Photoluminescence Of Phosphors Research Articles

Combustion Synthesis and Influence of Dy3+ ions on Structural and Photometric Attributes of Olivine-type LiMgPO4 Nanophosphors for Illumination Applications.

The low-cost technique of combustion synthesis was used to synthesize the trivalent Dysprosium (Dy3+) doped olivine type Lithium Magnesium Phosphate (LiMgPO4). X-ray diffraction (XRD) analysis verified the orthorhombic phase, corresponding to the space group Pnma. The crystallite size of 50.83nm was calculated using Debye-Scherre formula. FESEM technique was used to study the morphology of the sample which depicts its porous nature. High-Resolution Transmission Electron Microscopy (HRTEM) analysis provided an average particle size measurement of 65 ± 2.04nm. The phosphor's photoluminescence (PL) excitation spectrum revealed distinct peaks in the ultraviolet (UV) and near-ultraviolet (near UV) regions, aligning with the characteristics of Dy3+ ions. Four emission peaks were observed in the PL spectra at various wavelengths: 4F9/2→6H15/2 (482nm), 4F9/2→6H13/2 (578nm), 4F9/2→6H11/2 (663nm) and 4F9/2→6H9/2 (700nm). Near-white light emission was observed at the Commission International de l'Eclairage (CIE) coordinates of Dy3+ activated LiMgPO4 [LMP] phosphor, which were (x = 0.41, y = 0.42) with color purity of 49.20%. The band gap of the prepared phosphor was calculated using diffuse reflectance spectra, yielding a value of 4.47 ± 0.02eV. The results indicated that the synthesized phosphor had potential for various illumination applications when combined with other phosphors under near-UV stimulation.

Electroluminescent white quantum dot light-emitting diodes based on high pressure synthesis of graphitic C3N4 semiconductor

Graphitic carbon nitride (g-C3N4) has shown promising potentials for quantum dot light-emitting diodes (QLEDs), which might be an effective alternative of the mostly used Cd(Se,S)/Zn(S,Se) emitting layers and can achieve both low toxicity and high stability, meeting the goal of sustainable development. Herein, we for the first report a white electroluminescent QLED device with blue and orange dual-color emissions, which were attributed to the σ*-LP, π*- π, and π*-LP transitions, respectively, from a single-compound g-C3N4 quantum dots (QDs) by synthesizing the precursor at 0.8 Mpa high-pressure N2. By selectively exciting the δ and π bonds with X-ray, the luminescence mechanism was approved with the synchrotron radiation techniques of X-ray absorption near edge structure (XANES) and the X-ray excited optical luminescence (XEOL).The chromaticity coordinate changes from cayan color space with CIE (0.2034, 0.1939) to white color space with CIE (0.3009, 0.2697) as pressure increases from 0.06 to 0.8 Mpa, with the increased overlap of the δ* and π* orbital upon the contraction of crystal lattice. The breakthrough achieved in this work will promisingly promote the development of future white light sources as thin as paper for human home and office lighting by using direct current-driven electroluminescence of QDs, instead of photoluminescence of phosphors.

Effect of Ce<sup>3+</sup> Concentration and YAG Crystal Particles Size on Photoluminescence

Purpose of research. Determine the effect on the photoluminescence of phosphors from yttrium-aluminum garnet activated by cerium ions Ce3+, the size of its particles and the concentration of cerium ions in them.Methods. Structural electron and confocal microscopic, fluorescent, microspectral studies using a laser lex = 473 nm as an excitation source, energy dispersive, X-ray diffraction studies, as well as goniophotometric measurements on the radial distribution of light intensity excited by the LED matrix were carried out.Results. A detailed granulometric analysis of the particle sizes of phosphors was carried out for two samples from different manufacturers, cumulative distributions M(d) were constructed and their quantiles were established. Based on the results of measuring photoluminescence from individual particles in the compositions of phosphors based on YAG:Ce3+, a Stokes shift was detected in these samples: short-wavelength – for particles with sizes less than 10 μm and with low concentration and long-wavelength – with sizes greater than 10 μm with an increased concentration of over ~0.2% . The obtained microspectral size-emission dependences lem(d) and energy Imax(d) were consistent with the description based on the proposed physical mechanism of their formation by the 5d → 2F5/2 and 5d → 2F7/2 transitions.Conclusion. A short-wavelength shift of photoluminescence intensity maxima for particles smaller than 10 μm was discovered, due to a significant increase in the influence of surface stresses due to a reduction in the number of atoms. For larger particle sizes, the characteristic photoluminescence intensity maxima cease to depend on the wavelength. The radial distribution of luminous intensity determined by the goniophotometric method made it possible to calculate the value of the luminous flux equal to 1350 lm and 1140 lm, respectively, for LED matrices containing 8 LEDs with the studied phosphors.

Cинтетические укрытия вегетационных сооружений с интегрированным фотолюминофором в укоренении черенков туи западной

We have explored the effectiveness of using light-correcting covering materials for greenhouse structures when rooting the cuttings of various ornamental forms and varieties of the northern white-cedar (Thuja occidentalis L.). Two types of shelters have been tested: the modified spunbond at a density of 30 g/m2 with a photoluminescent phosphor integrated into its structure at a concentration of 0.8 % and the unmodified spunbond at the same density. Europeum-doped yttrium oxysulfide (Y2O2SEu) has been chosen as a photoluminescent phosphor. We have analyzed 11 varieties and forms of Thuja occidentalis L.: Rheingold, Mr. Bowling Ball, Woodwardii, Tiny Tim, Golden Smaragd, Mirjam, Golden Globe, Danica, Sunkist, Smaragd and Brabant. The response of the indicators of callusogenesis and rhizogenesis to the influence of a transformed light flux has been tested. A positive effect of the use of photoluminescent phosphors in rooting the stem cuttings of the northern white-cedar has been established. An increase in the indicators of regenerative ability and post-regenerative development of the root systems and the aboveground parts of the cuttings has been recorded, such as: the activity of callusogenesis, the number of adventitious roots formed, the length of the leading root, the total length of the root system, the height of the aboveground part and the diameter of the root collar. Callusogenesis has increased from 67.59 ± 2.05 % in the check to 76.81 ± 1.61 % when having integrated the photoluminescent phosphor. The number of adventitious roots formed has increased from 9.64 ± 0.43 to 11.44 ± 0.34 pcs., correspondingly. The total length of the root systems has increased from 64.56 ± 3.70 to 75.52 ± 2.77 cm, correspondingly. One-way analysis of variance confirmed the significance of the differences between the tested forms and varieties in each of the shelter options for most of the tested indicators. Two-way analysis of variance has revealed a significant effect of the positive impact of photoluminescent phosphors on callusogenesis, adventitious root formation, post-regenerative development of the root systems and the aboveground parts of the cuttings.

Green-emitting YBO3:Ce3+,Tb3+ phosphor photoluminescence characteristics for close UV stimulation

Through a solid state process, YBO<sub>3</sub>:Ce<sup>3+</sup>,Tb<sup>3+</sup> was created via rare earth oxides along with boric acid. The phosphor absorbs close-ultraviolet illumination through the transitions 4f-5d of Ce<sup>3+</sup>, then emits a wide spectrum of light through the transitions 5d-4f of Ce<sup>3+</sup> and a sharp spectrum of light through the transitions 4f-4f of Tb<sup>3+</sup>. Nonradioactive power transmission between Ce<sup>3+</sup> and Tb<sup>3+</sup> has been seen in samples with varying amounts of Ce<sup>3+</sup> and Tb<sup>3+</sup> using spectroscopic analysis. The quantities of Ce<sup>3+</sup> as well as Tb<sup>3+</sup> decides the hue for the YBO<sub>3</sub>:Ce<sup>3+</sup>,Tb<sup>3+</sup> emission, ranging between blue and green. The Y<sub>0.82</sub>Ce<sub>0.03</sub>Tb<sub>0.15</sub>BO<sub>3</sub> phosphor, which emits green light when optimized, has an exterior quantum effectiveness of 76.7% and an emission color of (0.309, 0.547). This phosphor's luminescence strength maintains 87% of its strength at ambient temperature, demonstrating enough heat stability for white illumination emitting diode implementations.

Wide-band blue-emitting in Ce3+ doped Ca2YZr2Al3O12 garnet-type phosphor designed via local structural lattice distortion and synthesized in nonreducing atmosphere

It is of great significance to explore blue photoluminescent phosphor for white light-emitting diodes excited by near-ultraviolet chip. However, it is very challenging to prepare efficient blue luminescence in phosphor by an unsophisticated synthesis process. In this work, a series of blue-emitting Ca 2 Y 1-x Zr 2 Al 3 O 12 : xCe 3+ phosphors are designed via local lattice distortion and synthesized in nonreducing atmosphere. The crystal structure of samples and the coordination environment of Ce 3+ have been investigated in detail by X-ray diffraction and Rietveld refinement method. The wide-band blue emission peaking at 460 nm is attributed to a relaxed crystal field strength. Based on dodecahedron distortion caused by unequal increase of Ce–O bond length, the wavelength of blue color luminescence tuning can be realized from 459 nm to 472 nm. In addition to the concentration quenching effect, the fluorescent lifetimes, thermal quenching effect, the internal quantum efficiency, CIE chromaticity coordinates and related mechanisms of samples have also been studied systematically. Using the representative sample with other tricolor phosphors on a 365 nm chip, a prototype LED device with chromaticity point of (0.394, 0.384) and high CRI (93.5) at CCT of 3755 K is fabricated. All the results suggest that Ca 2 Y 1-x Zr 2 Al 3 O 12 : xCe 3+ phosphors can be conducted as potential alternative of blue-emitting phosphor for near-ultraviolet pumped white light-emitting diodes.

Cooling photoluminescent phosphors in laser-excited white lighting with three-dimensional boron nitride networks

Laser-excited white lighting, which is achieved by laser diodes and phosphor converters, has garnered increasing interest in recent years due to their high-power and high-brightness characteristics. Nevertheless, two long-standing thermal issues remain formidable: first, the photoluminescent phosphors also generate heat due to the Stokes loss, which are the second heat source in the packaging but long ignored; second, the phosphors are embedded in low-thermal-conductivity silicone and the generated heat is rather inefficient to dissipate. As a result, the accumulated heat leads to high temperature in phosphor particles and even thermal quenching, which deteriorate the luminescence, chromaticity, and reliability. In this work, these problems are successfully addressed by establishing three-dimensional (3D) boron nitride (BN) networks to cool the silicone-embedded phosphor particles in a facile and scalable method. When lighted under the driven current of 900 mA, the working temperature of phosphor layer is dramatically decreased by 95.2 °C with the 3D-BN network without sacrificing the luminescence and chromaticity. Such strategy with excellent cooling performance, high reliability, and easy scalability may hold great promise for broader optoelectronics applications beyond laser-excited white lighting.

Preparation and properties of La(3-x)DyxBWO9 phosphors and La(3-x)DyxBWO9/PMMA composite films

A series of La(3-x)DyxBWO9 phosphors and La(3-x)DyxBWO9/PMMA composite films were prepared. The absorption and photoluminescence of phosphors as well as the transmittance and radioluminescence of the composite films were studied. La(3-x)DyxBWO9 phosphors mainly emit blue light at 486 nm and yellow light at 577 nm when excited at 310 nm, and the phosphors have good thermal stability. La(3-x)DyxBWO9/PMMA composite films have good transmittance and X-ray radiation properties. The results indicate that La(3-x)DyxBWO9 phosphors can be used in solid-state lighting devices, and the prepared composite films are expected to be used in fields such as X-ray imaging and radiation detection.

Scintillation and photoluminescence investigations of Gd2MoB2O9: CeF3 phosphors

The CeF3 doped Gd2-xMoB2O9 phosphors (where x = 0.00, 0.25, 0.50 and 0.75 mol%) were synthesized by the conventional high-temperature solid-state reaction method at 900 °C for 12 h in air. DSC and TGA analysis executed to study the optimum temperature for sintering. The structural, photoluminescence and X-ray luminescence properties were investigated. The structure of the samples was analyzed by using X-ray diffractometer (XRD). The absorption spectra were analyzed and found that absorption edge increased with the increasing concentration of CeF3. The photoluminescence of phosphors shows the overlapping of excitation and emission peaks in the range of 300 nm–450 nm. These emission peak correspond to the 5d – 4f transitions of Ce3+ ion. The optimum concentration of CeF3 in these phosphors is 0.50 mol% corresponding to maximum emission intensity. The X-ray induced optical luminescence spectra showed a strong emission peak at 411 nm the concentration quenching at 0.75 mol%, which is as efficient as 54.4% compared with bismuth germanium oxide (BGO) crystal. The luminescence decay increased with the increment of CeF3 concentration. From the optical properties investigated, it was found that the phosphors performed a strong and fast luminescence signal which is appropriate for the development of scintillators in X-ray detector devices.

Method of own forms for determination of separate bands

The problem of determining the separate bands of the phosphor photoluminescence spectrum described by the Gaussian function is solved by the method of decomposition into its own forms. This allows you to calculate two parameters of each band: amplitude and variance. An example is the photoluminescence spectrum of a ZnS:Mn single crystal. It consists of five separate bands. Two systems of fifth-order equations linear for one parameter of each band are obtained. This parameter is generalized and is equal to the product of the amplitude and the root of the variance. The coefficients of these systems depend on the second parameter. This non-linear parameter is related to variance. In order to simplify the two systems, the problem is solved in several stages. Based on the analysis of literary sources, the two largest bands are selected. In addition, the origin of coordinates is well chosen. This allows us to simplify both systems and completely determine the parameters of each of the largest bands from the systems of second-order equations. As a result of these simplifications, the order of the two systems and the parameters of the other three bands are reduced. Thus, the problem is reduced to solving a system of the second and third order nonlinear equations.

Luminescence properties of Cr3+-doped Al6Ge2O13 broadband near-infrared phosphor

Near-infrared (NIR) phosphor-converted light-emitting diodes (pc-LEDs) are gaining attention as new solid-state light sources for food safety and health monitoring. Herein, a series of Cr3+-doped Al6Ge2O13 (AGO) NIR phosphors were obtained by the high-temperature solid state reaction. The photoluminescence (PL) excitation spectrum of AGO:Cr3+ shows a strong broadband absorption in the 400–500 nm region, which corresponds well to the blue light chip. The phosphor's PL emission spectrum exhibits a broadband spanning 600–1000 nm. The integrated emission intensity of AGO:3%Cr3+ at 420 K can keep 81% of that at 300 K, demonstrating good luminous thermal stability. The near-infrared output power of pc-LED device integrating AGO:Cr3+ phosphor with a 430 nm blue light chip reaches 81.7 mW at 300 mA. The device's electroluminescence spectrum displays a broadband centered at 780 nm, with a full width at half maximum (FWHM) of 160 nm. These findings could drive the development of NIR pc-LED light sources for miniaturized near-infrared spectrometers.

Luminescence properties of a novel cyan-blue light emitting Ce3+doped SrZrSi2O7 phosphor

A novel Ce3+ doped SrZrSi2O7 (SZSO) phosphor with different doping concentration (0.05–1.5 mol %) were synthesized by conventional solid-state reaction method. To confirm crystal structure and phase purity of prepared phosphor X-ray diffractions (XRDs) have been done. Surface morphology, compositional and functional groups analysis were investigated using FE-SEM, EDXS & FTIR techniques. In order to study the optical properties of the synthesized phosphor photoluminescence and thermoluminescence were investigated in detailed. Photoluminescence studies of SZSO: Ce3+ phosphor shows strong broad excitation peak at 293 nm owing due to 4f → 5d transition and corresponding broad emission peak obtain at 480 nm due to 5d → 4f spin allowed transition. The optimum PL intensity obtain for 0.1 mol% Ce3+ doping concentration. CIE co-ordinate, color purity and CCT of prepared phosphor are also calculated which shows the SZSO: Ce3+ phosphor emits cyan-blue light, can be applicable for solid state lighting. Thermoluminescence of SZSO: Ce3+ phosphor shows two TL glow curve peaks at 56 °C and 130 °C temperature. The optimum TL intensity obtained for 0.2 mol% Ce3+ doped SZSO phosphor for 15 min UV irradiation time at 254 nm UV excitation source. TL emission spectra and fading effect are also analyzed. TL kinetic parameters are determined by peak shape method. Thermoluminescence properties shows that prepared SZSO: Ce3+ phosphor will be potential applicable for UV-dosimetry.

Two-color Emission in Dy3+-activated CaZnP2O7 Pyrophosphate for White LED

Abstract: CaZnP2O7 pyrophosphate phosphor doped with Dy3+ ions was synthesized by modified solid-state reaction. The crystalline phases were recognized using X-ray diffraction. Surface morphology was studied by scanning electron microscopy. Furthermore, the chromaticity coordinates' values were estimated from the emission spectra of CaZnP2O7:Dy3+. The phosphor photoluminescence emission spectra were found to have an excitation at around 353 nm showing two distinguishing bands centered at about 482 nm (Blue) and 575 nm (Yellow) corresponding to 4F9/2→6H15/2 and 4F9/2→6H13/2 transitions of Dy3+, respectively. These phosphors have strong absorption in the near-UV region. The intact study reveals that the present phosphors are suitable for color converter using UV light as the primary light source, which can be used as a blue/yellow phosphor excited by the n-UV LED chip and mixed with other color emission phosphors to obtain white light. Keywords: Chemical synthesis, Luminescence, X-ray diffraction, Optical properties.

Cooling Photoluminescent Phosphors in Laser-Excited White Lighting with Three-Dimensional Boron Nitride Networks

Cooling Photoluminescent Phosphors in Laser-Excited White Lighting with Three-Dimensional Boron Nitride Networks

Bright Stretchable White Alternating‐Current Electroluminescent Devices Enabled by Photoluminescent Phosphor

AbstractAlternating current‐driven electroluminescent (ACEL) devices have recently emerged as a potential candidate for next‐generation smart lighting, stretchable displays, and wearable electronics. Herein, a simple and efficient method is developed to fabricate high brightness, chromatic‐stable, and stretchable white ACEL devices through doping wide‐spectrum yellow photoluminescent phosphor into blue electroluminescent emissive layer. By tuning the ratio of electroluminescent to photoluminescent phosphors in the emissive layer, the optimized device achieved a maximum brightness of 3150 cd m−2 for white emission with Commison Internationale de L'Eclairage coordinates of (0.28, 0.34), and manifested a more stable chromaticity than traditional ACEL devices. Moreover, a digital display and stretchable white ACEL device (with a tensile strain of 150%) are demonstrated to show the generality of this approach. The high brightness white ACEL devices proposed in this work offer a simplified architecture with facile fabrication process and large‐area compatibility, which may find broad range of applications in wearable optoelectronics.

Synthesis and luminescent property of Sm3+ doped and (Sm3+, Zr4+) co-doped calcium stannate phosphors via co-precipitation and sintering

Sm 3+ doped calcium stannate (CaSnO 3 :Sm 3+ ) and (Sm 3+ , Zr 4+ )-co-doped calcium stannate (CaSnO 3 :Sm 3+ , Zr 4+ ) photoluminescent phosphors were synthesized via co-precipitation and subsequent sintering in oxidizing atmosphere at 1400 °C for 60 min with SnCl 4 ·5H 2 O, CaCl 2 ·2H 2 O, ZrO(NO 3 ) 2 · x H 2 O and Sm 2 O 3 as main raw materials. The synthesized samples were characterized by X-ray diffraction, scanning electron microscopy, energy dispersive spectroscopy, photoluminescent spectroscopy, luminescent decay curves, afterglow spectroscopy and thermo-luminescent glow curves. The results show that CaSnO 3 pure phase is synthesized in co-precipitation reaction at an optimum molar ratio of CaCl 2 ·2H 2 O:SnCl 4 ·5H 2 O of 1.4:1.0 and subsequent sintering at 1400 °C for 60 min. Calcium stannate as a host matrix can be doped with Sm 3+ ions or co-doped with Sm 3+ /Zr 4+ ions for the formation of white photoluminescent phosphors. CaSnO 3 :0.03Sm 3+ phosphor has an optimum photoluminescent intensity. Also, the fluorescent emission intensity of CaSnO 3 :0.03Sm 3+ ，0.04Zr 4+ phosphor under excitation of 365 nm wavelength can be enhanced due to Zr 4+ ions doping at an optimum doping amount y of 0.04. The CIE 1931 chromaticity coordinates change from (0.3600, 0.3535) for CaSnO 3 :0.03Sm 3+ phosphor to (0.3622, 0.3574) for CaSnO 3 :0.03Sm 3+ , 0.04Zr 4+ phosphor as the average crystalline size decreases from 71.5 to 68.3 nm and the unit cell volume increases from 0.2686 to 0.2775 nm 3 . In addition, the electron transition mechanism for the photoluminescent and long afterglow properties was also discussed. • The CaSnO 3 : x Sm 3+ , y Zr 4+ phosphors were prepared by co-precipitation and subsequent sintering in oxidizing atmosphere at 1400℃. • The incorporation of Zr 4+ into CaSnO 3 :0.03Sm 3+ phosphor increased the photoluminescent intensity and luminescent decay times.

Preparation of multifunctional long-persistent photoluminescence cellulose fibres.

Simple preparation of flame-retardant, photoluminescent, and superhydrophobic smart nanocomposite coating was developed and applied onto cotton fibres using the simple pad-dry-cure technique. This novel strategy involved the immobilization of rare-earth-doped aluminium strontium oxide (ASO; SrAl2 O4 :Eu+2 ,Dy+3 ) nanoparticles, environmentally friendly room temperature vulcanizing silicone rubber (RTV) and environmentally friendly Exolet AP422 (Ex). The fabrics were also able to produce a char film in the fire-resistant assessment, providing fibres with a self-extinguishing characteristic. Furthermore, the fire-retardant performance of the coated cotton samples remained resistant to washing over 35 laundry cycles. The superhydrophobicity of the treated fabrics was monitored to improve by increasing the photoluminescent phosphor nanoparticles. The produced transparent photoluminescent film displayed an absorption at 360 nm and an emission at 526 nm. The photoluminescent fabrics were observed to generate different colorimetric shades, including white, green-yellow and bright white as monitored by Commission Internationale de l'Éclairage laboratory colorimetric coordinates. Slow emissions were detected for the treated cotton fabrics as monitored by emission, ultraviolet-visible light absorption, lifetime, and decay time spectral profiles to indicate glow in the dark phosphorescence effect. Both comfort and mechanical properties of the coated fibres were evaluated by measuring their bending length and air permeability.

Improved thermal stability and luminescence properties of SrSi2O2N2:Eu2+ green phosphor by a heterogeneous precipitation protocol for solid-state lighting applications

The SrSi2O2N2:Eu2+ green-emitting phosphor, as a member of oxynitride phosphors, could greatly enhance the color quality of the white-light conversed by single yellow-emitting phosphor. However, SrSi2O2N2:Eu2+ phosphors prepared by traditional solid-state ways normally consist hard agglomerates with unevenly dispersed particles and therefore suppress the luminescence properties. This research proposes a heterogeneous precipitation protocol where precipitation process is introduced, in order to produce a precursor in the first phase. And in the second phase, a high-temperature solid-state process is adopted for obtaining the final product. The main results show that, for an optimized SrSi2O2N2:Eu2+ phosphor prepared using our protocol, (1) the SrSi2O2N2:Eu2+ particles are faceted and with smooth faces and (2) the phosphor photoluminescence, external quantum efficiency, stability against thermal exposure, and physical stability consistently outperform the current commercially used product. This research essentially provides an economic way for production of solid-state lighting with enhanced color quality.

Current progress and comparative study of performance of the energy saving lighting devices: a review

In the present scenario, rare earth activated phosphor materials are important families in luminescent materials, which is useful in various applications. Over the past few years, rare earth activated phosphor has gained a lot of attention from the society and research community due to its exceptional properties such as low cost, eco-friendly behavior, solution process ability, better PL properties, wider range of color tunability, color purity and defects tolerance etc. In this review, we first discuss energy saving lighting devices, after that, we have discussed those methods which are used to synthesize rare earth activated phosphors. We have been focusing on the modification and tailoring of the photoluminescence of phosphors, which may lead to the acquisition of new phosphors with tunable emission colors. In this review, we are discussed recently reported color tunable phosphors. At the end of the review, scope in lighting field, energy saving devices, and future scope also discussed.

Large and Versatile Plasmonic Enhancement of Photoluminescence Using Colloidal Metallic Nanocubes

Improving phosphor photoluminescence efficiency is a key parameter to boost the performances of many optical devices. In this work, colloidal silver nanocubes, homogeneously spread on a luminescent surface, have proved to help both injecting and extracting light in and out of the photoluminescent layer and hence contributed significantly to the enhancement of the fluorescence. This approach has been applied to two materials: the well-known Y$_3$Al$_5$O$_{12}$:Ce yellow phosphor and an optical quartz. The emission efficiency, for sol-gel derived YAG:Ce layers, has increased of 80\% in the presence of an optimal nanoparticle density -- whereas for quartz, a weakly fluorescent material, the photoluminescence signal can be enhanced by a 200-fold factor. A physical analysis based on simulations shows that the disorder is an important factor and that the surface density of Ag nanoparticles is a crucial parameter.