1 Introduction

In the past couple of decades, researchers focused on organic single crystals which bought important turn over for electronic components and device manufacturing, because of their molecular configuration that shapes their electrical and optical properties. An organic nonlinear optical material has to attract and great attention as they provide vital applications such as frequency doubling, optical switching, optical communication, optical information storage devices and signal processing [1]. In general, an organic compound presence of π-electron delocalization of the molecular structure is enhancing the nonlinear optical property of the material. The effective organic materials contain the donor and acceptor groups, and high π-delocalization has been conceded as a factor of leading to the larger nonlinearities [2]. In this regard, we chose an effective organic material of 4-nitrophenol (4-NP); it is a phenolic organic material of one-dimensional donor–π–acceptor system which contains both electron-accepting group (NO2) and electron-donating (OH) groups which are linked in the aromatic benzene ring. The presence of OH groups helps the formation of new salts with different organic and inorganic bases [3]. 4-Nitrophenol derivatives are promising of nonlinear optical materials as it possesses the linear donor–π–acceptor (D–π–A) conjugated chains, which give the strong π-electron delocalization effect, and these are liable to the formation of a strong hydrogen bond interactions. The centrosymmetric nature of the 4-nitrophenol (4-NP) crystal has high structural perfection with 115 °C as the melting point and it also does not undergo decomposition and phase transformation before melting point. Generally, the structure and symmetry of the crystal are important to determine its physicochemical properties. The single crystal of 4-nitrophenol (4-NP) has been successfully grown by the slow cooling and slow evaporation solution growth techniques (SEST) using acetone as the solvent [4]. According to structural consideration, the single crystal of 4-nitrophenol is built by the chain of hydrogen bond molecules. In fact, in the 4-NP construction, the benzene ring acts as a planner molecule with the presence of nitrogen and oxygen molecules. It is very well known that most of the practical applications required the good-quality and bulk-sized single crystal. Nowadays, researchers are contributing much attention to grow such kind of valid crystals in a short period, and for obtaining the desired result melt growth technique is a good choice. With this respect, in this paper we report the formation of bulk-sized 4-NP single crystal with dimensions up to 38 × 15 mm2 grown in the specifically designed ampule by the adoption of vertical Bridgman technique (VBT) for the first time and investigated the grown crystal-like optical, electrical, mechanical, laser-induced damage threshold (LDT), and nonlinear optical properties are discussed in details.

2 Experimental

2.1 Ampule design for crystal growth

A single-walled ampule having the conical end with a narrow opening at the upper end of the ampule has been extensively used for organic single-crystal growth. The notable design of the bottom of the single-wall ampule can restrain the inferior formation from entering the ampule to ensure that a good-quality single nucleation will appear at the beginning of the crystal growth. Moreover, the organic material and vacuum pressure in the interlayer act as thermal insulation during and after growth. Hence, the present material sufficient for single-walled ampule can prevent thermal fluctuations. The improved glass ampule is shown in Fig. 1a. To increase in cone length of ampoule improves the crystal quality. In this case, the commercially available 4-NP material can be charged into the ampule with the help of a neck funnel. The material descends into the bottom of the glass ampule along the long funnel without sticking in the inner pipe wall. The vacuum is necessary for the organic materials to grow by vertical Bridgman technique. The neck of the glass ampule is carefully sealed using an oxygen–acetylene flame after vacuum. Also, we used a length of the ampule to prevent the oxides and decomposition process in ampule at sealing time. This length is beneficial to avoid the oxidation of the material in maximum temperature during growth.

Fig. 1
figure 1

a Ampule design, b translation rate 1.0 mm, c translation rate 0.5 mm and d translation rate 0.3 mm

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2.2 Growth of 4-NP single crystal

In the experiment, 4-NP single crystal was grown in the designed single-wall ampule using a two-zone vertical Bridgman furnace. The ampule is completely rinsed with acetone and with deionized water for the removal of unwanted particles and then dried at 150 °C for 10 h. The commercially available 4-NP material was charged into the borosil ampule then the ampule was evacuated to 10−6 Torr and sealed carefully. The upper part of the furnace was maintained at the temperature at 115–120 °C, which was 0–5 °C above the melting point (115 °C) of 4-nitrophenol [4]. The material melted in the high-temperature zone and maintained here for 05 h. Accordingly, the material was completely homogenized to avoid the formation of bubbles during crystal growth. The translation of the liquid substance from the upper zone (hot zone) to the lower zone (cold zone) allows slow directional freezing of the liquid substance from the bottom to top of the growth vessel. The slow translation rate is used because the organic substances exhibit low thermal conductivity and high supercooling nature. The growth of high-quality organic single crystal can only choose very slow growth rates [6]. In the present experiment, we attempt three different translation rates such as 1 mm/h, 0.5 mm/h and 0.3 mm/h. The initial growth was started with the rate of 1 mm/h; this rate was not suitable for this material to form single nuclei in the bottom of the ampule as shown in Fig. 1b. The melted substance has grown with the second translation rate 0.5 mm/h causing the occurrence of multi-nucleation as shown in Fig. 1c. Both translation rates were very high translation rates for this material. Finally, we optimized the translation rate was 0.3 mm/h this time which initiated good-quality single nuclei and further grow the single crystal from bottom to top. Then, the temperature gradient was slowly decreased to room temperature at a rate of 1.5°C/h. The temperature profile of the furnace is shown in Fig. 2a. The grown crystal was carefully extracted from the ampule in a time of span of 10 days. The diamond wheel cutter is used to separate the crystal and ampule. The grown 4-NP single crystal, and cut and polished portion are shown in Fig. 2b, c, d.

Fig. 2
figure 2

a Temperature profile of the furnace, b 4-NP single crystal, c, d cut and polished crystal

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3 Results and discussion

3.1 Single crystal and powder XRD analysis

The single-crystal X-ray diffraction study provides information about the crystal structure and lattice parameters of title crystal. It is inferred that 4-NP crystallizes in the monoclinic system with a centrosymmetric space group of P21/c. The unit cell parameters were found to be a = 6.14 Å, b = 8.90 Å, c = 11.68 Å and the volume of the system V = 637.17 Å3. These values are in good accordance with the literature [7].

The powder X-ray diffraction analysis was carried out at room temperature using a BRUKER D8advance model with the two theta ranges from 10° to 80° and the scanning rate at 1°/min. A finely crushed sample of 4-NP has been used for this analysis. The recorded PXRD pattern of 4-NP is shown in Fig. 3.

Fig. 3
figure 3

Powder X-ray diffraction pattern of 4-NP single crystal

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The sharp, prominent peaks obtained by the powder X-ray pattern were correctly indexed with the help of powder X software program. Notably, the sharp, intense peaks are excellent evidence for the phase purity and crystallinity of the title crystal.

3.2 Optical studies

The UV–Vis–NIR absorption spectrum of 4-NP crystal with the thickness of 1.2 mm was recorded at room temperature using Elico SL218 Double beam UV–Vis–NIR spectrophotometer in the wavelength range of 200–1000 nm. This study provides valuable information about the electronic transition, lower cut-off wavelength, transparency window and the band gap of the title crystal. A well-polished portion of the grown single crystal was used for optical measurement. The recorded absorption spectrum of 4-NP is shown in Fig. 4a.

Fig. 4
figure 4

a UV–Vis–NIR absorption spectra and b energy band gap of 4-NP

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The lower cut-off wavelength of the present sample is found to be 405 nm which is due to the presence of π–π* electronic transition. The absence of the additional absorption in the region between 405 and 1000 nm is the well-desired property for the NLO [8]. The recorded transmittance spectrum of the 4-NP crystal is shown in Fig. 5. From this spectrum, it was observed that the crystal has a good optical transmittance of about 82% in the near-IR region while it exhibits 60–75% in the visible wavelength range and noticeably these values are slightly high compared with the reported value [4].

Fig. 5
figure 5

(4-NP) Single-crystal transmittance spectrum

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3.2.1 Determination of optical band gap

The optical absorption coefficient (α) was calculated from the transmittance data (T) using the following standard formula:

$$\alpha {\text{ }}={\text{ 2}}.{\text{3}}0{\text{3 log }}\left( {{\text{1}}/T} \right)/t,$$
(1)

where T is transmittance and t is a thickness of the crystal. The optical band gap (Eg) was estimated from the transmission spectra and the following formula gives the absorption coefficient (α) near the absorption edge:

$$\alpha {\text{h}}\nu {\text{ }}={\text{ A}}{\left( {{\text{h}}\nu - {\text{Eg}}} \right)^{({\text{1}}/{\text{2}})}}.$$
(2)

In the above equation, A is a constant, h is the Planck’s constant, Eg is the optical band gap of the crystal and ν is the frequency incident photons. The optical band gap was evaluated by plotting (αhν)1/2 against photon energy (eV) as shown in Fig. 4b. The energy band gap was calculated to be 2.84 eV. The wide band gap of the 4-NP crystal confirms the large transmittance in Vis–IR region [9]. For this result, the author claimed that the title material is fairly suitable for NLO applications compared to other organic NLO [10, 11].

3.3 Vickers microhardness test

Vickers microhardness test investigated a mechanical property of 4-NP single crystal. This study provides qualitative information such as hardness number, yield strength, stiffness constant, fracture toughness and deformation behavior of the 4-NP crystal. Generally, the hardness of the material depends on various parameters such as chemical bonding, lattice energy, the heat of formation, interatomic spacing and Debye temperature [12]. Practically speaking, hardness is the resistance offered by the sample for localized plastic deformation. It is measured by applying a load indenter of specified geometry on the material for specified length of time and the depth of penetration or dimensions of the resulting indentation were noted. In doing this, loads of different magnitude are applied over a dwell time of 10 s per each load. For each load of 10 g, 50 g and 70 g, the average lengths of the two diagonals of the indentations were measured using a Mitutoyo MH-112 microhardness tester Instrument. The hardness value increased with an increase of load up to 50 g; the hardness test could not continue above this load because the sample started cracking on 70 g due to the release of internal stress within the indentation. Moreover, it is well known that the hardness value of organic crystals is low compared to inorganic crystal because organic molecules have weak bonding forces of attraction. The Vicker’s hardness value of each load was calculated using the expression [9]:

$${H_{\text{V}}}={\text{ 1}}.{\text{8544 P}}/{{\text{d}}^{\text{2}}}\left( {{\text{kg}}\;{\text{m}}{{\text{m}}^{ - {\text{2}}}}} \right),$$
(3)

where P is the variation of applied load (in g) and d is the average square diagonal length (µm). Figure 6a shows the plot drawn between the applied loads and its corresponding hardness number for the 4-NP crystal. From the plot, it is clear that Vickers hardness value of the 4-NP crystal gradually increased with increase in the load; this is evident for the reverse indentation size effect (RISE), if n > 2. When the indenter deforms the sample, the dislocations are produced near the indentation site. The major contribution to increasing the hardness value is attributed to the very high stress required for analogous nucleation of dislocations in the small dislocation of free region indented. The RISE can be originated by the relative predominance of the nucleation and multiplication of dislocations [13].

Fig. 6
figure 6

a Variation of hardness with load, b plot of log p vs log d

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The log P as the function of log d gives a straight line depicted in Fig. 6b. The relation between load and the size of the indentation derived from Mayer’s law is shown in the following relationship:

$$P{\text{ }}=k{d^n}.$$
(4)

Taking logarithm on both sides and differentiating the above equation, we get:

$${\text{log }}P{\text{ }}=\log k+{\text{ }}n\log d,$$
(5)

where k is the material constant and ‘n’ is Meyer’s index or work hardening coefficient determined from the slope of the straight line by the least square fit. Hv should be increased with the increase of load if n > 2 and Hv decreases with increasing load for n < 2. These results might increase the possibilities of grown crystals towards NLO applications [14]. According to Onitschnn and Hanneman’s statement, the materials can be divided into two categories concerning work hardening coefficient (n) such as hard materials (1.0 ≤ n ≤ 1.6) and soft materials if n is above 1.6 [15]. Fortunately, for the present specimen, the value of ‘n’ was found to be 2.9, which is better compared with the reported crystals [4]. Hence, it is clear that the grown 4-NP crystal come under the soft material category and it is highly suitable for NLO applications [16]. Diamond indentation images of the 4-NP crystal for different loads (10, 30, 50 and 70 g) are shown in Fig. 7.

Fig. 7
figure 7

Indentation image of different loads

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Hardness values help us to calculate the yield strength of the target material using the following relation:

For Meyer’s index n > 2:

$${\sigma _\text{y}}=\frac{{\mathop H\nolimits_{\text{V}} }}{{2.9}}[1 - (n - 2)]{\left( {\frac{{12.5(n - 2)}}{{1 - (n - 2)}}} \right)^{n - 2}}\;{\text{kg}}/{\text{m}}{{\text{m}}^{\text{2}}},$$
(6)

where σy is the yield strength and Hv is the Vickers hardness of the title specimen. Yield strength is defined as the maximal stress that can be developed in a sample without plastic deformation [17]. Figure 8a shows the graph plotted between the respective load and its corresponding yield strength (σy). From this graph, it is clear that the yield strength increases with increasing the load. This proves that 4-NP single crystal has better mechanical strength up to 50 g. The elastic stiffness constant (C11) of the given crystal has been estimated from the Wooster’s empirical relation:

Fig. 8
figure 8

a Plot of yield strength and b stiffness constant vs variation load

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$${C_{{\text{11}}}}={\text{ }}{\left( {{H_{\text{v}}}} \right)^{{\text{7}}/{\text{4}}}}\left( {{\text{Pascal}}} \right).$$
(7)

It tends to provide an idea about the tightness of chemical bonding between neighboring atoms of the title crystal. Thus, the result of C11 indicates that the binding force between the ions is quite strong [18]. Figure 8b contributes to the plot between the load and the stiffness constant.

3.3.1 Fracture toughness (K C)

The fracture toughness (KC) is an essential parameter to select the materials for device applications [19]. The crack developed on a sample determines the fracture toughness using the relation:

$${K_{\text{C}}}={\text{ P}}/{\beta _0}{C^{{\text{3}}/{\text{2}}}}\left( {{\text{kg }}{{\text{m}}^{{\text{3}}/{\text{2}}}}} \right),$$
(8)

where P is the applied load, C the crack length measured from the center of the indentation point to the tip of the crack and β0 is geometrical constant; β0 is 7 for Vickers indenter. If c/a ≥ 2.5, then the sample undergoes medium crack and if c/a ≤ 2.5, then the crack is in Palmqvist category [20].The KC is calculated for cracking load 70 g, (KC = 12.83 kg m3/2) and the crack is in Palmqvist category.

The brittle index is an important property that affects the mechanical behavior of the material and gives an idea about fracture induced in a material without any significant deformation [13]. The brittle index (Bi) of material was calculated using the following relation:

$${B_{\text{i}}}={\text{ }}{H_{\text{V}}}/{\text{ }}{K_{\text{C}}}\left( {{\text{1}}{0^{ - {\text{4}}}}{{\text{m}}^{ - {\text{1}}/{\text{2}}}}} \right).$$
(9)

In the above equation, HV and KC represent the sample cracking load (g) and KC is the fracture toughness of the target material. The calculated values are listed in Table 1.

Table 1 Microhardness parameters
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3.4 Dielectric study

Here is an easy way to understand the electrical properties of the present crystal [21]. The dielectric constant and dielectric loss of the grown crystal were measured at various temperatures using HIOKI 3532-50 LCR HITESTER. Well-polished flat surface crystal of 4-NP (thickness of 2 mm) has been used for this study. The high-grade silver paste was applied on either surface of the crystal which enhances the uniform electrical contact between the two electrodes [22, 23]. The dielectric constant of the 4-NP crystal was calculated using the standard relation:

$${\varepsilon _{\text{r}}}=\frac{{Ct}}{{{\varepsilon _{\text{o}}}A}},$$
(10)

where εr is the dielectric constant, C the capacitance of the medium, t the thickness of the sample, εo the absolute permittivity of free space (8.854 × 10−12 F/m), and A is an area of the crystal. Figure 9 shows the plot of dielectric constant (εr) as a function of log frequency. It shows that the dielectric constant decreases with increase in frequency for all the temperatures. The higher value of dielectric constant at low frequency is a contribution of all four polarisations (electronic, atomic, ionic, and space charge). The large value of εr at lower frequency region pointed the presence of space charge polarisation and thus confirmed the purity and perfection of the 4-NP crystal which is the desirable property for various optical and communication devices [24, 25]. Figure 10 shows that the dielectric loss as a function of frequencies at various temperatures. This plot shows similar behavior as the dielectric constant. Hence, the low value of dielectric loss at high-frequency region suggests the good optical quality with a minor defect [26]. The 4-NP crystal can be considered as a smart candidate for the microelectronics industry, optoelectronic and NLO applications [27].

Fig. 9
figure 9

Dielectric constant with log frequency of 4-NP single crystal

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Fig. 10
figure 10

Dielectric loss of grown single crystal

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3.5 Laser-induced damage threshold (LDT)

It is one of the best studies to select efficient material for nonlinear applications. This measurement provides the detailed information about the optical tolerance of the target material. NLO materials not only depend on the linear and nonlinear optical properties, but it also depends on the surface quality and withstands high power intensities [28]. AQ-switched pulsed Nd:YAG laser of wavelength is 1064 nm, with the pulse width 10 ns and repetition rate of 10 Hz was used to measure the LDT value of the grown specimen. A well-polished surface of the 4-NP single crystal was taken for the present study. During the laser irradiation process, the laser beam spot directly falls on to the target material and create the damage on its surface and it was confirmed by the visible damage and cracking audio sound. The laser damage spot of the 4-NP sample is shown in Fig. 11.

Fig. 11
figure 11

Optical image of laser-damaged 4-NP single crystal

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The surface laser damage threshold was calculated using the following formula:

$${\text{Power density}}={\text{ }}E/\tau A{\text{ }}\left( {{\text{GW}}/{\text{c}}{{\text{m}}^{\text{2}}}} \right),$$
(11)

where E is the laser input energy (mJ), τ the pulse width (ns) and A is the area of the laser beam spot (mm). The laser damage threshold value calculated for the grown crystal was found to be 17.66 GW/cm2. The LDT value of 4-NP single crystal was compared with some well-known organic crystals [29,30,31,32]. Generally, the crystals having many dislocations have low LDT value. Thus, the 4-NP crystal is fairly suitable for the high-power laser application devices [33].

3.6 Z-scan study

The third-order nonlinear optical property of 4-NP single crystal has been investigated using Z-scan technique developed by Shakebahae et al. [34]. This method is an easy and accurate way compared to previous measurements such as beam distortion, waves mixing, nonlinear refraction interferometer and ellipse rotation [35]. For this study, measurement was carried out using a He–Ne laser with wavelength 632.8 nm and the input intensity of 5 mW. The input laser beam was made to pass through the Gaussian filter to come out in covert Gaussian form and then accurate single spot beam is allowed to pass the sample along Z-axis. The 4-NP crystal was moved across + Z to –Z direction using a stepper motor to change the intensity falling on the sample; the intensity of the input laser beam is I0 = 26.35 MW m−2. The incident laser beam was focused using a convex lens, the focal length is 30 mm and the calculated beam waist of the focal length is ω0 = 12.05 µm. The calculated Rayleigh length (ZR) of the Gaussian beam is found to be 0.78 mm (L < < ZR), which is higher than the thickness of the present sample (0.68 mm). The light-induced nonlinearity measured the normalized transmission of the 4-NP crystal. The sample transmission is corresponding to change in Z-position concerning the focal point. Open aperture (OA) Z-scan method is used to measure the nonlinear absorption (β) and closed aperture Z-scan is responsible for the nonlinear refraction. The sample determined that the intensity dependent nonlinear absorption was translated to the focal point and also that without placing the aperture in the front of the detector; it is called an open aperture. The normalized transmittance of the open and closed aperture curves of the 4-NP crystal is shown in Figs. 12 and 13.

Fig. 12
figure 12

Open aperture spectrum of 4-NP

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Fig. 13
figure 13

Closed aperture spectrum of 4-NP

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In the case of the closed aperture, the pre-focal peak followed by the post-focal valley suggests the negative nonlinear refractive index which is effective for the self-defocusing effect [36]. Open aperture curve reveals that the transmission has uniformity concerning the focus (Z = 0) and the minimum transmission (valley) is recorded. The 4-NP crystal exhibits reverse saturation absorption. The magnitude of the third-order NLO susceptibility of the material is calculated using the following formula [37].

The Rayleigh of the Gaussian laser beam was calculated using the formula [9]:

$${Z_\text{R}}=\frac{{K\omega _{0}^{2}}}{2},$$
(12)

where, K is the wave vector (9.924 × 106 /m) and ω0 is the beam waist radius at the focal point and following the formula:

$${\omega _0}=\frac{{f\lambda }}{D}\;\left( {\mu {\text{m}}} \right),$$
(13)

where f is the focal length of the lens, λ the wavelength of the light and D is the beam radius of the lens. The difference between the normalized maximum peak and minimum valley transmittances (ΔTp−v) is calculated using the following equation [38]:

$$\Delta {T_{p - v}}=0.406(1 - S{)^{0.25}}\left| {\Delta {\Phi _0}} \right|,$$
(14)
$${\text{S}}=1 - {\text{exp}}\frac{{ - 2{\text{r}}_{{\text{a}}}^{2}}}{{{{\varvec{\upomega}}}_{{\text{a}}}^{2}}},$$
(15)

where ׀∆Φ0׀ is on-axis phase shift at the focus, S the linear transmittance of aperture (S = 0.4795), ra the radius aperture (2 mm) and ωa is the transmittance beam radius of the aperture. The nonlinear refractive index (2) was calculated using the formula:n

$${n_2}=\frac{{\Delta {\Phi _0}}}{{\text{K}{\text{I}_0}{L_{\text{eff}}}}}\left( {{{\text{m}}^{\text{2}}}/{\text{W}}} \right),$$
(16)

where K is the wave number, I0 the intensity of the laser beam at the focal point and Leff is the sufficient thickness of the present sample which can be calculated using the formula Leff = [1 − exp (− αL)]/α, where α is the absorption coefficient and L is the thickness of the sample. The nonlinear absorption coefficient (β) was calculated using the following formula:

$$\beta =\frac{{2\sqrt 2 \Delta T}}{{{I_0}{L_{\text{eff}}}}}\;\left( {{\text{m}}/{\text{W}}} \right),$$
(17)

where ΔT is the peak value of the open aperture mode curve. The value of β is negative for reverse saturable absorption and positive of the two-photon absorption process [39,40,41,42]. The calculated values of n2 and β are used to determine the real and imaginary components of third-order nonlinear susceptibility using the following formula:

$$\text{Re} {\chi ^{(3)}}(\text{esu})=\frac{{1{0^{ - 4}}({\upvarepsilon _0}{C^2}n_{0}^{2}{n_2})}}{\pi }\left( {\frac{{\text{c}{\text{m}^2}}}{\text{W}}} \right),$$
(18)
$${\text{Im}}{\chi ^{\left( 3 \right)}}\left( {{\text{esu}}} \right)=\frac{{{{10}^{ - 2}}{\text{~}}({{{\varvec{\upvarepsilon}}}_0}{\text{~}}{C^2}{\text{n}}_{0}^{2}\lambda \beta )}}{{4{\pi ^2}}}\left( {\frac{{{\text{c}}{{\text{m}}^2}}}{{\text{W}}}} \right),$$
(19)

where ε0 is the free space permittivity (8.8518 × 10−12 Fm−1), C the vacuum velocity of light and n0 is the linear refractive index of the sample. Thus, the absolute value of third-order nonlinear susceptibility χ(3) is obtained by following the relation:

$$\left| {{\upchi ^{(3)}}} \right|={\left[ {{{\left( {\text{Re}({\upchi ^{(3)}})} \right)}^2}+{{\left( {\text{Im}({\upchi ^{(3)}})} \right)}^2}} \right]^{{\raise0.7ex\hbox{$1$} \!\mathord{\left/ {\vphantom {1 2}}\right.\kern-0pt}\!\lower0.7ex\hbox{$2$}}}}.$$
(20)

Here, it is worthy to measure that the calculated values of the refractive index (n2) and nonlinear absorption coefficient (β) of the 4-NP crystal are high compared with the previously reported NLO crystals [4, 43]. Moreover, the intermolecular charge transfer between the donor of OH unit to the acceptor of the NO2 unit may be responsible for tuning large third-order nonlinear activity of the 4-NP crystal. The experimental details and the third-order nonlinear optical parameters are listed in my previous paper [44]. The calculated Z-scan parameters such as nonlinear refractive index (n2), the nonlinear absorption coefficient (β), third-order susceptibility (χ) and the second-order hyperpolarizability of the 4-NP single crystal are given in Table 2. Based on the above finding, we may conclude that the 4-NP sample is potentially used for protection of night vision optical sensor, optical limiting and the high-power laser applications.

Table 2 Z-scan results
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4 Conclusion

An organic nonlinear optical 4-nitrophenol single crystal was grown by vertical Bridgman technique using single-wall ampule. The lattice parameters, phase purity and crystallinity of grown crystal were confirmed through the single crystal and powder X-ray diffraction studies. The UV–Vis–NIR spectrum reveals that the crystal is transparent between 405 nm and 1000 nm with a wide energy band gap of 2.84 eV. The Vickers hardness value increases with the load which indicates the reverse indentation size effect. The Meyer’s index n value is 2.9, it belongs to a soft material category, and the fracture toughness and brittle index of the present crystal are found to be 12.83 kg m3/2 and 0.1046 × 10−4 m−1/2, respectively. The minimum value of dielectric constant and dielectric loss at higher frequencies ensure that the 4-NP single crystal has a better optical response with fewer defects. The LDT value is found to be 17.66 GW/cm2 which is high compared with other familiar crystals. Z-scan measurement of 4-NP crystal exhibits self-defocusing behavior and reverse saturation absorption. Hence, overall experimental results suggest that 4-NP crystal is highly suitable for optoelectronic device applications.