**3. Development of methods of incorporation of the GaP nanoparticles into polymers**

Polyglycidyl methacrylate (PGMA), polyglycidyl methacrylate-co-polyoligoethyleneglycol methacrylate (PGMA-co-POEGMA) and biphenyl vinyl ether (BPVE) polymers were used to synthesize GaP nanocomposites suitable for light emissive luminescent device struc‐ tures. Some other polymers, dielectrics and with high electric conductivity, will be also in‐ vestigated in the process of preparation of this Chapter and used for elaboration of light emissive device structures.

Film nanocomposites of good quality with very bright and broad-band luminescence have been prepared. Quality and surface morphology of the nanocomposite films was studied in ambient air using AFM in taping mode on a Dimension 3100 (Digital Instruments, Inc.) micro‐ scope while luminescence of the nanocomposites films deposited by dip-coating from a sus‐ pension in water-ethanol mixture solution on the surface of a silica substrate was excited by the N2 laser nanosecond pulses at wavelength 337 nm and measured at room temperature.

The nanocomposites on the base of the noted above polymers were used for preparation and test of film light emissive device structures.

have been used for fabrication of blue light emissive GaP nanocomposites on the base of some optically and mechanically compatible with GaP polymers. The relevant luminescence

Advanced Light Emissive Device Structures http://dx.doi.org/10.5772/52416 13

Figure 9 shows the spectra for GaP/PGMA-co-POEGMA nanocomposites. Comparing the results for the nanocomposites prepared from GaP powder or suspension (Figure 9, spectra 1 and 2 respectively), it was established that the best quality have the nanocomposites ob‐ tained from the nanoparticles stored as a suspension in a suitable liquid (see spectrum 2).

**Figure 9.** Spectra of luminescence from GaP/ PGMA-co-POEGMA nanocomposites. Nanoparticles have been pre‐ pared using white P by mild aqueous synthesis and stored as the dry powder (spectrum 1) or suspension in a liq‐

**Figure 10.** Luminescence spectra of 2 GaP/BPVE nanocomposites produced on the base of 2 parties of GaP nanoparti‐

According to our measurements, the matrix polymers PGMA-co-POEGMA or BPVE used in this work provide no contribution to the spectra of luminescence of the based on these ma‐ trixes GaP nanocomposites presented in Figures 9 and 10, so, the nanocomposite spectra co‐

spectra are presented in Figures 9 and 10.

uid (spectrum 2).

cles prepared using different conditions.

Thickness of the polymer composite film was within 250-300 nm defined from AFM scratch ex‐ periment. The following procedures have been used in the fabrication of the nanocomposites:


More details on preparation and characterization of our GaP/polymers nanocomposites can be found in [31-36].

**Figure 8.** TEM image of GaP thoroughly ultrasonicated and dried nanoparticles obtained by mild aqueous synthesis (a) and AFM topography image of the GaP/PGMA nanocomposite (b).

Figure 8a shows the TEM images of GaP nanoparticles obtained by the aqueous synthesis. One can see GaP nanoparticles, having characteristic dimensions less than 10 nm. The wash‐ ed, thoroughly ultrasonicated and dried nanopowder contains mainly single nanoparticles, while the same powder obtained without ultrasonic treatment consists of the clusters with the dimensions of the order of 100 nm.

Figure 8b shows the AFM topography images of the GaP/PGMA film nanocomposite depos‐ ited by dip-coating from a suspension in water-ethanol mixture solution on the surface of a silica substrate. The AFM images demonstrated that no significant aggregation was caused by the polymerization. In general, individual particles were observed.

The thoroughly washed, ultrasonicated and dried nanopowders obtained by mild low tem‐ perature aqueous synthesis from white P as well as their specially prepared suspensions have been used for fabrication of blue light emissive GaP nanocomposites on the base of some optically and mechanically compatible with GaP polymers. The relevant luminescence spectra are presented in Figures 9 and 10.

The nanocomposites on the base of the noted above polymers were used for preparation and

Thickness of the polymer composite film was within 250-300 nm defined from AFM scratch ex‐ periment. The following procedures have been used in the fabrication of the nanocomposites: **1.** GaP powder was ultrasonicated in methylethylketone (MEK) using Branson 5210 ultra‐ sonic bath. Then, PGMA was added to the MEK solution. GaP to polymer ratio was less

**2.** GaP powder was dispersed in water-ethanol mixture (1:1 volume ratio) and ultrasoni‐ cated using Branson 5210 bath for 120 min. Then, PGMA-co- POEGMA was added in the form of water-ethanol mixture (1:1 volume ratio) solution. GaP to polymer ratio was less than 1:3. Nanocomposite films were deposited on quartz slides via dip-coating; **3.** GaP powder was dispersed in the biphenyl vinyl ether/dichloromethane (BPVE/DCM) solution; the solution was stirred and filtered from the excess of the powder. A few mL

More details on preparation and characterization of our GaP/polymers nanocomposites can

**Figure 8.** TEM image of GaP thoroughly ultrasonicated and dried nanoparticles obtained by mild aqueous synthesis

Figure 8a shows the TEM images of GaP nanoparticles obtained by the aqueous synthesis. One can see GaP nanoparticles, having characteristic dimensions less than 10 nm. The wash‐ ed, thoroughly ultrasonicated and dried nanopowder contains mainly single nanoparticles, while the same powder obtained without ultrasonic treatment consists of the clusters with

Figure 8b shows the AFM topography images of the GaP/PGMA film nanocomposite depos‐ ited by dip-coating from a suspension in water-ethanol mixture solution on the surface of a silica substrate. The AFM images demonstrated that no significant aggregation was caused

The thoroughly washed, ultrasonicated and dried nanopowders obtained by mild low tem‐ perature aqueous synthesis from white P as well as their specially prepared suspensions

by the polymerization. In general, individual particles were observed.

drops of the settled solution were casted onto silicon wafer.

(a) and AFM topography image of the GaP/PGMA nanocomposite (b).

the dimensions of the order of 100 nm.

test of film light emissive device structures.

12 Optoelectronics - Advanced Materials and Devices

than 1:10.

be found in [31-36].

Figure 9 shows the spectra for GaP/PGMA-co-POEGMA nanocomposites. Comparing the results for the nanocomposites prepared from GaP powder or suspension (Figure 9, spectra 1 and 2 respectively), it was established that the best quality have the nanocomposites ob‐ tained from the nanoparticles stored as a suspension in a suitable liquid (see spectrum 2).

**Figure 9.** Spectra of luminescence from GaP/ PGMA-co-POEGMA nanocomposites. Nanoparticles have been pre‐ pared using white P by mild aqueous synthesis and stored as the dry powder (spectrum 1) or suspension in a liq‐ uid (spectrum 2).

**Figure 10.** Luminescence spectra of 2 GaP/BPVE nanocomposites produced on the base of 2 parties of GaP nanoparti‐ cles prepared using different conditions.

According to our measurements, the matrix polymers PGMA-co-POEGMA or BPVE used in this work provide no contribution to the spectra of luminescence of the based on these ma‐ trixes GaP nanocomposites presented in Figures 9 and 10, so, the nanocomposite spectra co‐ incide with those obtained from the relevant GaP powders or suspensions. We note that in the GaP/BPVE nanocomposite the position of the luminescent maximum can be changed be‐ tween 2.5 – 3.2 eV and the brightness is 20-30 more than in the PGMA and PGMA-co-POEG‐ MA matrixes. We explain the broadening of the luminescence band and the shift of its maximum to low photon energies in luminescence of the nanocomposite based on the GaP powder in Figure 9, spectrum 1, by the presence of the nanoparticles with the dimensions of 10-100 nm in the powder. Meanwhile, suspensions containing the 10 nm nanoparticles ex‐ hibit pronounced quantum confinement effects since this diameter equals the Bohr diameter of the bound exciton in GaP.

longed room-temperature thermal annealing, and the interesting optical properties that ac‐ company such ordering. We demonstrate that long-term natural stimuli improve the perfection of our crystals, which can lead to novel heterogeneous systems and new semicon‐

Advanced Light Emissive Device Structures http://dx.doi.org/10.5772/52416 15

Our unique collection of long-term ordered perfect GaP single crystals gives opportunities to find deep fundamental analogies in properties of the perfect single crystals and nanopar‐ ticles as well as to predict and to realize in nanoparticles and perfect bulk crystals new inter‐

The long-term ordering of doped GaP and other semiconductors has been observed as an interesting accompanying process, which can only be studied in the situation when one has

Any attempt to accelerate the above noted processes, for instance, through annealing of GaP at increased temperatures cannot be successful because high-temperature processing results in thermal decomposition (due to P desorption) instead of improved crystal quality. There‐ fore successful thermal processing of GaP can only take place at temperatures below its sub‐ limation temperature, requiring a longer annealing time. Evaluated within the framework of the Ising model the characteristic time of the substitution reaction during N diffusion along P sites in GaP:N crystals at room temperature constitutes 10 -15 years [5]. Hence, the obser‐ vations of luminescence of the crystals made in the sixties and the nineties were then com‐

The pure and doped GaP crystals discussed herein were prepared nearly 50 years ago. Throughout the decades they have been used to investigate electro- and photoluminescence (PL), photoconductivity, bound excitons, nonlinear optics, and other phenomena. Accord‐ ingly, it is of interest also to monitor the change in crystal quality over the course of several

More specifically, since 2005, we have analyzed the optical and mechanical properties of sin‐ gle crystalline Si, some III–V semiconductors, and their ternary analog CdIn2S4, all of which were grown in the 1960s. Comparison of the properties of the same crystals has been per‐ formed in the 1960s, 1970s, 1980s, 1990s [1-12], and during 2000s [13–25] along with those of newly made GaP nanocrystals [26-28] and freshly prepared bulk single crystals [19-23]. We improved in the preparation of GaP nanocrystals the known methods of hydrothermal and colloidal synthesis taking into account that success of our activity depends on optimal choice of the types of chemical reactions, necessary chemicals and their purity, conditions of the synthesis (control accuracy, temperature, pressure, duration, etc.), methods and quality of purification of the nanocrystals, storage conditions for nanoparticles used in the further

Single crystals of semiconductors grown under laboratory conditions naturally contain a varied assortment of defects such as displaced host and impurity atoms, vacancies, disloca‐ tions, and impurity clusters. These defects result from the relatively rapid growth conditions and inevitably lead to the deterioration of the mechanical, electric, and optical properties of

the material, and therefore to rapid degradation of the associated devices.

a unique set of samples and the persistence to observe them over decade time scales.

pared with the results obtained in 2009-2012 in closed experimental conditions.

decades while the crystal is held under ambient conditions.

operations of fabrication of the GaP/nanocomposites.

ductor devices with high temporal stability.

esting properties and applications.

Figures 9 and 10 present a clear image of the quantum confinement effect in the GaP nano‐ particles. In accord with our data [28-30] the shift is about a few tenths of eV and, obviously, it is impossible to explain only through this effect the dramatic 1 eV enhancement to the re‐ gion of luminescence at 300 K on the high-energy side of the spectrum.

In order to explain this interesting phenomenon we postulate that the nanocrystals, much like the ideal long-term ordered bulk GaP single crystals, exhibit this huge increase in blue-shifted luminescence due to: (a) negligibly small influence of defects and non-radiative recombination of electron-hole pairs and very high efficiency of their radiative annihilation, (b) high perfec‐ tion of nanocrystal lattice, and (c) high transparency of nanocrystals due to their small dimen‐ sions for the light emitted from high points of the GaP Brillouin zones, for instance, in the direct transitions Γ<sup>1</sup> <sup>c</sup> - Γ15v between the conductive and valence bands with the photon energy at 300°K equal to 2.8 eV [40] and (d) high efficiency of this so called "hot" luminescence.

Our first attempts to prepare GaP nanoparticles [26] yielded room temperature lumines‐ cence with maximum shifted only to 2.4 eV in comparison with the new maximum at 3.2 eV. It confirms significant achievements in technology of GaP nanoparticles and GaP/polymers nanocomposites. On the base of these improved technologies for preparation of GaP nano‐ particles and GaP/polymer nanocomposites we can change within the broad limits the main parameters of luminescence and expect to create a framework for novel light emissive de‐ vice structures using dramatic 1 eV expansion of GaP luminescence to UV region.

The film device structures demonstrate broadband luminescence in the region from UV un‐ til yellow-red with controlled width and position of maximum with the luminous intensity up to 1 cd compared with industrial light emitting diodes.
