Different concentrations of Dy3+ ions activated Sr(1-x)TiO3: xDy(3+) phosphors were systematically prepared through modified citrate gel combustion route. They were characterized through powder X-ray diffractometry, surface morphology, concentration dependent and temperature dependent luminescence. The characteristic emission bands positioned at 483 nm, 578 nm and 665 nm were ascribed to F-4(9/2) -> H-6(15/2), F-4(9/2) -> H-6(13/2) and F-4(9/2) -> H-6(11/2) transitions, respectively. The colour purity of emitted luminescence was obtained as 41.24% upon 350 nm UV excitation. Considerably low colour purity leads the generation of warm white light with CIE coordinates (0.4163, 0.3842) and CCT of 3218 K. The study of concentration dependent emission results 1.5% of Dy3+ ions as an optimum concentration. The excited level decay reveal an energy transfer among the excited Dy3+ ions through exchange interaction process. The temperature dependent emission provides thermal activation energy of 0.30 eV. The SrTiO3: 1.5%Dy3+ phosphor retains 81.2% emission intensity even at 433 K confirming its good thermal stability and applicability for the design of white LEDs.

The SrTiO3 cubic perovskite phosphors activated with Eu3+ ions were synthesized through modified citrate gel combustion process. Powder X-ray diffraction technique was employed for structural analysis. These phosphors underwent inspection of morphological and elemental analysis via SEM and EDS, respectively. The UV-Visible diffuse reflectance was employed for the estimation of band gap energy. The luminescent features were investigated via excitation, emission and decay studies. The observed emission bands were assigned to D-5(0) -> F-7(J=0-4) intra 4f-4f transitions of Eu3+ ions. The SrTiO3: 0.07 Eu3+ phosphor was found producing intense red emission having a colour purity of 97.8 %, correlated colour temperature of 2601 K and an extraordinary thermal stability with an activation energy of 0.33 eV upon 394 nm nUV excitation shows its relevance for the design of lighting devices and the red component in tricolour phosphor based white LEDs.

The Er3+ activated Sr3Gd(1−x)(PO4)3 phosphors were synthesized via modified citrate sol-gel combustion method. Powder X-ray diffraction was adopted for phase examination. Field emission scanning electron microscopy was employed for morphology and elemental mapping. They exhibit Er3+ emission bands related to (2H11/2,4S3/2, 4F9/2) → 4I15/2 transitions up on 376 nm UV excitation. They produce potential greenish-yellow emission of colour purity of 94.71% with Commission International de I’Eclairage (CIE) coordinates (0.289, 0.698). The Er3+ doping was optimized as 1% for prominent luminescence. The CIE coordinates were predicted to assess their effectiveness through three different machine learning algorithms such as the Random Forest regression, Extreme Gradient Boosting regression and Light Gradient Boosting Machine regression. The findings show that all the three models have considerable accuracy for prediction with overall test root square, R2 ≥ 0.96285 and provide useful information for choosing appropriate CIE coordinates for real-world applications. The quenching temperature was found higher than 300 °C showing their good thermal stability with 0.235 eV activation energy. The optimal phosphor shows a maximum absolute sensitivity of 0.00464 K− 1 at 573 K and relative sensitivity of 0.934%K− 1 at 373 K. The Sr3Gd(PO4)3: 1%Er3+phosphor possess excellent optical as well as temperature sensing properties.

GdAl3(BO3)(4): Er3+ and Er3+/Yb3+ phosphors were prepared through solid state reaction method and characterized. The crystalline phase was studied by powder X-ray diffraction technique, the occurrence of several vibrational bonds was recognized by Fourier transform infrared spectroscopy and the surface morphology was verified by scanning electron microscopy. The down and up conversion emission spectra reveal three emission bands related to H-2(11/2) -> I-4(15/2) (similar to 521 nm), S-4(3/2) -> I-4(15/2) (similar to 547 nm) and F-4(9/2) -> I-4(15/2) (similar to 658 nm) transitions up on 377 nm and 980 nm excitation, respectively. An effective sensitization of Yb3+ ions improves the intensity of green emission upon 980 nm upconversion. The GdAl3(BO3)(4): 1 %Er3+/3 %Yb3+ phosphor exhibited a noteworthy thermal stability with an activation energy of 0.314 eV. The same was more potential for not only the design of green LEDs, but also for non-contact temperature sensing devices. It possesses an absolute sensitivity of 0.00415 K-1 at 473 K and relative sensitivity of 0.576 % K-1 at 373 K with an excellent thermal cycling repeatability.

Sr(1-x)TiO3:xSm3+ (0 ≤ x ≤ 2%) cubic perovskite phosphors were prepared through modified citrate gel combustion method. Phase purity was examined by powder X-ray diffraction technique. SEM and HRSEM were used for surface morphology and elemental mapping studies. The direct bandgap energy of SrTiO3:1%Sm3+ phosphor was estimated as 4.921 eV. Upon 408 nm excitation, they exhibit Sm3+ characteristic 4G5/2 → 6HJ (J = 5/2, 7/2, 9/2, 11/2) emission transitions. Optimized SrTiO3:1%Sm3+ phosphor produce warm orange-red emission of a high colour purity of 97.80% through CIE coordinates (0.563, 0.434) and holds 77.4% of its room temperature emission intensity even at 160oC showing good thermal stability. Temperature dependent emission analysis reveals an activation energy of 0.227 eV which leads a weak thermal quenching by activating non-radiative decay paths. Observed findings show that SrTiO3:1%Sm3+ phosphor is promising for lighting applications such as orange-red displays and as also a red component for phosphor based white-LEDs.

The present investigation explores the structural and optical properties of Sr3Gd(1-x)(PO4)3: xHo3+ phosphors synthesized through modified citrate sol-gel combustion process. The structural analysis through powder X-ray diffraction technique confirms the body centered cubic structure and it was confirmed by Rietveld analysis. The FESEM analysis explores the uniform distribution of agglomerated spherical particles. The elemental mapping reveals the uniformly distributed elements across the analyzed area and the energy dispersive spectroscopic study clarifies the presence of all the elements with proper weight percentage. The Fourier Transform infrared spectroscopic analysis reveals the presence of various structural bonds. The emission spectra revealed 5F3 -> 5I8 (524 nm, pale green), 5F4+5S2 -> 5I8 (548 nm, bright green) and 5F5 -> 5I8 (646 nm, red) transitions upon suitable excitation. The optimal concentration of Ho3+ ions was obtained as x = 1.0 mol% for intense green emission. The temperature dependent emission investigations support exceptional thermal stability with an activation energy of 0.34 eV. The Sr3Gd(PO4)3: Ho3+ (1.0 mol%) phosphor is well suited for lighting and display devices and also for white LEDs applications.

A series of oxyfluorophosphate glasses with the composition (60-x) P2O5 + 10 BiF3 +10 MgO + 10 ZnO + 10 KF + xEr2O3 (0 <= x >= 2.0 mol%) were prepared using conventional melt quenching method. The amorphous phase of studied glass samples was examined through powder x-ray diffraction. The optical properties were determined using UV-vis-NIR absorption, photoluminescence excitation and emission spectra. The radiative properties were determined using Judd-Ofelt and Fuchtbauer-Ladenburg theories. The optimal Er3+ doping concentration for efficient emission was determined by analysing the emission spectra under 377 nm excitation. The emission spectra of studied glasses exhibited characteristic emission bands of Er3+ ions corresponding to the 2H11/2 -> 4I15/2 (529 nm), 4S3/2 -> 4I15/2 (545 nm) and 4F9/2 -> 4I15/2 (684 nm) transitions. At higher Er3+ doping levels, the emission bands shift towards longer wavelengths showing a red shift. Upon 980 nm excitation for upconversion, the Er3+ ions emitted intense green luminescence through the 4S3/2 -> 4I15/2 (545 nm) transition. The applicability of studied glasses for the fabrication of green laser sources was discussed. The glass system containing 0.5 mol% of Er3+ ions was identified to be the optimal choice for designing green laser sources.

The CaF2 based oxyfluoroborosilicate glasses and glass ceramics doped with Er3+ ions were prepared via melt quench process followed by heat treatment and characterized for 1.53 mu m broadband applications. The optimized glass ceramic sample was obtained at 450oC/1h heat treatment. The Er3+ concentration was optimized as 1.0 mol % for efficient emission at 460 nm excitation through concentration dependent luminescence analysis. The spectroscopic parameters such as Omega lambda = 2,4,6 parameters and the radiative parameters such as spontaneous transition probability rates (AR), branching ratios (beta R) and decay times (tau R) were calculated applying the standard Judd-Ofelt theory. The effective bandwidth (Delta lambda eff), stimulated emission cross-section (sigma e), gain bandwidth (sigma e x Delta lambda eff), quantum efficiency (eta) and figure of merit (sigma e x tau R) were calculated as 25.78 nm, 13.42 x 10-21 cm2, 3.46 x 10-26 cm3, 82.83% and 5.32 x 10-23 cm2s, respectively for the optimized glass ceramic sample. The exchange type of energy transfer among the excited Er3+ ions results the quenching in luminescence and the nonexponentiality in decay curves. The systematic investigations carried out indicate that the glass ceramic obtained at 450oC/1h heat treatment was proficient for 1.53 mu m broadband fiber lasers and optical amplifiers in S and C band communication window.

The present investigation explores the structural and optical properties of Sr3Gd(1-x)(PO4)3: xHo3+ phosphors synthesized through modified citrate sol-gel combustion process. The structural analysis through powder X-ray diffraction technique confirms the body centered cubic structure and it was confirmed by Rietveld analysis. The FESEM analysis explores the uniform distribution of agglomerated spherical particles. The elemental mapping reveals the uniformly distributed elements across the analyzed area and the energy dispersive spectroscopic study clarifies the presence of all the elements with proper weight percentage. The Fourier Transform infrared spectroscopic analysis reveals the presence of various structural bonds. The emission spectra revealed 5F3 → 5I8 (524 nm, pale green), 5F4+5S2 → 5I8 (548 nm, bright green) and 5F5 → 5I8 (646 nm, red) transitions upon suitable excitation. The optimal concentration of Ho3+ ions was obtained as x = 1.0 mol% for intense green emission. The temperature dependent emission investigations support exceptional thermal stability with an activation energy of 0.34 eV. The Sr3Gd(PO4)3: Ho3+ (1.0 mol%) phosphor is well suited for lighting and display devices and also for white LEDs applications.

The structural and luminescence properties of Tm3+ doped CaF2 based oxyfluoroborosilicate glasses and glass ceramics were discussed. The critical glass ceramic (BSTm1.0GC2) nature was obtained through different heat treatment processes as 450 degrees C for 1 hand the concentration of Tm3+ ions was optimized as 1.0 mol% for efficient emission. The spectroscopic and laser characteristic parameters were evaluated applying the standard Judd-Ofelt theory. The emission of blue light through 1 D 2 -> 3 F 4 transition was studied by exciting at 360 nm UV wavelength. Upon 808 nm laser excitation, the glasses and glass ceramics produce 1.46 mu m emission through 3 H 4 -> 3 F 4 transition. The effective bandwidth (114.99 nm), stimulated emission cross-section (14.30 x 10-21 cm2), gain bandwidth (1644.74 x 10-28 cm3), figure of merit (10.21 x 10-24 cm2s) and the quantum yield (76 %) of 3 H 4 -> 3 F 4 transition made the BSTm1.0GC2 suitable as gain medium for 1.46 mu m NIR fiber laser applications.

The detailed study on impact of Yb3+ on spectroscopic and 1.54 μm broadband emission of Er3+ doped transparent oxyfluroborosilicate glass ceramics (GCs) with embedded CaF2 nanoparticles was presented. The studied GCs were prepared by controlled crystal nucleation and growth process at 450 °C/1 h. Thermogravimetry and differential scanning calorimetry results showed good thermal stability and fiber drawing capacity. The scanning electron microscope and transmission electron microscope studies confirmed the formation and the uniform distribution of CaF2 nanoparticles. Various radiative and laser characteristic features were calculated within the frame work of Judd–Ofelt theory. The NIR emission at 980 nm pumping showed an intense and broad emission band due to Er3+:4I13/2 → 4I15/2 transition. The emission spectra showed a quenching in luminescence beyond 3 mol

Yb3+-doped borosilicate-based glass and glass ceramics containing CaF2 nanocrystals prepared by conventional melt quench method followed by reheat treatment were characterized for NIR fiber lasers. The crystalline phase, morphology, and the presence of various functional groups were examined through powder X-ray diffraction, scanning electron microscopic, and Fourier transform infrared studies. The fiber drawing nature and the thermal stability were studied through differential scanning calorimetry. The X-ray diffraction and morphology investigations confirm the ceramic behavior of the studied samples with notable transparency. The optical band gap energy was estimated using the absorption spectra. The emission cross-section corresponding to Yb3+: 2F5/2→2F7/2 (981 nm) transition was determined from the Fuchtbauer–Ladenburg method, Mc Cumber theory, and the emission spectra. Considerably high-emission cross-section and gain coefficient values of glass ceramic obtained by heat treatment at 450 °C/1 h show its suitability to design 981-nm infrared fiber laser sources.

Trivalent neodymium (Nd3+) doped transparent oxyfluoroborosilicate glass and glass ceramics (GCs) comprising CaF2 nanoparticles (NPs) were fabricated via melt quench route followed by two step heat treatment process. The X-ray diffraction and scanning electron microscopic studies confirm the presence of CaF2 NPs. The GC environment for efficient luminescence was obtained at a heat treatment of 450 °C/1 h. The wavelength of pumping laser source was optimized as 808 nm by studying the luminescence properties at different excitations. The Nd3+ ions exhibit their characteristic emission transitions with peak maxima at around 0.89 μm (4F3/2 → 4I9/2), 1.06 μm (4F3/2 → 4I11/2) and 1.32 μm (4F3/2 → 4I13/2). The Nd3+ concentration was also optimized as 1.0 mol% for strong emission up on 808 nm pumping. Various spectroscopic, radiative and laser characteristic parameters were determined using Judd-Ofelt theory. The luminescence decay of 4F3/2 state was studied controlling the excitation and emission wavelengths at 808 and 1060 nm, respectively. The reasons for quenching in luminescence were discussed with suitable illustrations. The experimentally observed results confirm that the GC sample obtained at 450 °C/1 h heat treatment was highly appropriate to design 1.06 μm fiber lasers and optical amplifiers.

The Er3+-doped transparent glasses were the significant materials to design solid state visible lasers, near infrared lasers, upconverters, sensors and fiber amplifiers. The effect of Yb3+ sensitization on 1.53 mu m broadband and 548 nm upconversion green emissions in TeO2-WO3-GeO2-ErF3-YbF3 (TWGErYb) glasses were studied. They were characterized through structural, optical absorption, near infrared and upconversion studies. The Judd-Ofelt theory was adopted to estimate several spectroscopic and radiative parameters. The laser characteristic parameters such as stimulated emission cross sections, gain band widths, figure of merit and quantum efficiencies were evaluated. Conveying the energy from Yb3+ to Er3+ ions and the reasons for non-radiative losses were highlighted. The quenching in luminescence of 1.53 mu m broadband, the 548 nm upconversion green emissions and the enhanced decay time values due to self-absorption were studied. The fitting of decay curves of Er3+: 4I13/ 2 and Er3+: 4S3/2 emission states at higher Yb3+concentrations (>= 1.5 mol%) to Inokuti-Hirayama model were discussed. The TWGErYbx glasses containing 0.5Er3+/2.5Yb3+ show proficiency to design 548 nm green solid state lasers and 1.53 mu m broadband fiber lasers.

The GdAl3(BO3)4:xPr3+ (0 ≤ x ≤ 5.0 mol%) phosphors were prepared through solid state reaction route and characterized for various lighting applications. Powder X-ray diffraction investigations revel rhombohedral structure matched to JCPDS card no. 83-1907. The morphological studies confirm the agglomeration of particles with different size and shape. The emission spectra show various emission transitions originating from Pr3+:(3P1,0, 1D2) emission states to their lower lying energy states upon 274 nm NUV excitation with a red shift for x > 0.5 mol%. The colour perception analysis results an intense red luminescence due to efficient energy transfer from Gd3+ to Pr3+ ions. The temperature-dependent luminescence investigations show good thermal stability even beyond 150°C with an activation energy of 0.24 eV. The observed experimental results show the potentiality of GdAl3(BO3)4:0.5 Pr3+ phosphor for red emitting devices and red component in phosphor converted white LEDs.

A series of Gd 1– x Eu x Al 3 (BO 3 ) 4 red light‐emitting phosphors, where 0 ≤ x ≤ 15.0%, are prepared by high‐temperature solid‐phase method and characterized through X‐ray diffraction, Fourier‐transform infrared spectroscopy, scanning electron microscopy, photoluminescence emission and excitation, luminescence decay, and thermoluminescence studies. Under 274 and 396 nm UV excitations, intense red luminescence is observed through 5 D 0 → 7 F 0,1,2,3,4 transitions. Based on concentration‐dependent luminescence spectra, the Eu 3+ concentration is optimized to be 12.0% for efficient red luminescence. The Commission International de I’Eclairage coordinates and hence the color purity and correlated color temperature values are obtained from the emission spectra. The thermal stability is examined using the temperature‐dependent luminescence study. The high amount of color purity and thermal stability of Eu 0.12 Gd 0.88 Al 3 (BO 3 ) 4 phosphor shows its suitability as the best replacement for red component in phosphor‐converted white light‐emitting diodes (LEDs) as well as indoor plant growth LEDs.

Transparent Er3+/Tm3+ codoped CaF2 based oxyfluoroborosilicate glass-ceramics (BSEr1TmxGCs) with variable Tm3+ concentration were prepared through melt quench process followed by reheat treatment at 450 degrees C/1h. They were characterized through differential scanning calorimetry (DSC), powder X-ray diffraction (XRD), Fourier transform infrared (FTIR) Raman spectroscopy, near infrared (NIR) emission and luminescence decay. The formation of CaF2 nanocrystallites against oxyfluoroborosilicate glassy phase was confirmed by scanning electron microscopic (SEM) and hi-resolution transmission electron microscopic (HRTEM) studies. The NIR emission properties were investigated at 460 nm diode laser pumping. The applicability of BSEr1TmxGCs were examined by evaluating effective bandwidth (Delta lambda eff), stimulated emission cross-section (6e), gain bandwidth (6e x Delta lambda eff), figure of merit (6e x '6R) and quantum efficiency (fQE). The energy transfer efficiency (fET), rate of energy transfer (WET) between Er3+ and Tm3+ and the rate of non-radiative transitions (WNR) were also calculated. The comparative NIR emission performance suggests that the BSEr1Tm1GC has proficiency for 1530 nm broadband fiber lasers and optical amplifiers in short wavelength and conventional wavelength (S + C) band communication window.

The Li 6 AlGd (1− x ) (BO 3 ) 4 : x Tb 3+ (0 ≤ x ≤ 4.0 mol%) phosphors are fabricated via solid‐state reaction process. The structural investigations are carried out through powder X‐ray diffraction and Fourier transform infrared techniques. The morphology is examined using high‐resolution scanning electron microscope and transmission electron microscope. The temperature‐dependent luminescence properties are completed at 378 nm excitation. The photoluminescence excitation analysis is carried out by controlling the emission at 545 nm corresponding to Tb 3+ : 5 D 4 → 7 F 5 transition. The suitable excitation wavelength is selected as 378 nm for efficient emission by studying the emission spectra at several excitation wavelengths. The emission spectra show two groups of emission bands through Tb 3+ : 5 D 3 → 7 F J and Tb 3+ : 5 D 4 → 7 F J transitions. The concentration‐dependent investigations reveal the optimum Tb 3+ ions concentration as 2.0 mol% for intense luminescence. Upon 378 nm excitation, they produce greenish‐yellow luminescence of color purity 60% with CIE color coordinates (0.286, 0.572) close to the standard European Broadcasting Union Green Illuminant and they found suitability in the design of solid‐state lighting devices.

Different concentrations of Er3+ions doped TeO2-WO3-GeO2 transparent oxyfluoride glassy materials were fabricated by conventional melt quench method and analyzed through X-ray diffraction, Fourier Transform infrared, scanning electron microscope and energy dispersive X-ray, photoluminescence-excitation, visible emission and luminescence decay studies. Various physical, structural, spectroscopic and laser characteristic parameters were evaluated following the Judd-Ofelt theory. The studied glasses were capable of emitting intense green luminescence through (2H11/2,4S3/2) & RARR; 4I15/2 transitions. The emission of green luminescence was studied through down-conversion process at 377 nm excitation and up-conversion process at 980 nm excitation. The color coordinates were found to fall in the green region of chromaticity diagram and close to the European Broadcosting Union green illuminant. The evaluated branching ratio, stimulated emission cross-section, gain linewidth, figure of merit and the quantum efficiency corresponding to 4S3/2 & RARR; 4I15/2 transition suggests that the studied glasses find wide suitability to design green emitting solid state lighting devices.

The Bi 2 O 3 -B 2 O 3 -CaF 2 -EuF 3 (BiBCEu) glass and glass–ceramics were prepared by controlled heat treatment method for orange-red laser sources and characterized through X-ray diffraction, Fourier transform infrared, Raman, transmission electron microscopy, photoluminescence excitation, emission and luminescence decay studies. Up on 396 nm excitation, the BiBCEu glass–ceramics containing Bi 3 B 5 O 12 and CaF 2 nanocrystallites exhibit an enhanced orange-red luminescence through Eu 3+ : 5 D 0 → 7 F 2 (616 nm) transition. The radiative parameters such as radiative emission probability rate (A R ), luminescence branching ratio (β R ) and radiative decay time (τ R ) were determined using the intensities of Eu 3+ : 5 D 0 → 7 F J (J = 1, 2, 4) emission transitions following the Judd–Ofelt theory. The chromaticity coordinates of BiBCEu glass–ceramic heat treated at 575 °C for 10 h are situated in the orange-red region of the CIE diagram. The BiBCEu glass–ceramic synthesized at 575 °C for 10 h has an excellent proficiency for solid state orange-red laser sources.