Volume 38 (2020): Issue 1 (March 2020)

TiO₂ thin films were deposited by the energy filtrating magnetron sputtering (EFMS) technique and the traditional direct current magnetron sputtering (DMS) technique. The influence of the filtering electrode mesh number on the structure and optical properties of TiO₂ thin films was investigated. The structure, surface morphology and optical properties were characterized by XRD, SEM and ellipsometric spectroscopy, respectively. Results show that the TiO₂ thin films deposited by the DMS and EFMS techniques at the same deposition parameters are composed of the anatase phase exclusively. TiO₂ thin films deposited at lower deposition rate by the EFMS technique have lower crystallinity, smaller particle size and smoother surface. With increasing the mesh number, the refractive index, extinction coefficient and optical band gap are larger.

The purpose of this study was to determine the influence of different substrates (C45 steel, polycarbonate, glass) on the topography as well as tribological and mechanical properties (nanohardness, modulus of elasticity and friction force) of aluminum, gold and silver thin films. The 3D image analysis showed a strong influence of the substrate material on the topography of the studied thin films with no certain variation rule. Using the Oliver and Pharr method for determining nanohardness it was observed that, the smallest values were obtained for the thin films deposited on plastic substrate, followed by glass and C45 steel, regardless of the deposited material. The determination of the modulus of elasticity was done using the Hertzian method. The obtained results showed that the highest values of this parameter were obtained for the films deposited on plastic substrate, while the lowest values depended on both the deposited material and substrate. Friction force analysis for aluminum and gold showed a significant impact of the substrate material, with more constant values for gold. As a consequence, one must pay a particular attention when choosing the material for the substrate on which the thin films are deposited.

Zinc oxide (ZnO) thin films were deposited on Si (1 0 0) and glass substrates by sol-gel spin coating technique. Zinc acetate dihydrate, monoethanolamine and isopropanol were used as the sources for precursor solution and the resulting gel was used for the preparation of ZnO thin films. The films were annealed at different temperatures (100 °C to 500 °C) and the effect of annealing on the structural and optical properties was investigated. X-ray diffraction (XRD) and UV-Vis spectroscopy were used for the analysis of the films. The XRD results indicated the polycrystalline hexagonal structure of the ZnO films with (0 0 2) orientation. The optical properties of the films were studied using UV-Vis spectrophotometer in the wavelength range of 190 – 1100 nm. The optical characterization of the ZnO thin films showed the high transmittance of ~90 % for the films annealed at 400 °C. The films showed the absorbance ~360 – 390 nm and bandgap values of 3.40 – 3.10 eV, depending on the annealing temperature of the films.

Optical properties of cadmium oxide and uranium-doped CdO thin films synthesized by the sol-gel technique were investigated. The structural properties of the films were investigated using X-ray diffraction patterns of U-doped CdO. It was found that CdO-based films have a cubic NaCl structure. Structural properties of the films were investigated with atomic force microscopy (AFM). Reflectance, transmittance and absorption spectra of the films were measured with UV-Vis-NIR spectrophotometer. The photoluminescence (PL) behavior of the films was recorded using a fluorescence spectrophotometer. It was found that the nanostructure of the cadmium oxide film is controlled by U doping.

Glasses composed of ternary components (35 – x)Sb₂O₃–xBi₂O₃–65P₂O₅ (0 ⩽ x ⩽ 20 mol%) have been prepared and investigated as a potential alternative to lead-free glass for low temperature applications. Their structural properties were studied by Infrared Spectroscopy IR and Differential Thermal Analysis DTA. Results from the IR showed that Sb³⁺ and Bi³⁺ were responsible for glass network structure, which was supported by the diversification of density ρ and molar volume V_m with an increasing amount of Bi₂O₃. Glass transition temperature T_g, thermal stability, and coefficient of thermal expansion increased after substitution of Bi₂O₃ for Sb₂O₃ within the range of 0 mol% to 20 mol%. The water durability decreased and then increased; it could be attributed to the corrosion resistant P–O–Sb bonds. A typical sample of 25Sb₂O₃–10Bi₂O₃–65P₂O₅ possesses excellent properties and can be a promising candidate for further applications.

This study investigates microstructures and mechanical properties of the alloys obtained by adding Cu (0.7 % and 0.9 %) and Al (0.7 % and 0.9 %) to lead-free Sn-9Zn eutectic soldering alloy produced by investment casting method. The results show that Cu₅Zn₈ phase has formed in the structure of Cu added alloys and the Al₂O₃ phase has formed due to addition of Al. It was found that small and round-shaped Al₂O₃ phase increased the tensile strength of the new alloy compared to the eutectic alloy. In addition, it was observed that the microhardness of Cu added alloys was lower than that of Sn-9Zn eutectic alloy, but the microhardness of alloys containing Al was higher compared to the other eutectic Sn-9Zn alloy.

MoO₃ films were deposited by RF magnetron sputtering technique on glass and silicon substrates held at 473 K by sputtering of metallic molybdenum target at an oxygen partial pressure of 4 × 10⁻² Pa and at different sputtering pressures in the range of 2 Pa to 6 Pa. The influence of sputtering pressure on the structure and surface morphology, electrical and optical properties of the MoO₃ thin films was studied. X-ray diffraction studies suggest that the films deposited at a sputtering pressure of 2 Pa were polycrystalline in nature with mixed phase of α- and β-phase MoO₃, while those formed at sputtering pressure of 4 Pa and above were of α-phase MoO₃. Scanning electron micrographs showed a decrement in the size of the particles and their shapes changed from needle like structure to dense films with the increase of sputtering pressure. Fourier transform infrared spectroscopic studies confirmed the presence of characteristic vibration modes of Mo=O, Mo–O and Mo–O–Mo related to MoO₃. Electrical resistivity of the MoO₃ films decreased from 6.0 × 10⁴ Ω cm to 2 × 10⁴ Ω cm with an increase of sputtering pressure from 2 Pa to 6 Pa, respectively. Optical band gap of the films decreased from 3.12 eV to 2.86 eV with the increase of sputtering pressure from 2 Pa to 6 Pa, respectively.

Single crystals of L-asparagine doped ammonium tetroxalate dihydrate were grown using slow evaporation solution growth technique with deionized water as a solvent. The shift and intensity of the peaks in the single crystal X-ray diffraction and Fourier transform infrared analyses confirmed the inclusion of L-asparagine in the ammonium tetroxalate dihydrate crystal structure. The optical transmission characteristics viz. optical band gap, optical conductivity, etc., were determined. Thermal studies revealed the occurrence of anomalies at 135.3 °C and 221.7 °C leading to the possibility of phase transitions and thereby, ferroelectric behavior. Vickers microhardness studies enabled determination of various microhardness parameters. Dielectric behavior was analyzed by varying the temperature and frequency. Anomalies were observed at 135 °C and 221 °C suggesting the existence of ferroelectric nature of the compound. Self-defocusing effect was observed. The polarization-electric field hysteresis loops showed a pinched effect due to defects induced by inclusion of dopant. The crystals were characterized by single crystal XRD, FT-IR, DRS, UV-Vis-NIR, Vickers microhardness test as well as thermal and dielectric techniques. In brief, L-asparagine as a dopant in ammonium tetroxalate dihydrate altered various physical properties of the crystals. They were highly transparent in the visible region with a wider optical band gap, softer material than the parent, higher phase transition temperature of 135 °C, negative nonlinearity and self-defocusing ability.

This paper is a part of a natural dye solar cell project. Conductive transparent oxide (CTO) films have been deposited onto preheated glass substrates using a spray pyrolysis technique. The optical, electrical, structural properties as well as thermal annealing and gamma radiation response were studied. The average optical energy gap of doped films for direct allowed and direct forbidden transitions were found to be 3.92 and 3.68 eV, respectively. The plasmon frequency and plasmon energy after doping were found to be 3.48 × 10¹⁴ s ⁻¹ and 0.23 eV. The negative absorbance of the doped film was observed in UV-Vis range after applying both thermal annealing and γ-dose irradiation with 22 kGy. The negative refractive index of the doped film in UV range (220 – 300 nm) is promising for optical applications. The electron mobility μ_e reached a maximum of 27.4 cm² V⁻¹ s⁻¹ for Sb concentration of 10 %. The corresponding resistivity ρ, and sheet resistance R_s reached their minimum values of 1.1 × 10⁻³ Ω cm and 35 Ω sq⁻¹, respectively. The dopant concentration has been increased from 4.13 × 10¹⁹ to 2.1 × 10²⁰cm⁻³. The doped film was found to exhibit three diffraction peaks associated with (2 2 2), (2 0 0), and (2 1 1) reflection planes, of which the peak of (2 2 2) of Sb₂O₃ and the peak of (2 0 0) were very close.

In this study, Ca_4−xLa_2+xTi_5−xB_xO₁₇ (B = Al, Ga; x = 0, 1) ceramics were processed via a mixed oxide solid state sintering route and characterized using XRD, SEM, EDS and Vector Network Analyzer. Phase analysis of the samples showed single phase formation for the sample x = 0 while secondary phases formed for Ca_4−xLa_2+xTi_5−xB_xO₁₇ (B = Al, Ga; x = 1) ceramics. Ca₄La₂Ti₅O₁₇ exhibited ∈_r = 74, Q×f_o = 14,116 GHz and τ_f = 157 ppm/°C. The substitution of Ga or Al for Ti at the B-site of Ca₄La₂Ti₅O₁₇ ceramics significantly improved the microwave dielectric properties i.e. Ca₃La₃Ti₄GaO₁₇ and Ca₃La₃Ti₄AlO₁₇ have ∈_r = 44, Q×f_o = 16,128 GHz and τ_f = 7.3 ppm/°C and ∈_r = 46, Q×f_o = 13,754 GHz and τ_f = −2 ppm/°C, respectively. The microwave dielectric properties of these materials are suitable for high frequency microwave applications.

In this work, we show and discuss the surface structure picture of copper phthalocyanine (CuPc) thin films deposited from trifluoroacetic acid (TFA) solvent onto silicon substrates at ambient conditions by four solution processing methods, namely drop-casting, dip-coating, spin-casting and spray-coating. The CuPc films were studied by AFM, as the main technique, and complemented by micro-Raman spectroscopy. Essentially, such thin films consist of CuPc molecular nanoribbons of a fixed ~1 nm thickness. CuPc molecules are arranged in an in-plane direction and formed in stacks under a defined tilt angle with respect to the substrate surface (monolayer) or underlying CuPc layer (multilayer). The film morphology takes various forms depending on the solution concentration, number of layers, and the deposition method. For instance, the morphology varies from very wide (~600 nm) but flat (~1 nm) ribbons for films prepared by dip-coating to crystallized rod-like features (multi-layered ribbons) when obtained by spray-coating. The factors studied in this paper should be taken into consideration in designing and controlling the criteria for rigorous CuPc film architecture.

We report a new direct fabrication of the ZnO nanorods (NR) by hydrothermal method, in which the preparation of seed layer is eliminated. We show that the tuning of initial temperature rate during the hydrothermal process plays a key role in the structural modification of the ZnO NR. A highly oriented ZnO NR is successfully fabricated by using a low rate of initial temperature. The increase of optical absorption and electron transport was obtained by reducing the diameter and increasing distribution of the ZnO NR on the substrate. Interestingly, an additional absorption from the defects is obtained in the system, which plays an important role in expanding the optical absorption. Our system will provide a favourable characteristic for developing the high-performance optoelectronic devices with high optical absorption and high electron transport.

Geometrical structures, relative stabilities and electronic properties of neutral, cationic and anionic pure gold Aun+1λ{\rm{A}}u_{n + 1}^\lambda and Ag-doped bimetallic AgAunλ(λ=0,±1;n=1-12){\rm{AgAu}}_n^\lambda \left( {\lambda = 0, \pm 1;n = 1 - 12} \right) clusters have been systematically investigated by using density functional theory methodology. The optimized structures show that planar to three-dimensional structural transition occurs at n = 5 for cationic clusters. Due to strong relativistic effect of Au clusters, the ground state configurations of neutral and anionic bimetallic clusters favor planar geometry till n = 12. Silver atoms tend to occupy the most highly coordinated position and form the maximum number of bonds with Au atoms. The computed HOMO-LUMO energy gaps, fragmentation energies and second-order difference of energies show interesting odd-even oscillation behavior. The result indicates that AgAu₅, AgAu2+{\rm{AgAu}}_2^ + and AgAu2-{\rm{AgAu}}_2^ - are the most stable clusters in this molecular system. The DFT based descriptors of bimetallic clusters are also discussed and compared with pure gold clusters. The high value of correlation coefficient between HOMO-LUMO energy gaps and DFT based descriptors supports our analysis. A good agreement between experimental and theoretical data has been obtained in this study.

In this study, thin Al₂O₃ films (11 nm – 82 nm) were deposited by means of a recently developed pulse gas injection magnetron sputtering method and investigated by means of atomic force microscopy, spectroscopic ellipsometry and spectrophotometry. Quite low values of optical constants (1.581 to 1.648 at λ = 550 nm) of the alumina films are directly associated with specific growth conditions (pulse injection of the reactive or reactive + inert gas) in the pulse gas injection magnetron sputtering process. The light transmittance of Al₂O₃/glass systems (86 % to 90 %) is only a few percent lower than that calculated for glass (93 %).

α-Fe₂O₃ nanoparticles were synthesized via co-precipitation technique using ferric and ferrous salts and potassium hydroxide as precipitation agents. The samples were calcined at 350 °C, 550 °C and 750 °C for 3 hours. The obtained iron oxide was characterized by X-ray diffraction (XRD), thermogravimetric analysis (TGA), scanning electron microscopy (SEM), and dynamic light scattering (DLS). Crystallinity of the sample was studied by X-ray diffraction. SEM micrographs showed nonuniform size distribution of the particles forming agglomerates. TGA analysis revealed trace amount of weight loss and material stability for the samples calcined at temperatures above 500 °C. DLS results indicated that increasing of annealing temperature resulted in reduction of the particle size and more uniform size distribution. At the maximum annealing temperature of 750 °C, the mean diameter of the particles of 100 nm was observed.

Titanium aluminum nitride (TiAlN) thin films were deposited on Si(1 0 0 ) substrate using titanium and aluminum targets in 1:1 ratio at various N₂ flow rates using ion beam sputtering (IBS) technique. The morphology, particle and crystallite size of TiAlN thin films were estimated by field emission scanning electron microscope (FE-SEM), atomic force microscope (AFM), and grazing incidence X-ray diffraction (GIXRD) technique, respectively. The SEM images of the TiAlN thin films revealed smooth and uniform coating, whereas AFM images confirmed the particle size varying from 2.5 nm to 8.8 nm, respectively. The crystallite size and lattice strain were observed to vary from 4.79 nm to 5.5 nm and 0.0916 and 0.0844, respectively, with an increase in N₂ flow rate in the TiAlN thin films. The X-ray absorption near edge structure (XANES) results showed Ti L, N K and O K-edges of TiAlN coating within a range of 450 eV to 470 eV, 395 eV to 410 eV and 480 eV to 580 eV photon energy, respectively. The electronic structure and chemical bonding of state of c-TiAlN thin film of Ti L, N K and O K-edges were analyzed through semi-empirical curve fitting technique.

Biphenyl-4,4′-dicarboxylic acid (H₂BDA) was used as an organic linker to synthesize bismuth and lead based organic frameworks (1 and 2). The structural/morphological studies of these metal organic frameworks (MOFs) were done using UV-Vis, Fourier transform infrared spectroscopy (FT-IR), ¹H NMR, energy dispersive spectroscopy (EDXS), scanning electron microscopy (SEM), thermogravimetric analysis (TGA) and powder X-ray diffraction method. Surface area as determined by Brunauer-Emmett-Teller (BET) studies revealed better N₂ gas adsorption for MOF (1) compared to MOF (2). Both these MOFs exhibited good luminescence activity which was attributed to ligand-to-metal charge transfer transitions (LMCT).

Amorphous lead metaborate (Pb(BO₂)₂ H₂O) nanostructures were synthesized by a simpl and cost-effective synthesis method which is based on precipitation of lead ions using boric acid/sodium hydroxide buffer (pH 9.2) in the presence of polyethylene glycol (PEG). Scanning electron microscopy images showed that the average particle size is 30±9 nm and the particle shape is mostly spherical. The chemical formulation of Pb(BO₂)₂ H₂O was confirmed by infrared spectroscopy, inductively coupled plasma and thermal gravimetric analysis (TGA). The percentage of PEG molecules on the particle surface equal to 2.5 % was determined by TGA. Optical reflectance measurement was performed by UV-Vis spectroscopy. Based on the Kubelka-Munk function, it was calculated that the Pb(BO₂)₂ H₂O nanostructures have a direct band gap of 4.6 eV.

Poly(methyl methacrylate)-holmium orthovanadate (PMMA-HoVO₄) nanocomposites were synthesized using emulsifierfree emulsion polymerization system in two ways. In the first one, the HoVO₄ nanoparticle dispersion was added to the emulsion system before or after polymerization start (in situ polymerization). In the other one, nanoparticle dispersion and polymeric latex were mixed together at room temperature (blending). Crystalline HoVO₄ nanoparticles (about 60 nm) were synthesized by coprecipitation method. Three different composite latexes were synthesized by varying the potassium persulfate concentration and the time of HoVO₄ nanoparticles addition. According to the dynamic light scattering analysis, the size of the polymer beads in the latexes is between 244.8 nm and 502.5 nm and the PDI values are in the range of 0.005 to 0.206. Infrared spectral analysis showed that HoVO₄ caused some changes in the structure of the polymer. Luminescence measurements attempted to determine optical properties of the nanocomposites. The results have shown that HoVO₄ nanoparticles do not protect their structure due to the reaction with persulfate radicals but that they enter the polymer beads and change the luminescence properties of the polymer forming a new material with different properties.

New monomer, 4,4’-[(2,3-dihydrothieno[3,4-b][1,4]diorin-5-yl)vinyl]-1,1’-biphenyl (BPE), was synthesized, characterized and polymerized electrochemically via a potentiostatic method. The corresponding polymer poly(4,4’-[(2,3-dihydrothieno[3,4-b][1,4] diorin-5-yl)vinyl]-1,1’-biphenyl) (PBPE) obtained as a thin-layer film, was characterized by cyclic voltammetry, X-ray photoelectron spectroscopy, infrared spectroscopy and UV-Vis spectroscopy. The highest occupied molecular orbital (HOMO) and lowest unoccupied molecular orbital (LUMO) energy levels of the obtained polymer were determined from cyclic voltammograms as –4.89 eV and –3.81 eV, respectively. Its optical and electrochemical band gaps were calculated, and found to be 1.08 eV and 1.49 eV, respectively. PBPE can be used as a donor material in bilayer organic photovoltaic solar cells having PCBM as acceptor material.

Y₂O₃:Er³⁺ translucent ceramics was fabricated with addition of La(OH)₃ nanopowder as a sintering aid. The influence of La(OH)₃ addition on the microstructure, transmittance and upconversion luminescence of Y₂O₃:Er³⁺ ceramics was investigated in detail. The results show that the ceramics sample with 5 mol % La(OH)₃ additives exhibits finer microstructure with fewer pores and higher optical transmittance than others. It was proved that La(OH)₃ additives could greatly reduce the porosity and improve the transparency of Y₂O₃:Er³⁺ ceramics. By using a 980 nm diode laser as a pumping source, the Y₂O₃:Er³⁺ ceramics gave bright visible upconversion luminescence, which was ascribed to the radiative transitions of ²H_11/2,⁴S_3/2 →⁴I_15/2 and ⁴F_9/2 →⁴I_15/2 of Er³⁺ ions, respectively. The possible upconversion mechanism has been proposed accordingly.

In the present paper, using of SILVACO-TCAD numerical simulator for studying the enhancement in Pt/n-GaN Schottky diode current–voltage (I-V) characteristics by introduction of a layer of hafnium dioxide (HfO₂) (with a thickness e = 5 nm) between the Pt contact and semiconductor interface of GaN is reported. The simulation of I-V characteristics of Pt/n-GaN was done at a temperature of 300 K. However, the simulation of Pt/HfO₂/n-GaN structure was performed in a temperature range of 270 – 390 K at steps of 30 K. The electrical parameters: barrier height (Φ_b), ideality factor and series resistance have been calculated using different methods: conventional I-V, Norde, Cheung, Chattopadhyay and Mikhelashvili. Statistical analysis showed that the metal-insulator-semiconductor (Pt/HfO₂/n-GaN) structure has a barrier height of 0.79 eV which is higher compared with the (Pt/n-GaN) structure (0.56 eV). The parameters of modified Richardson ((ln(I0T2)-(q2σs022kT2)=ln(AA*)-q∅B0kT)(\left( {\ln \left( {{{{{\rm{I}}_0}} \over {{{\rm{T}}^{\rm{2}}}}}} \right) - \left( {{{{{\rm{q}}^2}\sigma _{{\rm{s}}0}^2} \over {2{\rm{k}}{{\rm{T}}^2}}}} \right) = \ln \left( {{\rm{AA*}}} \right) - {{{\rm{q}}{\emptyset _{{\rm{B}}0}}} \over {{\rm{kT}}}}} \right) equation versus (1kT{1 \over {{\rm{kT}}}}) have been extracted using the mentioned methods. The following values: ASimul*=22.65 A/cm2⋅K2{\rm{A}}_{{\rm{Simul}}}^* = 22.65\,{\rm{A/c}}{{\rm{m}}^{\rm{2}}} \cdot {{\rm{K}}^2}, 14.29 A/cm² K², 25.53 A/cm² K² and 21.75 A/cm² K² were found. The Chattopadhyay method occurred the best method for estimation the theoretical values of Richardson constant.

In this work, we report the effect of sandwiching of Au nanosheets on the structural and electrical properties of ZnSe thin films. The ZnSe films which are grown by the thermal evaporation technique onto glass and yttrium thin film substrates exhibit lattice deformation accompanied with lattice constant extension, grain size reduction and increased defect density upon Au nanosandwiching. The temperature dependent direct current conductivity analysis has shown that the 70 nm thick Au layers successfully increased the electrical conductivity by three orders of magnitude without causing degeneracy. On the other hand, the alternating current conductivity studies in the frequency domain of 10 MHz to 1800 MHz have shown that the alternating current conduction in ZnSe is dominated by both of quantum mechanical tunneling and correlated barrier hopping of electrons over the energy barriers formed at the grain boundaries. The Au nanosheets are observed to increase the density of localized states near Fermi level and reduce the average hopping energy by ~5 times. The conductivity, capacitance, impedance and reflection coefficient spectral analyses have shown that the nanosandwiching of Au between two layers of ZnSe makes the zinc selenide more appropriate for electronic applications and for applications which need microwave cavities.

The aim of this work was to investigate the effects of moderate vacuum conditions (10 Pa, 1 × 10³ Pa and 2 × 10⁴ Pa) on glass forming ability, thermal stability and aging behavior of Co₄₂Cu₁Fe₂₀Ta_5:5B_26:5Si₅ amorphous samples in terms of size and distribution of crystalline precipitates. The thinnest parts (300 μm) of the wedge-shaped samples were amorphous for all vacuum conditions, and they had similar compositional, structural and thermal characteristics. However, they represented different microstructural features after heat treatments at 950 K and 1100 K. The same phases precipitated in all samples but the amount and the size of the precipitates increased as the pressure was raised to the normal atmospheric value. The differences in the glass forming ability and the microstructure due to aging are considered to originate from lower thermal characteristics, such as relaxation and reduced glass temperature as well as γ parameter, resulting from the poor vacuum pressure used in the production process. The differences in the microstructures and hardness values caused by heat treatments have been observed.

In this paper, results of investigation on the impact of firing temperature on insulating properties of Low Temperature Cofired Ceramics are presented. Dissipation factor, volume resistivity and breakdown electric field intensity were determined for firing peak temperature in the range from 800 °C to 900 °C. The tests were performed for two commercial LTCC materials: 951 Green Tape (DuPont, USA) and SK47 (Keko, Slovenia). The results showed that the firing temperature had a significant effect on the dielectric loss factor, volume resistivity and lifetime at applied high voltage. No clear tendency was observed for dielectric strength in the analyzed firing temperature range.

As implied in the title, the triple-layer remote phosphor (TRP), constructed with the yellow YAG:Ce³⁺ layer at the bottom, the red CaMgSi₂O₆:Eu²⁺,Mn²⁺ phosphor layer on the top, and the green Ba₂Li₂Si₂O₇:Sn²⁺,Mn²⁺ phosphor layer between these two layers, is suggested in this paper to improve the color and luminescence of white LEDs (WLEDs). In order to control the red light for the purpose of increasing the color rendering index (CRI), it is suggested that the red CaMgSi₂O₆:Eu²⁺,Mn²⁺ phosphor should be applied in the TRP structure. Simultaneously, the structure uses the green Ba₂Li₂Si₂O₇:Sn²⁺,Mn²⁺ phosphor layer to control the green light, which increases the luminous efficacy (LE) of WLEDs. In addition, when the concentration of these two phosphors increases, the yellow YAG:Ce³⁺ concentration must be reduced to keep the average correlated color temperatures (ACCTs) stable at 6000 K to 8500 K. Besides, appropriate adjusting of CRI, LE, and color quality scale (CQS) is also analyzed by modifying the concentration of the green phosphor and red phosphor. The results show that the CRI can get better values if CaMgSi₂O₆:Eu²⁺,Mn²⁺ concentration is higher. In contrast, the CRI decreases dramatically when the concentration of Ba₂Li₂Si₂O₇:Sn²⁺,Mn²⁺ increases. Meanwhile, CQS can be significantly increased in the range of 10 % to 14 % CaMgSi₂O₆:Eu²⁺,Mn²⁺, regardless of the concentration of Ba₂Li₂Si₂O₇:Sn²⁺,Mn²⁺. In particular, along with the improvement of CRI and CQS, LE can also be increased by more than 40 % by reducing the scattered light and adding the green light. Obtained results are a valuable reference for manufacturers for improving WLEDs color and luminescence quality to produce a broader range of WLEDs with better quality fulfilling social needs.

Ho doped Ag₂S thin films were grown on the glass substrate by chemical bath deposition (CBD) method at room temperature. The bath contained aqueous solution of silver nitrate, thiourea, EDTA, ammonia and holmium nitrate. Silver nitrate was used as a silver (Ag⁺) ion source; thiourea as sulfur (S⁻) ion source, EDTA was a complexing agent while ammonia was used to maintain pH, Ho(NO₃)₃ was taken as a source of Ho ions. The optical absorption edge of undoped (pure) and Ho doped silver sulfide films was determined between 324 nm and 298 nm showing blue shift as compared to bulk Ag₂S. Band gaps calculated from Tauc plot also showed an increase in values for doped samples. The increase in band gap indicates reduced particle size in the prepared Ho doped films. The photoluminescence emission peaks were observed at around 578 nm to 601 nm wavelength and excitation peaks were found at 351 nm to 294 nm for undoped and doped films. The SEM micrograph consists of globular ball type and flower type structures observed in the prepared films of Ho doped Ag₂S.