Lanthanum oxyfluoride nanostructures prepared by modified sonochemical method and their use in the fields of optoelectronics and biotechnology

1 Introduction

In the recent years, the development of white light-emitting diodes (WLEDs) replaced all the conventional incandescent or fluorescent lamps due to its long lifetime, high brightness, eco-friendly and high efficiency characteristics (Lin and Liu, 2011; Park et al., 2003; Im et al., 2009). The phosphors converted WLEDs (pc-WLEDs) consist of near ultraviolet chips which find a wide range of applications due to excellent color stability and reproducibility (Chen et al., 2012; Zhang et al., 2013). Commercially available pc-WLEDs constitute InGaN chip with Y₃Al₅O₁₂:Ce³⁺ (YAG: Ce) phosphor suffer from low color rendering index and high correlated color temperature (CCT) due to the lack of red component in it (Hecht et al., 2009; Jung et al., 2006). Hence, rare earth doped particularly lanthanide-doped luminescent materials are considered to be an ideal hosts for better luminescence properties due to their high refractive index and low phonon energy. Further, these materials created new avenues for researches due to their possible applications in various biomedical fields such as biological labels, biosensors, multimodal bio-imaging, photodynamic therapy and drug delivery (Xing et al., 2016a, 2016b, 2016c; Zhang et al., 2016).

So far, various synthesis routes were used including solution combustion, sol – gel, co-precipitation, solid-state reaction, hydrothermal methods (Hu et al., 1999; Xia et al., 2009; Gai et al., 2014; Tana et al., 2011; Kaczmarek and Van Deun, 2013). Morphologies of the compounds not only control their properties but also enhance the effectiveness for the various applications (Alivisatos, 1996). However, in some of these routes it is difficult to control over the morphology, size and stoichiometric compositions. Therefore, a lot of research has been needed for the improvement of versatile synthesis routes. Ultrasound assisted sonochemical route was considered to be one of the better synthesis routes for fabrication of well-defined nano/superstructured materials. In this method, during the synthesis, ultrasound irradiation provides remarkable reaction conditions to initiate the chemical reaction (Suslick, 1990). The impact of the ultrasound force to acoustic cavitation leads to the formation, growth and implosive collapse of bubbles of the reaction mixture leads to superstructures (Suslick, 1996).

Generally fingerprints (FPs) encompass a mixture of substances originating from the sweat glands namely epidermis, secretory glands in the dermis along with intrinsic components including drugs, medication traces, metabolites and extrinsic contaminants namely blood, food contaminants, dirt and grease, hair and moistures (Darshan et al., 2016a). The ridge arrangement of the skin on human finger creates a distinctive FP. By touching an object, sweat emitted through the pores in the skin can be moved to the surface to leave an impression of the ridge pattern. Such invisible prints were recognized as a Latent fingerprints (LFPs) which are useful for the recognition and detection of individuals at forensic science.

For the past few decades, various visualization methods were established to enhance LFPs. Nevertheless, there still exist a lack of sensitivity and selectivity (Saif, 2013). Presently nanoparticles were utilized in forensic investigations due to small crystalline size, flexibility and ability to precisely tune their surface properties. The surface modification versatility of these materials may lead to accurate targeting and to increase selectivity (Cadd et al., 2015).

Powder dusting was simple and the most frequently used method for revealing the LFPs (Champod et al., 2004) in which powder of bronze, ferric oxide and rosin was used. These powders were unable to reveal LFPs on some relevant forensic surfaces as it was hazardous and uneven crystallite size. Alternatively, use of powder-based luminescent nanophosphors was the best solution to conquer such limitations. Rare earth doped nanophosphors have been extensively investigated as a potential labeling agents to visualize LFPs with high contrast, good sensitivity and reduced background hindrance due to smaller crystallite size and better adhesion efficiency (Darshan et al., 2016b). Furthermore, it was well established that the lanthanide ions were bio-compatible with low toxicity. Therefore, use of stable synthesized LaOF: Dy³⁺ in powder dusting method creates a significant interest for scientific community to visualize the LFPs as labeling agents.

The present work describes the synthesis of LaOF: Dy³⁺ (1–11 mol%) nanostructures (NS) by facile ultrasound assisted sonochemical route using A.V. gel as bio-surfactant. The effectiveness and unique properties of ultrasound for the fabrication of nanostructured materials were successfully explored. Further, to evaluate the potential applications of the prepared samples, the photoluminescence (PL) and photometric properties (CIE and CCT) were studied in detail. The optimized sample was used as a labeling agent for the visualization of LFPs on various forensic relevant surfaces.

2 Experimental

2.1

2.1 Synthesis

The precursors used for the preparation of LaOF NS were of analytical grade without further purification. The chemicals used were lanthanum nitrate [La (NO₃)₃.4H₂O (Sigma-Aldrich; 99.9%)], ammonium fluoride [NH₄F; (Sigma-Aldrich; 99.9%)] and dysprosium nitrate [Dy (NO₃)₃; (Sigma-Aldrich; 99.9%)]. A.V. gel was used as a bio-surfactant and the detailed preparation procedure for obtaining A.V. gel from aloe vera plant was reported elsewhere (Kavyashree et al., 2015). Stoichiometric quantities of the precursors and 50 ml of A.V. gel (bio-surfactant) and 150 ml of double distilled water were dissolved and mixed using magnetic stirrer for ∼25 min to get a clear solution. Resulting mixture was divided into various wt% from 5% to 30% W/V and subjected to sonochemical treatment with the help of Mrc Laboratory equipment model-AC 120H, probe, ultrasonic frequency of ∼20 kHz, power of ∼300 W and sonication time ∼1–6 h at a fixed temperature of 80 °C. NaOH was used as a precipitating agent and used to adjust pH value. The precipitate obtained at the end of the reaction was filtered several times using double distilled water and alcohol. The powder was dried at 80 °C for 3 h in a hot air oven and then heat treated at ∼700 °C for 3 h. The schematic illustration for the ultrasound assisted sonochemical synthesis is shown in Fig. 1.

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Figure 1

Schematic representation to represent the mechanism involved with the ultrasonic method of preparation.

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2.3

2.3 Visualization of LFPs using LaOF: Dy³⁺ (3 mol%) NS

The fresh FPs were deposited on various surfaces including glass, CD, mobile screen, marble, computer mouse and pet bottle. Before deposition, the standard procedure was followed to get the fingerprints as reported elsewhere (Darshan et al., 2016a,b,c,d). The optimized (3 mol%) NS was smoothly applied on the LFPs by powder dusting method and excess powder was removed by smooth brushing. A Nikon D3100/AF-S Nikkor 50 mm f/1.8G ED lens digital camera and a 254 nm UV light were used for the visualization of FPs. The schematic representation for the revelation of LFPs is shown in Fig. 2.

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Figure 2

The schematic representation for the development of LFPs using powder dusting method.

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3 Results and discussion

PXRD profiles of pure and Dy³⁺ (1–11 mol%) doped LaOF NS are shown in Fig. 3(a). All the patterns exhibit sharp and broad diffraction peaks and are well matched with the standard JCPDS card No.89-5168 (Dhananjaya et al., 2016). Further, no impurity peaks were observed with increase of Dy³⁺ concentration indicating that the product was pure. The broad diffraction peaks in the present studies were normally associated with crystallite size or strain present in the prepared sample. Debye – Scherrer’s relation was utilized to determine the average crystallite sizes as reported elsewhere (Venkataravanappa et al., 2016). In order to compare the crystallite sizes as well as strain present in the sample W – H plots were utilized and the obtained plots are given in Fig. 3(b) (Venkataravanappa et al., 2017). Further, the estimated average crystallite size as well as the lattice strains is given in Table 2. As can be evident from the table the lattice strain was found to be increase with Dy³⁺ concentration due to lattice distortion (Nagabhushana et al., 2016).

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Figure 3

(a) PXRD patterns and (b) W-H plots for LaOF: Dy3 + (1–11 mol%) NS (c) Rietveld refinement and (d) packing diagram for LaOF: Dy³⁺ (5 mol%) NS.

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Rietveld refinement method was used to evaluate the various structural parameters namely Pseudo-Voigt profile function (u, v and w), isothermal temperature factors (B_iso), background scale factor, atomic coordinates, etc. (Daruka Prasad et al., 2014). The observed, calculated and the difference PXRD profiles of LaOF: Dy³⁺ (3 mol%) are shown in Fig. 3(c). The experimental and calculated profiles showed nearly to zero in the intensity scale as illustrated by a line (Y_obs–Y_calc). The refined structural parameters for LaOF: Dy³⁺ (1–11 mol%) NS are summarized in Table 3. It was noticed that a slight variation in structural parameters with addition of Dy³⁺ ions in LaOF. The acceptable percentage difference between Dy and La in LaOF matrix was estimated using the relation (Darshan et al., 2016c):

Fig. 4 shows the SEM micrographs of LaOF: Dy³⁺ (3 mol%) NS prepared at different sonication times (1–6 h) with 30 ml of A.V. gel and pH = 5. When the sonication time was ∼1 h, all the structures appear to be almost spherical in shape and form a network structure (Fig. 4(a & b)). When the sonication time was increased to 2 h, it forms a spherical shaped network structure derived together to form a layer like structure consisting of several hollow pores (Fig. 4(c & d)). Further, when the sonication time was increased to 3 and 4 h, pores were found to be reduced (Fig. 4(e, f)). Finally, when the sonication time was further increased to 5 and 6 h, these hollow pores were almost reduced (Fig. 4(g, h)). The effect of concentration of bio-surfactant (A.V. gel) on the morphology of the prepared samples was also studied and is shown in Fig. 5. Initially, when the A.V. gel concentration was ∼5 ml small plate like structures were observed (Fig. 5(a)). When the concentration of A.V. gel was increased to 10 and 15 ml, the plate like structures were oriented in multi directions (Fig. 5(b & c)). Further when the A.V. gel concentration increased to 20 and 30 ml, plate like structures were undergoing self – assembly in a particular direction (Fig. 5(d & e)). Table 4 shows the list of major phytochemicals extracted in A. V. gel confirmed from Gas Chromatography Mass Spectroscopy (GCMS). Fig. 6 shows the egg box model for the trapping of LaOF: Dy³⁺ NS in the network of Guanosine content of the A.V. gel.

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Figure 4

SEM images of LaOF: Dy³⁺ (3 mol%) NS synthesized with different sonication times (a, b) 1 h, (c, d) 2 h, (e) 3 h, (f) 4 h, (g) 5 h and (h) 6 h with A.V. gel (30 ml) and pH = 5.

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Figure 5

SEM images of LaOF: Dy³⁺ (3 mol%) NS synthesized with different concentrations of A.V. gel (a) 5 ml, (b) 10 ml, (c) 15 ml, (d) 20 ml, and (e) 30 ml with 3 h ultrasonic irradiation time and pH = 5.

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Figure 6

The egg box model of LaOF: Dy³⁺ NS with Guanosine content of A.V. gel.

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Fig. 7 shows the SEM micrographs of LaOF: Dy³⁺ (3 mol%) NS synthesized with different pH values (1 – 11) in the presence of A.V. gel (30 ml) and 3 h ultrasound irradiation. At lower pH values (1 and 5) agglomerated flake like structures were obtained (Fig. 7(a & b)). As the pH value was further increased to 9 and 11, agglomerated flakes ripened to form a dumbbell shaped network structures (Fig. 7(c & d)). The effect of sonication power on the morphology of the prepared samples were also studied and is shown in Fig. 8. From the figure, it was clear that when the sonication power was 20 and 24 kHz, an uneven shaped structures with numerous pores were observed (Fig. 8(a & b)). However, with increase in sonication power to 26 & 30 kHz, the agglomeration in the structures was slightly reduced (Fig. 8(c & d)). To know the effect of ultrasound irradiation on morphology, normal mechanical stirring was applied for different time intervals (3 & 6 h). The obtained SEM morphology of LaOF: Dy³⁺ (3 mol%) is shown in Fig. 9. It was evident from the SEM micrographs, no definite shape and size of the particles were observed. The aforementioned results evident that, sonication irradiation time, concentration of A.V. gel, pH and sonication power play a vital role in tuning the morphology of the product.

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Figure 7

SEM images of LaOF: Dy³⁺ (3 mol%) NS synthesized with various pH values (1, 5, 9 and 11) in the presence of A.V. gel (30 ml) and 3 h ultrasound irradiation.

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Figure 8

SEM images of LaOF: Dy³⁺ (3 mol%) NS synthesized with different sonication power (20, 24, 26 and 30 kHz) in the presence of A.V. gel (30 ml) and 3 h ultrasound irradiation.

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Figure 9

SEM images of LaOF: Dy³⁺ (3 mol%) NS synthesized with normal mechanical stirring at (a) 3 h and (b) 6 h.

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The TEM images of LaOF: Dy³⁺ (3 mol%) NS is shown Fig. 10 (a). It was observed that particles were almost dumbbell in shape which was well matched to those obtained from SEM results. The interplanar spacing (d) was estimated from HRTEM and found to be ∼0.28 nm (Fig. 10(b & c)). Further, the product was shown to be highly crystalline in nature as can be evident from SAED patterns (Fig. 10(d)). The elements present in the products were confirmed from EDAX results (Fig. 10(e)).

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Figure 10

(a) TEM, (b) HRTEM, (c) enlarged portion of HRTEM, (d) SAED pattern and (e) EDAX of LaOF: Dy³⁺ (3 mol%) NS.

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The diffuse reflectance (DR) spectra of the prepared LaOF: Dy³⁺ (1–11 mol%) NS were recorded in the range of 200 – 1100 nm (Fig. 11(a)). A broad absorption band between 250 – 320 nm was due to the presence of charge transfer (CT) band of the host LaOF. The absorption bands recorded at ∼320, 348, 372, 399, 794, 899 and 1071 nm were assigned to the transitions from ground state of ⁶H_5/2 to ⁴L_19/2, ⁴I_11/2, ⁶P_7/2, I_13/2, ⁶F_5/2, ⁶F_7/2, and ⁶F_9/2 + ⁶H_7/2 for the Dy³⁺ ions (Munirathnam et al., 2016; Neharika et al., 2016). The bands at ∼794, 899 and 1071 were due to 4f - 4f transitions of Dy³⁺ ions. The peaks at 275 nm and 313 nm were due to the ⁸S_7/2 → ⁶J and ⁶P_J → ⁸S_7/2 transitions of La³⁺ ions (Escobedo Morales et al., 2007). The direct energy band gap (E_g) of the synthesized LaOF: Dy³⁺ (1–11 mol%) NS was estimated by the Kubelka-Munk (K-M) theory. The K - M function F (R_∞) and photon energy ( $h\nu$ ) were estimated by relations reported elsewhere (Som et al., 2014). The value of E_g was estimated by plotting a graph of F(R)² versus $h\nu$ and extrapolating the linear fitted regions to F(R)² = 0 (Fig. 11(b)). The obtained values were tabulated and are presented in Table 2. As can be seen from the table, a small variation in E_g values was due to the disorder in the host as well as defects caused during synthesis (Ravikumar et al., 2014).

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Figure 11

(a) DR spectra and (b) E_g plots of LaOF: Dy³⁺ (1–11 mol%) NS.

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Fig. 12 shows the FTIR spectra of LaOF: Dy³⁺ (1–11 mol%) NS were recorded in the range 300–4000 cm⁻¹. The spectra exhibit two characteristic absorption bands at ∼500 and 370 cm⁻¹ were attributed to La–O vibrations (Dhananjaya et al., 2016). The weak absorption band observed at ∼1540 cm⁻¹ was due to the adsorption of CO₃²⁻ from the surrounding atmosphere. The peak obtained at ∼3690 cm⁻¹ was attributed to the bending vibration of surface adsorbed water molecule.

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Figure 12

FTIR spectra of LaOF: Dy³⁺ (1–11 mol%) NS.

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Fig. 13(a) shows the PL excitation spectrum of LaOF: Dy³⁺ (3 mol%) NS monitored at 574 nm emission. The excitation spectrum consists of three important regions i.e., f - f transition, charge transfer transition and band to band absorption. The first part of the spectra consists of peaks centered at ∼324, 350, 366, 386, 425 and 448 nm were attributed to ⁶H_15/2 → ⁴M_17/2, ⁶H_15/2 → ⁴M_15/2, ⁶H_15/2 → ⁴I_11/2, ⁶H_15/2 → ⁴I_13/2, ⁶H_15/2 → ⁴G_11/2 and ⁶H_15/2 → ⁴I_15/2 transitions of Dy³⁺ ions (Yadav et al., 2017). Further, the spectra exhibit strong excitation bands at ∼350–448 nm which specify that dopant Dy³⁺ in LaOF host was considered to be an efficient phosphor for near ultraviolet (NUV) white LEDs. The position of charge transfer band (CTB) was estimated by Jorgensen relation (Darshan et al., 2016d). By utilizing the values of ${\chi }_{\mathit{opt}}(X)$  = 1.1 and ${\chi }_{\mathit{opt}}({\text{Dy}}^{3+})$  = 1.22, the location of O² → Dy³⁺ CTB can be estimated and found to be ∼277 nm. The asymmetric peak at ∼315 nm was related to absorption band in the host LaOF matrix.

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Figure 13

(a) Excitation spectrum, (b) emission spectra, (c) variation of PL intensity and asymmetric ratio with Dy³⁺ concentration and (d) energy level diagram of Dy³⁺ ions.

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Fig. 13(b) shows the emission spectra of LaOF: Dy³⁺ (1–11 mol%) NS was recorded upon excited at 354 nm at room temperature (RT). The spectra exhibit a sharp and intense peaks at blue (483 nm; ⁴F_9/2 → ⁶H_15/2), yellow (574 nm; ⁴F_9/2 → ⁶H_13/2) and red (674 nm; ⁴F_9/2 → ⁶H_11/2) (Yadav et al., 2017; Devaraja et al., 2014). From the figure, it was clear that yellow region was more prominent when compared to other two regions. The most intense peak at ∼574 and ∼483 nm corresponds to electric dipole and magnetic dipoles of the Dy³⁺ ions respectively. The effect of Dy³⁺ ions on the PL emission intensity was studied and is shown in Fig. 13(c). It was noticed that PL intensity increases up to 3 mol% and afterward it starts diminishes due to concentration quenching (Blasse, 1986). Further, the asymmetric ratio (A₂₁) was estimated using the relation (Dhanalakshmi et al., 2017):

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Figure 14

Schematic representation of concentration quenching phenomena in Dy³⁺ ions.

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Figure 15

Logarithmic plot of x and (I/x) in LaOF: Dy³⁺ (1–11 mol%) NS.

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Fig. 16(a) shows the Commission Internationale de I’Eclairage (CIE), 1931 chromaticity diagram (Publication CIE no 17.4 Colorimetry, 1987; Publication CIE no 15.2 Colorimetry, 1986) of LaOF: Dy³⁺ NS under 384 nm excitation and the corresponding color coordinate values are given in Table 5. From the diagram, it was apparent that all of the CIE values of LaOF: Dy³⁺ NS were well located in white light region. Further, it was noticed that the white light color of the NS was tuned by changing the Dy³⁺ concentrations. Correlated Color Temperature CCT was calculated by transforming the (x, y) coordinates of the light source to (U₀, V₀) by following relations:

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Figure 16

(a) CIE and (b) CCT diagram of LaOF: Dy³⁺ (1–11 mol%) NS.

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The CCT diagram of LaOF: Dy³⁺ (1–11 mol%) NS is shown in Fig. 16(b). Further, CCT values were also estimated based on McCamy empirical relation (McCamy, 1992):

Generally, the visualization of LFPs on various surfaces was practically challenged for forensic investigators due to absorption of the constituents of LFPs by these materials. To evaluate the versatility of the prepared sample, LFPs were visualized on different surfaces namely glass, marble, computer mouse, CD, mobile screen, PET bottle (Fig. 17). Interestingly, a minutiae ridge patterns such as core, termination, bifurcation, hook, island and bridge were visualized on all surfaces without any background interference.

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Figure 17

Finger print images visualized by using LaOF: Dy³⁺ (3 mol%) NS on (a) glass, (b) marble, (c) computer mouse, (d) CD, (e) mobile screen and (f) PET bottle.

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Fig. 18 shows the post processed fingerprint image on glass surface visualized using optimized LaOF: Dy³⁺ (3 mol%) NS. From the figure, it was evident that the synthesized product was noticeably enhanced level 2 minutiae ridge patterns effortlessly due to their smaller crystallite size. The magnified images of various permanent minutiae are also shown in Fig. 18. The level 3 patterns (sweat pores) were innovative details for authentication of individuals in forensic analysis where partial fingerprints or lack of explicit level 2 details were covered with this level. From the Fig. 18, it was clear that in addition to level 2 patterns, level 3 substructures (sweat pores) from which the sweat can be secreted, could also be enhanced. Fig. 19 shows the different fingerprint patterns (loop and whorl) that were visualized on glass surface. It was evident that, the images were clear and useful for identification of individuals

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Figure 18

High-resolution fluorescence image of fingerprint. The magnified images shows minutiae ridge patterns (1) core, (2) termination, (3) bifurcation, (4) island, (5) bridge, (6) Hook and (7) sweat pores.

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Figure 19

Fingerprint images visualized by LaOF: Dy³⁺ (3 mol%) NS display (a) loop and (b) Whorl.

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In the present work, we successfully explored novel LaOF: Dy³⁺ (3 mol%) NS as a labeling agent to visualize LFPs on different surfaces. The visualized LFPs exhibit high efficiency (because procedure involves simple setup and rapid and performed less than 5 min) and high sensitivity (because no color hindrance and chemical constituents can be observed due to smaller crystalline size).

The tested pathogenic microorganisms were accountable for plentiful diseases, cases of hospital infection, colonization of medical devices, and also testified for the ability to acquire resistance (Chen et al., 2015). The MIC and MBC values of synthesized LaOF: Dy³⁺ (3 mol%) NS with different concentrations of A.V. gel against bacteria are listed in Table 6. In Gram-negative bacteria, NS synthesized with 1% of A.V. gel showed a MIC at 0.25 μg/mL for E. coli and 0.025 μg/mL for K. pneumoniae and P. aerugeinosa. However, the MICs were observed for Gram-positive bacteria (S. aureus) with 0.25 μg/mL (Fig. 20). The bactericidal activity of NS was decreased with the increase in concentration of A.V. gel (Table 6). In MBC test, 0.25 μg/mL was high enough to destroy K. pneumonia and P. aeruginosa. On the other hand, in S. aureus and E. coli showed similar effect at 2.5 μg/ mL. However, NS prepared with 11% of A.V. gel was showed MBC of 25 μg/mL for S. aureus, E. coli, K. pneumonia and P. aeruginosa (Table 6).

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Figure 20

Antibacterial activity of LaOF: Dy³⁺ (3 mol%) NS synthesized using different concentrations of A.V. gel (A-1%, B-3%, C-5%, D-7%, E-9%, F-11%) on human pathogenic bacteria.

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The percentage inhibition of Fusarium oxysporum in terms of colony growth diameters was studied after 7 days of incubation with optimized LaOF: Dy³⁺ (3 mol%) NS as shown in Table 7. The percentage inhibition was enhanced from 12.10 to 93.92 with increase in LaOF: Dy³⁺ (3 mol%) concentration (100–700 μg/mL) (Fig. 21). As can be evident from the table, significant variations were observed with different concentrations of LaOF: Dy³⁺ (3 mol%) NS. Further, 700 μg/mL of NS effectively inhibited the growth of Fusarium oxysporum (Fig. 21). The variation of percentage inhibition (F. oxysporum) with different concentrations (100–700 μg/mL) of LaOF: Dy³⁺ (3 mol%) NS is shown in Fig. 22.

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Figure 21

Antifungal effect of LaOF: Dy³⁺ (3 mol%) NS on Fusarium oxysporum (Concentration in µg/ml).

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Figure 22

The effective inhibition of Fusarium oxysporum by LaOF: Dy³⁺ (3 mol%) NS by dose dependent manner.

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From the above results, it was clear that NS derived fungicides can be achieved in a simple cost-effective manner and appropriate to articulate the new categories of nano-biotic components. To the best of our knowledge, this was the first report on antimicrobial studies of lanthanum oxyfluoride NS. Therefore, lanthanum oxyfluoride NS can offer future applications as antimicrobial drug in medicine, agriculture and water purification technology.

4 Conclusions

For the first time, white light emitting LaOF: Dy³⁺ (1–11 mol%) NS was prepared by ultrasound assisted sonochemical method using A.V. gel as bio-surfactant. Various experimental parameters were used to study the morphology of the product. TEM results indicate that the particles were in nano size between 25 and 35 nm. From DR spectra, direct energy gap (E_g) values were estimated and found to be in the range ∼4.13–4.53 eV. The emission peaks at ∼324, 350, 366, 386, 425 and 448 nm were attributed to ⁶H_15/2 → ⁴M_17/2, ⁶H_15/2 → ⁴M_15/2, ⁶H_15/2 → ⁴I_11/2, ⁶H_15/2 → ⁴I_13/2,⁶H_15/2 → ⁴G_11/2, ⁶H_15/2 → ⁴I_15/2 transitions of Dy³⁺ ions respectively. The CIE and CCT values of 3 mol% doped LaOF clearly showed, that the phosphor was highly useful in display applications. The optimized NS showed high resistance toward microbicidal and antifungal activities. Successfully visualized LFPs were obtained with high contrast, high resolution, and low background interference effectively on various surfaces. It was anticipated that this optimized phosphor finds wide utility in FP labeling agent of advanced forensic science and in biotechnology particularly in antimicrobial therapy.