifts due to the quantum confinement effect. Furthermore, EFMs can be used as photocatalysts to degrade methyl orange and to create white-LED with CIE of (0.2935, 0.3304) and color temperature of 7227 k.

Conditions for thermally stable color characteristics of trichromatic white light-emitting diodes

We present a method to stabilize color characteristics from a trichromatic white light-emitting diode (LED) consisting of red, green, and blue (RGB) LEDs under varying ambient temperatures. Through colorimetric analyses, it was found that the trichromatic white LED could maintain its chromaticity coordinate by adjusting the light output power (LOP) of green and red LEDs as the temperature varied. Moreover, the correlated color temperature (CCT) could be invariant to the external temperature change by controlling only the LOP of a red LED. Using the developed mathematical model and temperature-dependent spectral data of commercial RGB LED samples, we determined the power ratios between RGB LEDs needed to achieve thermally stable color coordinates or CCT as the heat sink temperature varied from 20 to 100 °C. When operating under thermally stable CCT conditions, the chromaticity coordinate of the trichromatic LED moved along the iso-CCT line with only a minor color deviation as the temperature increased to 100 °C. The presented approach requires adjusting the power of only one LED to achieve thermally stable CCT operation in a trichromatic white LED, which is expected to simplify LED control circuits significantly.

Replication of Leaf Surface Structures on Flat Phosphor-Converted LEDs for Enhanced Angular Color Uniformity.

We explored the use of biomimetic structures, including those that mimic leaf structures, to enhance the angular color uniformity of flat phosphor-converted light-emitting diodes (pcLEDs). The distinct microstructures found on natural leaf surfaces, such as micro-scale bumps, ridges, and hierarchical patterns, have inspired the design of artificial microstructures that can improve light extraction, scattering, and overall optical performance in LED applications. The effects of these leaf surface microstructures on the phosphor layer of flat pcLEDs were evaluated. An imprinting technique was employed to directly replicate the surface morphology structures from fresh plant leaves. The results indicated that this method provided excellent scattering capability and reduced the disparity in light output between blue and yellow light emissions from flat pcLEDs at various angles. Subsequently, uniform correlated color temperature in the flat pcLEDs was achieved, reducing the yellow ring effect. Furthermore, the availability of diverse wrinkle and surface patterns from a wide range of natural prototypes could reduce design costs compared with traditional mold fabrication, making the method suitable for application in mass production.

Low current driven blue-violet light-emitting diodes based on p-GaN/i-Ga2O3/n-Ga2O3:Si structure

This paper reports a low current driven LED with p-GaN/i-Ga2O3/n-Ga2O3:Si structure prepared by radio frequency (RF) magnetron sputtering, the driving current of the device is only 0.02 mA. Compared with the reported drive current of the LEDs, the reduction is 100 or even 1000 times. Through the study of its electrical properties, it was found that it had excellent rectification characteristics at different ambient temperatures and the turn-on voltage was about 1.8 V. In addition, the leakage current was as low as 4.30 × 10-8 mA. Through the electroluminescence test, it was found that the device had the function of emitting in the ultraviolet (363 nm) and visible (425 nm) region, which realized the blue-violet luminescence at room temperature. Furthermore, the device had excellent high temperature color stability and ultra-low color temperature of 1924 K. The color coordinate of the device at room temperature was (0.1905,0.0955). A detailed study was conducted on the electroluminescence mechanism of the device through its band structure, and the causes of the luminescence were analyzed through the Gaussian fitting of the EL spectrum.

Spectral characteristics of highly thermally stable Eu3+-doped P2O5-B2O3-ZnO-BaO glasses for tricolor WLEDs and red lasers

In this study, Eu3+doped P2O5-B2O3-ZnO-BaO (PBZB) glasses were synthesized using the melt-quenching method. Phonon sideband analysis enables the determination of the glasses' phonon energy at 1212 cm−1, which agrees with the data derived from the FTIR spectrum. Under excitation at 393 nm, the PBZB glasses all exhibit a high-purity red emission with a color purity nearly 100 % and a correlated color temperature below 4000 K, as well as their chromaticity coordinates close roughly to those of standard red light (0.67, 0.33). Optimal red emission is achieved in the PBZB glasses with a Eu2O3 concentration of 2.0 mol%. The luminescence lifetimes of Eu3+ ions, being in the millisecond range, exhibit an initial increase followed by a decrease. Based on the Inokuti-Hirayama model, the energy transfer process among Eu3+ ions is primarily driven by the d-d interactions and occurs predominantly within the clusters of the Eu3+-Eu3+ ions. Further substantiation of the high covalency and asymmetry of the Eu3+-O2− bonds is supported by the Judd-Ofelt theory calculations. The glass doped with 2.0 mol% Eu2O3 demonstrates an enhanced branching ratio, emission cross-section, gain bandwidth, and optical gain, confirming its potential for applications in high-gain lasers. Temperature-dependent emission spectra reveal the PBZB glasses' excellent thermal and chromaticity stability across 298–473 K. At 150 °C, the emission intensity at 612 nm for the 2.0 mol% Eu2O3-doped PBZB glass maintains 72 % of its initial value, with a chromaticity shift of only 4.36 × 10−3, substantially below the criteria of 0.015. Consequently, this study confirms the significant potential of 2.0 mol% Eu2O3-doped PBZB glass for applications in tricolor WLEDs and red lasers.

Comparative analysis of Sm3+-doped BaWO4 and CaWO4 phosphors: Properties and application in latent fingerprints and anti-counterfeiting

Self-activated tungstates doped with lanthanide ions are an excellent class of phosphor materials, exhibiting promising luminescence efficiency as well as stability which opens up their vast arena of applications. In this work, a detailed comparative study has been carried out on Sm3+ doped Ba/CaWO4 phosphors, synthesized via solid state reaction route. The structural, morphological and photo-physical properties have been investigated through various analytical techniques. The optical band gap and the refractive index of the phosphors have been estimated through diffuse reflectance spectroscopy. A 5-fold enhancement of the emission intensity is observed in CaWO4 as compared to BaWO4 phosphors owing to high asymmetrical environment. The underlying mechanisms of photoluminescence and energy transfer process (WO42+→Sm3+) are discussed in detail. The colour tuning from orange red to pure red emission is obtained from the Commission International de l′Eclairage (CIE) diagram. Better luminescent properties with desirable quantum yield, absorption efficiency and suitable Correlated Colour Temperature (CCT) and colour purity (91 %) values allow the optimised phosphors for diverse potential applications such as solid-state lighting, security ink for anti-counterfeiting, latent fingerprint detection, etc.