Photoluminescence Decay Profiles Research Articles

Dy3+ doped KCa(PO3)3 phosphor for white light generation: structural and luminescent studies

Abstract Using the traditional solid-state reaction approach, Dy3+ ions doped KCa(PO3)3 phosphors have been synthesized to investigate their luminescent properties to produce high-quality white light for solid-state lighting applications, particularly in white LEDs. X-ray diffraction (XRD) patterns were used to examine the structure and phase of the phosphors. Using scanning electron microscopy (SEM), the morphology of the as-synthesized phosphor has been investigated. Fourier transform infrared spectroscopy (FT-IR) has been used to investigate several vibrational bands seen in the phosphor. Using diffuse reflectance spectra (DRS), the as-synthesized phosphors' optical band gap values have been estimated. When Dy3+ ions are excited at 350 nm, the photoluminescence (PL) spectra characteristics observed for the activated KCa(PO3)3 phosphor show strong white area emission at 575 nm, which is related to the 4F99/2 → 6H13/2 transition of Dy3+ ions. Additionally, the concentration quenching of Dy3+ ions doped at 4 mol% is seen in the PL spectra. Based on the observed PL spectra, the computed CIE chromaticity coordinates for the doped KCa(PO3)3 phosphors show that the optimised 4.0mol% Dy3+ doped phosphor is located in the deep white area. The lifespan of the as-titled phosphors decreases as the amount of Dy3+ ions increases in the host lattice. Additionally, the PL decay profiles shows a dual exponential behaviour when excited at 350 nm, with an emission wavelength at 575 nm. On the basis of the results of the aforementioned studies, we wish to project Dy3+ ion doped KCa(PO3)3 phosphors as white light generating materials in w-LEDs and for other photonic applications.

Impact of La doping on the optoelectronic and structural properties of CsPbIBr2 perovskite solar cell

Inorganic lead halide perovskite solar cells (IPSC) have high power conversion efficiency (PCE). Currently, heteroatom substitution is a promising method for enhancing the properties of perovskite materials and the performance of associated devices. This study outlines the production process of a perovskite solar cell made from inorganic CsPbIBr2 with a 4 % La doping. The cubic crystal structure with large grain size and small band gap energy is observed at 4 % La–CsPbIBr2. The optoelectronic and structural characteristics of CsPbIBr2 perovskite solar cells have been substantiated through various methodologies, such as the determination of space charge restricted current, examination of the photoluminescence decay profile, assessment of charge transfer resistance, and utilization of Mott Schottky analysis. The incorporation of lanthanum-doped cesium lead iodide bromide (La-doped CsPbIBr2) resulted in a notable enhancement in both the open circuit voltage (Voc), and the short circuit current density (Jsc), leading to a much higher overall efficiency of 9.89 % compared to the pristine counterpart, which exhibited an efficiency of 8.62 %.

Highly Efficient HTM-Free Tin Perovskite Solar Cells with Outstanding Stability Exceeding 10000 h.

The bottleneck in the rapid development of tin-based perovskite solar cells (TPSCs) is the inherent chemical instability. Although this is being addressed continuously, the device performance has not improved further due to the use of PEDOT:PSS as the hole-transport material (HTM), which has poor long-term stability. Herein we have applied commercial ITO nanoparticles over ITO glass substrates and altered the surface chemistry of the ITO electrode via a simple two-step thermal annealing, followed by a UV-ozone treatment. These surface-modified ITO electrodes display promising interfacial characteristics, such as a suitable band alignment owing to significantly reduced surface carbon contamination, increased In-O bonding, and reduced oxygen vacancies, that enabled fabrication of an HTM-free TPSC device according to a two-step method. The fabricated device possessed an outstanding power conversion efficiency (PCE) of 9.7%, along with a superior long-term stability by retaining over 90% of the initial PCE upon shelf storage in a glovebox for a period of over 10000 h. The application of ITO nanoparticles led to effective interfacial passivation, whose impacts on the long-term durability were assessed using electrochemical impedance spectroscopy, time-resolved photoluminescence decay profiles, and femtosecond transient absorption spectroscopy techniques.

Efficient tunable photoluminescence of Dy3+/Eu3+ co-doped OFSZBS glasses for warm white LEDs

A series of oxyfluoride strontium zinc borosilicate (OFSZBS) glasses co-doped with Dy3+/Eu3+ ions was prepared via melt quench method. The structural properties were examined using XRD and scanning electron microscope (SEM) with energy dispersive X-ray analysis (EDX) on DE2.0 and undoped OFSZBS glasses, respectively. UV–Vis absorption spectroscopy was used to evaluate the direct & indirect energy band gaps. At different excitations (348, 362, 385 and 393 nm), the photoluminescence (PL) spectra were observed with tuned light. Warm white light was generated through the Dy3+ (4F9/2→6H15/2, 6H13/2) and Eu3+ (5D0→7F2) transitions. Dexter Reisfield approximation applied to PL data revealed a dipole-dipole (d-d) mechanism accountable for the energy transfer (non-radiative) between sensitizer (Dy3+) and activator (Eu3+) ions. The energy transfer efficiency in the co-doped glass samples was found between 8% to 50%, depending on the doping. The Inokuti-Hirayama (I-H) fitting of PL decay profiles also confirm the energy transfer mechanism. The CIE chromaticity color coordinates observed for OFSZBSDE2.0 glass also confirm the color tunability. The above findings reveal the applications of as-prepared Dy3+/Eu3+ co-doped OFSZBS glasses excited using n-UV light for warm white LEDs and tuned devices.

ZnPSe3 as ultrabright indirect band-gap system with microsecond excitonic lifetimes.

ZnPSe3 was identified as a two-dimensional material wherein valley and spin can be optically controlled in technologically relevant timescales. We report an optical characterization of ZnPSe3 crystals that show indirect band-gap characteristics in combination with unusually strong photoluminescence. We found evidence of interband recombination from photoexcited electron-hole states with lifetimes in a microsecond timescale. Through a comparative analysis of photoluminescence and photoluminescence excitation spectra, we reconstructed the electronic band scheme relevant to fundamental processes of light absorption, carrier relaxation, and radiative recombination through interband pathways and annihilation of defect-bound excitons. The investigation of the radiative processes in the presence of a magnetic field revealed spin splitting of electronic states contributing to the ground excitonic states. Consequently, the magnetic field induces an imbalance in the number of excitons with the opposite angular momentum according to the thermal equilibrium as seen in the photoluminescence decay profiles resolved by circular polarization.

Near-infrared photoluminescence studies of neodymium ions doped SrO-Al2O3-BaCl2-B2O3-TeO2 glasses for laser and fiber amplifier applications

This paper reports, preparation and characterization of Neodymium (Nd3+) ions doped Oxy Chloro Boro Tellurite (OCBT) glasses. The influence of Nd3+ ions concentration on physical, absorption, emission, and decay properties of OCBT glasses were studied in detailed using spectroscopic techniques. The experimental oscillator strengths measured from the absorption spectral data were subjected for Judd-Oflet (JO) analysis to estimate the best fit JO parametes and the dependent radiative properties of the as prepared glasses. The photoluminescence (PL) spectra recorded under 824 nm laser diode excitation reveal three emission peaks positioned at 887, 1064 and 1340 nm pertaining to 4F3/2→4I9/2, 4F3/2→4I11/2 and 4F3/2→4I13/2 transitions respectively. Correlation of radiative parameters information with PL spectral data allows to estimate various lasing parameters like emission cross section (σsec), gain bandwidth (σsec×ΔλP) and optical gain (σsec×τR). The PL decay spectra recorded for the as prepared glasses for 4F3/2→4I11/2 intense emission transition (observed at 1064 nm) reveal single exponential nature. The experimental lifetimes (τexp) measured from the PL decay profiles are correlated with the radiative lifetimes (τR) measured from the JO analysis to estimate quantum efficiency (η%) of the titled glasses. Among all the as prepared OCBTNd samples, 1 mol% of Nd3+ ions doped OCBTglass sample flourishes highest quantum efficiency. From the productive results obtained, it can be suggested that OCBTNd1.0 glass grabs plenty of applications in solid state lasers technology, fabrication of optical fiber amplifiers and NIR laser applications.

Structural and luminescence characteristics of thermally stable Dy3+ doped oxyfluoride strontium zinc borosilicate glasses for photonic device applications

Structural, thermal, and photoluminescence (PL) characteristics of a series of Dy3+ doped Oxyfluoride Strontium Zinc Borosilicate (OFSZBS) glasses have been investigated. The XRD of 1.0 mol% Dy3+ ions doped OFSZBS glass and FT-IR investigations conducted on an un-doped as well as all the Dy3+ ions doped OFSZBS glasses confirm the non-crystalline nature and distinct functional groups present in it respectively. The Differential Scanning Calorimetry (DSC) thermogram recorded for an un-doped OFSZBS glass reveals thermal stability (ΔT) and transition temperature (Tg). The optical band gaps were computed using the Tau'c method. Under 348 nm pumping wavelengths, the Photoluminescence (PL) spectra of the as-synthesized OFSZBSDy glass samples exhibit blue (450 nm), yellow (575 nm), and red (650 nm) color transitions. The PL intensity increases with Dy3+ ions concentration up to 1 mol% and after that intensity decreases due to the concentration quenching effect. The PL decay profiles reported at higher concentrations were best fitted to the Inokuti-Hirayama (I-H) model for s = 6, indicating the energy transfer process as dipole–dipole in nature. The result obtained from the I-H model is in consonance with that of Dexter's theory. At 448 K, the PL intensity is up to 85% of room temperature, indicating that the as-synthesized glasses have exceptional thermal stability. Relatively higher values of quantum efficiency (η), emission cross-sectional area (σse), and probability of radiative transition (AR) observed for 1 mol% Dy3+ ions doped OFSZBS glasses declare their suitability in photonic devices under n-UV/blue pumping wavelength.

Optical characteristics of Eu3+ doped alumino borophosphate glass containing Al3+, Zn2+, Li2+, Sr2+ and Ba2+ ions

Europium (Eu3+) doped alumino borophosphate glass (ABP) containing Al3+, Zn2+, Li2+, Sr2+, and Ba2+ was formed by melt quenching method. FT-IR spectroscopy in the range 400–4000 cm−1 was used to describe the vibrational spectrum of the glass sample in order to define the various structural units. The optical absorption spectra of the glass revealed two weak bands due to 7F0 → 5L6 and 7F0 → 5D2 transition of Eu3+ in the UV–Vis range. The direct and indirect band-gap energies were calculated using Tauc’s plot. The refractive index (n) of the prepared glass medium was measured to be decreases as the wavelength increases, and it is varying from 2.25 to 2.07 over the visible region. A photoluminescence spectrum was obtained on non-irradiated glass sample, and the spectra analysis indicated emission peaks (at 593 nm, 615 nm, 653 nm and 703 nm) attributable to the presence of Eu3+. The photo-luminescence decay profile of 5D0 → 7F2 (614 nm) of Eu3+ was also performed to investigate the effect of excitation wavelengths. The luminescence colours of the prepared glass sample were entirely fall on red region (x = 0.648 and y = 0.336) with the dominant wavelength 610 nm in the CIE 1931 chromaticity map. Using CIE chromaticity coordinates, the excitation purity (Pe), colour purity (Pcolour), colorimetric purity (Pcol) and Colour correlated temperature (CCT) were also evaluated. After irradiating the glass with γ-rays at a dosage of 2 kGy, the structural changes caused by the reduction of Eu3+ into Eu2+ ion in the glass matrix was examined using the EPR spectrum as well as its thermo-luminescence characteristics was also studied in the temperature range 300–650 K. The glow curve could be well defined as a superposition of five peaks in the temperature range, and the peaks were explained by second-order kinetics.

Temperature‐Dependent Exciton Dynamics in CdTe Quantum Dot Superlattices Fabricated via Layer‐by‐Layer Assembly

AbstractThe formation of minibands in quantum dot (QD) superlattices (SLs) dramatically increases the mobility of carriers, giving a new way to apply QDs for optoelectronic devices. In previous studies on QDSLs, only a few studies have investigated the temperature dependence of the photoluminescence (PL) properties of QDSLs focusing on the formation of minibands. Here, a new model is proposed that simultaneously considers the extended and localized exciton states formed in the QDSLs to clarify the PL mechanism of QDSLs. By systematically investigating the temperature dependence of absorption, PL spectra, and PL decay profiles in CdTe QDSLs, it is found that the Stokes shift becomes smaller and the PL decay time of the miniband edge PL becomes longer with an increase in temperature. The elucidated PL mechanism of QDSLs will help clarify further photoexcited dynamics and their physical mechanism intrinsically appearing in the QDSLs with the miniband.

Photoluminescence characteristics of Sm3+/Eu3+ co-doped LPZABS glasses for solar cell applications

A series of Sm3+/Eu3+ co-doped LPZABS (lithium lead zinc alumino borosilicate) transparent glasses were synthesized by the melt quench method. Fluorescent characteristics and energy transfer mechanisms were analyzed thoroughly. The amorphous nature of the glasses was confirmed from the observed X-ray diffraction patterns. An expansion in photoluminescence (PL) excitation of Eu3+ ions was observed on sensitizing it with Sm3+ ions in the title compounds. The PL emission spectra obtained for different excitations show bands due to Sm3+ and Eu3+ ions with increment in intensity on increasing Eu3+ ion concentration. On implementing the Dexter energy transfer formula & Reisfeld's approximation to PL emission spectra and the Inokuti-Hirayama (I–H) model to PL decay profiles, the dipole-dipole interaction among activator and sensitizer is revealed. Chromaticity coordinates (CIE) gradually relocate from the orange to the red region on increasing Eu3+ ion concentration in Sm3+/Eu3+ co-doped LPZABS glasses. The Sm3+/Eu3+ co-doped LPZABS glasses have the potential for downshifting of n-UV & blue exciting photons into visible red color photons which make it useful for copper phthalocyanine (CuPc) solar cell applications.

Energy transfer dynamics in thermally stable Sm3+/ Eu3+ co-doped AEAlBS glasses for near UV triggered photonic device applications

Transparent, Sm3+/Eu3+ co-doped alkaline earth alumino borosilicate (AEAlBS) glasses have been synthesized by employing melt quenching process and explored their down-shifting luminescent properties to understand their utility in visible red photonic devices applications. The amorphous (non-crystalline) nature of the as-prepared glasses was analyzed with help of an X-ray powder diffraction (XRD) pattern, containing a broad peak. Photoluminescence (PL) properties demonstrate that the glasses can be proficiently excited by near-UV with a dominant peak centered at 402 nm. The PL emission spectra exhibit four emission peaks with an intense peak placed at 599 nm under 402 nm excitation. The optimum emission intensity was obtained for 0.5 mol% Sm3+ ions doped in AEAlBS glasses. In the present work, Sm3+ ion is acting as an effective sensitizer for Eu3+ activator in AEAlBS glasses, and part of energy gets transferred from sensitizer (Sm3+) to activator (Eu3+) ions. The PL intensity of Eu3+ ions is increasing at the expense of a decrease in the intensity of Eu3+ ion peaks in the co-doping AEAlBS glasses at λex = 402 nm. The efficient ET from sensitizer to activator ions proved to be dipole-dipole in nature via employing Dexter's formula with Reisfeld's approximation. The experimental lifetime values calculated from the PL decay profiles are decreasing with the surge in Eu3+ ion concentration in the as-prepared glasses. Inokuti Hirayama (I-H) model applied to the PL decay profiles confirms the ET process responsible for a decrease in experimental lifetimes as dipole-dipole in nature. The outcome of the I-H model is in consonance with the result given by Dexter theory. The CIE coordinates for single Sm3+ doped glasses are falling in the orange region and gradually surge into the red region by co-doping with Eu3+ ions in AEAlBS glasses. The temperature-dependent emission analysis reveals that the PL intensity at 150 °C and 200 °C perseveres up to 94.34 and 91.30% of the PL intensity at ambient temperature, respectively. All the obtained results contemplate the superiority of the multifunctional Sm3+/Eu3+ co-doped AEAlBS glasses for near UV triggered photonic device applications.

Selective Hydrothermal Synthesis of Water-Soluble CdTe and CdTe/CdS Colloidal Quantum Dots by Controlling the Te/Cd Molar Ratio of the Precursor Solution

Abstract During the synthesis of CdTe quantum dots (QDs) by the hydrothermal method, a CdS shell layer is naturally formed by the thermal decomposition of thiol ligands, and CdTe/CdS core/shell QDs are produced. Herein, we investigate the selective synthesis of CdTe and CdTe/CdS QDs to control the thermal decomposition of thiol ligands by changing the Te/Cd molar ratio of the precursor solutions. From the experimental results of X-ray photoelectron spectroscopy and optical properties of absorption and photoluminescence (PL) spectra and PL decay profiles of the synthesized colloidal QDs, it was found that the formation of the CdS shell can be controlled by varying the Te/Cd ratio of the precursor solution. Thus, the selective synthesis of CdTe and CdTe/CdS QDs with the same PL energy but different PL decay times is possible.

Defect driven tunable optical properties of Li+ and Zr4+ co-doped Eu3+: MgF2 compounds

A novel approach of defect engineering in Eu3+ doped MgF2 compounds has been carried out in order to tune the optical properties of Eu3+ ion. Upon doping various co-dopant ions such as Li+ and Zr4+ ions, it has been observed for the first time in the photoluminescence (PL) study that such co-dopant ion would control the characteristics transition lines of Eu3+ ions and results in tunable color characteristics of the phosphor materials. While Li+ co-doping results in a higher intense magnetic dipole (MD) line (5D0 → 7F1), doping with Zr4+ results in an intense electric dipole (ED) line (5D0 → 7F2). Further, Li+ co-doping also results in an unusual highly intense 5D0 → 7F4 line. From PL decay profile it has been observed that although for both cases of the co-dopant ions two different Eu3+ components are found to exist, their contribution is completely different. From positron annihilation lifetime study it was observed that various Mg-vacancies and their cluster forms are responsible for the tunable emission characteristics. First principle based theoretical study has also been carried out to understand the configuration of various cluster vacancies as suggested by their respective positron lifetime values. The short-lived Eu3+ component, which gives rise to highly intense 5D0 → 7F4 line, originates from a Mg-site at the surface of the particle and close to a vacancy cluster VC1. While the long lived Eu3+ component is responsible for highly intense ED line and close to Mg mono- or di-vacancies in the bulk of the particle. Therefore, defects (both dopant impurity ions and lattice vacancies) play a significant role in tuning the emission characteristics of Eu3+ doped MgF2 compounds.

Optical properties of Sm3+ions doped 10SrO-(10−x)Al2O3-10BaCl2-60B2O3-10TeO2 glasses for reddish orange laser applications

In the present work, oxy chloro boro tellurite (OCBT) glasses were prepared with the composition 10SrO-(10−x)Al2O3-10BaCl2-60B2O3-10TeO2-rSm2O (where r = 0.5, 1.0, 1.5, 2.0 and 2.5 mol%) using melt quenching technique. Several optical properties were studied after thorough analysis of absorption, excitation, photoluminescence (PL) and PL decay profiles of these glasses. Judd-Ofelt parameters evaluated from the absorption spectra are used to understand the asymmetry around the Sm3+ ions in the present reported glasses. An effort has been made to understand the PL properties of these glasses by evaluating the key parameters such as branching ratios and stimulated emission cross-sections and quantum efficiencies. In the process of understanding mutual interaction between the Sm3+ ions, Inokuti-Hirayama (I-H) method is applied. CIE color co-ordinates also measured to confirm the reddish orange emission from these glasses. From all obtained parameters, it can be suggested that OCBTSm1.0 glass is aptly suitable for reddish orange laser applications.

Surface plasmon coupling effects on the förster resonance energy transfer from quantum dot into rhodamine 6G

Rhodamine 6G (R6G) molecules linked CdZnSeS/ZnS green-emitting quantum dots (QDs) are self-assembled onto Ag nanoparticles (NPs) for studying the surface plasmon (SP) coupling effect on the Förster resonance energy transfer (FRET) process from QD into R6G. SP coupling can enhance the emission efficiency of QD such that FRET has to compete with QD emission for transferring energy into R6G. It is found that FRET efficiency is reduced under the SP coupling condition. Although R6G emission efficiency can also be enhanced through SP coupling when it is directly linked onto Ag NP, the enhancement decreases when R6G is linked onto QD and then the QD-R6G complex is self-assembled onto Ag NP. In particular, R6G emission efficiency can be reduced through SP coupling when the number of R6G molecules linked onto a QD is high. A rate-equation model is built for resembling the measured photoluminescence decay profiles and providing us with more detailed explanations for the observed FRET and SP coupling behaviors.

Tunable luminescence and realization of warm white light via energy transfer from Dy3+/Er3+/Sm3+ triply doped glasses for photonic applications

The spectroscopic exploration of Dy 3+ /Er 3+ /Sm 3+ singly, doubly and triply doped BaO + ZnF 2 +K 2 O + SiO 2 +B 2 O 3 glasses have been carried out through photoluminescence excitation and emission, decay profiles, CIE color co-ordinates and correlated color temperature (CCT) values. Co-occurrence of Dy 3+ , Er 3+ and Sm 3+ luminescent bands in the fluorescence spectra of Dy 3+ /Er 3+ /Sm 3+ triply doped multicomponent borosilicate glasses with different excitation wavelengths (348, 374, 379 and 400 nm) emphasizes the existence of energy transfer processes and is studied in detail. The luminescence intensity of Er 3+ and Sm 3+ bands has shown a remarkable reduction with the increase in Dy 3+ content, whereas Dy 3+ bands seemed to be enhanced monotonously. Luminescent kinetics of as-prepared samples were investigated thoroughly by using recorded decay profiles and the observed decrement in lifetime values validated proposed Er 3+ (or Sm 3+ ) to Dy 3+ energy transfer routes. The energy transfer efficiency was considerably increased with the increase in concentration of Dy 3+ ions and is substantially interpreted using partial energy level diagrams. The estimated CCT values and CIE color co-ordinates of the prepared samples were significantly changed from reddish-orange to warm white light and it suggests the suitability of the material for lighting applications. • Multicomponent borosilicate glass is optically activated with Dy 3+ /Er 3+ /Sm 3+ ions. • The influence of Dy 3+ ions on the spectroscopic properties of triply doped glasses was examined. • Luminescent kinetics of as-prepared samples were investigated thoroughly by using photoluminescence decay profiles. • Energy transfer from Er 3+ (or Sm 3+ ) to Dy 3+ occurs. • Tunable luminescence was observed in the glassy system under different excitation wavelengths.

Concentration dependent neodymium doped oxy fluoroborate glasses for 1.08 μm laser applications

Different concentrations of neodymium-doped (Nd3+ ions) Oxy Fluoroborate (OFB) glasses were fabricated and systematically analyzed by employing spectroscopic techniques such as optical absorption, photoluminescence (PL) and PL decay spectral measurements to understand the NIR lasing potentialities. The information pertaining to absorption spectral features were subjected to Judd-Ofelt (J-O) analysis to understand the radiative properties such as transition probability (AR), radiative lifetime (τR) and branching ratios (βR) possessed by the as prepared Nd3+ ions doped OFB glasses. By correlating the radiative properties with the emission and PL decay spectral profiles, the emission cross-sections (σse) and quantum efficiency values are evaluated for the prominent fluorescent levels of Nd3+ ions in the as prepared glasses. Under 808 nm diode laser excitation, all the OFB glasses under investigation showcased two prominent NIR emissions at 1085 nm (4F3/2 → 4I11/2) and 1328 nm (4F3/2 → 4I13/2). The intensities of both the emission peaks escalates with increases in Nd3+ ions concentration up to 1 mol% and beyond decreases showcasing concentration quenching. The experimental lifetime values estimated from the single exponential PL decay profiles of 4F3/2 level are decreasing monotonously with increase in Nd3+ ions concentration in the as prepared OFB glasses. Relatively higher branching ratios, emission cross-sections and quantum efficiency values estimated for Nd3+ ions doped OFB glasses indicates the potential usage of the as prepared glasses for 1.08 μm laser applications.

Investigation of physical and spectroscopic properties of WO3 doped zinc-lithium-dysprosium borotellurite glasses

Abstract A set of WO3 doped zinc-lithium-dysprosium-borotellurite glasses in the compositions, (B2O3)0.2–(TeO2)0.3-x–(ZnO)0.28 –(Li2CO3)0.2 –(Dy2O3)0.02–(WO3)x; x = 0.02 to 0.12 (labeled as W1, W2, W3, W4, W5 and W6 respectively) have been synthesized. Amorphous nature of the samples has been confirmed and density measured. Molar volume, oxygen packing density and field strength were determined. Optical absorption spectra were recorded. Band gap values are found to increase with WO3 content up to 0.08 mol fractions and decreases for further amounts of WO3. Urbach energy behaved in the opposite fashion to that of band gap with WO3 content. These results are attributed to bonding defects and the number of non-bridging oxygen. Refractive index, molar refractivity, molar electronic polarizability, reflection loss, metallization ratio, oscillator strengths and Judd-Ofelt (J-O) intensity parameters have been determined. Based on the observed trends of JO intensity parameters, lasing ability of the glasses and their optical quality has been discussed. Photoluminescence (PL) spectra have been recorded and they exhibited three bands namely, 4F9/2 → 6H15/2 (blue), 6H13/2 (yellow) and 6H11/2 (red). The observed ratio of intensity of yellow to blue band inferred that asymmetry around rare earth ions decreases with increase of WO3 content. Using PL decay profiles, the lifetime (τexp) for yellow emission has been determined. Using the values of τexp and estimated radiative lifetime (τR), the quantum efficiency (η) has been determined and for 4F9/2 → 6H13/2 transition and, it is found to be in the range from 43% to 67% for the present glasses. Based on JO parameters, quantum efficiency and other radiative parameters, W4 glass is proposed for lasing in yellow region. For the first time, effect of WO3 on the optical properties of zinc-lithium-dysprosium-borotellurite glasses has been thoroughly investigated.

Influence of annealing treatment on the luminescent properties of Ta:β-Ga2O3 single crystal**Project supported by the National Natural Science Foundation of China (Grant No. 51802327) and the Science and Technology Commission of Shanghai Municipality, China (Grant No. 18511110500).

Ta5+ doped β-Ga2O3 single crystals were grown by using the optical floating zone method, and then annealed in the air and nitrogen gas at 1400 °C for 20 hours. The transmittance spectra, photoluminescence (PL), x-ray irradiation spectra, and PL decay profiles of the samples were measured at room temperature. The relevant results show that the optical transmittance of the samples annealed in the air or nitrogen gas was improved. By drawing the –hv graph, it can be seen that the band gap decreased after being annealed in the air, but increased in nitrogen gas. The PL spectra and x-ray irradiation spectra show that the luminescent intensity of the sample annealed in the air increased substantially, while decreased for the sample annealed in nitrogen. The PL decay time of the Ta:β-Ga2O3 annealed in the air increased significantly compared with that of the Ta:β-Ga2O3 sample without annealing, but the tendency after annealing in nitrogen gas was opposite.

Effect of Sm3+ ions concentration on borosilicate glasses for reddish orange luminescent device applications

Zinc Bismuth Strontium Borosilicate (ZnBiSrBSi) glasses doped with varying concentrations of samarium (Sm3+) ions have been synthesized via melt quenching technique and characterized by using XRD, SEM, optical absorption, excitation, Photoluminescence (PL) and decay spectral measurements. The amorphous nature of the as prepared glass has been confirmed by XRD and SEM measurements. The PL spectra recorded for the as-prepared glasses under 403 nm excitation show four emission bands from 4G5/2 level to 6HJ (J = 5/2, 7/2, 9/2 and 11/2). Among the four emission transitions, 4G5/2 → 6H7/2 transition at 600 nm is having highest intensity. The intensity of PL spectra in the titled glasses increases with increase in Sm3+ ions concentration up to 0.5 mol% and beyond decreases due to concentration quenching. Dexter theory applied to the emission spectral features reveals the energy transfer mechanism between Sm3+- Sm3+ ions as dipole-dipole in nature. The experimental lifetimes measured from the PL decay profiles for the intense 4G5/2 → 6H7/2 transition decreases with increase in Sm3+ ions concentration due to energy transfer between Sm3+-Sm3+ ions. All the aforementioned studies finally reveal that 0.5 mol% of Sm3+ ions in ZnBiSrBSi glasses is optimum in fabricating the reddish orange luminescent devices.